EP2347215A1 - Method and device for interferometry - Google Patents

Method and device for interferometry

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Publication number
EP2347215A1
EP2347215A1 EP09741220A EP09741220A EP2347215A1 EP 2347215 A1 EP2347215 A1 EP 2347215A1 EP 09741220 A EP09741220 A EP 09741220A EP 09741220 A EP09741220 A EP 09741220A EP 2347215 A1 EP2347215 A1 EP 2347215A1
Authority
EP
European Patent Office
Prior art keywords
signal
frequency comb
scan
delta
object
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09741220A
Other languages
German (de)
French (fr)
Inventor
Klaus KÖRNER
Wolfgang Osten
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Stuttgart Universitaet
Original Assignee
Stuttgart Universitaet
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to DE102008052003 priority Critical
Priority to DE102008052814 priority
Priority to DE200810062879 priority patent/DE102008062879B4/en
Application filed by Stuttgart Universitaet filed Critical Stuttgart Universitaet
Priority to PCT/EP2009/007327 priority patent/WO2010040570A1/en
Publication of EP2347215A1 publication Critical patent/EP2347215A1/en
Application status is Withdrawn legal-status Critical

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02001Interferometers for determining dimensional properties of, or relations between, measurement objects characterised by manipulating or generating specific radiation properties
    • G01B9/02002Frequency variation
    • G01B9/02004Frequency variation by using a continuous frequency sweep or scan
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02001Interferometers for determining dimensional properties of, or relations between, measurement objects characterised by manipulating or generating specific radiation properties
    • G01B9/02007Two or more frequencies or sources used for interferometric measurement
    • G01B9/02008Two or more frequencies or sources used for interferometric measurement by using a frequency comb
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02034Interferometers for determining dimensional properties of, or relations between, measurement objects characterised by particularly shaped beams or wavefronts
    • G01B9/02035Shaping the focal point, e.g. elongated focus
    • G01B9/02036Shaping the focal point, e.g. elongated focus by using chromatic effects, e.g. a wavelength dependent focal point
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02041Interferometers for determining dimensional properties of, or relations between, measurement objects characterised by particular imaging or detection techniques
    • G01B9/02042Confocal imaging
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02055Interferometers for determining dimensional properties of, or relations between, measurement objects characterised by error reduction techniques
    • G01B9/02056Passive error reduction, i.e. not varying during measurement, e.g. by constructional details of optics
    • G01B9/02057Passive error reduction, i.e. not varying during measurement, e.g. by constructional details of optics by using common path configuration, i.e. reference and object path almost entirely overlapping
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00Instruments as specified in the subgroups and characterised by the use of optical measuring means
    • G01B9/02Interferometers for determining dimensional properties of, or relations between, measurement objects
    • G01B9/02091Tomographic low coherence interferometers, e.g. optical coherence tomography
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B21/00Microscopes
    • G02B21/0004Microscopes specially adapted for specific applications
    • G02B21/002Scanning microscopes
    • G02B21/0024Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
    • G02B21/0052Optical details of the image generation
    • G02B21/0056Optical details of the image generation based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2210/00Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
    • G01B2210/50Using chromatic effects to achieve wavelength-dependent depth resolution
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/25Fabry-Perot in interferometer, e.g. etalon, cavity
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/30Grating as beam-splitter

Abstract

The invention relates to a method and to an arrangement for scalable confocal interferometry for distance measurement, for 3-D detection of an object, for OC tomography with an object imaging interferometer and at least one light source. The interferometer has an optical path difference not equal to zero at each optically detected object element. Thus, the maxima of a sinusoidal frequency wavelet, associated with each detected object element, each have a frequency difference ?f_Objekt. In order to record the object, at least one spectrally integrally detecting, rastered detector is arranged. Preferably, the light source is designed with a frequency comb, and the frequency comb differences ?f_Quelle are changed in a predefined manner over time in a scan during measuring. In the process, the frequency differences ?f_Quelle are made equal to the frequency difference ?f_Objekt or equal to an integer multiple of the frequency differences ?f_Objekt at least once for each object element. However, this can also occur through a scan in the object imaging interferometer. In the scan, a modulation in a signal profile is produced and sequentially detected by means of the rastered detector. The present magnitude of the frequency comb differences ?f_Quelle in said signal profile, for example, at the modulation maximum, is determined and is subsequently used to calculate the associated optical path difference of a detected object element. Distances of object elements or changes in the optical path lengths, for example, for a biological microobject, are determined therefrom in a process by imaging.

Description

 Method and apparatus for interferometry

background

The sequential recording of data from different depths of the object space by means of focussing is known to play a functional role in microscopic white light interferometry. There are hints in the following writings:

[1] Balasubramanian N: Optical System for surface topography measurement. US patent. No. 4,340,306 (1982),

[2] Cinema GS, Chim S: Mirau correlation microscope. Appl. Opt. 29 (1990) 3775-3783,

[3] Byron SL, Timothy CS: Profilometry with a coherence scanning microscope. Appl. Opt. 29 (1990) 3784-3788,

[4] Dresel Th, Häusler G, Venzke H: Three-dimensional sensing of rough sufaces by coherence radar. Appl. Opt. 31 (1992) 919-925,

[5] Deck L, de Groot P: High-speed noncontact profiler based on scanning white-light interferometry. Appl. Opt. 33 (1994) 7334-7338,

[6] Windecker R, Haible P, Tiziani H J: Fast coherence scanning interferometry for measuring smooth, rough and spherical surfaces. J. Opt. Soc. At 42 (1995) 2059-2069.

The approaches [2] [3] [5] [6] to white-light interferometry, often referred to as short-coherence interferometry, are usually limited to the microscopic range. These approaches are not widely scalable with respect to resolution and depth measurement in the direction of coarser scales, since these methods are usually very closely tied to the used wavelength of the light wavelength. Short-coherence interferometry in the infrared spectral range usually leads to many technical problems and high costs. In addition, the approaches [1], [2], [3], [4], [5] and [6] and the approach of G. Häusler, shown in DE 10 2005 023 212 B4 [7], in one Measuring arrangement or sensor arrangement only partially miniaturized, since in this case the object or the reference arm of the interferometer must be formed with moving components, since in one of the two arms, the optical path difference has to be changed according to the method. This requires a certain volume of construction for the means for moving components in one of these arms. The application of approach [7] requires means for changing the optical path length in both the reference arm and the object arm. In many cases, for example when used in an endoscope, this can only be achieved with comparatively great technical complexity and comparatively high costs.

In addition, white-light interferometry sensors based on the approaches described in [1] - [7] do not generally permit measurements on objects with distances between object and sensor in the range of one or several meters for measurements with a high volume minimization, since during measurement the optical path length in the reference arm must be made at least once equal to the optical path length in the object arm. This leads to a considerable volume of the sensor even in folded arrangements in the rule.

In the publication by T. Bajraszewski et al., "Improved spectral optical coherence tomography using optical frequency comb" [8] in Optics Express 17 March 2008 / Vol. 16, No. 6, pp. 4163 to 4176, an OCT arrangement (OCT = Optical Coherence Tomography) with an ophthalmic frequency comb laser, wherein the OCT array includes a tunable Fabry-Perot interferometer in a frequency comb laser array and includes a spectrometer OCT A fast area single-shot measurement can only be carried out with great technical effort since the detection of an object takes place laterally in series. The document US Pat. No. 7391 520 B2 [9] shows an OCT batch with a detector with a multiplicity of spectral channels, ie a spectrometer. However, due to the particular necessity of using a spectrometer in the optical measuring system, an object can not be recorded in a planar or pictorial manner at one time, but as a rule only at points; So the areal detection of an object must be done laterally serial. This is certainly acceptable for the applications described in [8] and [9]. However, these approaches still do not allow any application for the measurement of macroscopic objects, but are limited for economic reasons to the measurement of comparatively small objects. Also, the measurement of objects of great depth and distance with such approaches is rather not possible.

In the publication by Choi, S .; Shioda, T .; Tanaka, Y .; Kurokawa, T .: Frequency-Comb-Based Interference Microscope with a Line-Type Image Sensor, Japanese Journal of Applied Physics Vol. 10A, 2007, pp. 6842-6847 [10] describes an interference microscope with a frequency comb laser tuning the frequency intervals. With this approach, however, no object with a comparatively large depth extent is completely measurable if a comparatively large numerical aperture is to be used in the object image in order to achieve a high lateral resolution. Furthermore, for the use of this approach for the rapid measurement of an object with a comparatively large depth extent either a high-speed camera, or a short-pulsed frequency comb laser source or a fast Abschattvorrichtung is absolutely necessary, since then required fast tuning of the frequency intervals of the frequency comb laser also gives a large phase angular velocity in the interference phenomenon to be sampled at the output of the interferometer. These means are either expensive and expensive or ultimately lead to signals with a rather poor signal-to-noise ratio in the detection of the interference phenomenon.

Known approaches with a, the object two-beam interferometer associated second scanning two-beam interferometer, as in the document GB 2355210 A of K. Ehrmann, provide interference signals with a reduced contrast, which can complicate the signal evaluation. Moreover, this does not give the possibility of scalability of the measuring method with respect to a large depth measuring range.

In DD 240824 A3, the application of a Fabry-Perot etalon in reflection in a spectral white-light two-beam interferometer has already been described by J. Schwider in 1972 as an adjustment aid. Also by J. Schwider 1994 the application of a rather thin Fabry-Perot resonator in the beam path of a spectral white light two-beam interferometer is described in DE 44 05 450 A1, even with larger distances between an object and a reference surface in a Fizeau Interferometer still obtain evaluable interferograms. This was about the visualization of interference. A recording of objects with confocal filtering is not possible here. The possibility of scalability of the measuring method with respect to a large depth measuring range is not given here.

Furthermore, the patent application DE 3623265 A1 in FIG. 7 shows a Fabry-Perot interferometer for measuring the position of a mirror in conjunction with a second interferometer for generating a spatially spread interferogram. With such an arrangement extended mirror, but not small objects can be touched, as a sharp imaging of small objects via a multi-beam interferometer is rather limited.

Description of the invention

Object of the present invention is to provide a weitskalig customizable interferometry with high measurement and sampling accuracy and a high robustness of the measurement. This object is achieved by a method according to claim 1 and an apparatus according to claim 11. Preferred embodiments are subject of the dependent claims.

In one aspect, the invention thus provides a method of interferometry, which comprises: Generating an electromagnetic measurement signal (hereinafter also referred to as "light");

Splitting the measuring signal into a scanning beam component and a reference beam component (in the manner of a two-beam interferometer);

Irradiating at least one object point with at least a portion of the scanning beam component;

Generating an interference signal by superimposing a portion of the scanning beam component reflected by the at least one object point on the reference beam component, wherein the portion of the scanning beam component reflected in the interference signal by the at least one object point has an optical path difference x_O relative to the reference beam component that depends on the position of the object point, in particular zero wherein the measurement signal is generated with a frequency comb spectrum with the same frequency comb intervals Δf_Signal the individual frequency components and / or wherein the interference signal is conditioned or filtered by means of a frequency comb filter such that the filtered interference signal only a frequency comb spectrum with the same frequency comb intervals Δf_Signal of the individual frequency components has; and wherein the method further comprises: temporally changing the frequency comb distances Δf_Signal in the frequency comb spectrum of the measurement signal or the filtered interference signal and / or the optical path difference x_O such that the frequency comb intervals Δf_Signal at least temporarily an integer multiple of the quotient c / x_O from the Speed of light c and the optical path difference x_O correspond; and

Detecting an intensity and / or intensity change of the interference signal for a plurality of frequency comb intervals Δf_Signal and / or for a plurality of optical path differences x_O.

