DE102010006239B3 - Interferometric arrangement e.g. Michelson interferometer, for determining e.g. distance of polished glass surface, has track lines for forming triangle such that preset amount of lateral shear is caused between reference and object bundles - Google Patents

Abstract

The arrangement has a short coherent electromagnetic radiation source for illuminating an object, and a detector (12) for detecting electromagnetic radiations (1). An interference microscope has an end reflector (8) with three plane mirrors (9-11) arranged in a reference optical path (R) as a reference reflector, where surfaces of the mirrors lie perpendicular to a common reference plane (BE). Track lines of the plane represented by the surfaces form a triangle in the plane such that preset amount of lateral shear is caused between a reference bundle and an object bundle. An independent claim is also included for an interferometric method for determining distance, depth, profile, shape, ripples and/or roughness or optical path length of a technical or biological object or for use in an optical coherence tomography.

Description

State of the art

In the published patent application DE 10 2006 015 387 A1 [1] by M. Hering et al. Describes an interferometric measuring device based on white-light interferometry, also known as short-coherence interferometry, in which the wavefronts of the reflected object beam and that of the reflected reference beam are tilted by a certain angle relative to one another by means of a tilting device are, so that a spatial interferogram can arise as a single-shot record. For example, this angular amount is realized here in a heavily modified Linnik-interferometer arrangement, which also has features of a Mach-Zehnder interferometer, by a tilting mirror, which is passed only once by the light on the way to the detection. The tilting mirror is subordinate to the Linnik arrangement, is located in an infinity beam path for the object light and is still part of the interferometer.

With the measurement method based on this optical arrangement, one or more spatial interferograms, even as a line stack on a matrix camera, can be fully provided as single-shot data sets in the period of image capture.

It is particularly advantageous in this approach with the tilting mirror in the infinity beam path that the spatial frequency for the centroid wavelength, or the center of gravity wave number, in the spatial interferogram at the output of the interferometer in a first approximation is not affected by the inclination of the object surface in relation to the interferometer. This invariance of the spatial frequency represents a major advantage for the evaluation of spatial interferograms.

However, this subordinate tilting device described in [1] is expensive - even in the adjustment - and generally quite vulnerable to undesired misalignments and thus the interferometer is usually not long-term stability. Thus, the waveform of a short-coherent spatial interferogram can change in an unknown manner, which can represent a significant disadvantage for the evaluation.

A targeted change in the angle by tilt device, for example, to change the spatial frequency for the centroid wavelength in the spatial interferogram predetermined, can lead to an unwanted lateral displacement of the object wavefront and reference wavefront during detection, the only consuming or by an adjustment in some cases not to compensate. Thus, in this arrangement, the ability to change the spatial frequency for the center wavelength in the spatial interferogram in a simple manner, severely limited. Furthermore, a suboptimal adjustment of the rather complex interferometer can permanently lead to only partial lateral coverage of the object wavefront and reference wavefront, which is a source of measurement errors or severely limit the depth measurement range, since the interference effect disappears in the absence of superimposition.

In the publication by M. Hering et al. In Applied Optics, vol. 48, number 3, pages 525 to 538 of 20 January 2009 [2], the measured spatial interferograms in the potential of this approach according to [1]. The in the presented interferometric one-shot measurement arrangement is an experimental setup for study purposes and is for the economic implementation rather complex and too voluminous and also very easy to adjust. The optical principle requires that in this case the technical and constructive measures to achieve a high mechanical stability and temperature stability, quite expensive. Typical measurement results based on this approach were already reported by M. Hering in 2006 in the Proceedings of SPIE, Vol. 6188, 61880E-1 to 61880E-11 in the 7 represented [3].

Obtaining spatial interferograms for the one-shot measurement technique, for example, for measuring the distance or the profile by means of inclination device in the form of a plane tilting mirror in the interferometer, but this always outside the objektabbildenden and outside of the focused reference beam path, ie in an infinity beam path is considered as the prior art considered here.

In this principle, the inclination of an object surface with respect to the interferometer advantageously does not lead to a change of the spatial frequency for the centroid wavelength, or the centroid wave number, in a spatial interferogram. However, the interference contrast can approach the value zero even at slight tilting of the object surface.

A comparatively high interference contrast in the detected spatial interferogram can only be achieved over a comparatively large tilt angle range of the object surface if this object surface is illuminated by means of optics with a high numerical aperture and laterally almost diffraction-limited focus points or focused line images.

In contrast, Michelson-type interferometers are with a plane reference mirror in which the spatial frequency for the centroid wavelength in a spatial interferogram at the output of the interferometer by tilting the reference mirror or by tilting the object relative to the interferometer or the interferometer with respect to the object to change , for measuring objects with varying and unknown surface inclination with respect to the evaluation of spatial interferograms not of interest here. Therefore, approaches on this basis are not considered to be prior art in relation to this invention and, therefore, will not be considered further here.

The acquisition of spatial interferograms for the one-shot measurement technique by means of lateral shear between object and reference wavefronts at the output of a two-beam interferometer basically represents another possibility of generating spatial interferograms for the one-shot measurement technique, for example for detecting the distance Because lateral shears can be used in an optical arrangement as a basis for generating interference of mutually inclined wavefronts. A classic approach is to use a Michelson interferometer with two ridge reflectors to create the required lateral shear. This approach with two ridge reflectors is typically used for wavefront analysis and is well known to those skilled in the art, see D. Malaccra, Optical Shop Testing, John Wiley & Sons, Inc., 1992, pp. 140-141, 4 .16 [4] and also WH Steel, Interferometry, Cambridge University Press, 1967, p. 83 last paragraph to p. 84 above [5].

In order to be able to use this interferometer approach with two roof edge reflectors for the distance measurement and profile measurement, an additional plane mirror must therefore be assigned to the object surface in the object beam path of the interferometer, this plane mirror then forming a roof edge with the object surface. In the reference beam path in this case the second roof edge reflector is arranged. This arrangement provides with appropriate adjustment lateral shear, avoids the wavefront inversion, but usually has clear disadvantages because of the volume in the object beam path, so in terms of accessibility to the object, for example, when measuring indoors.

Also known is that of D. Kelsall in 1959 in Proc. Phys. Society, 73, p. 470, 1 [6] published the approach using two triple reflectors as final reflectors of a Michelson interferometer. The lateral displacement of a triple reflector also creates a lateral shear between object and reference wavefronts at the output of a Michelson interferometer. The use of a triple reflector in the reference beam path of a Michelson interferometer is, however, to the best of our knowledge, already on F. Twyman and A. Green back, sa U.S. Patent 1,565,533 . 6 , [7] back.

This interferometer approach as an arrangement for an interferometric sensor for distance measurement u. a. to use, in which a plane mirror of the triple reflector in the form of a cube corner, also known as Corner Cube, is replaced by the object surface leads to the object or the object surface in the object beam path still a roof edge reflector or two plane mirror must order if the unwanted wavefront inversion between object and reference radiation should be avoided. However, this considerably increases the sensor volume, which is very disadvantageous for many applications or this completely excludes the use of such a solution. Also, in this case no invariance of the lateral shear and thus the inclination of the interfering wavefronts, for example, given to lateral drifting away of the triple reference reflector or the object itself. Thus, the spatial frequency for the center wavelength in the spatial interferogram change, which can be very disadvantageous for the evaluation.

Description of the invention

The object of the invention is, firstly, cost-effective and, above all, robust one-shot measurement technology for detecting distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form or also for optical coherence tomography (OCT), in particular with single-shot multi-point probing, for economic use.

So that is the inventive task to solve the optical probing of the object surface or an object volume with an interferometer optical signals in bestgeeigneter, so the best possible evaluable waveform for a punctiform, line-like field or even a flat measuring field with many individual measuring points without a mechanical, time-serial provide depth scan.

In doing so, many laterally adjacent object elements or object points should be able to be appropriate at the same time. That is, there is the task of providing readily evaluable optical signals in the optical probing of objects by the method according to the invention and the arrangement according to the invention by means of an interferometer measuring the object as quickly as possible.

The spatial frequency for the centroid wavelength, or the centroid, kS in a spatial interferogram should be highly constant or predetermined and highly independent of the inclination of the object surface. In particular, the problem to be solved, the amount of inclination of interfering wavefronts that form a spatial interferogram on a detector, with simple means to realize cost-effective, long-term stable and largely invariable by environmental influences. The misalignments typically occurring when using an optical system by changing the position of components, also by temperature changes in the environment as well as by varying mechanical stresses, eg. B. in the holding elements of the components in the measuring system, should have no or only a relatively small effect on the amount of inclination of the interfering wavefronts in the detection. Of course, this can of course only be achieved if the spectrum of the interfering light remains invariable.

Fields of application of the inventive solution should be: The microform and the micro-profile measurement, the measurement of roughness and the mini-form measurement, the shape measurement on not or little cooperative surfaces, as well as z. B. human liver tissue. An example of the application of the invention is also the detection of the microform at the inner ear in humans in the surgical operation phase. The use in endoscopic 3D systems should lead to well-miniaturized sensor solutions with high measurement accuracy.

Another field of application is also the measurement of unpolished aspheres and free-form surfaces.

A particular motivation for the application of the invention is the utilization of the interferometric amplification of a weak object signal for measurements also in a mesoscopic scale. This is of great advantage, for example, in mechanical engineering, where measuring uncertainty in the sub-micron range is not always necessary when measuring many technical objects. By using the interferometric amplification, also known as "interferometric gain", even object elements of the lowest reflectivity should be able to be measured relatively well in depth, for example with a measurement uncertainty in the single-digit micrometer range. Therefore, the highly accurate measurement of the shape of partially reflecting, low light scattering and thereby inclined gear tooth surfaces should also represent a preferred field of application of the invention.

The measuring arrangement and the method should also be used for optical coherence tomography (OCT), in particular with multi-point probing, for technical or biological objects.

In the measuring arrangement according to the invention, the use of agents for dispersive spectroscopy should always be possible.

Here, the term light is always used as a synonym for electromagnetic radiation from the terahertz, over the infrared to the deep UV range.

Features of the main claim of the arrangement

• 1. It is a method and an arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, in a layer form, or even for optical Coherence tomography (OCT) for technical or biological objects. The arrangement will be described below. The following means are used in the process: A source of short-coherent electromagnetic radiation for illuminating the object, An interferometer, in particular also in the form of an interference microscope, with an object and at least one reference beam, in which at least one end reflector is arranged, and a measuring plane in the object beam, in which at least approximately the optically to be measured surface or volume elements of Object are located. - As well as at least one screened detector for detecting electromagnetic radiation in the form of at least one spatial interferogram.

The source of short-coherent electromagnetic radiation is also referred to below as the light source, light in the sense of electromagnetic radiation being understood to mean terahertz, IR, VIS or UV radiation. The light source can produce a laterally finely structured illumination pattern on the object. In this case, the light source can be a point emitter, a lateral line emitter or a group of point emitters in line or matrix form even with individually switchable point-shaped or line-shaped lighting elements.

The light source may be a single or multi-color LED or OLED, a super-luminescent diode, a supercontinuum light source, a frequency comb-based laser, a Halogen lamp or light sources based on incandescent light.

The rasterized detector may be a grayscale or color CCD or grayscale or color CMOS camera in line or matrix form.

The wave-optical depth of field defines here at least approximately the depth range of the measuring arrangement in which the measuring plane is located, so that it is also possible here to speak of a measuring volume in the object volume. This must be the surface or volume elements coming to the optical probing.

According to the invention, at least one end reflector with three plane mirrors as the reference reflector, ie at least one three-plane mirror reference end reflector, is arranged in the reference beam path of the interferometer, and the surfaces of these three plane mirrors each lie at least approximately perpendicular to a common reference plane BE.

The three spur lines of the planes, which are represented by the surfaces of the three plane mirrors, form in the reference plane BE a triangle ABC, so that there is a lateral shear between reference and object bundles in this interferometer, which represents a distance with the amount delta_q. The distances AB, BC and CA of this triangle ABC must have a certain length. For example, the length of each stretch may typically be on the order of a few tenths of a millimeter to a few millimeters of mm. The angles of this triangle are neither extremely pointed nor is this triangle a right triangle. The resulting lateral shear may have an amount delta_q on the order of typically from 0.1 mm to several millimeters. In an arrangement with a laterally high-resolution microscope and a centroid wavelength in the UV range, however, the amount delta_q can also be in the order of a few hundredths of a millimeter. This is based on correspondingly small lengths of the distances AB, BC and CA and the corresponding three angles of the triangle ABC. This approach is widely scalable in terms of the amount delta_q.

The lateral shear of the amount delta_q between reference and object bundles exists in the virtual mirror plane VSE of the three-plane mirror reference end reflector in the reference beam path. The virtual mirror plane VSE is at least approximately optically conjugate with the measurement plane ME of the object beam path by beam splitting. In this case, the three-plane mirror reference end reflector is angularly aligned so that electromagnetic radiation passes from the reference beam path to the screened detector.

A Spurgerade is known as the intersecting line between a plane in space, here in each case a plane which is defined by a plane mirror surface, and a ground plane, here the reference plane BE in the performing geometry.

A lateral displacement of a three-plane mirror reference end reflector does not result in a change in the amount of lateral shear delta_q. This invariance is regarded as a great technical advantage, since this results in a high robustness of the signal generation over such misalignments. This invariance is also a good prerequisite for the use of double-slit or double-hole apertures in an imaging detection beam path, since a constant amount of the lateral shear delta_q in the detection beam path leads to a long-term constant distance spatially coherent point images. By means of a double diaphragm, which can also be represented by a spatial light modulator, these spatially coherent point images can be used to produce point-diffraction interferograms with a high contrast. The measurement plane ME in the object beam path and the plane in which the double diaphragm is located are at least approximately optically conjugate.

The three-plane mirror reference end reflector is a reflector which generates a lateral shear in the interferometer according to the invention. As already mentioned, the three-mirror reference end reflector has a virtual mirror plane VSE. This virtual mirror plane VSE can be spatially assigned to the occurrence of the lateral shears. For example, the interference of an object spherical wave and a reference spherical wave, which are generated by the interferometer and whose spherical centers are separated by a lateral shear of the amount delta_q, at least in a limited portion of the detector plane to a spatial interferogram with an at least approximately constant spatial frequency for the Center wavelength because the interfering wave surfaces on the detector are inclined to each other. In a limited section of the spherical wave surfaces, these are generally sufficiently well approximated by plane waves. This interference phenomenon of two spatially coherent spherical wave surfaces to be registered on a detector is sufficiently known to the person skilled in the art as the classic Young's double-slit experiment, the gap distance d in the double-slit experiment corresponding here to the lateral shear with the amount delta_q.