By detecting values of the intensity and / or intensity change of the interference signal for a plurality of frequency comb distances Δf_Signal and / or for a plurality of optical path differences x_O thus becomes In particular, a signal waveform of the interference signal as a function of the changed or variable frequency comb intervals or determined in dependence on the optical path difference.

Thus, an electromagnetic measurement signal with a frequency comb spectrum is particularly preferably generated such that the frequency comb distances Δf_Signal of the measurement signal (hereinafter also referred to as Δf_Source) in a modulation interval [Δf_Signal_min; Δf_Signal_max] (hereinafter also referred to as [Δf_Source_min; Δf_Source_max]) of Frequency comb intervals are changed over time. This temporal change can take place in various ways, as will be shown below in some examples. As a frequency comb spectrum, a spectrum is referred to in a conventional manner, which is represented on the frequency composed of a plurality of equidistant frequency components, wherein the distances between adjacent frequency components in the frequency space as the frequency comb intervals Δf_Signal be drawn. Not necessarily all frequency components must occur with the same intensity. Preferably, the intensity of the discrete frequency components is distributed according to or similar to a Gaussian curve, with the intensities of the frequency components decreasing from higher to lower frequencies starting from a central frequency.

In particular, it has been recognized in one aspect of the invention that in the case of mutual detuning of a frequency comb spectrum in the signal path (eg in the measurement signal and / or in the interference signal) and the optical retardation x_O of the two beam paths in the two-beam interferometer an easily detectable modulation of intensity and / or Intensity change of the interference signal can be achieved. In particular, when changing or scanning the frequency comb distances Δf_Source relative to the optical path difference x_O then results in a resonance in the interference signal when the frequency comb intervals Δf_Quelle a frequency comb resonance distance Δf_Source_Res corresponding to an integer multiple of the frequency distance Δf_Objekt = c / x_O from the Quotients between the speed of light c and the optical Path difference x_O, ie Δf_Source = n • c / x_O where n = 1, 2, 3. in the

The meaning of the invention is also the correspondence between the frequency comb distances Δf_Source and the frequency spacing Δf_object = c / x_O from the quotient between the speed of light c and the optical path difference x_O, ie Δf_Source = c / x_O, as an integer multiple (with n = 1). to understand.

In the range of a resonance, ie around this resonance condition, in particular within the modulation interval (Δf_source_min <Δf_Source_Res; Δf_Source_max> Δf_Source_Res]) of the frequency comb distances, a particularly strong modulation of the intensity of the interference signal with change of the frequency comb distances Δf_Source relative to the optical Retardation x_O observed. This modulation can be detected very easily and with high accuracy by means of a simple detector element. For this purpose, the intensity or intensity change is preferably detected for a plurality of frequency comb distances Δf_Source within the modulation interval around the at least one frequency comb resonance distance Δf_Source_Res. In another preferred embodiment, the intensity or intensity change is preferably detected for a multiplicity of different optical path differences x_O around at least one resonance condition.

Preferably, a frequency comb modulation distance .DELTA.f_source_mod is determined from the detected values of the interference signal, in particular the intensity and / or intensity change, in particular as the frequency comb distance at the maximum modulation of the detected signal waveform of the interference signal and / or as the frequency comb interval at the signal maximum in the detected signal waveform of the interference signal and / or as a frequency comb spacing in the signal centroid of the detected signal waveform of the interference signal. Preferably, the determined frequency comb modulation distance Δf_Quelle_Mod is stored and / or evaluated. Preferably, the frequency comb modulation distance .DELTA.f_Source_Mod determined in this way corresponds, to a good approximation, to the frequency comb resonance distance Δf_Source_Res. Therefore, can be determined from the Frequency comb modulation distance Δf_Source_Mod preferably information about the underlying optical path difference x_O, and thus determine an absolute and / or relative position of the at least one object point.

In particular, no complex detection by means of a spectrometer is required in an interferometry method according to the present invention. Rather, a spectrally integrating detector element is preferably used, at least in spectral subranges. This is in particular easier and cheaper to provide than high-resolution spectrometer, on the other hand, it achieves a particularly high sensitivity. Due to the possible omission of the use of complex, sensitive and high-resolution spectrometers for detection, the invention achieves a particularly simple and interference-insensitive interferometry with particularly high resolution, in particular for spatially resolved measurements or surveys or images of objects or their position in different sizes.

In this case, the principle according to the invention is not limited to a specific spectral range of the electromagnetic measurement signal or electromagnetic radiation (hereinafter also without limitation "light") and / or a specific order of magnitude of the objects to be examined The resolution capability is preferably limited only by diffraction effects of the electromagnetic radiation used, ie, it depends on the wavelength of the radiation used, a shorter wavelength thus preferably allowing a higher spatial resolution Resolution.

Preferably, an excerpt, in particular a pixel or a cell, of a spatially resolving detector, in particular a detector array or detector array, having a multiplicity of optical detector elements is used as the optical detector element. Above all, by the possible omission of the use of a high-resolution spectrometer (eg a diffractive Grating spectrometer) can be efficiently generated by the use of a detector array (also referred to as rasterized detector), such as a CCD camera and / or CMOS camera, simultaneously a spatially two-dimensional image. A spectral resolution is not required or already anticipated by the superposition of the resonance behavior of the two-beam interferometer and the frequency comb spectrum. Preferably, therefore, a spectrally integrating, rasterized detector is used, at least in spectral subareas.

Preferably, generating the electromagnetic measurement signal comprises: generating an electromagnetic output signal having a continuous spectrum; and conditioning or filtering the output signal by means of a detunable multibeam interferometer for generating the electromagnetic measurement signal with a frequency comb spectrum such that the frequency comb intervals Δf_Signal of the measurement signal in a modulation interval ([Δf_Signal_min; Δf_Signal_max]) of the frequency comb intervals are changed over time.

In this case, a Fabry-Perot interferometer is preferably used as a multi-beam interferometer. For example, a superluminescent diode is used to generate the substantially continuous spectrum output signal. In another preferred embodiment, the electromagnetic measurement signal is generated by means of a tunable frequency comb laser.

Preferably, the method comprises determining a frequency comb modulation distance Δf_Source_Mod from the detected values of the intensity and / or intensity changes of the interference signal (ie with the aid of or with the aid of the acquired values of the intensity and / or intensity changes of the interference signal), wherein the frequency-comb modulation distance Δf_Source_Mod especially as frequency comb distance Δf_Signal in the maximum modulation of the detected signal waveform of the interference signal; and / or as a frequency comb distance Δf_Signal at the maximum signal in the detected waveform of the interference signal and / or; is determined as frequency comb distance Δf_Signal in the signal center of gravity of the detected signal waveform of the interference signal. Thus, in particular the frequency comb distance Δf_Signal is temporally changed in a predetermined manner, while the intensity and / or intensity change of the interference signal is measured or detected at a plurality of values of the frequency comb distance Δf__Signal. As frequency comb modulation distance .DELTA.f_Source_Mod the value of the predetermined and changed frequency comb spacing .DELTA.f_Signal is preferably determined therefrom, wherein the maximum of the modulation of the detected signal waveform of the interference signal and / or the signal maximum in the detected waveform of the interference signal and / or the signal centroid of the detected waveform of the Interference signal occurs. The signal center of gravity is preferably the mean value of the frequency comb distance Δf_signal weighted with the magnitude of the detected values of the intensity and / or intensity changes of the interference signal.

Particularly preferably, the method comprises determining a value of the optical path difference x_O from the frequency-comb modulation distance Δf_Source_Mod according to x_O = c / Δf_Source_Mod with the speed of light c.

Preferably, the method comprises: a first scan (hereinafter also sometimes referred to as a long scan) in such a way that the frequency comb distances Δf_Signal are thereby changed continuously; and a second scan (hereinafter also occasionally called short scan) executed repeatedly (in particular periodically) during the first scan, such that the optical path difference x_O is continuously changed such that the continuous change in the quotient c / x O caused thereby Sign after at least temporarily the first Scan effected continuous change of the frequency comb intervals .DELTA.f_Signal, wherein the detection of an intensity and / or intensity change of the interference signal takes place during each of the second scan. Preferably, the detection of an intensity and / or intensity change of the interference signal takes place in a period of the repeated second scanning process, in which the change of the frequency comb distances Δf_Signal corresponds to the sign after the change of the quotient c / x_O. As a result, a reduction of the phase angular velocity in the interference image is efficiently effected during the creation of a photograph with the detector element.

In another preferred embodiment, the method comprises: a first scan (hereinafter also sometimes called a long scan) in such a way that the optical path difference x_O is continuously changed; and a second scanning process performed during the first scan (hereinafter occasionally also referred to as short scan) in such a way that the frequency comb distances Δf_Signal are continuously changed such that the change of the frequency comb distances Δf_Signal according to the sign at least temporarily corresponds to the continuous change in the quotient c / x_O caused by the first scan, the detection of an intensity and / or intensity change of the interference signal in each case taking place during the second scanning process. Preferably, the detection of an intensity and / or intensity change of the interference signal takes place in a period of the repeated second scanning process, in which the change of the frequency comb distances Δf_Signal corresponds to the sign after the change of the quotient c / x_O. As a result, a reduction of the phase angular velocity in the interference image is efficiently effected during the creation of a photograph with the detector element. Preferably, an intensity and / or intensity change is detected during a detector integration period ΔtD during which the phase in the interference signal changes by no more than 180 degrees in magnitude.

The second scanning process preferably has a sawtooth curve of the optical path difference x_O or the reciprocal 1 / Δf_signal of the frequency comb intervals Δf_Signal over time, the detection of an intensity and / or intensity change of the interference signal occurring during the long edge of the sawtooth curve.

In another preferred embodiment, the second scanning process takes place in the form of a harmonic oscillation of the optical path difference x_O or of the inverse value 1 / Δf_signal of the frequency comb distances Δf_Signal over time, wherein the detection of an intensity and / or intensity change of the interference signal takes place in a period of time, which contains the passage of the harmonic oscillation through the point or point of inflection of the movement in the positional space (ie in particular that point with maximum speed) in which the change of the frequency comb distances Δf_Signal corresponds to the sign after the change of the quotient c / x_O. This preferably corresponds to the maximum point of the intensity or modulation in the interference signal.

In addition, the invention provides an apparatus for interferometry, comprising: a measurement signal source for generating an electromagnetic measurement signal; an interferometer arrangement which is designed to split the measuring signal, in particular by means of a beam splitter element of the interferometer arrangement, into a scanning beam component and a reference beam component; to irradiate at least one object point with at least a part of the scanning beam component, in particular by means of a lens of the interferometer arrangement; and an interference signal is generated by superimposing a portion of the scanning beam component reflected by the at least one object point on the reference beam component, wherein the portion of the scanning beam component reflected by the at least one object point in the interference signal has an optical path difference x_O relative to the reference beam component dependent on the position of the object point; wherein the measurement signal source is adapted to generate the measurement signal with a frequency comb spectrum with equal frequency comb intervals Δf_Signal the individual frequency components and / or wherein the apparatus further comprises a frequency comb filter which is adapted to filter the interference signal such that the filtered interference signal only one Frequency comb spectrum with the same frequency comb intervals Δf_Signal the individual frequency components has; and wherein the device further comprises: a control device for temporally changing the frequency comb distances Δf_Signal in the frequency comb spectrum of the measurement signal or the filtered interference signal and / or the optical path difference x_O such that the frequency comb distances Δf_Signal at least temporarily an integer multiple of the quotient c / x_O from the speed of light c and the optical path difference x_O correspond; and at least one detector element for detecting an intensity and / or intensity change of the interference signal for a plurality of frequency comb distances Δf_Signal and / or for a plurality of optical path differences x_O.

Preferably, the interferometer arrangement comprises a Fizeau interferometer and / or a Michelson interferometer and / or a Twyman Green interferometer and / or a Mirau interferometer and / or a Linnik interferometer and / or a Mach-Zehnder interferometer. In a preferred embodiment, the measurement signal source comprises a tunable frequency comb laser. In a further preferred embodiment, the measuring signal source comprises: a radiation source for generating an electromagnetic output signal with a continuous spectrum; and a frequency comb filter, in particular a tunable multi-beam interferometer, such as a Fabry-Perot interferometer, with an adjustable or variable delay length Y, for filtering the output signal for generating the electromagnetic measurement signal with a frequency comb spectrum such that the frequency comb intervals Δf_Signal of Measuring signal in a modulation interval ([Δf_Signal_min; Δf_Signal_max]) of the frequency comb intervals are temporally changeable.

Preferably, the measuring signal source comprises a first signal scanning device for performing a first scanning or signal scanning operation (hereinafter also sometimes referred to as long scan) in such a way that an optical delay length or path length Y of the signal path in the measuring signal source is changed continuously , and a second signal scanning device for carrying out a second scanning or signal scanning process (hereinafter also occasionally also referred to as short scan) which is repeated (in particular periodically) during the first signal scanning, in such a way that the optical delay length or Path length Y of the signal path in the measuring signal source is continuously changed such that the change in the optical delay length by the second signal scanning operation is opposite to the sign after at least temporarily the change of the optical delay length by the first signal scanning operation.

The method for interferometry thus preferably comprises a corresponding first or second signal scanning process. Preferably, the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second signal scanning process. Preferably, the detection of an intensity and / or change in intensity of the Interference signal in a period of the repeatedly performed second signal scanning operation in which the change of the optical delay length by the second signal scanning operation is opposite to the sign after the change of the optical delay length by the first signal scanning operation. As a result, a reduction of the phase angular velocity in the interference image is efficiently effected during the creation of a photograph with the detector element. The first and second signal scanning device preferably form two spatially separate scanners (one for the long and one for the short scan) in the measurement signal source. Due to their predetermined, synchronized interaction, at least approximately a step function is preferably formed for the frequency spacings over time. Thus, the phase angle velocity preferably does not change at regular time intervals or only so slightly that an interference image can then be recorded by a screened detector in each case with particularly good resolution. This is especially advantageous for miniaturized measuring systems with a small numerical aperture, since then preferably no mechanical scanning process has to be performed on the sensor.

The device preferably comprises an optical waveguide for transmitting the measurement signal from the measurement signal source to the interferometer arrangement.

The control device is preferably designed to synchronously control a first and a second scanning process in such a way that the frequency comb distances Δf_signal are changed continuously in the first scanning process; and in which the optical path difference x_O repeatedly executed during the first scan scan is continuously changed such that the continuous change in the quotient c / x_O caused thereby corresponds to the frequency comb distances Δf_Signal according to the sign after at least the continuous scan caused in the first scan process and wherein the control device is designed to control the at least one detector element such that the detection of an intensity and / or Intensitätsänderung of the interference signal in each case during the second scan takes place.

In another preferred embodiment, the control device is designed to synchronously control a first and a second scanning process such that in the first scanning process the optical path difference x_O is changed continuously; and in the second scan repeatedly executed during the first scan advance, the frequency comb distances Δf_Signal are continuously changed such that the change corresponds to the frequency comb intervals Δf_Signal following the sign after at least temporarily the continuous change in the quotient c / x_O caused by the first scan, and wherein the control device is designed to control the at least one detector element such that the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scanning process.

Thus, the invention achieves in particular measuring systems with a wide-scale customizable measuring or scanning accuracy - depending on the need from subnanometer resolution to millimeter resolution - the economic use to supply. The goal here is also a high robustness of the measurement.

At the same time, it should be possible to measure with miniaturized sensors, even at large object distances or large object depths or even on difficult object surfaces, at the expense of possibly lower depth resolution.

This is achieved, in particular, that in the optical probing of the object surface at different depths of the object space or object distances electromagnetic (optical) signals from these depths, for example, at object distances of the order of one meter, in a particularly suitable, especially particularly good evaluable waveform for a planar field of view or at least for a linear field of view. It can do it preferably many laterally adjacent object elements or object points become appropriate at the same time. In particular, it is thus achieved to provide readily analyzable electromagnetic (optical) signals in the electromagnetic (optical) probing of objects by the method according to the invention by means of a camera which preferably measures areally and / or linearly. The obtained electromagnetic (optical) signals lead in particular to comparatively good, in particular clearly evaluable measurement results. In particular, it is possible to dispense with the use of a spectrometer or several spectrometers in the interferometric measuring system. Preferably, however, color cameras can be used as detectors.

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

In addition, for measurements even in a larger or a coarser scale by use of the invention even with the use of light sources having a spectral width at half maximum of, for example, only 5 nm to 10 nm still signals of high uniqueness won. The use of spectrally narrow-band light sources brings considerable technical and economic advantages in the realization of an optical measuring system, since thereby the chromatic influences and aberrations of the optical components used play a rather minor role.

Another advantage here is also to be able to measure with wide scale, with different, trained according to the inventive approach sensors, each in all three spatial coordinates - including the depth. This is preferably also possible in a measuring volume of, for example, 20 μm × 20 μm × 20 μm up to one cubic meter. The limits with regard to the ascertainable measurement volume upwards are determined only by the available light energy and also by the available measurement time. In the microscopic scale, preferably only the diffraction limit makes A limiting factor in the lateral resolution noticeable, whereby the achievable effective lateral resolution can be further increased by means of suitable numerical methods. With the depth resolution, a subnanometer resolution is achieved when using suitable components. Thus there is a wide scalability of the measurement method, in particular with regard to the measurement resolution in depth. Preferably, a sensor has comparably small dimensions.

Fields of application of the inventive solution are in particular: the microform and the microprofile measurement, the measurement of roughness as well as the mini-form measurement, the shape measurement on no or little cooperative surfaces, as well as e.g. human liver tissue. An example of the application of the invention here is also the detection of the microform on the inner ear in humans in the surgical operation phase and the intraoral shape detection of human teeth.

Another preferred field of application of the invention is the form detection on technical teeth in gears and on objects with a high aspect ratio. In addition, a preferred field of application is the highly accurate measurement of the shape of partially reflecting, weakly light scattering and thereby strongly inclined gear tooth surfaces.

Another preferred field of application is the measurement of polished and unpolished aspheres in transmission as well as specular aspheres, spectacle lenses and free-form surfaces, in particular for optical imaging.

The invention can also be used in particular for geometric measurements in ophthalmology. The use in endoscopic 3D systems leads to well-miniaturized sensor solutions with high measurement accuracy.

The invention is in particular also for the determination of the optical thickness n '* d, with n' as optical refractive index and d as the geometric path length, or the optical path lengths n '* d of biological micro-objects, cells or cell components in the label-free diagnostics and analysis used. In this case, cells or cell components can be measured laterally with high resolution, that is also with images, with regard to the distribution and variation of their optical thicknesses. In addition, living cells or constituents of living cells can also be detected pictorially in transmitted or incident light with regard to the optical thick distributions or their changes in a process.

With the method and the apparatus for interferometry, in particular for scalable confocal interferometry in transmitted light or incident light in a scanning scanning process, preferably also data from an optical volume memory, for example in the form of an optical multi-layer memory, can be read, so that the method preferably also for fast reading optical data from optical volume storage can be used.

A particularly advantageous motivation for the application of the invention in various applications is the utilization of the "interferometry gain" for measurements even on a macroscopic scale, which is of great advantage, for example, in mechanical engineering, because many objects do not require interferometric depth resolution, but of the known one Benefit from "interferometry gain". Thus, by means of interferometry, even object elements of the lowest reflectivity can be measured relatively well in depth.

In a preferred embodiment, the invention provides a method and an apparatus or arrangement for scalable confocal interferometry in transmitted light or reflected light in a scanning measuring process for the relative or absolute depth measurement or distance measurement of a technical or biological object or object elements, for microscopic, mesoscopic or macroscopic 2D or 3D acquisition of technical or biological objects or for OC tomography or OC microscopy or for endoscopic 2D or 3D metrology or for measuring layer thicknesses, resolved laterally or over time, or their lateral or temporal changes.

With the method and the device or arrangement for scalable confocal Interferometry in transmitted light or reflected light in a scanning scanning operation, preferably also data from an optical volume memory, for example in the form of an optical multi-layer memory, are read, so that the method can be used in particular for the rapid readout of optical data from optical volume stores. In this case, the presence and the geometric distribution of reflective or light-scattering elements in a volume of a data carrier are detected.

Hereinafter, a preferred method will be described. In particular, the following means are used in the process:

either a confocal, object-imaging interferometer with at least approximately two-beam characteristics

and / or a chromatic-confocal object-imaging interferometer with at least approximated two-beam characteristic - ie with a predetermined chromatic depth splitting of foci in the object space,

at least one light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

In this case, the object-imaging interferometer preferably has a non-zero optical path difference x_O at each optically detected object element. This should preferably be at least two micrometers. However, the optical path difference can typically be much larger - in extreme cases up to the range of several millimeters or up to several meters. On the basis of this optical path difference x_O, the maxima of an at least approximately sinusoidal frequency wavelet computationally each have a frequency separation of Δf_object = c / x_O - with c equal to the vacuum light velocity and x_O equal to the optical one Path difference in the object-imaging two-beam interferometer, belonging to each optical captured object element. The size Δf_object corresponds exactly to the period length in the wavelet.

Furthermore, preferably at least in spectral subareas, a spectrally integrally detecting, rasterized detector, that is to say for example with very many with pixels, is arranged for this electromagnetic radiation. In particular, this screened detector is thus preferably formed with a single spectral channel in each pixel. So this can be a common grayscale CCD or grayscale CMOS camera that only registers gray values but no colors in each pixel. The use of a color camera is possible, which is also not yet regarded as a spectrometer, but as a camera with three or four spectral channels.

Preferably, the light source is formed as a frequency comb light source in the optical system. The frequency comb preferably covers a certain spectral range. The frequency comb distances of the light source .DELTA.f_Source are changed in the measurement process gradually over the time predetermined in the entire spectral range of the light source. These frequency comb intervals can change in the range of a few parts per thousand up to a few percent of the initial value. In extreme cases, the changes may even be a multiple or a small fraction of the output value of the frequency comb distances Δf_Source. These changes in the frequency comb distances Δf_Source, can thus - made relatively large - be made very large.