The lateral-shear with the amount delta_q serves as a basis for the generation of one or more spatial interferograms, which are not or only slightly influenced by the inclination of the object surface in their spatial frequency for the centroid wavelength when the point-shaped center of the object spherical wave is on a surface element, so the object by focused light at least approximately punctiform is illuminated. The prerequisite for this, of course, is the constancy of the spectrum of the light components coming to the interference. This invariance of the spatial frequency for the centroid wavelength is for the evaluation of spatial interferograms of very great advantage, since here, for example, due to the advance knowledge of the spatial frequency for the centroid wavelength in the signal robust and relatively fast lock-in. Approaches may be used, which are at least approximately set to this spatial frequency for the centroid wavelength. Algorithms based on a lock-in approach make it possible to provide depth information with comparatively low measurement uncertainty even from strongly noisy and aberration-influenced signals, in this case spatial interferograms. Since a source of short-coherent electromagnetic radiation is used here, short-coherence integerograms arise here, which have an envelope. In the simplest case, the maximum or the centroid of the envelope can be used, for example for determining the depth of an object point or the optical path length at a point of an object. In this case, the optical layer thickness of transparent media can be determined. This is particularly simple if the layer thickness is greater than the coherence length of the electromagnetic radiation of the source, since then the maxima or the centroids of the envelope of the short-coherence integerograms are clearly separated. The chirp effect occurring in the short-coherence interferogram of the lower-lying object point due to dispersion in the refractive medium can be treated model-supported during the evaluation.

On the rasterized detector, a short-coherent spatial interferogram is preferably detected for each object point in a laterally extended area, so that a complete line profile can be obtained by taking a single image with preferably many adjacent spatial interferograms and their evaluation.

It should be noted here that in principle end reflectors with an arbitrary odd number 2n + 1 of plane mirror surfaces - with n greater than / equal to 2 - can be used as reference reflectors, if these plane mirror surfaces are perpendicular to a reference plane BE and only happen once , In all these cases, the lateral shear delta_q required for the measurement process is generated. In addition, optimally no inversion of the reference wavefront occurs in relation to the object wavefront, if there is only a single reflection or an odd number also 2n + 1 - where n is greater than / equal to 1 - at the object or other planar mirror surfaces. In this case, the difference between the number of reflections between reference and object beam path must be 2n, with n greater than or equal to 0. Both from an economic point of view as well as for the sake of optimal sensor design and sensor manufacturing, the use of an end reflector with three plane mirrors as a reference reflector and a direct optical probing of the object without further plane mirror, so that a one-time reflection in the object beam path, for the great majority the best technical and economical solution (A1).

Other features of the arrangement

• 2. Preferably, in the arrangement for robust interferometry, the three spur lines in the reference plane BE form an obtuse-angled triangle ABC. It is advantageous here that with such a mirror arrangement, the angle of incidence on the three plane mirrors-even those of the marginal rays of a lighting beam-can be kept below 60 °. For example, when half the opening angle of the illumination beam 8, 6 degrees, that is, the numerical aperture is about 0.15, and the angle values are 21 degrees, 24 degrees and Altgrad degrees 135 (A2).
• 3. Preferably, in the arrangement for robust interferometry, the three spur lines in the reference plane BE form an acute-angled triangle ABC. For example, the angle values in the size of 52, 64 and 64 may be old degrees. It is advantageous in this case that the production of a three-mirror reference end reflector, in which the track straight lines of the three plane mirrors form an acute-angled triangle, is generally comparatively simple, for example by single-point diamond machining or impression technology, since accessibility to the Surfaces of the three plane mirrors are usually well given. However, there are comparatively large angles of incidence on the three plane mirrors, which can have a considerable influence on the polarization of the light and the polarization-dependent reflectance.
• 4. Preferably, in the arrangement for robust interferometry, the three plane mirrors are arranged in the form of a pharynx. A mirror arrangement in pharyngeal shape can be produced comparatively well.
• 5. Preferably, in the arrangement for robust interferometry, the three plane mirrors are arranged in labyrinth form. So three single plane mirror surfaces are each more open in a three-plane mirror reference end-reflector Mirror Dragon or arranged as a mirror labyrinth. In this case, the beam path in the three-plane mirror reference end reflector when throat in crossed form. In the labyrinth, however, the beam path can be formed in irregular or regular M-shape. In this case, one or more three-mirror reference end reflectors can be miniaturized in a metal plate. In particular, the production of the three-mirror reference end reflectors in pharyngeal shape offers the single-point diamond machining technique. But it can also be the impression, embossing or printing technique used.
• 6. Preferably, in the arrangement for robust interferometry, the three-plane mirror reference end reflector is angularly arranged in the interferometer such that the main beam of the outgoing reference beam propagates after passing the three-plane mirror reference end reflector at least approximately parallel to the main beam of the incoming reference beam , In this case, the offset of the principal rays then has the magnitude of the lateral shear delta_q. An advantage for the evaluation of interferograms is that the lateral shear of the amount delta_q is invariant with respect to lateral displacements of the reference reflector. Furthermore, there is no wavefront inversion between object and reference radiation in a three-plane mirror reference end reflector having three mutually inclined plan mirrors. This considerably reduces the requirements for the illumination optics.

When using a light source with beam shaping optics for illuminating the object with a focus spot or a linear illumination with the longitudinal axis in the direction of the cutting line g plays a small tilting of a monolithic trained and thus inherently rigid three-mirror reference end reflector a practically subordinate role.

In a high-vibration environment, a pulsed light source can be used to obtain well-interpretable spatial interferogram signals.

• 7. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie ein Objektiv mit der Brennweite f13' bzw. f17', welches das Objektbündel in Richtung Detektion kollimiert, so angeordnet, dass dessen dem Objekt zugewandte Brennebene F13 bzw. F17 mit der virtuellen Spiegelebene VSE des Drei-Planspiegel-Referenz-Endreflektors zusammenfällt. Oder durch eine weitere Abbildungsstufe zwischen einem Objektiv zur Kollimierung und der virtuellen Spiegelebene VSE des Drei-Planspiegel-Referenz-Endreflektors kann dieses Zusammenfallen als optische Konjugation (VSE-F13 bzw. VSE-F17) erreicht werden. Die optische Konjugation kann auch durch Strahlvereinigung erzeugt werden. Die virtuelle Spiegelebene VSE des Drei-Planspiegel-Referenz-Endreflektors, die auch als die virtuelle Reflexionsebene dieses Endreflektors angesehen werden kann, stellt dann eine zur Messebene des Objektstrahlenganges optisch konjugierte Ebene dar. Die Lateral-Shear vom Betrag delta_q entsteht in diesem Fall auch in der Brennebene F13 bzw. F17 des Objektivs welches das Objektbündel in Richtung Detektion kollimiert.

If the focal point BF of a reference beam falls on the virtual mirror plane VSE of the three-mirror reference end reflector, this is offset by the lateral shear with the amount delta_q in the virtual mirror plane VSE and the focus point BF 'is formed. The distance representing the lateral shear with the amount delta_q is always parallel to the line of intersection g of the reference plane BE and the virtual mirror plane VSE.

• 7. Preferably, in the arrangement for robust interferometry, a lens with the focal length f13 'or f17', which collimates the object beam in the direction of detection, is arranged so that its object facing focal plane F13 or F17 with the virtual mirror plane VSE of the three Plane mirror reference end reflector coincides. Or by a further imaging stage between a lens for collimation and the virtual mirror plane VSE of the three-plane mirror reference end reflector, this coincidence can be achieved as optical conjugation (VSE-F13 or VSE-F17). The optical conjugation can also be generated by beam combination. The virtual mirror plane VSE of the three-plane mirror reference end reflector, which can also be regarded as the virtual reflection plane of this end reflector, then represents a plane optically conjugate to the measurement plane of the object beam path. The lateral shear of the amount delta_q also arises in this case the focal plane F13 or F17 of the objective which collimates the object beam in the direction of detection.

The virtual mirror plane VSE thus represents exactly one module-fixed plane in the described three-plane mirror reference end reflector with three plane mirrors on which the main beam of an incident homocentric beam can impinge perpendicularly. Furthermore, the center BF of the homocentric beam may lie in the virtual mirror plane VSE. Then the center of the failing homocentric bundle BF 'around the lateral shear is offset by the amount delta_q in the VSE and its principal ray is also perpendicular to the VSE. In this case, the connection path of the two bundle centers, which indeed has the amount, ie the length, delta_q, is parallel to the reference plane BE, which is defined by the three plane mirror surfaces.

With this inventive approach, the spatial interferograms of all object points located on any point of the usable object field which is at least approximately in the focal plane (F13) can be detected on the same detector surface. For there is no lateral movement of the object bundle in the focal plane (F13 ') as a function of the lateral position of a measuring point in the object field. Ideally, in the case of an axis-perpendicularly adjusted plane mirror as an object lying in the focal plane F13 and highly corrected optics, the arbitrary points in the object field can then be used to scan through the illumination pattern in the object field, the maximums of the envelopes of the short-coherence interferogram or their focal points at least approximately at the same location, ie in each case the same pixel or in their immediate vicinity, on the detector. At a weak tilt of the plane mirror about an axis perpendicular to the reference plane BE and time-sequential scanning of the plane mirror with light points of a controlled light source along a Line parallel to the reference plane BE are the focal points ideally then on the detector also on a line.

• 8. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Lateral-Shear vom Betrag delta_q kleiner als der Betrag oder gleich 30% des Betrags der Brennweite f13' des Objektivs, welches das Objektbündel am Ausgang des Interferometers kollimiert. Der Betrag delta_q der Lateral-Shear sollte das Feld, in dem das Objektiv gut korrigiert ist, nicht überschreiten. In der Regel ist die Lateral-Shear deutlich kleiner als 10% des Betrags der Brennweite f13' bzw. der Brennweite f17' zu wählen.
• 9. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie der gerasterte Detektor jeweils zumindest näherungsweise in der Brennebene (F13') eines Objektivs, welches das Objektbündel am Ausgang des Interferometers kollimiert, angeordnet oder der gerasterte Detektor ist in Lichtrichtung in einer – dieser Brennebene (F13') nachgeordneten und – zu dieser Brennebene (F13') optisch konjugierten Ebene EK angeordnet, wobei die optische Konjugation von Brennebene (F13') und der Ebene EK durch mindestens ein Strahlenbüschel gegeben ist. Das bedeutet, es werden Punkte dieser Brennebene (F13') in die Ebene EK durch mindestens ein Strahlenbüschel abgebildet.
• 10. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Achse y einer Zylinderoptik parallel zu einer Geraden g angeordnet ist, welche die Schnittgerade von der Bezugsebene BE und der virtuellen Spiegelebene VSE darstellt.

When positioning an object in the focal plane F13 in the object beam path, wherein the detection of spatial interferograms in the focal plane F13 'or an optically conjugate plane, the spatial frequency for the centroid wavelength, or the center of gravity wave, the spatial interferograms is not affected by the inclination of the object surface if this is spectrally non-selective, ie gray, for example. However, for a high contrast of the interference, it is advantageous if the object is illuminated punctiform or linearly by focused light. This invariance of the spatial frequency for the centroid wavelength, which exists only under the condition of a constant light spectrum is for the evaluation of spatial interferograms of great advantage, since here, for example, due to the advance knowledge of this spatial frequency in the signal robust and relatively fast lock-in approaches to Application can be used, which are at least approximately set to this spatial frequency for the centroid wavelength. Algorithms based on a lock-in approach make it possible to provide depth information with a comparatively reduced measurement uncertainty even from strongly noisy and aberration-influenced signals, in this case spatial interferograms.

• 8. Preferably, in the arrangement for robust interferometry, the lateral shear of magnitude delta_q is less than or equal to 30% of the amount of focal length f13 'of the objective, which collimates the object beam at the output of the interferometer. The amount delta_q of the lateral shear should not exceed the field where the lens is well corrected. As a rule, the lateral shear should be chosen to be significantly smaller than 10% of the amount of the focal length f13 'or the focal length f17'.
• 9. Preferably, in the arrangement for robust interferometry, the screened detector is arranged at least approximately in the focal plane (F13 ') of a lens which collimates the object beam at the output of the interferometer, or the screened detector is in the light direction in one - this focal plane (F13 ') arranged downstream and - to this focal plane (F13') optically conjugate level EK, wherein the optical conjugation of the focal plane (F13 ') and the plane EK is given by at least one beam of radiation. This means that points of this focal plane (F13 ') are imaged into the plane EK by at least one ray bundle.
• 10. Preferably, in the arrangement for robust interferometry, the axis y of a cylinder optic is arranged parallel to a straight line g, which represents the line of intersection of the reference plane BE and the virtual mirror plane VSE.

For the light returning from an optically touched object point and the superposed reference light, this leads to a one-dimensional focusing of the interfering light along a line and thus leads to a comparatively high light concentration of the interfering wavefronts, here in cylindrical form. In addition, this beam guidance gives the possibility of simultaneously recording the spatial interferograms of a plurality of object points, for example those along a line LO, on the object. The detection of these line-shaped interferograms takes place in each case also in a line-like area, ie. H. along one or fewer lines of the rasterized detector. The longitudinal axes of these linear areas are each perpendicular to this line LO.