In this case, preferably either the light source is represented by a spectral continuum light source or at least by a quasi-continuum light source, and this light source is preferably followed by a multi-beam interferometer with predetermined change in the optical delay length Y of the multi-beam interferometer in the measurement process that at least approximately a frequency comb characteristic is formed in the detection. This reordering refers to the entire space of the optical system, including the space immediately in front of the screened receiver, , ie in the detection beam path. So the multi-beam interferometer is always downstream of the light source and upstream of the rasterized detector. In the case of a Fabry-Perot interferometer, the delay length Y = 2 L with L as the distance of the interferometer end mirror. This applies exactly only to a vacuum arrangement, or approximately for an air arrangement, when the refractive index is approximated by the value one. In the case of the multiple successive detection of the electromagnetic radiation in the measurement process, a predetermined change of the frequency comb is carried out with respect to the frequency spacings of the maxima or spikes by means of predetermined changing of this optical delay length Y, whereby the frequency spacings Δf_source of the maxima or of the spikes in the frequency comb respectively Δf_source = c / Y be, with c as the vacuum light velocity, and these frequency intervals .DELTA.f_Source be changed in the measuring operation by means of predetermined changing the optical delay length Y predetermined. This can be done by means of a piezo-translator on the mirror of a Fabry-Perot interferometer.

On the other hand, it is also possible to represent the light source by a frequency comb laser having an optical delay length Y. This frequency comb laser is formed with an at least approximately equidistant frequency comb, but over the time predetermined variable frequency intervals Δf_Source of the maxima or spikes in the frequency comb.

The frequency intervals Δf_Source corresponding to the predetermined changing the frequency comb in the scanning measurement process at least once exactly an integer multiple n, with n = 1, 2, 3, 4, 5, 6, 7, ..., the arithmetic frequency intervals Δf_Objekt = c / x_O with c equal to the vacuum speed of light and x_O equal to the optical path difference in the (object-imaging) two-beam interferometer associated with each optically detected object element P.

Then, the delay length Y in the frequency comb light source is an integer part of the optical path difference x_O in the object imaging Two-beam interferometer or the delay length Y is equal to the optical path difference x_O, which corresponds to the case n = 1. Thus: x_O = n -Y, where n = 1, 2, 3 ....

This equality is produced by varying the delay path length Y in the light source at least once during the measurement process for each object object or object being probed, whereby a short-period modulation in the signal sequence occurs. This waveform is repeatedly scanned over time by means of spectrally integrally detecting, rasterized detector, wherein at least one pixel of this spectrally integrally detecting, rasterized detector is optically associated with each of an object element. The pixels of a color camera can here also be regarded as spectrally integrally detecting sensor elements in comparison to the sensor elements of a spectrometer.

The

either for maximum modulation of the signal curve,

- or the signal maximum of the waveform

or the magnitude of the frequency spacings associated with the signal centroid of the waveform is determined directly from the frequency comb light source as the value "Δf Source_Mod" (sometimes referred to herein as frequency comb modulation spacing) or from the parameters of the frequency comb light source, such as the delay length Y = 2L, calculated and stored.

In this case, the delay length Y_Mod can be determined by the occurrence of the modulation of the signal profile with Y_Mod = 2L_Mod from the current distance L_Mod of the end mirror of a multi-beam interferometer by an associated measuring system. In the case of a multi-beam interferometer in air, the refractive index can generally be well approximated with the value one, especially on the microscopic scale. It is also possible that for different object elements i only changes in the delay length Y_Mod i for the different object elements i are determined and evaluated by the actual distances L_Mod i the end mirror of the multi-beam Interferometers are determined and stored and the calculation of the associated optical path differences x_O i made accessible.

By the predetermined scan of the frequency distances of the light source so Δf_Quelle and ΔfJDbjekt an object element at a time, so at least comparatively briefly, once made equal in the measuring process, or the frequency intervals of the light source .DELTA.f_Source be at least comparatively short time an integer multiple n of the computational frequency spacing Δf_Objekt ,

Thus, by the predetermined scan, the frequency spacings of the light source Δf_source at a time in the measurement process are made equal to an integer multiple n of Δf_object of the frequency wavelet of the object computationally determinable with Δf_object = c / x_O.

When the frequency intervals .DELTA.f_source are changed in a predetermined manner-that is to say in the measuring process-the rastered detector of electromagnetic radiation is successively read out several times, and in each pixel of the rasterised detector the intensities are summed up, at least in part, spectrally integrally. The detector can be a planar monochrome CCD or a CMOS camera. In this case, each object element is assigned at least approximately one pixel by optical imaging. By means of a color camera, coarse information about object distances can be obtained in the chromatic-confocal approach by evaluating the intensities in the color pixels.

But it is also possible that the detector is a color CCD or color CMOS camera. Then each object element is assigned three or four pixels, but in different spectral ranges.

Thus, in the case of the predetermined changing of the frequency spacings Δf_Source for each detectable object element, the case Δf_source = n « Δf_object, or x = n« Y, with n = 1, 2, 3 ... is reached at least once. At least one short-period signal modulation in the waveform generated, detected and evaluated.

In this case, either the known predetermined change in the optical delay length Y of the multi-beam interferometer based on the change of the frequency spacings Δf_Source, the appearance of the short-period signal modulation in the waveform of the optical path difference x_O of the associated object element or at least the difference of the optical path difference in relation to neighbor object elements from the value "Δf_Source_Mod".

- Or, it is the optical retardation x_O associated with an object element, also absolutely with respect to the position "Y = 0" in the multi-beam interferometer from the value "Δf_Source_Mod" determined if the optical retardation length Y of the same absolutely by measuring Y known is done.

Or, in a frequency comb laser with a predetermined variable frequency comb and exact knowledge of the respective frequency spacings Δf_Source when the short-period signal modulation occurs in the waveform, the associated frequency spacings "Δf_Source_Mod" are determined and the optical path difference x_O of the associated object element with x_O = c / Δf_Source_Mod calculated from the values "Δf_Source_Mod".

- Or, it is from the known predetermined change in the frequency spacings .DELTA.f_Source at least one information about the optical path difference x_O of the associated object element with respect to adjacent object elements, ie the difference of the respective optical path difference to at least one adjacent object element, calculated by the at the occurrence of the short-period signal modulation in the waveform the associated with each object element i frequency intervals Δf_Source_Mod i can be determined.

Preferably, with at least approximately knowledge of the optical refractive index n 'or the refractive index distribution in the object space, the distance z_O of each optically detected object element is determined at least approximately mathematically, either absolutely or in relation to adjacent object elements from the predetermined optical path difference with the relationship x_O = 2n'-z_O ,

Preferably, however, the determination of the optical path difference x_O or its changes Δx_O over time may also be the target of the measurement alone, for example in the measurement of thin biological objects.

In the case of chromatic depth splitting, confocal discrimination of the total spectrum of the light source, also referred to as the global spectrum, in the chromatic-confocal approach always uses only a partial region, ie. it only contributes to a part of the total spectrum of the light source for signal formation in the pixels of the screened detector. The chromatic depth splitting therefore increases the depth, distance or distance measuring range at a given numerical aperture, but at the same time reduces the depth resolution, since the half-width of the detected signal increases with decreasing spectral range used. This reduces the depth measurement resolution.

By preferably predetermined choice of the degree of chromatic splitting in the object illumination and object detection so depth measuring range and depth measurement resolution, respectively

Distance measurement range and distance measurement resolution to be selected in the measurement by the choice of the size of the chromatic power of a sensor and thus the coming to detection spectral width of the light used. If there is no chromatic splitting in the sensor, only the width of the total spectrum of the light source, ie the wavenumber range contributing to the detection, determines the achievable depth measurement resolution. In arrangements with an object-imaging system with a rather small or very small numerical aperture for measurements on a coarse scale, the chromatic depth splitting can be completely dispensed with if the wave-optical depth of field is sufficiently large for the measurement task.

The signal modulation in the detected signal profile is preferably evaluated for determining the absolute or relative object depth, if the case occurs when the frequency comb is changed in a predetermined manner

Δf_Source_Mod = Δf_Object occurs, which corresponds to the case x_O = Y_Mod. In this case, n = 1. Then, there is no subsampling of the signal curve and, as a rule, a comparatively good signal-to-noise ratio is produced.

In the case of an optical undersampling, that is to say n greater than 1, the necessary scan path or scan area is advantageously reduced by the factor n of the undersampling. However, the waveforms then may need to be sampled finer in depth, as these then become narrower in width over the wavenumber.

It is also possible to detect several signal waveforms with a signal modulation by changing the frequency intervals .DELTA.f_Source sequentially. From the respectively known optical delay length changes .DELTA.Y1, .DELTA.Y2, .DELTA.Y3..., Which are assigned to the signal curves with a signal modulation when they occur, their order n can then be determined absolutely. From this, the respective delay path length Y1, Y2, Y3 .... absolute and from this the optical path difference x_O for each detected object element in the object-imaging interferometer can be calculated absolutely by means of a comparatively simple linear system of equations. From this, the object depth position z_O or the distance of an object element with respect to a system reference can then be determined. Furthermore, it is also preferably possible for the light source to be designed as a frequency comb light source with a fixed optical retardation length Y in the optical system, preferably as a frequency comb microsampler, as already described in the 2007 literature. The frequency comb distances Δf_Source are thus kept constant. In the measurement process, the optical path difference x of the object-imaging interferometer is consequently altered by moving this object-imaging interferometer as a compact miniaturized module in the depth direction sensitively in the measurement process in relation to the object and the rasterized detector is read several times. Again, the signal waveform is evaluated in the occurrence of the equality of optical path difference x_O in an object element and optical delay length Y. Here, the object-imaging interferometer is preferably designed as a slim, miniaturized Fizeau interferometer, which thus has common path properties. Moving such an optical system mechanically sensitively in the direction of light is in many cases technically feasible.

Furthermore, preferably the size of the chromatic refractive power in the object-imaging interferometer, whereby the degree of depth splitting changes, can be adapted specifically to the depth of the object to be measured.

Furthermore, it is possible, preferably to adapt the width of the light spectrum used, that is to say the wavenumber range, as a function of the surface properties of the object and also of the dispersion of the optical medium in the object space and the desired depth resolution. For this purpose, the light source can be constructed, for example, from individual light sources, for example superluminescent diodes, each having a downstream Fabry-Perot interferometer. This means that the Fabry-Perot interferometer is upstream of the rasterized detector. The superluminescent diodes are operated and switched individually or in smaller groups, in order to work with well-adapted spectral ranges, in order to generate well-evaluable optical signal characteristics for the respective object. It is also possible to use controllable spectral filters when using strong light sources, which the width of the control and adjust the spectrum used. For a strong dispersion in the optical medium of the object space can greatly reduce the modulation depth in the signal curve if the spectral range used is too broad. Although a strong limitation of the spectral range used, ie the wavenumber or frequency range, brings about a reduction in the measurement accuracy by increasing the half-width of the signal, the measurement is possibly made possible in the first place.

However, preferably only the optical path difference, or the optical path length, in a point or element of a micro-object, for example a living cell, can be detected. That is, the geometric path length is not or less of interest. This may be of great interest in marker-free monitoring of biological cells or cell constituents, since the information on the course of subcellular processes is significantly reflected in many processes, above all in the change in the optical path length. This change is then measured in high resolution over time. In addition, deposits of extremely thin layers on substrates can also be detected. These layers may consist of proteins, for example. The elimination of the dispersion can be done in any case by using the same media, usually liquids, in the object space and in the multi-beam interferometer or laser resonator, wherein the optical attenuation of the medium is observed.

However, preferably only the optical path difference, or the optical path length, in a point or element of a micro-object can be detected. This may be of great interest in the marker-free monitoring of biological cells or cell constituents, since the information on the progress of subcellular processes is significantly reflected in the change in the optical path length. This is then measured high-resolution over time.

Furthermore, the dispersion of the multi-beam interferometer can preferably be made at least approximately equal to the dispersion in the object space. This is well possible when measuring biological objects in aqueous solution in which the multi-beam interferometer, preferably an encapsulated Fabry-Perot interferometer, is also operated in water, so that multi-beam interference takes place in the Fabry-Perot interferometer in water. This leads to signal curves with a high degree of modulation, since the dispersions can be adjusted quite well.

Preferably, the following is also proposed: Thus, as already described, a predetermined scan of the frequency spacings of the frequency comb light source is carried out, which is referred to hereinafter as FC long scan with the time Δt_lang_fc, since this is preferably continuous and preferably at least as is performed long as a modulation occurs in the waveform, so a variable interference pattern at the output of the object-imaging interferometer arises.

As already described, this FC long scan is to be carried out via the change Δy in the delay length Y in a multi-beam interferometer or via the change Δy in the optical delay length Y in the resonator of a frequency comb laser. Preferably, at least three short scans synchronized with this FC long scan are preferably performed simultaneously with the long scan, ie the predetermined scan of the frequency distances of the light source, either in the reference arm or in the object arm of the object-imaging interferometer, which scans are significantly shorter in their time duration Δt_kurz_lnt as the duration Δt_lang_fc of the long scan. These short scans cause - at least for a portion of the time Δt_kurz_lnt - a reduction in the phase angle velocity in the rasterized detector to be picked interference image, including a phase angle velocity with the amount zero, by in the period .DELTA.t_kurz_lnt both the amount of the delay length Y and the amount of optical retardation x_O each increase both or each reduce both. The resulting phase angular velocity dφ / dt in radians is thus at least in the long scan of the frequency comb light source synchronized short scan of the object imaging interferometer approximately:

dφ / dt = [2π-nΔY / (Δt_kurz_lnt -λ_S)] - [2π-Δx_O / (Δt_kurz_lnt -λ_S)]

with n as the integer ordinal number, with ΔY / Δt_kurz_lnt as a change Δy of the delay length Y in the time period Δt_kurz_lnt in the short scan, that is a speed, and λ_S as the centroid wavelength and Δx_O / Δt_kurz_lnt as the change Δx_O of the optical path difference x_O in the time period Δt_kurz_lnt. The phase angular velocity dφ / dt becomes zero when the magnitudes and the sign of nΔY and Δx_O in the time period Δt_kurz_lnt are the same.

This presupposes that for n = 1 in the time duration Δt_kurz_lnt, ie in the short scan process, both ΔY and Δx_O increase in both cases by the same amount or both decrease by the same amount. In this case, the phase angular velocity dφ / dt can also reach zero due to the synchronization of the FC long scan and the short scan. For the amount zero, the interference pattern does not change in the period Δt_kurz_lnt.

These short scans, which change the optical path difference in the object-imaging interferometer, are preferably carried out in the reference arm with advantage if the object-imaging interferometer is designed with a chromatic-confocal beam path in the object arm. In this case, there is thus a chromatic depth splitting, which allows a sharp image of the optically touched object elements in the measuring range, so that a scan in the object arm is usually superfluous. This also has constructive advantages for a miniaturization of the measuring device or arrangement, since the object arm can thus remain free of movement means. In a device or arrangement with the requirement for a comparatively large depth measuring range, however, the short scans can preferably also be carried out in the object arm.

Each individual short scan is preferably performed such that there is a change in the optical path difference Δx_O in the object imaging Interferometer comes, this change is preferably a maximum of one third of the change nΔY in the long scan, with Y as the delay length of the multi-beam interferometer or the resonator of the frequency comb laser, where n is the already introduced integer multiple with n = 1, 2, 3 ... represents. Typically, the change in the optical path difference Δx_O in the object-imaging interferometer in a short scan is more likely to be one-tenth of the change nΔY, or even less. For n = 1, this means for the change of the optical path difference Δx_O in the object-imaging interferometer, more than a tenth or even less of the change ΔY of the multi-beam interferometer or of the resonator of the frequency comb laser during the long scan.

In the period of a short scan Δt_kurz_lnt preferably at least one interference image is recorded by means of a rastered detector with the detector integration time tD, preferably in the detector integration period .DELTA.tD, the phase in the interference image changes by a maximum of 180 degrees in magnitude, but typically only in the amount between zero degrees and 90 degrees. The case of zero-degree phase change in the detector integration period ΔtD means that the FC long scan and each short scan are exactly synchronized. In the case of n = 1 and zero degrees of phase change, it follows that in the detector integration period ΔtD, preferably, the amount of change of the optical path difference in the object-imaging interferometer is at least approximately equal

the amount of change 2ΔL twice the mirror spacing 2L in a Fabry-Perot interferometer or at least approximately equal to the amount of change ΔY of the delay length Y in a cyclic multibeam interferometer,

or at least approximately equal to the amount of change ΔY of

Delay length Y is made in a resonator of a frequency comb laser.

The duration of a short scan Δt_kurz_lnt can be at least approximately the same the detector integration period .DELTA.tD be made.

In the case of zero-degree phase change, the interference phenomenon in the detected pixels of the rasterized detector in the detector integration period ΔtD then remains at least approximately unchanged in practice. For the change of the optical path difference in the object-imaging interferometer or in a multi-beam interferometer or in the resonator of a frequency comb laser synchronized working piezo actuator can be arranged.

Preferably, the short scans further at least approximately a sawtooth curve of the optical path difference x_O of the object-imaging interferometer over time, wherein the inclusion of interference images by rasterized detector within the period .DELTA.t_kurz_lnt in the sawtooth preferably takes place when the long edge of the tooth is traversed. The length of time for the long edge preferably corresponds at least approximately to the integration time duration ΔtD of the rastered detector. Preferably, the amount of change in the optical path difference in the object-imaging interferometer between two directly successive short scans is freely selectable. Preferably, the magnitude of this change in magnitude is at least approximately equal to the magnitude of the centroid wavelength in the spectrum used.

Furthermore, it is preferably possible that short scans are preferably performed at least approximately in the form of a harmonic oscillation. This means that the optical path difference x_O in the object-imaging interferometer changes at least approximately harmonically oscillating. The inclusion of interference images by means of rastered detector takes place within the period Δt_kurz_lnt preferably in at least approximately linear part of the path-time curve of the oscillation, wherein the oscillation amplitude is chosen so that the phase change of the interference in the detector integration period .DELTA.tD is at most 180 degrees, rather but preferably a value below 90 Old degree approximates.

In this case, the image pickup frequency is preferably made equal to the frequency of the harmonic oscillation or an integral multiple thereof.

Thus, at least three short scans are preferably carried out per FC long scan and thus at least three interference images are recorded by means of a rasterized detector in the FC long scan. As a rule, however, at least ten short scans are preferably carried out, and thus ten interference images are recorded in the FC long scan, but usually preferably hardly more than one hundred interference images. However, without the synchronized short scans, for example, typically at least one hundred to one thousand interference images would need to be captured in the FC long scan, or it would be necessary to work with short exposure during detection. This is relatively technically complicated or time consuming.

The advantage of this method with additional short scan to the FC long scan is that there is a high utilization of the available light energy in the detection since the sum of the detector integration times in the FC long scan is quite 90% of the duration of the long scan can amount. It is also of great advantage that this method can be used with technically and economically very interesting interferometers, in particular two-beam interferometers, which, in principle, have a path difference which is always different from zero. Here are representative of all interferometers with a non-zero optical retardation only the Fizeau interferometer with an object located away from the reference surface, the asymmetric Linnik interferometer with a triple reflector in the reference arm and the asymmetrical Mach-Zehnder interferometer are given as examples ,

Furthermore, it is also possible that several interference images are recorded by means of rasterized detector per short scan. The rastered detector can be designed as a monochrome or color matrix CCD or CMOS camera. In a preferred apparatus or arrangement for scalable confocal interferometry in transmitted light or incident light in a scanning measuring operation for relative or absolute depth measurement or distance measurement of a technical or biological object or object elements, for microscopic, mesoscopic or macroscopic 2D or 3D detection of technical or biological objects or for OC tomography or OC microscopy or for endoscopic 2D or 3D metrology of technical or biological objects or for measuring layer thicknesses, resolved laterally or over time, or their lateral or temporal changes, the following means are used:

- either a confocal, object-imaging interferometer with at least approximately two-beam characteristic

- Or a chromatic-confocal, object-imaging interferometer with at least approximately two-beam characteristic - ie with a predetermined chromatic depth splitting of foci in the object space

and at least one light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

In this case, the object-imaging interferometer at each optically detected object element on a preferably different from zero optical path difference. This should preferably be at least two micrometers. However, the optical path difference in the interferometer typically also be much larger - in the extreme case to the range of several millimeters to several meters. On the basis of this optical path difference, the maxima of an at least approximately sinusoidal frequency wavelet computationally each have a frequency separation of Δf_object = c / x_O - with c equal to the vacuum speed of light and x_0 equal to the optical path difference in the object-imaging two-beam interferometer, belonging to each optically detected Object element. The size Δf_object corresponds exactly to the period length in the wavelet.

Furthermore, at least one raster detector, which is spectrally integrally detecting at least in spectral subareas, is arranged for this electromagnetic radiation.

Preferably, the light source is in the optical as a frequency comb light source

System formed whose frequency comb intervals .DELTA.f_Source be changed in the measurement process gradually over time predetermined.

In this case, either the light source is represented by a spectral continuum light source or at least by a quasi-continuum light source and this light source is followed by a multi-beam interferometer with predetermined measurement of the simple optical delay length Y of the multi-beam interferometer. The multi-beam interferometer is provided with means for varying the simple optical delay length Y. The multi-beam interferometer preferably has a high finesse in order to achieve good discrimination.

- Or the light source is represented by a frequency comb laser with the optical delay length Y and this frequency comb laser is formed with an at least approximately equidistant frequency comb, but over the time predetermined variable frequency intervals .DELTA.f_Source of maxima or spikes in the frequency comb. This frequency comb laser is provided with means for varying the simple optical delay length Y. The frequency comb laser may also be designed as a terahertz laser. It is also possible that the frequency comb laser is preferably formed with a micro-resonator, ie a comparatively small optical delay length Y, with a wavelength range in the infrared range between 1400 nm and 1700 nm and a frequency spacing of several 100 GHz. Furthermore, it is also possible that preferably a plurality of frequency comb lasers are operated in parallel, for example one each in the red, in the green and in the blue spectral range and for detection, preferably a conventional RGB three-chip color camera is used. Then each object element optically preferably three pixels (RGB) are assigned. Depending on the chromatic depth splitting then objects can be optically scanned simultaneously at different depths or distances, resulting in a significant reduction of the measurement times by parallelization and to increase the reliability of the measurement by redundancy.

Furthermore, the multi-beam interferometer may preferably be formed by means of a cyclic fiber optic fiber arrangement. The tuning of the multi-beam interferometer is preferably carried out by a highly dynamic, computer-controlled mechanical stretching of the fibers. The fibers are preferably wound on a computer-controllable piezo-expansion rod.