• 11. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie im Referenzstrahlengang eine Vielzahl von miniaturisierten Drei-Planspiegel-Referenz-Endreflektoren in Form eines Arrays angeordnet. Damit kann ein Objektfeld wie bei einem Nadelkissen oder einem Nagelbrett mit einer steuerbaren Lichtquelle zeitsequenziell durch Fokuspunkte abgetastet werden, wodurch beispielsweise eine Formmessung an einem kleinen Objekt begrenzter Tiefenausdehnung, beispielsweise eine Mikrodelle oder eine flache Schmiertasche in einem Metallkörper, möglich ist (A3).
• 12. Vorzugsweise erfolgt bei der Anordnung zur robusten Interferometrie die Anordnung von Drei-Planspiegel-Referenz-Endreflektoren in diesem Array in einer linien-, flächenhaften oder einer dreidimensionalen Struktur. Dabei können jeweils Messpunkte entlang einer Linie gleichzeitig in einem Schuss aufgenommen werden.
• 13. Vorzugsweise sind bei der Anordnung zur robusten Interferometrie miniaturisierte Drei-Planspiegel-Referenz-Endreflektoren in Form einer dreidimensionalen Treppen-Struktur angeordnet. Damit können schwach geneigte Objektoberflächen vermessen werden, ohne dass die Schwerpunkte der Einhüllenden der Interferogramme stark lateral verschoben sind.
• 14. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Quelle kurzkohärenter elektromagnetischer Strahlung als ein Punktmatrixstrahler ausgebildet.
• 15. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Punktmatrix auf der Quelle kurzkohärenter elektromagnetischer Strahlung verdreht um einen spitzen Winkel zur Schnittlinie der interferierenden Wellenfronten auf dem gerasterten Detektor angeordnet. Die Drehachse ist dabei also senkrecht zur VSE und parallel zur BE angeordnet. So kann gleichzeitig eine Vielzahl von Interferogrammen auf dem Detektor platziert werden.
• 16. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Quelle kurzkohärenter elektromagnetischer Strahlung mit schaltbaren Punktlichtquellen ausgebildet. Damit ist das Abtastmuster frei wählbar, beispielsweise auch nach Relevanz von Objektmerkmalen aus Vorab-Informationen.
• 17. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die gerasterte Lichtquelle mit schaltbaren Linienlichtquellen ausgebildet. Damit kann ein Objektfeld zur Formmessung besonders schnell vermessen werden.
• 18. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Quelle kurzkohärenter elektromagnetischer Strahlung zur lateral feinstrukturierten Beleuchtung eines Objekts mittels eines schaltbaren räumlichen Lichtmodulator-Arrays ausgebildet, so dass diese Quelle kurzkohärenter elektromagnetischer Strahlung lateral schaltbar ausgebildet ist. Damit ist eine hohe Flexibilität gegeben. Damit sind unterschiedliche Beleuchtungsmuster auf dem Objekt in einer zeitlichen Folge realisierbar, so dass beispielsweise bei einer Ausbildung des Referenzreflektors mit linienhaften, miniaturisierten Drei-Spiegel-Referenz-Endreflektoren nacheinander jeweils eine Beleuchtung von dem Objekt mit einer einzelnen Linie und von definierten Orten auf dem Gesamt-Referenzreflektor erfolgt bis das Objektfeld vollständig beispielsweise durch eine sich schrittweise lateral fortbewegende Linie abgescannt ist. Die laterale Dichte des Abtastmusters ist wählbar, wodurch relevante Bereiche bei Bedarf mit einer höheren Abtastdichte vermessen werden können (A4).
• 19. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie im Referenzstrahlengang eine räumliche Korrespondenz zwischen der lateralen Struktur des Beleuchtungsmusters und der lateralen Anordnung von miniaturisierten Drei-Planspiegel-Referenz-Endreflektoren gegeben, so dass jedem miniaturisierten Drei-Planspiegel-Referenz-Endreflektor mindestens ein Lichtfleck oder eine Lichtlinie der Lichtquelle, zumindest in der Zeitdauer der Zeitdauer einer Bildaufnahme, zugeordnet ist.
• 20. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie mindestens eine Doppelblende auf der Basis von Spalten oder Pinholes in einer gemeinsam benutzten Abbildungsstufe für Referenz- und Objektstrahlung angeordnet. Dabei ist eine erste Öffnung der Doppelblende der Referenzstrahlung und eine zweite Öffnung der Objektstrahlung vorbehalten. So kann eine konfokale Diskriminierung der Objektstrahlung durchgeführt werden. Der erste Bereich dient zum Durchtritt des Referenzlichtes in Richtung Detektor und kann aber auch unerwünschtes Störlicht aus dem Referenzstrahlengang ausblenden. Die Spalte bzw. Pinholes, also die Blendenelemente, können aber auch so fein ausgebildet sein, dass Zylinder-, bzw. Kugelwellen hoher räumlicher Kohärenz gebildet werden (A5).
• 21. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie die Doppelblende () in einer zur Messebene ME optisch konjugierten Ebene angeordnet, wobei die optisch konjugierte Ebene durch mindestens ein Strahlenbüschel dargestellt ist. So kann eine konfokale Diskriminierung von Objektstrahlung durchgeführt werden.
• 22. Vorzugsweise sind bei der Anordnung zur robusten Interferometrie Mittel zur vorbestimmt gesteuerten Änderung des Abstands und/oder der Lage der Spalte oder der Pinholes der Doppelblende angeordnet, damit die konfokale Filterung optimal erfolgen kann.
• 23. Vorzugsweise sind bei der Anordnung zur robusten Interferometrie im Objektstrahlengang Mittel zur chromatischen Tiefenaufspaltung von Foki angeordnet. So kann ein deutlich größerer Tiefenmessbereich bei dennoch beugungsbegrenzter lateraler Auflösung als die wellenoptische Schärfentiefe realisiert werden. Dieser Ansatz, insbesondere mit einer Multipunkt-Antastung des Objekts, kann mit einem Linnik-Typ-Interferometer mit einer vergleichsweise geringen Numerischen Apertur gut umgesetzt werden. Hierbei können die Mittel zur chromatischen Tiefenaufspaltung in der Fourier-Ebene des objektabbildenden Objektivs angeordnet sein. Es kann hierzu ein diffraktiv-optisches Element eingesetzt werden. Die Anordnung eines diffraktiv-optischen Elements in der Fourier-Ebene wurde bereits in DE 103 21 895 A1 dargestellt. Dies führt zu einem konstanten Abbildungsmaßstab für Strahlung aller Wellenlängen (A6).
• 24. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie im Objektstrahlengang mindestens eine konfokal diskriminierende Blende angeordnet. Diese ermöglicht bei der chromatischen Tiefenaufspaltung nur den Durchtritt von Licht, welches auf der Objektoberfläche oder in einem teiltransparenten Objekt an einem Lichtstreuer scharf fokussiert war (A7).

The scanning of an object along a line with a multitude of spatial interferograms and consequently the calculation of a profile has already been described by M. Hering et al. In [3].

• 11. Preferably, in the arrangement for robust interferometry in the reference beam path, a multiplicity of miniaturized three-plane mirror reference end reflectors are arranged in the form of an array. Thus, an object field as in a pincushion or a nail board with a controllable light source can be scanned time-sequentially by focus points, whereby, for example, a shape measurement on a small object of limited depth extent, for example a microdelle or a flat lubricating pocket in a metal body, is possible (A3).
• 12. Preferably, in the arrangement for robust interferometry, the arrangement of three-plane mirror reference end reflectors in this array takes place in a line-like, planar or three-dimensional structure. In each case, measuring points along a line can be recorded simultaneously in one shot.
• 13. In the arrangement for robust interferometry, miniaturized three-plane mirror reference end reflectors are preferably arranged in the form of a three-dimensional staircase structure. In this way, slightly inclined object surfaces can be measured without the center of gravity of the interferogram envelope being shifted much laterally.
• 14. Preferably, in the arrangement for robust interferometry, the source of short-coherent electromagnetic radiation is formed as a dot matrix radiator.
• 15. Preferably, in the arrangement for robust interferometry, the dot matrix is on The source of short-coherent electromagnetic radiation is rotated at an acute angle to the intersection of the interfering wavefronts on the rasterized detector. The axis of rotation is thus arranged perpendicular to the VSE and parallel to the BE. At the same time, a large number of interferograms can be placed on the detector.
• 16. Preferably, in the arrangement for robust interferometry, the source of short-coherent electromagnetic radiation is formed with switchable point light sources. Thus, the scanning pattern is freely selectable, for example, according to relevance of object features from pre-information.
• 17. Preferably, the rastered light source is formed with switchable line light sources in the arrangement for robust interferometry. This allows an object field for form measurement to be measured particularly quickly.
• 18. In the arrangement for robust interferometry, the source of short-coherent electromagnetic radiation for laterally finely structured illumination of an object is preferably formed by means of a switchable spatial light modulator array, so that this source of short-coherent electromagnetic radiation is formed laterally switchable. This gives a high degree of flexibility. Thus, different illumination patterns on the object in a time sequence can be realized, so that, for example, in an embodiment of the reference reflector with linear, miniaturized three-mirror reference Endreflektoren successively each illumination of the object with a single line and defined locations on the whole Referee Reflector takes place until the object field is completely scanned, for example, by a stepwise laterally moving line. The lateral density of the scan pattern is selectable, allowing relevant areas to be measured at higher sample density if required (A4).
• 19. Preferably, in the arrangement for robust interferometry in the reference beam path, there is a spatial correspondence between the lateral structure of the illumination pattern and the lateral arrangement of miniaturized three-plane mirror reference end reflectors, so that each miniaturized three-plane mirror reference end reflector has at least one light spot or a light line of the light source, at least in the period of time of an image recording, is assigned.
• 20. In the arrangement for robust interferometry, at least one double diaphragm based on columns or pinholes is preferably arranged in a jointly used reference and object radiation imaging stage. In this case, a first opening of the double diaphragm of the reference radiation and a second opening of the object radiation is reserved. Thus, a confocal discrimination of the object radiation can be performed. The first area serves for the passage of the reference light in the direction of the detector and can also hide unwanted stray light from the reference beam path. However, the gaps or pinholes, that is to say the diaphragm elements, can also be designed so finely that cylinder or spherical waves of high spatial coherence are formed (A5).
• 21. Preferably, in the arrangement for robust interferometry, the double diaphragm (12) is arranged in a plane optically conjugate with the measurement plane ME, wherein the optically conjugate plane is represented by at least one radiation pencil. Thus, a confocal discrimination of object radiation can be performed.
• 22. Preferably, in the arrangement for robust interferometry means are arranged for the predetermined controlled change in the distance and / or the position of the column or pinholes of the double diaphragm, so that the confocal filtering can be carried out optimally.
• 23. Preferably, means for chromatic depth splitting of foci are arranged in the arrangement for robust interferometry in the object beam path. Thus, a significantly greater depth measuring range can be realized with a diffraction-limited lateral resolution than the wave-optical depth of field. This approach, particularly with multi-point probing of the object, can be well implemented with a Linnik-type interferometer with a comparatively small numerical aperture. In this case, the chromatic depth splitting means may be arranged in the Fourier plane of the object-imaging objective. It can be used for this purpose a diffractive-optical element. The arrangement of a diffractive-optical element in the Fourier plane was already in DE 103 21 895 A1 shown. This leads to a constant magnification for radiation of all wavelengths (A6).
• 24. Preferably, at least one confocal discriminating diaphragm is arranged in the arrangement for robust interferometry in the object beam path. In the case of chromatic depth splitting, this only allows the passage of light which was sharply focused on the object surface or in a partially transparent object on a light scatterer (A7).

Focused radiation for object illumination is thus reflected and / or scattered on the object, once again passing through the means for chromatic depth splitting of foci, whereby a wavelength-dependent refractive power is effective, which leads to at least partial collimation of the portions of the electromagnetic radiation, which focuses on or in Have formed object. Subsequently, the collimated electromagnetic radiation passes through a lens for focusing and then at least partially the confocal discriminating aperture. Only the portions of the electromagnetic radiation which have formed foci on or in the object can essentially pass through this confocal discriminating aperture.

In this case, this confocal discriminating aperture can also be used to produce foci for structured object illumination. Then, this aperture is interspersed twice by radiation, that is, by backward and back propagating radiation. In this case, this aperture is located at the input of the interferometer. After the return of object and reference radiation to the interferometer input, which then also represents the interferometer output, there is confocal discrimination of object light and interference on the detector.

• 25. Vorzugsweise ist bei der Anordnung zur robusten Interferometrie das Interferometer im Grundtyp als Michelson-, Linnik-, Mirau- oder Schulz-Minor-Interferometer ausgebildet und mindestens ein Drei-Spiegel-Referenz-Endreflektor im Referenzstrahlengang angeordnet. Die numerische Apertur ist dabei nicht extrem hoch zu wählen, da sonst die Reflexion mittels eines Drei-Planspiegel-Referenz-Endreflektors nicht mehr möglich ist. Der Schwerpunkt des Einsatzes der erfindungsgemäßen Anordnung liegt deshalb recht eindeutig im Bereich einer mittleren oder geringeren numerischen Apertur für Objektbeleuchtung und Detektion.

It is advantageous here if the means for chromatic depth splitting of foci for the mean wavelength of the spectrum of the electromagnetic radiation used have the refractive power zero, that is to say refractive power compensated, for example as a diffractive refractive system with opposing refractive power of the components. Then, with a corresponding compensation of the optical path lengths in the reference beam path, the interferometer can be operated at least approximately zero at the optical path difference zero or in a comparatively narrow range around the optical path difference zero and the dispersion is largely negligible. Advantageously, this approach can be used in a Linnik-type interferometer in which infinitely corrected microscope objectives are used. In this Linnik-type interferometer at least a three-mirror reference end reflector is arranged in the reference beam path.

• 25. Preferably, in the arrangement for robust interferometry, the interferometer in the basic type is designed as a Michelson, Linnik, Mirau or Schulz minor interferometer, and at least one three-mirror reference end reflector is arranged in the reference beam path. The numerical aperture is not extremely high to choose, otherwise the reflection by means of a three-plane mirror reference end reflector is no longer possible. The focus of the use of the arrangement according to the invention therefore lies quite clearly in the range of a medium or lower numerical aperture for object illumination and detection.

For example, a lens with a numerical aperture of 0.2 can still be used quite well in conjunction with a three-plane mirror reference end reflector in the reference beam path.

In a Michelson interferometer arrangement, it is possible to deviate far from the perpendicularity between the reference beam and the object beam path. Thus, an angle between the main beams of reference and object radiation of 160 degrees is preferably a good option for realizing a slim sensor with good accessibility to the measurement object.

• 26. Vorzugsweise sind bei der Anordnung zur robusten Interferometrie Mittel zur vorbestimmten Variation der numerischen Apertur der Beleuchtung angeordnet. Damit kann der wellenoptische Schärfentiefebereich optimal an eine Messaufgabe angepasst werden.

In a Mirau or Schulz minor interferometer, the center shading, which occurs through the reference reflector, by the use of a double-slit or double-pinhole aperture with a suitable gap or pinhole distance, which are each formed very fine, so one Point-Diffraction arrangement represent, be made harmless. However, this can cause significant light losses. However, this is usually technically feasible with light sources of high spatial coherence and light output (A8).

• 26. Preferably, in the arrangement for robust interferometry means are arranged for the predetermined variation of the numerical aperture of the illumination. Thus, the wave-optical depth of field can be optimally adapted to a measuring task.

For the occasional measurement task that an object surface is to be inclined to the optical axis of the object beam path appropriate, for example, a 45 ° chamfer surface on a fine-milled workpiece, an additional plane mirror of the object surface can be assigned in the object beam path of the interferometer, said plane mirror with the object surface then at least approximately should include a right angle, so at least approximately forms a 90 ° roof edge. In the reference beam path in this case a 90 ° roof edge reflector is arranged, the mirror surfaces should always experience only a single reflection. This arrangement in conjunction with a Michelson interferometer provides lateral shear, avoids the wavefront inversion, but usually has clear disadvantages because of the volume in the object beam path, so in terms of accessibility to the object, for example, indoors, and will therefore not here followed up. This Michelson interferometer arrangement, with the possibility of generating lateral shear by means of two double-sided reflectors, is classical and is generally used for wavefront analysis, s. a. [4] and [5].

To use the approach published in [6] with two triple reflectors in a Michelson interferometer, here as an arrangement for an interferometric sensor for distance measurement, among others a plane mirror of the triple reflector in the form of a cube corner, also known as corner cube, is replaced by the object surface leads to the object in the object beam path still having to assign a roof edge reflector when the unwanted wavefront inversion between object and reference radiation is to be avoided. This is a possible sensor solution, but increases the whole sensor volume considerably, which is very disadvantageous for many applications or excludes the use of such a solution completely. Again, there is no invariance of the lateral shear - and thus the inclination of the interfering wavefronts, for example, given lateral drifting away of the triple reference reflector or the object itself. Thus, the spatial frequency in the spatial interferogram change, which can be disadvantageous.