In a further preferred apparatus or arrangement for scalable confocal interferometry in transmitted light or reflected light for the relative or absolute depth measurement or distance measurement of a technical or object elements, for microscopic, mesoscopic or macroscopic 2D or 3D detection of objects or for OC tomography or OC microscopy or for endoscopic 2D or 3D metrology of technical or biological objects or for determining layer thickness in a scanning measuring process, the following means are used:

- either a confocal, object-imaging interferometer with at least approximately two-beam characteristic

- or a chromatic-confocal, object-imaging interferometer with at least approximately two-beam characteristic - ie with a predetermined chromatic depth splitting of foci in the object space - and at least one light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

- It is preferably on the one hand, the light source represented by a spectral continuum light source or by a quasi-continuum light source and this light source downstream of a multi-beam interferometer.

Or the light source is preferably on the other hand represented by a frequency comb laser with the optical delay length Y. This frequency comb laser is preferably formed with a micro-resonator.

In this case, the object-imaging interferometer always has a non-zero optical path difference x_O at each optically detected object element. On the basis of this optical path difference x_O, the maxima of an at least approximately sinusoidal frequency wavelet computationally each have a frequency separation of Δf_object = c / x_O - with c equal to the vacuum light velocity and x_O equal to the optical one Path difference in the object-imaging interferometer, associated with the respectively optically detected object element. The size Δf_object corresponds exactly to the period length in the wavelet.

Furthermore, at least one raster detector, which is spectrally integrally detecting at least in spectral subareas, is arranged for this electromagnetic radiation.

Preferably, the object-imaging interferometer means are predetermined

Associated with changing the optical path difference.

Thus, the frequency separations of an at least approximately sinusoidal frequency wavelet with the frequency spacings Δf_object = c / x_O - with c equal to the vacuum speed of light and x_O equal to the optical path difference in an object element - can preferably be changed in a predetermined manner. So can the Case that the optical path difference x_O is equal to the fixed optical retardation length Y when changing the optical path difference, and a modulated signal waveform can be detected from the at least approximately knowledge of the refractive index in the object medium depth or distance information for an object element at least approximately mathematically be determined. In this case, the sensor is tuned so that the optical delay length Y is set so that if this delay length Y and optical path difference x_O in an object element is equal to a sharp image of this object element to a pixel of the screened detector.

Furthermore, in the device or arrangement for scalable confocal interferometry, the multi-beam interferometer or the frequency comb laser is preferably constructed with optical waveguides.

Furthermore, in the apparatus or arrangement for scalable confocal interferometry, the multi-beam interferometer or the frequency comb laser preferably has a cyclic beam path.

The object-imaging interferometer may preferably also be designed as a Fizeau interferometer, Michelson interferometer, Twyman-Green interferometer, Mirau interferometer, Linnik interferometer - also with triple reflector in the reference arm - or Mach-Zehnder interferometer. In each case, an imaging system for object illumination and object detection is assigned to the interferometer.

This is a preferred method for scalable interferometry in transmitted light or reflected light in a scanning measuring process for relative or absolute depth measurement or distance measurement of a technical or biological object or object elements, for microscopic, mesoscopic or macroscopic 2D or 3D detection of technical or biological Objects or for OC tomography or OC microscopy or for endoscopic 2D or 3D measurement technology or for measuring layer thicknesses, resolved laterally or over time, or their lateral or temporal changes.

With the preferred method for scalable interferometry in transmitted light or incident light in a scanning scanning process, it is also possible to read out data from an optical volume memory, for example in the form of an optical multi-layer memory, so that the method can basically also be used for fast reading of optical data from optical volume stores , In this case, the presence and the geometric distribution of reflective or light-scattering elements in a volume of a data carrier are detected.

The following describes a preferred method for scalable interferometry in transmitted light or incident light in a scanning measuring process.

Preferably, the following means are used in the process:

either an object-imaging interferometer with at least approximated two-beam characteristic

or a confocal, object-imaging interferometer with at least approximately two-beam characteristics,

at least one light source, in which case light in the sense of electromagnetic radiation of terahertz over IR, VIS to UV radiation is understood.

In this case, the object-imaging interferometer has a non-zero optical path difference x_O at each optically detected object element. This optical path difference x_O should have at least the magnitude of the shortest wavelength of the light source coming to the detection. However, the optical path difference can typically be much larger - in extreme cases up to the range of several millimeters or even up to several meters. On the basis of this optical path difference x_O have the maxima one - to an optically detected object element respectively associated - at least approximately sinusoidal frequency wavelet computationally a frequency spacing of

Δf_object = c / x_O on - with c equal to the vacuum speed of light and x_O equal to the optical path difference in the object-imaging interferometer associated with the respective optically detected object element. The size Δf_object corresponds to the period length in the wavelet.

Furthermore, at least, a spectrally integrally detecting, at least in spectral subranges, rasterized detector, that is, for example, with a great many pixels, arranged for this electromagnetic radiation. As a rule, this screened detector is therefore preferably formed with a single spectral channel in each pixel. So this can be a common grayscale CCD or grayscale CMOS camera that only registers gray values but no colors in each pixel. The use of a color camera is possible, which is also not yet regarded as a spectrometer, but as a camera with three or four spectral channels.

In the interferometric method according to a preferred embodiment of the invention, the optical path difference in the measurement of an object, ie in the measuring process, in the object-imaging interferometer changes at least approximately continuously or quasi-continuously changed, wherein either the optical path in the object arm or the optical path in the reference the same is changed at least approximately continuously, so an interferometer remains unchanged in each case. This change in gait represents an interferometer long scan which takes place in the time period Δtjangjnt.

Preferably, the light source is formed as a frequency comb light source in the optical system. The frequency comb covers a certain spectral range. The frequency comb distances of the light source Δf_Source are changed in the measurement process over time, predetermined in the entire spectral range of the light source. These changes in the frequency comb distances Δf_Source are called Short scans, which are performed in the period .DELTA.t_kurz_fc and synchronized to the interferometer long scan and the rasterized detector

- And either the light source on the one hand by a spectral continuum light source or at least by a quasi-continuum light source is shown and this light source is a multi-beam interferometer with predetermining in the measurement changing the optical delay length Y of the multi-beam interferometer, so that at least approximately a frequency comb characteristic is formed in the detection. This reordering refers to the entire space of the optical system, including the space immediately in front of the rasterized receiver, ie in the detection beam path. So the multi-beam interferometer is always downstream of the light source and upstream of the rasterized detector. In the case of a Fabry-Perot interferometer, the delay length Y = 2 L with L as the distance of the interferometer end mirror. This applies exactly only to a vacuum arrangement, or approximately for an air arrangement, when the refractive index is approximated by the value one.

On the other hand, it is also possible to represent the light source by a frequency comb laser having an optical delay length Y. This frequency comb laser is formed with an at least approximately equidistant frequency comb, but over the time predetermined variable frequency intervals Δf_Source of the maxima or spikes in the frequency comb

Preferably, in the detection of the electromagnetic radiation in the measuring process, the predetermined change of the frequency comb with respect to the frequency intervals of the maxima or spikes is performed by means of predetermined changes of this optical delay length Y as a short scan and in the period Δtjangjnt of the interferometer long scan at least three short Scan performed the frequency comb light source. In this case, the time duration Δtjangjnt is at least three times as long as the time duration Δtjαirzjc. The frequency spacings Δf_Source of the maxima or spikes in the frequency comb are each Δf_Source = c / Y with c as the vacuum speed of light. These frequency spacings Δf_Source are predeterminedly changed in the measuring process by means of predetermined changing of the optical delay length Y.

Preferably, at least three FC short scans synchronized to this interferometer long scan are thus simultaneously carried out for the interferometer long scan, either in the reference arm or in the object arm of the object-imaging interferometer, which in their time duration Δt_kurz_fc is significantly shorter than the time duration Δtjangjnt of the Long scans are done. These short scans preferably cause - at least for a portion of the time Δt_kurz_fc - a reduction in the phase angle velocity in the rasterized detector to be included interference image, including a phase angle velocity with the amount zero, by in the period .DELTA.t_kurz_fc both the amount of the delay length Y and the amount of the optical path difference x_O each enlarge both or both reduce in size.

The resulting phase angular velocity dφ / dt in radians is thus at least approximately in each case in the short scan of the frequency comb light source:

dφ / dt = [2π-Δx_O / (Δt_kurz_fc • λ_S)] - [2ττ-nΔY / (Δt_kurz_fc • λ_S)]

wherein the short scan is synchronized with the long scan of the object imaging interferometer, with n as an integer atomic number n = 1, 2, 3 ..., and Δx_O / Δt_short_fc as the change Δx_O of the optical path difference x_O in the period Δt_short_fc and with ΔY / Δt_kurz_fc as a change Δy of the delay length Y in the time period Δt_kurz_fc in the short scan, ie a speed, and λ_S as the centroid wavelength. The phase angular velocity dφ / dt becomes zero when the magnitudes and the sign of n * ΔY and Δx_O are equal in the period Δt_kurz_lnt.

This implies that for n = 1 in the time duration Δt_short_fc, ie in the FC short scan process, both ΔY and Δx_O are both the same amount zoom in or reduce each by the same amount. The phase angular velocity dφ / dt can also reach zero due to the synchronization of the interferometer long scan and FC short scan, so that the interference pattern does not change in the time period Δt_kurz_fc.

The frequency spacings Δf_object = c / x_O - with c equal to the vacuum speed of light and x_O equal to the optical path difference in the object-imaging interferometer, belonging to a respective optically detected object element P, preferably correspond to the predetermined change in the path difference x_O in the object-imaging interferometer in the scanning measuring process in the duration Δtjangjnt of this interferometer long scan at least once and at least approximately an integral fraction of the frequency spacings Δf_source = c / Y such that Δf_object = Δf_source / n, where n = 1, 2, 3, 4 ....

The optical path difference x_O in the object-imaging interferometer then amounts to an integer multiple of the delay length Y in the frequency comb light source at least approximately in the time duration Δt_kurz_fc of at least one single short scan

x_O = n -Y

with n = 1, 2, 3, 4 .... applies. Thus, the delay length Y in the time duration Δt_kurz_fc of a single FC short scan can be at least approximately equal to the optical path difference x_O, which corresponds to the case n = 1. Thus, in the period Δt_kurz_fc of at least one FC short scan, at least approximately:

x_O = Y

be realized. This equality is achieved by preferably continuously varying the optical path difference x_O of the object-imaging interferometer generated at least once and at least approximately in the measuring process for each probed object element or object. The waveform is repeatedly sampled in the period of time Δtjangjnt by means of spectrally integrally detecting, screened detector, wherein at least one pixel of this spectrally integrally detecting, rasterized detector is optically associated with each of an object element. The pixels of a color camera can here also be regarded as spectrally integrally detecting sensor elements in comparison to the sensor elements of a spectrometer.

The

either for maximum modulation of the signal curve,

- or the signal maximum of the waveform

or the size of the frequency spacings associated with the signal centroid of the signal waveform is calculated and stored as the value "Δf Object_Mod" from the parameters of the object-imaging interferometer, preferably the depth position of the object-imaging interferometer.

In this case, the depth position of each object element in the occurrence of the modulation of the waveform by the object-forming interferometer or components thereof associated Wegmesssystems, for example on the object itself or, for example, on the mechanical basis of the object-forming interferometer, and a scaling of the value "Δf Objekt_Mod" on the measured values the distance measurement are determined.

It is also possible that for different object elements i only changes in the measured values of the displacement measurement for the different object elements i are determined and evaluated by preferably measuring values of the displacement measurement when modulation occurs in each, belonging to an object element pixels are stored and for the calculation of the depth position of each object element can be used. In this case, phase information can also be determined. In the measurement process, the rastered detector of electromagnetic radiation is read out several times successively, and in each pixel of the rasterized detector, the intensities are at least partially summed spectrally in their entirety. The detector can be a planar monochrome CCD or a CMOS camera. In this case, each object element is assigned at least approximately one pixel by optical imaging.

But it is also possible that the detector is a color CCD or color CMOS camera. Then each object element is assigned three or four pixels, but in different spectral ranges.

Preferably, with at least approximately knowledge of the optical refractive index n 'or the refractive index distribution in the object space, the distance z_O of each optically detected object element is absolute or in relation to adjacent object elements from the previously determined for example at the modulation maximum optical path difference with the relationship x_O = 2n' • z_O determined at least approximately by calculation.

Preferably, however, the determination of the optical path difference x_O or its changes Δx_O over time may also be the target of the measurement alone, for example in the measurement of thin biological objects.

In the case of the interferometer long scan, preferably in the object arm, a relative movement is carried out between the object-imaging interferometer or at least components thereof and the object, so that a focussing in the object space takes place in the time duration Δtjangjnt, and at least at one point in time Δtjangjnt the object or Elements of the object are at least approximately sharply imaged optically.

Furthermore, in the method for scalable interferometry, the short scans preferably at least approximately have a sawtooth curve of the optical delay length Y over time. Furthermore, in the preferred method for scalable interferometry, the inclusion of interference images by means of a rastered detector within the time period Δt_kurz_fc preferably takes place when the long edge of the tooth is traversed during the sawtooth curve.

Furthermore, in the method for scalable interferometry, the amount of change in the optical path difference in the object-imaging interferometer between two directly successive short scans is preferably freely selectable.

Furthermore, in the method for scalable interferometry, short scans are preferably performed at least approximately in the form of a harmonic oscillation and the recording of interference images by rastered detector preferably takes place in the at least approximately linear part of the course of the delay length Y over the time of the oscillation within the period Δt_kurz_fc. In this case, the oscillation amplitude is furthermore preferably selected such that the phase change of the interference in the detector integration period ΔtD is at most 180 degrees. The image pickup frequency of the rasterized detector is preferably selected to be equal to the frequency of the harmonic oscillation or an integral multiple thereof.

The imaging of the object can preferably be carried out in a telecentric, central perspective or pericentric manner, the latter for example for the minimally invasive surgical technique, laparoscopy.

On the one hand, the light source may preferably be formed as a frequency comb laser with a macro-resonator with frequency spacings of several 100 MHz. This macro-resonator can be designed to be tunable in frequency comb with respect to its frequency intervals.

The light source may preferably be formed on the other hand as a frequency comb laser with a micro-resonator with frequency intervals of several 100 GHz. This micro-resonator can be designed to be tunable in frequency comb with respect to its frequency intervals.

The object imaging system must be designed to be at least approximately diffraction-limited, since otherwise no well evaluable signals. However, the numerical aperture of the object-imaging system can be chosen within very wide limits according to the task and the technical possibilities. Values of NA = 1, 3 for water immersion and up to NA = 0.001 for air systems can be realized for the imaging system.

The magnitude of the chromatic refractive power in the object illumination and imaging is preferably selected so that the resulting depth splitting of the foci is adapted in each case to the depth of the object to be measured. Thus, refocusing of the object-imaging system is not necessary.

Description of the figures

The invention will be described by way of example with reference to the preferred embodiments shown in Figures 1 to 26. Here, the term light is always used as a synonym for electromagnetic radiation from the terahertz, over the infrared to the deep UV spectrum.

FIG. 1 shows the sensor on the basis of a chromatic-confocal, two-beam spectral interferometer with a multi-beam interferometer arranged downstream of the light source for a relatively small object field with respect to the focal length of the object-imaging system. The light from a high-intensity, fiber-coupled superluminescent diode 1 a in the near infrared range is coupled by means of focusing optics 2 in a single-mode fiber 3, exits from this at the output 4 of the singlemode fiber 3 again, is collimated by a lens 5 and enters a Fabry Per-interferometer 6, here designed as a Fabry-Perot interferometer 6 with the mirror spacing L, which is associated with a piezo actuator 25a. Between the fiber-coupled superluminescent diode 1a and the Fabry-Perot Interferometer 6 is an optical isolator, not shown here, which should apply to all subsequent embodiments. This Fabry-Perot interferometer has two highly mirrored semitransparent mirrors 7 and 8 with the mirror spacing L, so that high-finesse multi-beam interference exists at the output of the Fabry-Perot interferometer 6. Thus, from the incoming continuum spectrum, or quasi-continuum spectrum of the superluminescent diode 1, a multi-beam interference spectrum with frequency comb characteristic is generated. The transmitted, narrow-band spectral components form a comb with equidistant distances Δf_Source in the wavenumber space, the k-space, or the frequency space, the f-space. The distances of the maxima of the transmitted, narrow-band intensities always have the same wavenumber difference .DELTA.f_source because of the multi-beam interference. The light leaving the Fabry-Perot interferometer 6 with spectral comb characteristic passes through a beam splitter 9 and reaches a microlens array 10 with microlenses 11. Foci are formed. These are imaged by the lens 12 to infinity. The light passes in the focal plane of the objective 12 a diffractive zone lens 13 with a light-diffusing effect, which is designed as a phase grating. Here, zeros are formed in the zeroth order, which act as reference bundle R_0, and bundles in the first order O_1λ, which bundles represent chromatic-depth-split, discretized object bundles which, after focusing by means of GRIN lens 14 and refractive surface 16, have different depth positions of the focuses Form object space, so that over the wavelength λ for each imaged focus of a microlens a discretized focus chain 18 is formed, but only at those points in the spectrum where transmission through the transmission maxima of the comb spectrum of the Fabry-Perot interferometer 6 exists. The objective 12, the diffractive zone lens 13, the GRIN lens 14 and the refractive surface 16 together form a chromatic imaging system 15. The reference beams R_0, which have arisen in the zeroth diffraction order after the diffractive zone lens 13, become focused on the refractive surface 16 focused, whereby there arises a relatively small field of Foki, said refractive surface 16 also represents the reference surface in the two-beam interferometer. On the refractive Surface 16 is a beam splitter layer 17 with a relatively low reflectance. The reference beams R_0 are reflected back into the sensor after reflection at the beam splitter layer 17. By contrast, the bundles in the first order O_1λ reach the object space, where the object 19 is located, which is hit exactly or at least approximately in each object element by one of the focuses of the focus chain 18. The backscattered from the surface of the object 19 light all bundles in the order O_1λ pass through the refractive surface 16 and the GRIN lens 14 again to the diffractive zone lens 13. There arise at the diffractive structure of the reference beam R_0 by light diffraction in the zeroth diffraction order now reference bundle R_0_0 and from the object bundles O_1λ by diffraction of light in the first diffraction order now the object bundle O_1λ_1. Both the reference bundles R_0_0 and the discretized object bundles O_1λ_1 undergo confocal discrimination at the confocal aperture 21 after reentry into the microlens array 10, coupling out through the beam splitter 9 and focusing through the objective 20. From there, the lens 22 is used the image on the CCD camera 23, so that in each pixel of this CCD camera 23 each consist of a reference beam and in the presence of a detected object element also a confocal discriminated object bundle. Interference arises between these bundles. Due to the confocal discrimination, only light from the object bundles O_1λ_1 comes to pixels of the CCD camera 23, which was focused approximately sharply. Object bundles, that is, which were imaged at least approximately sharply on the surface of the object 19 with a wavelength λ, are also sharply imaged onto a pixel of this CCD camera 23 by the design of the optical arrangement. When changing the optical delay length in the Fabry-Perot interferometer 6, the intensities are scanned by means of CCD camera 23. The synchronization, control and the electric drive for changing the delay length Y of the Fabry-Perot interferometer 6 by means of piezo-actuator 25a and the control of the CCD camera 23 via the not shown electronic modules of the electronic system 26 for system control and Synchronization, which also includes a computer, which also takes over the evaluation of the camera signals. FIG. 2 shows the intensity striking a pixel 23a of the CCD camera 23-as the mirror distance L in the Fabry-Perot interferometer 6 changes-from a detected object element of the object 19 imaged on the pixel 23a. Here, the optical system is dispersion-free and has a negligible phase offset. Shown is the intensity profile in the form of a wavelet on the pixel 23a of the CCD camera 23 when the mirror distance L is changed in the Fabry-Perot interferometer 6 at a constant speed and the case .DELTA.f_Objekt equal Δf_Source when changing the mirror distance L is reached and traversed. Here, the object element touched by the pixel 23a is 1 mm away from the reference surface 16. The light source 1 a in this case has a spectrum with gaussian envelope with the wavelength range of 720 nm to 920 nm.

FIG. 3 shows an object wavelet determined mathematically with Δf_object = c / x_O, calculated for an optical path difference of x_O = 200 μm, the spectrum of the light source having a Gaussian profile. This is in particular a theoretically expected wave packet (wavelet), which would result from an interference of a component of an incident light with a continuous Gaussian spectrum reflected at the object 19 and a component 19 reflected from the object 19. This object wavelet could possibly even be detected in an optical system according to FIG. 1 by means of a suitable continuum light source and by means of a high-resolution spectrometer, if the Fabry-Perot interferometer 6 is then removed and the continuum light source has a Gaussian profile in the spectrum having. Since, in the actual measurement, the light incident on the beam splitter layer 17 does not have a continuous spectrum but a frequency comb spectrum, the wave packet shown in FIG. 3 does not arise directly. However, this wave packet illustrates the interference condition in the used two-beam interferometer.

FIG. 4 shows the comb spectrum at a time t1 when the optical delay length Y, represented here by the mirror spacing L with Y = 2L, is still is comparatively small, so the delay length Y1 is slightly smaller than the optical path difference x_O in a probed object element. As the mirror spacing L increases, the frequency spacing Δf_source decreases. This is shown in FIG. In particular, the transmission of the Fabry-Perot interferometer 6 is shown in FIG. 4 and FIG. Thus, it is not directly related to the spectrum of the light emerging in the embodiment of FIG. 1 at the Fabry-Perot interferometer 6, which likewise has only a finite spectral width, for example due to a finite spectral width of the light source used.

FIGS. 6 and 7 show the case of the equality of the frequency spacings of Δf_source and Δf_object, ie the case: Δf_source = Δf_object at an object point P of the object 19 in FIG. 1. When this case occurs, a signal modulation occurs in the signal curve over the mirror distance L in the Fabry -Erot interferometer 6.

This waveform is shown in FIG. Here, the waveform recorded in the frequency comb scan by continuously varying the mirror distance L of the Fabry-Perot interferometer 6 is shown in a pixel 23a of the CCD camera 23, which results by summing all the spectral components which could pass through the confocal aperture 21. Here, the optical path difference x_O = 200 microns and the spectral range with enveloping Gaussian profile is between 1300 nm and 1800 nm. The chromatic confinement of the spectrum by confocal discrimination is therefore low here, since the chromatic depth splitting is also low here. Only the underlying spectral range in wavenumber or frequency space determines the half width of the signal modulation over the mirror distance L and thus over the optical delay length Y = 2L. The optical path difference x_O of the object-imaging interferometer has no influence on this half-width. However, phase offset and dispersion can significantly alter the waveform captured in a pixel, and can cause signal asymmetries as well as skew or chirping, so that these signals must be evaluated with a little greater numerical effort. Nevertheless, even then the waveform remains relatively simple. However, the influence of Speckling in probing rough surfaces, ie phase fluctuations from spectral element to spectral element, can also change the signal shape considerably. This influence can be at least somewhat reduced in the case of cooperative object surfaces, if appropriate by comparatively fast lateral movement of the microlenses, but this can somewhat reduce the lateral resolution.