Preferably, for oblique illumination of an object surface, two further plane mirrors, one each on the right and one on the left, be flanking assigned and in the reference beam path is the already described three-mirror reference end reflector with obtuse or acute-angled triangle ABC of Spurgeraden. In this case, the difference in the number of reference plane and object path plane mirror surfaces once passed by the light is zero so that wavefront inversion does not occur. The amount delta_q of the lateral shear can hereby be set freely by laterally sliding the end reflector with three plane mirrors. This arrangement allows to illuminate almost flat object surfaces very obliquely, for example, with an incident angle of 85 °. For example, oblique interferometry for straightness, shape and waviness detection on comparatively rough technical surfaces, such as precision machined flat metal surfaces, can be operated. As a result of the oblique incidence, it is known to reduce the depth measuring sensitivity of the interferometer by the factor of the cosine of this angle of incidence on the object surface, also known as lambda elongation.

Is in the object beam path of the inventive arrangement, a 90 ° -Umlenkspiegel example used to measure on the inner wall of a small hole that is passed both in the outward and in the return of the light, this 90 ° -Umlenkspiegel is due to the double reflection on the same without any Influence on the orientation of the object wavefronts in the detection and thus can remain unnoticed with regard to the problem of wavefront inversion.

Characteristics of the procedure

• 27. In the method for robust interferometry for the detection of distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form, or also for optical coherence tomography (OCT), with the means of the arrangement in the preamble, the method steps are: Generating at least one object beam of electromagnetic radiation for illuminating the object, Generating at least one reference beam by means of beam splitting in an interferometer, Generating spatial short-coherence interference of object and reference beams, • Detection of spatial short-coherence interference on a screened detector of electromagnetic radiation carried out.

• • im Referenzstrahlengang drei direkt aufeinanderfolgende Reflexionen an je drei Planspiegeln durchgeführt,
• • dabei liegen die Flächen dieser drei Planspiegel jeweils zumindest näherungsweise senkrecht zu einer gemeinsamen Bezugsebene BE und bilden somit einen Drei-Planspiegel-Referenz-Endreflektor
• • und durch die drei Reflexionen wird eine Lateral-Shear mit dem Betrag delta_q zwischen Objektstrahlenbündel und Referenzstrahlenbündel im Interferometer eingeführt, wodurch auf dem gerasterten Detektor mindestens ein räumliches Kurzkohärenz-Interferogramm erzeugt wird,
• • und mindestens ein räumliches Interferogramm wird zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder der optischen Weglänge eines Objekts, auch in der optischen Kohärenz-Tomografie, ausgewertet.

According to the invention

• In the reference beam path, three directly successive reflections are carried out on three plane mirrors each,
• • The surfaces of these three plane mirrors are each at least approximately perpendicular to a common reference plane BE and thus form a three-plane mirror reference end reflector
• And the three reflections introduce a lateral shear of the amount delta_q between the object beam and the reference beam in the interferometer, thereby producing at least one spatial short-coherence interferogram on the screened detector,
• And at least one spatial interferogram is evaluated to obtain information about distance, depth, profile, shape, waviness and / or roughness or the optical path length of an object, also in optical coherence tomography.

The invariance of the lateral shear with the amount delta_q between the object beam and reference beam against lateral displacements of the three-plane mirror reference end reflector represents a great advantage, since the spatial frequency for the center wavelength of the spatial interferogram with a fixed spectrum of the light source, for , B. is constant even when thermally caused lateral drifting away of the reflector as a monolithic assembly. In contrast, shifting the reflector in depth, due to the changing optical path length, leads to lateral displacement of the spatial interferogram on the detector (A9).

Features to dependent claims of the method

• 28. In the method for robust interferometry, a point-like or a laterally structured illumination of the object is preferably carried out in order to minimize, for example, the scattered light (A10).
• 29. In the method for robust interferometry, the reflections of the main beam of the reference beam are preferably carried out such that the points of impact of the main beam of the reference beam on the three plane mirrors lie at least approximately in a common plane, which is aligned parallel to the common reference plane BE.
• 30. The method of robust interferometry is preferably performed after the objective ( 13 ), which collimates the object bundle, in its subordinate focal plane F13 '- from the predetermined lateral shear delta_q of reference and object bundles in the lens ( 13 ) upstream focal plane F13, which represents the measurement plane ME of the arrangement, - generates a tilt by the angle delta_beta of the main beams of reference and object bundles.

• – entweder in dieser Brennebene (F13')
• – oder in einer zu dieser Brennebene (F13') in Lichtrichtung nachgeordneten, optisch konjugierten Ebene durchgeführt, wobei diese nachgeordnete, optisch konjugierte Ebene mindestens durch ein Strahlenbüschel in einer Ebene dargestellt ist.

In addition, the detection of a spatially extended two-beam interferogram

• Either in this focal plane (F13 ')
• - Or in a to this focal plane (F13 ') downstream in the light direction, optically conjugate plane, said subordinate, optically conjugate plane is at least represented by a pencil of rays in a plane.

• 31. Beim Verfahren zur robusten Interferometrie wird vorzugsweise eine Strahlformung von Referenzstrahlenbündel und Objektstrahlenbündel mittels abbildender Zylinder-Optik mit Fokussierung von mindestens einem Strahlenbüschel in die Brennebene (F13') des objektabbildenden Objektivs durchgeführt.
• 32. Beim Verfahren zur robusten Interferometrie wird vorzugsweise eine Strahlformung von Referenzstrahlenbündel und Objektstrahlenbündel mittels abbildender Zylinder-Optik mit Fokussierung von mindestens einem Strahlenbüschel in eine zur Brennebene (F13') des objektabbildenden Objektivs in Lichtrichtung nachgeordneten, optisch konjugierten Ebene durchgeführt und diese konjugierte Ebene ist mindestens durch ein Strahlenbüschel gegeben.
• 33. Beim Verfahren zur robusten Interferometrie wird vorzugsweise ein Ausschnitt der Brennebene (F13') durch eine in Lichtrichtung nachfolgende, anamorphotische Abbildungsstufe zumindest näherungsweise durch ein erstes Strahlenbüschel, dessen Fläche senkrecht Schnittlinie von Referenz- und Objektwellenfront in der Brennebene (F13') angeordnet ist, auf den Detektor abgebildet. Außerdem wird jeder optisch erfasste Objektpunkt vorzugsweise durch ein zweites Strahlenbüschel, das senkrecht zum ersten ausgerichtet ist, auf den Detektor fokussiert abgebildet, so dass für jeden optisch erfassten Objektpunkt auf dem Detektor mindestens ein räumlich ausgedehntes, linienförmiges Zweistrahl-Interferogramm zumindest näherungsweise in Linienform erzeugt wird und die linienförmigen Zweistrahl-Interferogramme der optisch erfassten Objektpunkte vorzugsweise auf dem Detektor in Stapelform angeordnet werden, wobei jedem linienförmigen Zweistrahl-Interferogramm ein eigener Bereich auf dem Detektor reserviert ist.

The advantage here is that the tilt of the main beams of reference and object bundles to each other by the angle delta_beta against a change in position, such as translations in all three spatial axes, a rigid, ie monolithic three-plane mirror reference end reflector in the reference beam path invariant is. This also applies to the object and the beam splitter, for example in a Michelson-type interferometer. Smaller rotations of the inherently rigid three-plane mirror reference end reflector, the object or the beam splitter in the interferometer arrangement, which is used for both beam splitting and combining, also result in no or only a second order influence on the magnitude of the angle delta_beta in which, with a temporally constant light source spectrum and a gray, black or white object surface, the spatial frequency for the centroid wavelength in the spatial interferogram can be regarded as virtually invariable. Even a colored object surface usually has only a relatively small influence on the spatial frequency for the centroid wavelength. However, exceptions can be layer systems, such as spectral bandpasses.

• 31. In the method for robust interferometry, beam shaping of reference beam and object beam is preferably carried out by means of imaging cylinder optics with focusing of at least one beam of rays in the focal plane (F13 ') of the object-imaging lens.
• 32. In the method for robust interferometry is preferably carried out a beam shaping of reference beam and object beam by imaging cylinder optics with focusing of at least one pencil of rays in the focal plane (F13 ') of the object-imaging lens in the light direction downstream, optically conjugate plane and this conjugate plane given at least by a ray bundle.
• 33. In the method for robust interferometry is preferably a section of the focal plane (F13 ') by a subsequent light direction, anamorphic imaging stage at least approximately by a first bundle of rays whose surface is arranged perpendicular line of intersection of reference and object wavefront in the focal plane (F13') , imaged on the detector. In addition, each optically detected object point is preferably imaged focused on the detector by a second beam bundle, which is aligned perpendicular to the first, so that at least one spatially extended, line-shaped two-beam interferogram is generated at least approximately in line form for each optically detected object point on the detector and the line-shaped two-beam interferograms of the optically detected object points are preferably arranged on the detector in stack form, each line-shaped two-beam interferogram having its own area reserved on the detector.

• 34. Beim Verfahren zur robusten Interferometrie wird vorzugsweise eine lateral feinstrukturierte Beleuchtung vom Objekt und dem Drei-Planspiegel-Referenz-Endreflektor in Form eines zeitseriell schaltbaren Beleuchtungsmusters durchgeführt und nach jedem Schaltvorgang wird mindestens ein räumliches Interferogramm mit dem gerasterten Detektor aufgenommen.
• 35. Beim Verfahren zur robusten Interferometrie werden vorzugsweise die Messebene ME und die zu den Messpunkten der Messebene ME optisch korrespondierenden miniaturisierten Drei-Spiegel-Referenz-Endreflektoren im Referenzstrahlengang zeitlich lateral abgescannt, indem die Quelle kurzkohärenter elektromagnetischer Strahlung zur lateral feinstrukturierten Beleuchtung, welche also schaltbar ausgebildet ist, unterschiedliche laterale Bereiche des Objekts nach und nach beleuchtet und bei jedem Beleuchtungsmuster räumliche Interferogramme mittels gerastertem Detektor aufgenommen werden.
• 36. Beim Verfahren zur robusten Interferometrie erfolgt der laterale Scan des Beleuchtungsmusters in der Messebene ME vorzugsweise schrittweise und entsprechend der lateralen Abstände der einzelnen Drei-Spiegel-Referenz-Endreflektoren im Referenzstrahlengang.
• 37. Beim Verfahren zur robusten Interferometrie wird der Drei-Planspiegel-Referenz-Endreflektor vorzugsweise synchronisiert mit dem Beleuchtungsmuster lateral verschoben. So kann die Messebene ME nach und nach, also über der Zeit, optisch lateral abgetastet werden.
• 38. Beim Verfahren zur robusten Interferometrie sind die Reflexionsgrade benachbarter Mikro-Referenzreflektoren vorzugsweise stark unterschiedlich ausgeführt. Durch Beleuchten eines anderen Drei-Spiegel-Referenz-Endreflektors, der einen stark anderen Reflexionsgrad aufweist, und lateralem Nachpositionieren des Sensors zum Objekt kann eine bessere Anpassung der Intensität des Referenzbündels an die Intensität des Objektbündels erreicht werden, insbesondere wenn ein Objektbereich einen sehr geringen Reflexionsgrad aufweist.
• 39. Beim Verfahren zur robusten Interferometrie ist vorzugsweise mindestens ein Drei-Planspiegel-Referenz-Endreflektor in einem Metall- oder Kunststoffkörper durch eine Single-Point-Diamantbearbeitungstechnik hergestellt. Dies kann hochgenau und vergleichsweise kostengünstig erfolgen (A11).
• 40. Beim Verfahren zur robusten Interferometrie ist vorzugsweise mindestens ein Drei-Planspiegel-Referenz-Endreflektor durch Abformtechnik hergestellt.
• 41. Beim Verfahren zur robusten Interferometrie ist vorzugsweise mindestens ein Drei-Planspiegel-Referenz-Endreflektor durch Ätztechnik hergestellt.
• 42. Beim Verfahren zur robusten Interferometrie ist vorzugsweise mindestens ein Drei-Planspiegel-Referenz-Endreflektor durch Abform-, Heiß- oder Kaltpräge- oder auch Drucktechnik hergestellt.
• 43. Beim Verfahren zur robusten Interferometrie wird vorzugsweise die Phase mindestens eines räumlichen Interferogramms zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder optische Weglänge eines Objekts ausgewertet.
• 44. Beim Verfahren zur robusten Interferometrie wird vorzugsweise der Schwerpunkt der Einhüllenden mindestens eines räumlichen Interferogramms zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder optische Weglänge eines Objekts ausgewertet.
• 45. Beim Verfahren zur robusten Interferometrie wird vorzugsweise das Maximum der Einhüllenden mindestens eines räumlichen Interferogramms zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder optische Weglänge eines Objekts ausgewertet.
• 46. Beim Verfahren zur robusten Interferometrie wird vorzugsweise der Gleichanteil mindestens eines räumlichen Interferogramms zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder optische Weglänge eines Objekts ausgewertet. Aus räumlichen Verteilung des Gleichanteils des räumlichen Interferogramms können Informationen über das Objekt gewonnen werden.
• 47. Beim Verfahren zur robusten Interferometrie wird vorzugsweise im Objektstrahlengang eine chromatische Tiefenaufspaltung von Foki mit spektral brechkraftvariablen Mitteln im Objektstrahlengang vorbestimmt durchgeführt. Damit kann der Tiefenmessbereich vergrößert werden.
• 48. Beim Verfahren zur robusten Interferometrie wird vorzugsweise Strahlung vom Objekt nach dem zweiten Passieren der spektral brechkraftvariablen Mittel konfokal diskriminiert. Anschließend wird diese Strahlung vom Objekt mit Strahlung aus dem Referenzstrahlengang zur Bildung von mindestens einem räumlichen Interferogramm überlagert und die Intensitätsverteilung des räumlichen Interferogramms wird einer Fourier-Transformation nach dem Verfahren der Fourier-Transformations-Spektroskopie unterzogen, um das Spektrum auch von konfokal diskriminierter Strahlung vom Objekt nach chromatischer Tiefenaufspaltung zu gewinnen, um aus diesem Spektrum den Abstand, die Tiefe, das Profil, die Form, Welligkeit und/oder die Rauheit oder die optische Weglänge eines Objekts zu ermitteln. Hierzu kann eine Schwerpunktauswertung erfolgen. Hierbei führen im Wesentlichen nur die Wellenlängenanteile zu merklichen Anteilen im Spektrum, die auf dem Objekt scharf fokussiert waren, also dort Foki ausgebildet haben, und demzufolge eine konfokale Blende passieren konnten. Der spektral breitbandige Intensitätsanteil aus dem Referenzstrahlengang schlägt sich nicht in einer Modulation im Interferogramm nieder und somit auch nicht im durch Fourier-Transformation errechneten Spektrum, da die breitbandigen Intensitätsanteile aus dem Objektstrahlengang aufgrund der Tiefenaufspaltung von Foki mit nachfolgender konfokaler Diskriminierung bereits verloren gegangen sind und somit nicht zur Interferenzbildung beitragen können. Spektral vergleichsweise breitbandig ist hier nur der Anteil des Lichts aus dem Referenzstrahlengang, der aber wegen der fehlenden spektral breitbandigen Objektlichtanteile nicht zu einer Modulation im Interferogramm führen kann. Somit ergibt sich nach der Fourier-Transformation des räumlichen Interferogramms ein vergleichsweise schmalbandiges Spektrum von an der konfokalen Blende hindurchgelassener Strahlung aus dem Objektstrahlengang. Die Modulation ist in einem derartigen Interferogramm bei starker chromatischer Tiefenaufspaltung nicht sehr groß, aber aufgrund der vergrößerten Kohärenzlänge durch die konfokale Separierung spektral eingegrenzter Lichtanteile räumlich vergleichsweise stärker ausgedehnt. Durch die Fourier-Transformation des räumlichen Interferogramms kann die Schwerpunktwellenlänge der an der konfokalen Blende jeweils – in Abhängigkeit vom Objektabstand – hindurchgelassenen Strahlung vergleichsweise genau numerisch ermittelt werden. So kann durch eine Kalibrierung der Abstand, die Tiefe, das Profil, die Form, Welligkeit und/oder die Rauheit oder die optische Weglänge eines Objekts ermittelt werden. Dieser Ansatz erübrigt die Verwendung eines dispersiven Spektrometers zur Bestimmung des Spektrums beim chromatisch-konfokalen Verfahren. Dieser Ansatz mit Fourier-Transformation des räumlichen Interferogramms zur Gewinnung eines chromatisch-konfokalen Signals kann hier zusätzlich eingesetzt werden, um multivariat oder multiskalig messen zu können.
• 49. Vorzugsweise wird Objektstrahlung aus der nachgeordneten Brennebene F13', welche die Fourier-Ebene des objektabbildenden Strahlenganges darstellt und in der Regel auch die Pupillenebene darstellen kann, durch die in Lichtrichtung dieser Brennebene F13' nachfolgende Strahlteilung aus dem Hauptstrahlengang ausgekoppelt. Diese Objektstrahlung wird zeitlich synchron zur Aufnahme von räumlichen Interferogrammen auf demselben oder einem zeitlich mit dem gerasterten Detektor synchronisierten Detektor mittels Abbildung zur Detektion gebracht. Damit können sowohl die von einem optisch angetasteten Objektpunkt sich ergebende Pupillenausleuchtung als auch das räumliche Interferogramm genau dieses Objektpunktes zeitgleich auf ein und demselben Kamera-Chip oder zwei zueinander elektronisch synchronisierten Kamera-Chips zur Verfügung stehen.

Each two-beam interferogram in this case has an average modulation frequency resulting from the geometry of the interferometer arrangement and the light source spectrum, including spectral reflection properties, which is thus predetermined.

• 34. In the method for robust interferometry preferably a laterally finely structured illumination of the object and the three-plane mirror reference end reflector is performed in the form of a time-series switchable illumination pattern and after each switching operation, at least one spatial interferogram is recorded with the rastered detector.
• 35. In the method for robust interferometry preferably the measuring plane ME and the miniaturized to the measuring points of the measuring plane ME miniaturized three-mirror reference end reflectors in Reference beam path scanned laterally in time by the source of short-coherent electromagnetic radiation for laterally finely structured illumination, which is designed switchable, gradually illuminate different lateral areas of the object and spatial interferograms are recorded by rasterized detector with each illumination pattern.
• 36. In the method for robust interferometry, the lateral scan of the illumination pattern in the measurement plane ME preferably takes place stepwise and corresponding to the lateral distances of the individual three-mirror reference end reflectors in the reference beam path.
• 37. In the method of robust interferometry, the three-plane mirror reference end-reflector is preferably laterally shifted in synchronization with the illumination pattern. Thus, the measurement level ME can be scanned optically laterally over time, so over time.
• 38. In the method of robust interferometry, the reflectivities of adjacent micro-reference reflectors are preferably made very different. By illuminating another three-mirror reference end reflector, which has a very different reflectance, and later repositioning the sensor to the object, a better matching of the intensity of the reference beam to the intensity of the object beam can be achieved, especially if an object area has a very low reflectance having.
• 39. In the method of robust interferometry, preferably at least one three-plane mirror reference end reflector is fabricated in a metal or plastic body by a single-point diamond machining technique. This can be done with high precision and comparatively cheaply (A11).
• 40. In the method for robust interferometry, preferably at least one three-plane mirror reference end reflector is made by molding.
• 41. In the method for robust interferometry, preferably at least one three-plane mirror reference end reflector is made by etching.
• 42. In the method for robust interferometry, preferably at least one three-plane mirror reference end reflector is produced by molding, hot or cold embossing or also printing technology.
• 43. In the method of robust interferometry, the phase of at least one spatial interferogram is preferably evaluated to obtain information about distance, depth, profile, shape, waviness and / or roughness or optical path length of an object.
• 44. In the robust interferometry method, the center of gravity of the envelope of at least one spatial interferogram is preferably evaluated to obtain information about distance, depth, profile, shape, waviness and / or roughness or optical path length of an object.
• 45. In the method for robust interferometry, the maximum of the envelope of at least one spatial interferogram is preferably evaluated for obtaining information about distance, depth, profile, shape, waviness and / or roughness or optical path length of an object.
• 46. In the method of robust interferometry, the DC component of at least one spatial interferogram is preferably evaluated to obtain information about distance, depth, profile, shape, waviness and / or roughness or optical path length of an object. From spatial distribution of the DC component of the spatial interferogram, information about the object can be obtained.
• 47. In the method for robust interferometry, a chromatic depth splitting of foci with spectrally refractive-power-variable means in the object beam path is preferably carried out in the object beam path in a predetermined manner. This allows the depth measuring range to be increased.
• 48. In the method for robust interferometry, radiation from the object is preferably confocally discriminated after the second passage of the spectrally refractive power variable means. Subsequently, this radiation is superimposed by the object with radiation from the reference beam path to form at least one spatial interferogram and the intensity distribution of the spatial interferogram is subjected to a Fourier transform according to the method of Fourier transform spectroscopy to the spectrum of confocal discriminated radiation from To extract the object after chromatic depth splitting to determine from this spectrum the distance, depth, profile, shape, waviness and / or roughness or optical path length of an object. For this purpose, a focus analysis can be done. In this case, essentially only the wavelength components lead to significant proportions in the spectrum, which were sharply focused on the object, that is, where they formed foci, and consequently could pass through a confocal diaphragm. The spectrally broadband intensity component from the reference beam path is not reflected in a modulation in the interferogram and thus not in the spectrum calculated by Fourier transformation, since the broadband intensity components from the object beam path have already been lost due to the depth splitting of foci with subsequent confocal discrimination and thus can not contribute to the formation of interference. Spectral In this case, only the proportion of light from the reference beam path is comparatively broad-band, but because of the lack of spectrally broadband object light components, this can not lead to a modulation in the interferogram. Thus, after the Fourier transformation of the spatial interferogram, a comparatively narrow-band spectrum of radiation transmitted through the confocal aperture results from the object beam path. The modulation is not very large in such an interferogram with strong chromatic depth splitting, but due to the increased coherence length by the confocal separation spectrally limited light components spatially relatively more extensive. By means of the Fourier transformation of the spatial interferogram, the centroid wavelength of the radiation transmitted at the confocal diaphragm in each case-as a function of the object distance-can be determined comparatively accurately numerically. Thus, calibration can be used to determine the distance, depth, profile, shape, waviness and / or roughness or optical path length of an object. This approach eliminates the need for a dispersive spectrometer to determine the chromatic confocal spectrum. This approach with Fourier transformation of the spatial interferogram to obtain a chromatic-confocal signal can additionally be used here in order to be able to measure multivariate or multiscale.
• 49. Preferably, object radiation from the downstream focal plane F13 ', which represents the Fourier plane of the object-imaging beam path and, as a rule, can also represent the pupil plane, is coupled out of the main beam path by the beam splitting following in the light direction of this focal plane F13'. This object radiation is brought into temporal synchronism with the recording of spatial interferograms on the same or a time synchronized with the rasterized detector detector by means of imaging for detection. Thus, both the pupil illumination resulting from an optically touched object point and the spatial interferogram of precisely this object point can be simultaneously available on one and the same camera chip or two camera chips synchronized with one another electronically.

In this case, the reference beam which is optionally coupled therewith at the beam splitter from the main beam path in this secondary beam path for pupil observation is thereby blocked, for example in the vicinity of a focal point thereof, ie where object and reference radiation are clearly spatially separated. So it is possible that only the object radiation can come to the detection. A beam splitter for decoupling covering both object and reference beam paths, which for example represents a high-precision manufactured cube of stress-free quality glass, introduces dispersion and optical path length change both in the object beam and the reference beam path in the same or almost the same way and is therefore white light Interference virtually absent, since ideally the optical path difference as the difference of the path lengths of object and reference radiation by inserting this decoupling beam splitter cube practically does not change here.

Thus, the form of the illumination of the pupil plane, that is to say the intensity distribution in the pupil surface, which coincides for the most part with the Fourier plane of the object-imaging objective, can also be detected in real time of the interferogram recording. The illumination of this pupil plane is largely determined by object properties, such as surface gradient and microstructure of the object being probed, and thus also contains very essential information about the characteristic of the appropriate object point. In particular, little cooperative measuring points of the object or measured points with special features such as object edges can be clearly recognized, correspondingly classified and fed to the further processing or to the sorting out.

The information from the illumination of the pupil plane and the spatial interferogram of one or more object points in a specific measurement situation can be combined for a more comprehensive description of the object by means of a model.

The reference radiation of the interferometer is thus clearly hidden, which is comparatively easy by this arrangement with lateral shear. This relatively easy acquisition of the pupil illumination represents a very particular advantage of this arrangement according to the invention and can not in known scanning white light interferometers rather or only with very considerable technical effort, for example, to compensate for the optical paths and the dispersion in a white light interferometer, in real time will be realized.

The absolutely simultaneous acquisition of the pupil illumination and the spatial interferogram is absolutely necessary for measurements of rough or three-dimensionally finely structured surfaces in an environment even with comparatively small vibration amplitudes, in which case a pulsed or flashed light source can be used. With vibrations, the pupil illumination and the spatial interferogram can be very fast and significant, so even in a period of less than ten milliseconds, change significantly, especially when speckle occur in the optical signals.

Characteristics of the secondary claim of the arrangement

• 50. It is a method and arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and flatness deviation on technical specular objects, in particular polished or ultra-precision machined glass and metal surfaces. The arrangement will be described below. The following means are used in the process: A monochromatic or quasi-monochromatic source of electromagnetic radiation for illuminating the object, An interferometer, in particular also in the form of an interference microscope, with an object and at least one reference beam path, in which at least one end reflector is arranged, and a measuring plane in the object beam path, in which at least approximately the optically to be measured surface or volume elements of Object are located. And at least one screened detector for detecting electromagnetic radiation in the form of at least one spatial interferogram.

The source of electromagnetic radiation is also referred to below as light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

The light source thus represents a monochromatic or quasi-monochromatic light source, for example a laser light source.

The light source can produce a laterally finely structured illumination pattern on the object. In this case, the light source can be a point emitter, a lateral line emitter or a group of point emitters in line or matrix form even with individually switchable point-shaped or line-shaped lighting elements.

According to the invention, at least one end reflector with three plane mirrors as the reference reflector, ie at least one three-plane mirror reference end reflector, is arranged in the reference beam path of the interferometer, and the surfaces of these three plane mirrors each lie at least approximately perpendicular to a common reference plane BE.

The three spur lines of the planes, which are represented by the surfaces of the three plane mirrors, form in the reference plane BE a triangle ABC, so that there is a lateral shear between reference and object bundles in this interferometer, which represents a distance with the amount delta_q. The distances AB, BC and CA of this triangle ABC must have a certain length. For example, the lengths of these sections may typically each be on the order of a few tenths of a millimeter to a few millimeters mm. The angles of this triangle are neither extremely pointed, nor is this triangle a right triangle. The resulting lateral shear may have an amount delta_q on the order of typically from 0.1 mm to several millimeters. In an arrangement with a laterally high-resolution microscope and a centroid wavelength in the UV range, however, the amount delta_q can also be on the order of a few hundredths of a millimeter. This is based on correspondingly small lengths of the distances AB, BC and CA and the corresponding three angles of the triangle ABC. This approach is widely scalable in terms of the amount delta_q.

The lateral shear of the amount delta_q between reference and object bundles exists in the virtual mirror plane VSE of the three-plane mirror reference end reflector in the reference beam path. The virtual mirror plane VSE is at least approximately optically conjugate with the measurement plane ME of the object beam path by beam splitting. In this case, the three-plane mirror reference end reflector is angularly aligned so that electromagnetic radiation passes from the reference beam path to the screened detector.

A lateral displacement of a three-plane mirror reference end reflector does not result in a change in the amount of lateral shear delta_q. This invariance is regarded as a great technical advantage, since this results in a high robustness of the signal generation over such misalignments.

The three-plane mirror reference end reflector is a reflector which generates a lateral shear in the interferometer according to the invention. As already mentioned, the three-mirror reference end reflector has a virtual mirror plane VSE. This virtual mirror plane VSE can be spatially assigned to the occurrence of the lateral shears. For example, the interference of an object spherical wave and a reference spherical wave, which are generated by the interferometer and whose spherical centers are separated by a lateral shear of the amount delta_q, at least in a limited portion of the detector plane to a spatial interferogram with an at least approximately constant spatial frequency for the Center wavelength because the interfering wave surfaces on the Detector are inclined to each other. In a limited section of the spherical wave surfaces, these are generally sufficiently well approximated by plane waves. This interference phenomenon of two spatially coherent spherical wave surfaces to be registered on a detector is sufficiently known to the person skilled in the art as the classic Young's double-slit experiment, the gap distance d in the double-slit experiment corresponding here to the lateral shear with the amount delta_q.

The lateral-shear with the amount delta_q serves as a basis for the generation of one or more spatial interferograms, which are not or only slightly influenced by the inclination of the object surface in their stripe spacing, if the point-like center of the object spherical wave on a surface element is located, so the object is illuminated by focused light at least approximately punctiform. This invariance of the stripe distance is for the evaluation of spatial interferograms of great advantage, since here, for example, due to the advance knowledge of the stripe spacing in the signal robust and relatively fast lock-in approaches for determining the phase position of the spatial interferogram can be used, at least approximately to the Spatial frequency of the spatial interferogram are set, which is at least approximately known in advance. In order to determine the phase position of the spatial interferogram, however, comparatively simple phase evaluation approaches may also be used, such as the 5-phase evaluation algorithm according to J. Schwider. However, it is also possible to use phase evaluation algorithms which calculate on the order of magnitude 100 intensity values to a phase value modulo 2 PI.

On the rasterized detector, a spatial interferogram is preferably detected for each object point in a laterally extended area, so that a complete line profile can be obtained by taking a single image with preferably many adjacent spatial interferograms, which are formed by beam shaping, and their evaluation.

This arrangement can be used with particular advantage when polished flat or weakly curved objects are to be measured in a vibrating environment in a very short time, where the interferometric approach with temporal phase shifting can not be used and only a few measuring points, for example along a line to Suffice testing. The measurement is particularly simple here if there is a priori knowledge about the measurement object, a steady surface of the same can be assumed and the typical, expected deviations from the desired geometry are on the order of magnitude of the wavelength of light used or significantly lower or the deviations from the setpoint geometry changes very little laterally over the measurement object (A12).

Characteristics of another additional claim of the arrangement

• 51. It is a method and arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and flatness deviation on technical specular objects, in particular polished or ultra-precision machined glass and metal surfaces. The arrangement will be described below. The following means are used in the process:
• A monochromatic or quasi-monochromatic source of electromagnetic radiation and also a source of short-coherent electromagnetic radiation for illuminating the object,
• An interferometer, in particular also in the form of an interference microscope, with an object and at least one reference beam path, in which at least one end reflector is arranged, and a measuring plane in the object beam path, in which at least approximately the optically to be measured surface or volume elements of Object are located.
• And at least one screened detector for detecting electromagnetic radiation in the form of at least one spatial interferogram.

The source of electromagnetic radiation is also referred to below as light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

The light source is a monochromatic or quasi-monochromatic light source, for example a laser light source. In addition, a source of short-coherent electromagnetic radiation for illuminating the object is also arranged. This wavelength is dominant in the overall spectrum. At this wavelength, the aberrations of the optical arrangement, especially in the pupil of the optical system for object imaging, have a minimum.

The light source can produce a laterally finely structured illumination pattern on the object. In this case, the light source can be a point emitter, a lateral line emitter or a group of point emitters in line or matrix form even with individually switchable point-shaped or line-shaped lighting elements.

According to the invention, at least one end reflector with three plane mirrors as a reference reflector, ie at least one three-plane mirror reference end reflector, is arranged in the reference beam path of the interferometer, and the surfaces of these three plane mirrors lie at least approximately perpendicular to a common reference plane BE.

In addition, means for spectral splitting in the detection beam path are provided in the arrangement, so that spatial interferograms are separated according to the wavelength. Here is the well-known approach to spectral interferometry used. Thus, the spatial interferogram of the light source with monochromatic or quasi-monochromatic radiation on the screened detector for highly accurate phase evaluation can be separated. At the same time, spatial interferograms with different wavelengths are separated so that a multi-wavelength approach can be used for evaluation. By adding several spatial interferograms with different wavelengths, a numerically generated short-coherence interferogram can be calculated and evaluated in a known manner. Thus, by means of short-coherence interferogram or multi-wavelength technique, the absolute fringe order or a reference fringe in the spatial interferogram pattern can be determined. From the spatial interferogram of the light source with monochromatic or quasi-monochromatic radiation, the phase position for determining a highly accurate depth or distance information in a measuring point is determined numerically. This involves the highest-precision measurement of polished or ultra-precision machined surfaces, ie resolution and measurement uncertainty in the sub-lambda range, for example for measuring the shape of optics in the EUV range.

According to the invention, the three spur lines of the planes, which are represented by the surfaces of the three plane mirrors, form in the reference plane BE a triangle ABC, so that there is a lateral shear between reference and object bundles in this interferometer, which represents a distance with the amount delta_q. The distances AB, BC and CA of this triangle ABC must have a certain length. For example, the lengths of these sections may typically each be on the order of a few tenths of a millimeter to a few millimeters. The angles of this triangle are neither extremely pointed nor is this triangle a right triangle. The resulting lateral shear may have an amount delta_q on the order of typically from 0.1 mm to several millimeters. In an arrangement with a laterally high-resolution microscope and a centroid wavelength in the UV range, however, the amount delta_q can also be on the order of a few hundredths of a millimeter. This is based on correspondingly small lengths of the distances AB, BC and CA and the corresponding three angles of the triangle ABC. This approach is widely scalable in terms of the amount delta_q.

The lateral shear of the amount delta_q between reference and object bundles exists in the virtual mirror plane VSE of the three-plane mirror reference end reflector in the reference beam path. The virtual mirror plane VSE is at least approximately optically conjugate with the measurement plane ME of the object beam path by beam splitting. In this case, the three-plane mirror reference end reflector is angularly aligned so that electromagnetic radiation passes from the reference beam path to the screened detector.

A lateral displacement of a three-plane mirror reference end reflector does not result in a change in the amount of lateral shear delta_q. This invariance is regarded as a great technical advantage, since this results in a high robustness of the signal generation over such misalignments.

The three-plane mirror reference end reflector is a reflector which generates a lateral shear in the interferometer according to the invention. As already mentioned, the three-mirror reference end reflector has a virtual mirror plane VSE. This virtual mirror plane VSE can be spatially assigned to the occurrence of the lateral shears. For example, the interference of an object spherical wave and a reference spherical wave, which are generated by the interferometer and whose spherical centers are separated by a lateral shear of the amount delta_q, at least in a limited portion of the detector plane to a spatial interferogram with an at least approximately constant spatial frequency for the Center wavelength because the interfering wave surfaces on the detector are inclined to each other. In a limited section of the spherical wave surfaces, these are generally sufficiently well approximated by plane waves. This interference phenomenon of two spatially coherent spherical wave surfaces to be registered on a detector is sufficiently known to the person skilled in the art as the classic Young's double-slit experiment, the gap distance d in the double-slit experiment corresponding here to the lateral shear with the amount delta_q.

The lateral-shear with the amount delta_q serves as a basis for the generation of one or more spatial interferograms, which are not or only slightly influenced by the inclination of the object surface in their stripe spacing, if the point-like center of the object spherical wave on one Surface element is located, so the object is illuminated by focused light at least approximately punctiform. This invariance of the stripe distance is for the evaluation of spatial interferograms of great advantage, since here, for example, due to the advance knowledge of the stripe spacing in the signal robust and relatively fast lock-in approaches for determining the phase position of the spatial interferogram can be used, at least approximately to the Spatial frequency of the spatial interferogram are set, which is at least approximately known in advance. In order to determine the phase position of the spatial interferogram, it is also possible to use comparatively simple phase evaluation approaches, such as the 5-phase evaluation algorithm according to J. Schwider. However, it is also possible to use phase evaluation algorithms which calculate on the order of magnitude 100 intensity values to a phase value modulo 2 PI.

On the rasterized detector, a spatial interferogram of the light source with mono- or quasi-monochromatic radiation is preferably detected for each object point in a laterally extended area, as well as spatial short-coherence interferograms, which are spatially separated by the spectral means in the detection beam path. So that by recording a single image with preferably many adjacent spatial interferograms, which are formed by beam shaping, a unique and highly accurate depth or distance information can be obtained.

This arrangement can be used with particular advantage when polished flat or weakly curved objects are to be measured in a vibrating environment in a very short time, where the interferometric approach with temporal phase shifting can not be used and only a few measuring points, for example along a line to Suffice testing. The measurement is particularly simple here if there is a priori knowledge about the object to be measured, a steady surface of the same can be assumed and the typical, expected deviations from the desired geometry are on the order of magnitude of the wavelength of light used or significantly less, or the deviations from the setpoint geometry changes very little laterally over the measurement object (A13).

Characteristics of a secondary claim of the procedure

• 52. In the method of robust interferometry for the detection of distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form, or also for optical coherence tomography (OCT), with the means of the arrangement in the preamble, the method steps are performed. Generating at least one object beam of electromagnetic radiation for illuminating the object, Generating at least one reference beam by means of beam splitting in an interferometer, Generating spatial short-coherence interference of object and reference beams, • Detection of spatial short-coherence interference on a screened detector of electromagnetic radiation carried out.

• • im Referenzstrahlengang drei direkt aufeinanderfolgende Reflexionen an je drei Planspiegeln durchgeführt.
• • Dabei liegen die Flächen dieser drei Planspiegel jeweils zumindest näherungsweise senkrecht zu einer gemeinsamen Bezugsebene BE und bilden somit einen Drei-Planspiegel-Referenz-Endreflektor.
• • Durch die drei Reflexionen wird eine Lateral-Shear mit dem Betrag delta_q zwischen Objektstrahlenbündel und Referenzstrahlenbündel im Interferometer eingeführt, wodurch auf dem gerasterten Detektor mindestens ein räumliches Kurzkohärenz-Interferogramm erzeugt wird.
• • Es wird eine spektrale Aufspaltung von Objekt- und Referenzstrahlung im Detektionsstrahlengang durchgeführt.
• • Mindestens ein räumliches Interferogramm-Muster mit spektraler Aufspaltung wird zur Gewinnung von Informationen über Abstand, Tiefe, Profil, Form, Welligkeit und/oder Rauheit oder der optischen Weglänge eines Objekts, auch in der optischen Kohärenz-Tomografie, detektiert und ausgewertet.

According to the invention

• • In the reference beam path, three directly successive reflections are performed on each of three plane mirrors.
• The surfaces of these three plane mirrors are each at least approximately perpendicular to a common reference plane BE and thus form a three-plane mirror reference end reflector.
• • The three reflections introduce a lateral shear of the amount delta_q between the object beam and the reference beam in the interferometer, producing at least one spatial short-coherence interferogram on the screened detector.
• • A spectral splitting of object and reference radiation in the detection beam path is performed.
• • At least one spatial interferogram pattern with spectral splitting is detected and evaluated to obtain information about distance, depth, profile, shape, waviness and / or roughness or the optical path length of an object, also in optical coherence tomography.

This makes it possible to selectively select spatial interferograms spectrally. For example, if the source of short-coherent radiation is associated with a laser diode. As a result, in a spectral range in which the aberrations of the optical system represent a minimum, the phase position of the interferogram can be determined with high precision. The interferograms of other spectral regions serve to determine the zero order stripe (A14).

Description of the figures

The invention is exemplified by the 1 to 30 described.

Here, the term light is always synonymous with terahertz electromagnetic radiation, used across the infrared to the deep UV spectrum.

The 1 shows a sensor based on a Michelson interferometer. The light from a spectrally comparatively broadband light source 1 in the near-infrared range is by means of a beam-shaping optics 2 brought into a small focus spot FF, in which case the arrangement of a pinhole is possible, is achieved by a lens 3 collimated and by a comparatively low-aperture focusing lens 4 with a numerical aperture of 0.05 refocused and then passes into a Michelson-type interferometer with a beam splitter 5 and a beam splitter surface 6 where the light is split into a reference beam R and an object beam O. That the beam splitter 5 rectilinearly passing object light bundles O hits in focus at the measuring point MP on the specular object surface of the object 7 , which is almost in the ME trade fair center here. The object surface should be within the wave-optical depth of field of the focused light. The object 7 returning light is at the beam splitter surface 6 by reflection via the interferometer output IA in the direction of the screened detector 12 directed. Shown is the object main beam OHS. The light, which after entering the interferometer at the beam splitter 5 is reflected in the reference beam R, reaches a three-plane mirror reference end reflector 8th that from the three plan mirrors 9 . 10 and 11 exists, each of which is perpendicular to the reference plane BE, which should be here in the drawing plane. The three plane mirrors 9 . 10 and 11 represent a rigid, compact assembly. The position of the three plane mirrors 9 . 10 and 11 is always regarded as mutually immutable in the following.

The three Spurgeraden the three levels, which through the three surfaces of the plane mirror 9 . 10 and 11 spanned and resulting from the intersection of these planes with the reference plane BE, here form an obtuse triangle ABC in the reference plane BE. With AB is here a part of the Spurgeraden, here from the plane of the plane mirror surface 11 is shown represented.

At the three-plane mirror reference end reflector 8th the incident reference beam experiences a lateral shear of magnitude delta_q. The location of the formation of the lateral shear is assigned to the virtual mirror plane VSE. The virtual mirror plane VSE represents the virtual reflection plane of this three-plane mirror reference end reflector 8th and results from the position of the three-plane mirror reference end reflector 8th in the room and is built-in, if the three-plane mirror reference end reflector 8th is considered as a monolith. The straight line g represents the straight line between the plane BE and the virtual mirror plane VSE, wherein the virtual mirror plane VSE is perpendicular to the reference plane BE. In this case, the virtual mirror plane VSE is intended to represent, relative to the interferometer output IA, a plane optically conjugate with the measuring plane ME of the object beam path, which is achieved by an adjustment of the interferometer. The three-plane mirror reference end reflector 8th Reflected reference beams, represented by the reference main beam RHS leaves the interferometer after passing straight through the beam splitter 5 with the beam splitter surface 6 via the interferometer output IA, also passes to the screened detector 12 and there comes to interference with the light from the object beam path. This creates a spatial interferogram on the screened detector 12 with at least approximately constant spatial frequency for the centroid wavelength, since the there interfering spherical waves are relatively far away from their centers and the rasterized detector 12 has only a comparatively small area. The ratios in the interference correspond to sufficiently small focus points here those in Young's double-slit experiment with two pinholes. The angle between the tangent planes TR and TO of reference and object spherical waves form an angle delta_beta at the point of penetration of the line of symmetry SL in the plane of the drawing, from which the stripe distance dS for the center of gravity wavelength lambda hardly increases at least approximately dS = (lambda_chwer * r) / delta_q (1) gives, if r, the distance of the centers of the two spherical waves from the reference and object beam path from the detection plane on the detector 12 represents, wherein the center of the spherical wave in the reference beam path coincides with the virtual beam focus BFV '.

The optical path difference can be made almost zero in the interferometer for all wavelengths, if a nearly perfect beam splitter cube with the same optical path lengths is used here. Smaller deviations of the two optical path lengths in the cube in the range of a few micrometers, however, are generally still tolerable well and result in the spatial interferogram on the screened detector 12 In addition to a constant lateral displacement of the interferogram wavelet also to an asymmetry of the envelope. However, this can be taken into account by the algorithms of the evaluation. By moving the three-plane mirror reference end reflector 8th The center of gravity of the interferogram wavelet can be centered on the screened detector 12 be positioned.

The optical path difference is in the interferometer shown here by a small Storage of the reflecting surface of the object 7 from the measurement plane ME at a time t1 not exactly zero. This leads to the formation of a spatial short-coherence interferogram KKI with a maximum of the magnitude y (t1) shifted laterally to the symmetry line SL of the two principal rays. Is the object surface of the object 7 At the time t2 in a different depth position, a maximum of the spatial short-coherence interferogram laterally shifted by the amount (-) y (t2) arises in the form of a wavelet.

This arrangement of a three-plane mirror reference end reflector 8th in the form that the triangle ABC of the straight line is obtuse, leads to the advantage that the angles of incidence on the three plane mirrors for the main beam of the reference beam can each be chosen so that too large angle of incidence, so grazing incidence, even for marginal rays of a focused beam be avoided.

Not shown here are means for surface illumination of the object 7 and means for planar imaging of the object 7 on another camera, in order to be able to approach relevant measuring positions by means of sensor actuators. This is prior art and is assumed in all subsequent arrangements.

The 2 represents the three-plane mirror reference end reflector 8th with the three plan mirrors 9 . 10 and 11 whose straight-line form the triangle ABC. These Spurgeraden emerge by the cut of the planes, by the surfaces of the plane mirror 9 . 10 and 11 be spanned, with the reference planes BE, which coincides here with the plane of the drawing.

The three plane mirrors 9 . 10 and 11 are manufactured here by a single-point diamond machining.

The three-plane mirror reference end reflector 8th corresponds to a virtual plane mirror in the virtual mirror plane VSE. This virtual plane mirror generates a lateral shear delta_q in the virtual mirror plane VSE. In the depth, so the distance from the beam splitter cube 5 is the three-plane mirror reference end reflector 8th in this case arranged by adjustment so that the bundle focus BF of an incident homocentric bundle 1 with the incident main beam EHS_1 on the virtual mirror plane VSE as the virtual focal point BFV. In addition, the main beam EHS_1 should be incident perpendicular to the virtual mirror plane VSE. Due to the lateral shear, this virtual focal point BFV undergoes a shift by the amount delta_q_1 and now arises virtually as BFV '. Apparently, starting from the virtual focus point BFV ', the return of the light begins in the direction of the beam splitter cube 5 and interferometer output IA. Here, too, the main beam of the outgoing beam AHS_1 is perpendicular to the virtual mirror plane VSE.

It is advantageous that the real focal point BF of the homocentric bundle 1 , or the center of a spherical wave, not on one of the plane mirror surfaces 9 or 10 lies, but arises in air. As a result, the fine microstructure, which as a rule is present on the plane mirror surfaces by the diamond micro-machining, can not be applied to the detector 12 be shown sharply, especially if this plane mirror surface is well outside the optical depth of field. The light scattering that results from this fine microstructure is eliminated in the further beam path by a confocal discrimination.

For a parallel offset bundle with the principal rays EHS_2 and AHS_2, the amount of lateral shear is delta_q_2. With perfect plane mirrors and in each case vertical position relative to the reference plane BE, the following applies here: The amount of the lateral shear delta_q is equal to the amount delta_q_1. and also equal to the amount delta_q_2 and thus applies delta_q_1 = delta_q_2 = delta_q (2) and there is an invariance of the amount of lateral shear delta_q versus a variable beam incidence height.

The 3 indicates that in a three-plane mirror reference end reflector 8th the lateral shear delta_q always takes place in an excellent plane, the virtual mirror plane VSE. This distance, which represents the lateral shear with the amount delta_q, is immutable in magnitude and is determined by the distance of the jet piercing points DP and DP 'in the virtual mirror plane VSE. This virtual mirror plane VSE is in a rigid three-plane mirror reference end reflector 8th stationary. The three-plane mirror reference end reflector shown on the right 8th is shifted by the distance v from the one shown on the left and it is still observed no emigration of the output beam in the context of character accuracy, because PA1 and PA2 are at the same height. This shows the invariance of a three-plane mirror reference end-reulector 8th with respect to the beam exit from lateral displacements thereof.

However, the influence of tilting the assembly is "three-plane mirror reference end reflector 8th ", Shown here with rotation about a vertical axis, on an incident bundle or a wavefront comparable to the tilting of a plane mirror. So the three-plane mirror reference end reflector has to be 6 as in itself rigid assembly also be angularly adjusted to the main beam of the bundle at least approximately perpendicular to the virtual Mirror plane VSE to minimize the lateral offset of the interfering wavefronts in the detection plane of interference. A tilt of the assembly "three-plane mirror reference end reflector 8th "Around a vertical axis can also lead to a reduction in the contrast of the interference in the detection plane. With a very small focus diameter, however, this influence on the contrast of the interference defuses considerably.

The 4 provides a three-plane mirror reference end reflector 8th with the plane mirrors 9 . 10 , and 11 in M-shape. This M-shape arrangement also corresponds to a virtual planar mirror with an additional lateral shear delta_q. A homocentric bundle with the incident principal ray EHS and the real focus point BF on the plane mirror 11 In the virtual mirror plane VSE of BFV, the lateral shear is offset by the amount delta_q and the virtual focal point BFV 'is created. Also this three-plane mirror reference end reflector 8th in M-shape, it must be angularly aligned like a plane mirror in a classic Michelson interferometer to bring the light into interference.

The 5 provides a three-plane mirror reference end reflector 8th with the plane mirrors 9 . 10 , and 11 on the basis of an acute-angled triangle ABC of the three spur lines dar. Here, working with linearly polarized light with s-polarization, in order to ensure a high degree of reflection even in grazing incidence of light. The bundle focus BF is created on the mirror surface 10 , which make higher demands on the "cleanliness" of the same and a low residual roughness of the mirror surface 10 must be given.

The 6 shows a light source, not shown here 1 illuminated light modulator 15 , which turns on successively, so that at each time t1, t2, t3 there is a focused beam in a different lateral position. In the reference beam path is a reference reflector 18 arranged, which consists of a plurality of mutually parallel three-plane mirror reference end reflectors 8.1 . 8.2 . 8.i ... is constructed, each of which is assigned in succession in a telecentric beam path, a homocentric bundle with a bundle focus BFV in the virtual mirror plane. The optical beam path with the light modulator 15 and the lens 4 with a small numerical aperture of 0.05 is constructed so that the bundle foci each at the time ti in a three-plane mirror reference end reflectors 8.i and there experience a lateral shear with the amount delta_gi, wherein this amount delta_q from position to position due to a Präzisionsfertigung the reference reflector 18 to change as little as possible. So you can temporally succession on the object 7 different object positions are approached pointwise and the resulting spatial interferograms by means of a large-scale screened detector 12 be recorded. The light source with the light modulator 15 is hereby switched through laterally sequentially. The wave-optical depth of field is Tz.

The 7 shows a reference reflector 118 of three-plane mirror reference end reflectors 8.i in a linear structure based on an arrangement of M-shaped plane mirrors. Again, the lighting is time sequential.

The 8th shows a sensor based on a Michelson interferometer for a relatively large object field, ie at the upper end of the microscopic scale. The light from a spectrally comparatively broadband light source 1 in the near-infrared range is by means of a beam-shaping optics 2 brought into a focal point line FPL, whereby the arrangement of a gap is possible here. The light of the focal point line FPL is through a lens 3 collimated and through a focusing lens 4 with a numerical aperture of 0.05 refocused and then passes into a Michelson-type interferometer with a beam splitter 5 and a beam splitter surface 6 where the light is split into a reference beam R and an object beam O. That the beam splitter 5 rectilinearly passing object light bundles O is focused on the object surface of the object 7 , which is located here almost in the measurement level ME and forms a measurement point line MPL. The object surface should be located within the wave-optical depth of field of the focused light Tz. The object 7 returning light is at the beam splitter surface 6 by reflection via the interferometer output IA in the direction of the screened detector 12 directed. Shown is the object main beam OS-BE in the plane BE.

The light, which after entering the interferometer at the beam splitter 5 is reflected in the reference beam R, reaches a three-plane mirror reference end reflector 8th that from the three plan mirrors 9 . 10 and 11 consists.

At the three-plane mirror reference end reflector 8th Each focal point of the incident reference light experiences a lateral shear of the amount delta_q. The place of origin of the lateral shear is the virtual mirror plane VSE.

The virtual mirror plane VSE in this case, based on the interferometer output IA, represents a plane optically conjugate with the measuring plane ME of the object beam path, which is given by the adjustment of the interferometer. The three-plane mirror reference end reflector 8th reflected Reference light, represented by the reference main beam RS-BE leaves the interferometer after passing straight through the beam splitter 5 with the beam splitter surface 6 via the interferometer output IA.

The comparatively long focal length lens 13 , with a focal length of 120 mm is a cylinder lens 14 downstream with the cylinder axis y '. The rasterized detector 12 is in the focal plane F13 'of the lens 13 which also has the Fourier plane of this lens 13 represents. To determine the position of the Fourier plane here alone the refractive power of the lens 13 considered. In this case, the measurement plane ME is at least approximately in the focal plane F13 of the objective 13 , After the lens 13 For example, a reference wave RW and an object wave OW each include the angle delta_beta, which is a quotient of the amount delta_q of the lateral shear and the focal length f13 'in radians. The angle delta_beta is to be regarded as constant here because of the invariance of the amount delta_q of the lateral shear, and thus also the interference fringe width dS, which is difficult for the centroid wavelength Lambda at least approximately dS = (lambda_chwer · f ') / delta_q (3) results.

In detail A is the cylinder mirror assembly 14 shown from the cylinder mirrors 14a and 14b and which the measuring points P1 and P2 in the measuring plane ME by beam tufts in the measuring point images P1 'and P2' on the rasterized detector 12 in cooperation with the lens 13 maps. Due to the resulting refractive power of the lens 13 and the cylinder optics 14 are the measurement plane ME and the level of the screened detector 12 through beam tufts, which through the cylinder mirror assembly 14 be focused, optically conjugated.

Detail B represents the plane of the screened detector 12 with the spatial short-coherence interferograms KKI of the individual measuring points of the measuring point line MPL.

The detail C shows the spatial interferogram of a measuring point Pi and the detail D represents a point-wise calculated profile z (x) of the object from the short-coherence interferogram 7 along the measuring point line MPL dar.

The 9 shows an unfolded with respect to the interferometer beam path with the lateral shear of the amount delta_q and a downstream cylinder optics 114 , This serves to form a stack of spatial short-coherence interferograms on the screened detector 12 , The plane of the rasterized detector 12 is optically conjugate to the focal plane F13 'of the lens 13 through the rotationally symmetrical lenses 15 and 17 , At the same time there is an optical conjugation to the double gap plane 16 and to the measurement level ME by the imaging of bundles of rays through the cylinder optics 114 , Here is the cylinder optics 114 chromatically and well corrected in terms of distortion. The axis y 'of the cylinder optics 114 lies parallel to the plane BE and also parallel to the straight line g in the section of the reference plane BE and the virtual mirror plane VSE.

The 10 represents a 90 ° rotated view. It is the optical conjugation of the object points P1, P2 from the object 7 as well as P1 ', P2' and P1 ", P2" in the detector plane.

The 11 shows an arrangement in which different measurement points can be spatially addressed in an object field. The light from a source of short-coherent radiation 101 with beam shaping optics and spatial light modulator happens the lenses 3 and 4 and enters the Michelson interferometer. Shown here is an array 18 of linear three-plane mirror reference end reflectors 8.i which is arranged in the reference beam path. The object 70 , here a sealing disk for flatness testing, is illuminated simultaneously with a number of light points for measuring flatness, in which case a reference light point R and an object light point O belong to each measuring point, which form a pair of coherent light points, from which a spatial interferogram is generated. After picture according to the beam path to 8th arises in the plane of the detector 12 , the Fourier plane F13 ', a stack of spatial short-coherence interferograms KKI, from which the flatness deviation over the angle φ can be calculated. Prerequisite is a calibration of the measuring system, for example with a plane mirror in the object position.

The 12 shows a biological layered object 700 , The layered object 700 is illuminated simultaneously with a number of light spots at time t1. Reflections occur at each layer, resulting in short coherent spatial interferograms. After picture according to the beam path after the 9 and 10 arises in the plane of the detector 12 , the Fourier plane F13 ', a stack of pairs of spatial short-coherence interferograms KKI that make up the optical thickness oD of the biological layered object 700 can be determined via a lateral coordinate.

In the 13 is due to the source of short-coherent radiation 101 by controlling the spatial light modulator at time t2 another area of the biological layered object 700 , so a laterally slightly displaced area along a line, addressed.

Thus, the course of the optical thickness oD of the biological layered object 700 spatially resolved, here along the coordinate y. A prerequisite here is also a calibration of the measuring system.

In the 14 is a Linnik-type interferometer for use as a multipoint sensor shown. The light from a spectrally comparatively broadband light source 1 in the near-infrared region becomes after passing a beam splitter 66 - For later decoupling of the light - by means of a beam shaping optics 2 brought into a focal point line FPL. In the plane of the focal point line FPL is an asymmetrical confocal multi-double iris 116b , which is shown in detail E. The light of the foci of the focus point line FPL passes through the pinholes in the left area of the aperture 116b therethrough. The objective 3 collimates the bundles from the individual pinholes, which subsequently into the Linnik-type interferometer with a numerical aperture of 0.25 of the lenses 113-R and 113-O enter. The low-loss beam splitter layer 6 This interferometer is highly transmissive, here the degree of transmission is 85%, so that even weakly reflecting objects can be measured well.

In the object beam path of this Linnik-type interferometer here is a refractive power-compensated objective system 19 used with a diffractive-optical element for chromatic depth splitting of Foki to increase the depth measuring range. The lens system 19 has the refractive power zero for the centroid wavelength in the spectrum used, so behaves the lens system 19 for the center wavelength in terms of refractive power as a plane parallel plate. For wavelengths above and below the centroid wavelength, divergent or convergent beams thus result if, for the centroid wavelength, there is a bundle with the focal point at infinity. The chromatic depth splitting is intended to increase the depth measuring range of the system by about a factor of 5 compared to the wavelength of the optical fiber depth of field, which results from the numerical aperture and the spectrum used. In the reference beam path is a compensation element 20 arranged to equalize the optical path difference.

The evaluation of the spatial interferograms is done here by a focus analysis of the chromatic-confocal discrimination significantly widened spatial interferogram KKI, which still represents a short-coherence interferogram. The object 7 returning light is at the asymmetric confocal multi-double aperture 116b in the left area confocally discriminated by the pinholes. That after reflection at the three-plane mirror reference end reflector 8th light returning from the interferometer passes the right-hand area of the confocal multi-double iris, which is large relative to the pinholes 116b , Object and reference light will be after passing through the confocal multi-double iris 116b by means of a beam splitter 66 decoupled in the detection beam path. By means of the imaging stage, consisting of the rotationally symmetrical lens 17 and the cylinder optics 14 , the generation of a stack of spatial interferograms, of which the center of gravity of the envelope is evaluated. The detail F shows a single spatial interferogram KKI, from which the center of gravity of the envelope is evaluated. In this case, however, the spatial frequency in the spatial short-coherence interferogram KKI is also dependent on the depth of the object 7 dependent, since the focal length changes due to the confocal suppression of spectral components. This must be considered during the evaluation.

Therefore, here, so in the case of a chromatic depth splitting of foci in the object beam path, alternatively to the emphasis analysis of the envelope of the spatial short-coherence interferogram KKI to perform a Fourier transform the intensity distribution of the spatial interferogram to from the spatial short-coherence interferogram KKI, s , a. Detail F, to determine the spectrum of the confocal discriminated light. This is shown in detail G. The centroid wave number kS, with kS = 2Pi / centroid wavelength, this spectrum depends in each measurement point - due to the chromatic depth splitting in the object beam path - directly from the depth z of a suitable object point. This corresponds to the chromatic-confocal approach, which is used here by determining the centroid wave number kS by means of a fast Fourier transformation of the intensity distribution of spatial interferograms. The numerical relationship between the center of gravity wave number kS and the depth z of a suitable object point can be stored as a result of a sensor calibration in a table and made available by computer in the measurement process.

The 15 represents a Linnik-type interferometer for use as a dot sensor. Detail H shows the symmetrical confocal double iris used here 116a with only two openings. The beam path corresponds to that in 14 and described in detail E. However, the pupil illumination PA is also detected here. This is done by a beam splitter 67 made possible.

The detail I in 15 represents the spatial interferogram and the pupil illumination on the rasterized detector 12 For a point sensor can here a pupil observation with blocked reference beam path to the same screened detector 12 respectively. This is possible in real time. In the upper area of the detector 12 is a spatial short-coherence interferogram (KKI) and recorded in the lower part of the pupil illumination PA. This contains essential information about the characteristic of the appropriate object point. However, the pupil imaging is done here without an illustration of the cylinder optics 14 with appropriate optical means on the detector 12 ,

The 16 shows an arrangement based on a Michelson-type interferometer for multi-point scanning along a line. In addition, the system has a large angle between the object and reference arm to allow a comparatively slim sensor design.

The light from a spectrally comparatively broadband light source 1 in the near-infrared range is by means of a beam-shaping optics 2 brought into a focal point line FPL and passes through the aperture arrangement 116b through the pinholes. Before that, there was another passage through a beam splitter 51 , which serves the later decoupling. The light of the focus point line FPL becomes after the aperture arrangement 116b through a lens 3 collimated and through a focusing lens 4 with a numerical aperture of 0.05 refocused and then passes into the Michelson-type interferometer with a comparatively slightly tilted double-plate beam splitter 51 and a beam splitter surface 6 where the incident light is split into a reference beam R and an object beam O. The object 7 and the three-plane mirror reference end reflector 8th returning light passes over the double plate beam splitter 52 again towards the aperture arrangement 116b , Here the object light is through the pinholes in the right part of the aperture arrangement 116b confocally discriminated. The reference light passes through the comparatively large opening in the left part of the diaphragm arrangement 116b without confocal discrimination. At the beam splitter 51 the extraction takes place in the direction of detection via the lens 17 and the cylinder optics 14 which is used to form linear short-coherence interferograms KKI in the Fourier plane of the objective 17 leads, which by means of rastered detector 12 from which the profile can be calculated via the coordinate x.

The 17 FIG. 12 illustrates a Michelson-type interferometer arrangement for one-point scanning. The light from a spectrally comparatively broadband light source 1 in the near-infrared range is by means of a beam-shaping optics 2 brought into a focal point line FPL and passes through the aperture arrangement 116a through the pinholes. Before that, there was another passage through a beam splitter 51 , which serves the later decoupling. The light of the focal point is after the aperture arrangement 116a having a pinhole and a comparatively large opening through a lens 3 collimated and through a focusing lens 4 with a numerical aperture of 0.08 again and then enters the Michelson-type interferometer with a comparatively slightly tilted double-plate beam splitter 51 and a beam splitter surface 6 where the incident light is split into a reference beam R and an object beam O. The object 7 and the three-plane mirror reference end reflector 8th returning light passes over the double plate beam splitter 52 again towards the aperture arrangement 116a , Here, the object light is through the pinhole in the right part of the aperture arrangement 116b confocally discriminated. The reference light passes through the comparatively large opening in the left part of the diaphragm arrangement 116a without confocal discrimination. At the beam splitter 51 the extraction takes place in the direction of detection via the lens 17 and the cylinder optics 14 which is used to form a single, linear short-coherence interferogram KKI in the Fourier plane F17 'of the objective 17 leads, by means of a rastered line detector 102 is taken, from which a measuring point MP on the object 7 which contains distance information can be calculated.

The 18 illustrates a Michelson-type interferometer based arrangement for one-point scanning along a line. The light from a spectrally comparatively broadband light source 1 in the near-infrared range is by means of a beam-shaping optics 2 brought into a focal point line FPL and passes through the aperture arrangement 116a through the pinholes. Before that, there was another passage through a beam splitter 51 , which serves the later decoupling. The light of the focal point is after the aperture arrangement 116a having a pinhole and a comparatively large opening through a lens 3 collimated and by a comparatively long focal length focusing lens 4 with a numerical aperture of 0.1 refocused and then enters the Michelson-type interferometer with a comparatively slightly tilted double-plate beam splitter 51 and a beam splitter surface 6 where the incident light is split into a reference beam R and an object beam O. In the object beam path is a diffractive-optical phase element 21 arranged in the form of a Fresnel lens with positive refractive power. A depth splitting of foci in the depth range delta_z_chrom takes place in the object space, as a result of which the depth measuring range is increased approximately to 400 μm. The object 7 and the three-plane mirror reference end reflector 8th returning light passes over the double plate beam splitter 52 again towards the aperture arrangement 116a , Here, the object light is through the pinhole in the right part of the aperture arrangement 116b Confocal discriminated, where only the spectral components of the light can pass through the pinhole, previously sharp on the object 7 were pictured. The reference light passes through the comparatively large opening in the left part of the diaphragm arrangement 116a without confocal discrimination. At the beam splitter 51 the extraction takes place in the direction of detection via the lens 17 and the cylinder optics 14 which is used to form a single, linear short-coherence interferogram KKI in the Fourier plane F17 'of the objective 17 leads, by means of a rastered line detector 102 is taken, from which a measuring point MP on the object 7 which contains distance information can be calculated. For this purpose, the comparatively wide linear short-coherence interferogram KKI is subjected to a fast Fourier transformation in order to determine the centroid wave number kS, see detail J, from which the depth information is obtained via the measuring point MP. Alternatively, it is also possible to carry out a determination of the center of gravity of the linear short-coherence interferogram KKI for determining the depth information about the measuring point MP.

The 19 FIG. 12 illustrates an arrangement based on a Michelson-type interferometer for the one-point scan shown in FIG 17 builds. Additionally, in the light source assembly 110 a wavelength-stabilized laser diode not shown here in detail integrated. In addition, there are means for spectroscopic splitting in the detection beam path, here in the form of a phase grating 22 , where the axis of the spectral splitting is here in the plane of the drawing and parallel to the y-axis. So it comes on the detector for lateral splitting. 20 shows the resulting interference patterns, also known as Müllersche stripes or as Tolansky stripes. The spatial interferogram KKI-22 represents one of many linear short-coherence interferograms on the rasterized detector 12 The spatial interferogram mon_Int derives from the laser diode and is used for highly accurate phase evaluation, while the spread short-coherence interferograms in the calculation on the basis of a multi-wavelength approach, the zeroth stripe order and thus provide the absolute depth or distance information for the measuring point MP on the object 7 , In addition, the pupil illumination is also detected in order to obtain the angular spectrum of the appropriate object point. This gives information about further features of the surface in the measuring point MP.

Claims (14)

Arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form, or also for optical coherence tomography (OCT), which means includes: • a source of short-coherent electromagnetic radiation ( 1 . 101 ) for illuminating the object, • an interferometer, in particular also in the form of an interference microscope, with an object (O) and at least one reference beam path (R), in which at least one end reflector is arranged, and a measuring plane (ME) in Object beam path in which at least approximately the optically to be measured surface or volume elements of the object ( 7 ) are located. • as well as at least one screened detector ( 12 . 102 ) for the detection of electromagnetic radiation in the form of at least one spatial interferogram, characterized in that in the reference beam path of the interferometer • at least one end reflector ( 8th . 8i ) with three plane mirrors ( 9 . 10 . 11 ) is arranged as a reference reflector in the reference beam path and the surfaces of these three plane mirror ( 9 . 10 . 11 ) are each at least approximately perpendicular to a common reference plane BE • and the three Spurgeraden the levels, which by the surfaces of the three plane mirror ( 9 . 10 . 11 ) in the reference plane BE form a triangle ABC, so that in this interferometer between reference (RS) and object bundle (OS) a lateral shear of the amount delta_q exists. Arrangement for robust interferometry according to claim 1, characterized in that the three spur lines (AB, BC, CA) form an obtuse-angled triangle ABC in the reference plane BE. Arrangement for robust interferometry according to at least one of claims 1 and 2, characterized in that in the reference beam path a plurality of miniaturized three-plane mirror reference end reflectors ( 8th . 8i ) in the form of an array ( 18 ) is arranged. Arrangement for robust interferometry according to at least one of claims 1 to 3, characterized in that the source of short-coherent electromagnetic radiation ( 1 . 101 . 110 ) for laterally finely structured illumination of an object ( 7 . 70 . 700 ) by means of a switchable spatial light modulator array ( 15 ) is trained. Arrangement for robust interferometry according to at least one of claims 1 to 4, characterized in that at least one Double iris ( 16 . 116a . 116b ) based on columns or pinholes in a shared mapping stage ( 15 . 17 ) is arranged for reference and object radiation, wherein a first opening of the double diaphragm ( 16 . 116a . 116b ) of the reference radiation and a second aperture of the object radiation is reserved. Arrangement for robust interferometry according to at least one of claims 1 to 5, characterized in that in the object beam path means ( 19 . 21 ) are arranged for chromatic depth splitting of foci. Arrangement for robust interferometry according to at least one of claims 1 to 23, characterized in that in the object beam path at least one confocal discriminating diaphragm ( 16 . 116a . 116b ) is arranged. Arrangement for robust interferometry according to at least one of Claims 1 to 7, characterized in that the interferometer in the basic type is designed as a Michelson, Linnik, Mirau or Schulz-Minor interferometer and at least one three-mirror reference end reflector ( 8th . 8i ) is arranged in the reference beam path. Method for robust interferometry for detecting distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form, or also for optical coherence tomography (OCT) with the means in The generic term of the arrangement according to claim 1 and the A method steps: generating at least one object beam of electromagnetic radiation for illuminating the object ( 7 . 70 . 700 ), • generating at least one reference beam by means of beam splitting in an interferometer, • generating spatial short-coherence interference of object and reference beams, • detecting spatial short-coherence interference on a screened detector ( 12 . 102 ) electromagnetic radiation, characterized in that • in the reference beam path three, directly successive reflections on three plan mirrors ( 9 . 10 . 11 ), while the surfaces of these three plane mirrors ( 9 . 10 . 11 ) are each at least approximately perpendicular to a common reference plane BE and thus a three-plane mirror reference end reflector ( 8th . 8i ) is introduced by the three reflections, a lateral shear with the amount delta_q between the object beam and the reference beam in the interferometer, whereby on the rasterized detector ( 12 . 102 ) at least one spatial short-coherence interferogram is generated, and • at least one spatial interferogram for obtaining information about distance, depth, profile, shape, waviness and / or roughness or the optical path length of an object ( 7 . 70 . 700 ), also in optical coherence tomography. Method for robust interferometry according to claim 9, characterized in that a punctiform or laterally structured illumination of the object ( 7 . 70 . 700 ) he follows. Method for robust interferometry according to at least one of Claims 9 and 10, characterized in that at least one three-plane mirror reference end reflector ( 8th . 8i ) in a metal or plastic body ( 18 ) is made by a single point diamond machining technique. Arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and flatness deviation in or on technical objects, comprising the following means: a monochromatic or quasi-monochromatic source of electromagnetic radiation ( 1 . 101 ) for illuminating the object, • an interferometer, in particular also in the form of an interference microscope, with an object (O) and at least one reference beam path (R), in which at least one end reflector is arranged, and a measuring plane (ME) in Object beam path in which at least approximately the optically to be measured surface or volume elements of the object ( 7 . 70 . 700 ) are located. • as well as at least one screened detector ( 12 . 102 ) for the detection of electromagnetic radiation in the form of at least one spatial interferogram, characterized in that in the reference beam path of the interferometer • at least one end reflector ( 8th . 8i ) with three plane mirrors ( 9 . 10 . 11 ) is arranged as a reference reflector in the reference beam path and the surfaces of these three plane mirror ( 9 . 10 . 11 ) are each at least approximately perpendicular to a common reference plane BE • and the three Spurgeraden the levels, which by the surfaces of the three plane mirror ( 9 . 10 . 11 ), in the reference plane BE form a triangle ABC, so that there is a lateral shear of the amount delta_q in this interferometer between reference and object bundles. Arrangement for robust interferometry for detecting distance, depth, profile, shape, waviness and flatness deviation in or on technical objects, which comprises the following means: a monochromatic or quasi-monochromatic source of electromagnetic radiation and also a source ( 1 . 101 ) of short coherent electromagnetic radiation for illuminating the object ( 7 . 70 . 700 ), • an interferometer, in particular also in the form of an interference microscope, with an object (O) and at least one reference beam path (R), in which at least one end reflector is arranged, and a measurement plane (ME) in the object beam path, in the at least approximately the optically to be measured surface or volume elements of the object ( 7 . 70 . 700 ) are located. • as well as at least one screened detector ( 12 . 102 ) for the detection of electromagnetic radiation in the form of at least one spatial interferogram, characterized in that in the reference beam path of the interferometer • at least one end reflector ( 8th . 8i ) with three plane mirrors ( 9 . 10 . 11 ) is arranged as a reference reflector in the reference beam path and the surfaces of these three plane mirror ( 9 . 10 . 11 ) are each at least approximately perpendicular to a common reference plane BE • and the three Spurgeraden the levels, which by the surfaces of the three plane mirror ( 9 . 10 . 11 ), in the reference plane BE form a triangle ABC, so that in this interferometer between reference (R) and object bundle (O) there is a lateral shear of the amount delta_q. 19 . 21 ) are arranged for spectral splitting in the detection beam path. Method for robust interferometry for detecting distance, depth, profile, shape, waviness and / or roughness or the optical path length in or on technical or biological objects, also in layer form, or also for optical coherence tomography (OCT) with the means in The generic term of the arrangement according to claim 12 and the method steps: generating at least one object beam of electromagnetic radiation for illuminating the object ( 7 . 70 . 700 ), • generating at least one reference beam by means of beam splitting in an interferometer, • generating spatial short-coherence interference of object and reference beams, • detecting spatial short-coherence interference on a screened detector ( 12 . 102 ) electromagnetic radiation, characterized in that • in the reference beam path three directly successive reflections on each of three plane mirrors ( 8th . 9 . 10 ), wherein the surfaces of these three plane mirrors each lie at least approximately perpendicular to a common reference plane BE and thus a three-plane mirror reference end reflector ( 8th . 8i ) and the three reflections introduce a lateral shear with the amount delta_q between the object beam and the reference beam in the interferometer, whereby on the screened detector ( 12 . 102 ) at least one spatial short-coherence interferogram is generated, and • a spectral splitting of object and reference radiation in the detection beam path is performed • and at least one spatial interferogram pattern with spectral splitting to obtain information about distance, depth, profile, shape, ripple and roughness or the optical path length of an object ( 7 . 70 . 700 ), also in optical coherence tomography, is detected and evaluated.

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