FIG. 9 shows signal curves plotted over the variable distance L of the end mirrors of the Fabry-Perot interferometer 6 for a plurality of orders n with n = 1, 2, 3... For a spectral range from 720 nm to 920 nm with a Gaussian envelope and the optical path difference for an optically detected object element in the object-imaging interferometer of x_O = 2 mm. These signal profiles can then be detected in each case in a pixel of the CCD camera 23 that is optically associated with the object element. For the case n = 1, each pin of a frequency comb hits exactly one period of the object wavelet. For the case n = 2, each needle of a frequency comb strikes every other period of the object wavelet, for the case n = 3 every needle of a frequency comb strikes every third period of the object wavelet, etc. The case for n = 1 is a waveform in a pixel 23a already shown in Figure 2.

FIGS. 10 to 13 show in detail the possible signal curves for the orders n with n = 1, 2, 3, 4, the signal curve in FIG. 10 corresponding to the signal curve in FIG. As the ordinal number n increases, the signals become smaller and smaller in the half-width, becoming narrower and less intense. The distance of the modulated signals to each other also becomes smaller and smaller with increasing n. If a plurality of signal profiles with orders n> 1 are recorded, the absolute order of these signal profiles can be determined by means of a comparatively simple system of equations via the changes Δl_ 2-3 and Δ L 3-4, shown in FIG. 9, usually by means of a linear system of equations. be determined. This then results in the optical Path difference x_O in the object-imaging interferometer for each optically detected object element. The distance or the depth of an object element P can then be calculated at least approximately from this optical path difference x_O, even if the refractive index in the object space is at least approximately known.

FIG. 14 shows an optical arrangement with chromatic properties in the object beam path and achromatic properties for the reference beam path. The application is provided for macroscopic objects 19 at about one meter from the optical measuring system. A tunable frequency comb laser 1 b having a delay length of Y is arranged. The delay length Y is definably changed by +/- ΔY in the resonator of the frequency comb laser 1 b by driver modules of the electronic system 26. The frequency comb laser 1b is followed by an optical isolator, not shown here. The light of this frequency comb laser 1b is coupled by means of focusing optics 2 in a single-mode fiber 3, exits from this at the output 4 of the singlemode fiber 3 again and is collimated by a lens 5. The light passes through a beam splitter 9 and reaches a microlens array 10 with microlenses 11. Foci are formed. These are imaged by the lens 12 to infinity. The light passes in the focal plane of the objective 12 a diffractive zone lens 13 with a light-diffusing effect, which is designed as a phase grating. Here, zeros in the zeroth order, which function as reference beams R_0, and beams in the first order O_1λ are formed, these beams representing chromatic-depth split, discretized bundles of objects. In the optical system 15 is a refractive surface 16, wherein this refractive surface 16 also represents the reference surface in the two-beam interferometer. The objective 12, the diffractive zone lens 13, a diffusing lens 24 and the refractive surface 16 together form a chromatic imaging system 15. The diffusing objective 24, which is designed as a dispersion-free mirror objective, serves to optically touch the object 19 at a distance of about one meter , The reference beams R_0, which have arisen in the zeroth diffraction order after the diffractive zone lens 13, are applied to the refractive surface 16 sharply focused, creating a relatively small field of foci there. On the refractive surface 16 is a beam splitter layer 17 with a relatively low reflectance. The diverging lens 24 thus serves to increase the distance between the focus chain 18 produced by chromatic splitting and the measurement of a macroscopic field. FIG. 15 shows the intensity wavelet resulting on the pixel 23a of the CCD camera 23 during the Y-scan of the tunable frequency comb laser 1b. From this intensity wavelet, in the presence of an object element in the depth measuring range, the maximum of the envelope can be determined by means of suitable and known evaluation algorithms by a computer in order to calculate the depth position of each detectable object element of the object 19.

FIG. 16 shows a device or arrangement which is suitable above all for microscopic or mesoscopic application with a tunable frequency comb laser 1b having a delay length with a mean value of Y, variable in the resonator by +/- ΔY. The tunable frequency comb laser 1 b is tuned in a long scan. The course over time is shown in FIG. 17. The light of this frequency comb laser 1 b in FIG. 16 is coupled into a singlemode fiber 3 by means of focusing optics 2, emerges therefrom again at the output 4 of the singlemode fiber 3 and is collimated by an objective 5. The light passes through a beam splitter 9 and reaches a pinhole array 110 with pinholes 111. These pinholes 111 are imaged by the objective 12 to infinity. The light passes in the focal plane of the objective 12 a diffractive zone lens 13 with a light-diffusing effect, which is designed as a phase grating. Here are zeroth-order beams which act as reference beams R_0 and beams in the first order O_1λ, these beams representing chromatic-depth split, discretized object beams. The objective 12, the diffractive zone lens 13 and the objective 14a for focusing together form a chromatic imaging system 15. The reference beams R_0, which have arisen in the zeroth diffraction order after the diffractive zone lens 13, are applied to the refractive surface 16a on the plane-parallel plate 116 by means of an objective 14a sharply focused, creating a relatively small field of foci there. In this case, this refractive surface 16 at the same time also the reference surface in the two-beam interferometer, here a Fizeau interferometer, is. On the refractive surface 16a of the plane parallel plate 116 is a beam splitter layer 17 with comparatively low reflectance. The reference beams R_0 are reflected back into the sensor after reflection at the beam splitter layer 17. By contrast, the bundles in the first order O_1λ reach the object space, where the stationary object 19 is located, which is hit exactly or at least approximately in each object element by one of the focuses of the focus chain 18. The backscattered from the surface of the object 19 light all bundles in the order O_1λ passes the plane parallel plate 116 and passes through the lens 14a again to the diffractive zone lens 13. There arise at the diffractive structure of the reference beam R_0 by diffraction light in the zeroth diffraction order now Reference bundle R_0_0 and from the object bundles O_1λ by diffraction of light in the first diffraction order now the object bundle O_1λ_1. Both the unrepresented reference bundles R_0_0 and the discretized object bundles O_1λ_1 undergo confocal discrimination at the pinhole array 110 with pinholes 111. From the pinhole array 110 via the lenses 20, 22 and the aperture 21 to avoid reflections an image on a CCD camera 23, so that in each pixel of this CCD camera 23 each have a reference beam and in the presence of a detected object elements also a confocal discriminated object bundle so that occurs between these bundles of interference. Due to the confocal discrimination, only light from the object bundles O_1λ_1 reaches the pixels of the CCD camera 23, which was focused approximately sharply. Object bundles, that is, which were at least approximately sharply imaged onto the surface of the object 19 with a wavelength λ, are also sharply imaged onto a pixel of this CCD camera 23 by the design of the optical arrangement. The plane-parallel plate 116 performs in the measuring process by means of piezoelectric actuator 25a several axial short scans in a sawtooth shape, which are synchronized in the duration of the short scan .DELTA.t_kurz_lnt for long scan of the frequency comb laser 1 b and read the CCD camera 23, so that in the duration of the short scan Δt_kurz_lnt both the delay length Y of the frequency comb. Increase the laser 1 b as well as the optical retardation x_O in the Fizeau interferometer by the same amount. The temporal relationship is shown in FIG. The synchronization, control and electrical drive of frequency comb laser 1 b, piezo actuator 25 a and CCD camera 23 via the not shown electronic modules of the electronic system 26 for system control, which also includes a computer, which also includes the evaluation of the camera signals takes over. The amount of magnification here corresponds to the centroid wavelength λ_S. The change in the phase angle in the duration of the short scan Δt_kurz_lnt is thus at least approximately zero and in this time duration Δt_kurz_lnt an image is recorded by means of a CCD camera 23. After rapid resetting of the plane parallel plate 116 by means of a piezoelectric actuator, a short scan synchronized with the long scan and a new image acquisition takes place again, the interference phase in each pixel of the CCD camera 23 being at least approximately 756 degrees of degree in relation to the previous short scan during the subsequent scan. Scan has changed because between the two consecutive short scans the optical retardation has changed by 2.1 centroid wavelengths λ_S. As a result of this scanning of the comparatively high-frequency interference wavelet (not shown here), in each pixel of the CCD camera 23, for example in the pixel 23a, over the time Δt_lang_fc, a significantly lower frequency wavelet compared to the interference wavelet is produced, shown in FIG a relatively small number of images of the CCD camera 23 can be scanned. The synchronization of short and long scan shown in FIGS. 16 to 19 also makes the use of cost-effective video-frequency cameras with regard to the achievable measuring times still technically meaningful. These cameras allow the described measuring arrangement a comparatively fast and complete measurement of objects with a relatively large depth extent, which can be achieved, especially because of the relatively long integration times of the video-frequency cameras in the rule, a relatively high signal-to-noise ratio.

In particular, FIG. 20 shows an approach for the measurement of microscopically small objects 19 with a comparatively large numerical aperture and thus smaller Therefore, with a depth extension of the object 19, greater than the wavelength of the optical depth of field, it is necessary to perform a depth scan in order to be able to image all the object details once in the serial measuring process. The light source used is a tunable frequency comb laser 1b having a delay length with an average value of Y = 95 mm. The tunable frequency comb laser 1 b is tuned harmonically oscillating at a frequency of 100 hertz, wherein the amplitude of the vibration here is ΔY = 0.261 microns. The temporal relationship is shown in FIG. This oscillation is a short scan. The light of the frequency comb laser 1 b is coupled by means of focusing optics 2 in a single-mode fiber 3, exits from this at the output 4 of the singlemode fiber 3 again, by means of lens 124 to a rotating Mattscheibe 105 steered, where a field is illuminated on this. This luminous field is imaged by a lens 5 in the pupil of the mirror lens 127. The light is incident on a beam splitter 109, which has a beam splitter layer 109a and a beam splitter layer 109b and belongs to an object imaging two-beam interferometer. The light reflected at the beam splitter layer 109a passes back through the triple reflector 126 in the beam splitter 109 and now passes through the beam splitter layer 109b and passes through the lens 22 on the CCD camera 23. The light passing through the beam splitter layer 109a then passes through the mirror lens 127 and passes on the object 19, which is moved in the measuring process in depth. The temporal relationship is made visible in FIG. Thus, in the long scan, each object element of the object 19 is once imaged in a wave-optical manner onto the CCD camera 23 by reflecting the backscattered light after passing through the mirror objective 127 at the beam splitter layer 109b and imaging it onto the CCD camera 23 via the objective 22 , Here it comes to the interference with the light, which has spread in the reference beam path over the triple reflector 126 and the beam splitter 109 has passed with the beam splitter layer 109b in transmission. The CCD camera 23 records a stack of images during the measuring process, the image recording frequency here being 400 Hz. The centroid wavelength is λ_S = 820 nm. The half-width of the spectrum of the used light of the frequency comb laser 1b is about 200 nm. The object-imaging two-beam interferometer in FIG. 20 has, on average, an optical path difference x_O of 95 mm, which corresponds to the mean optical delay length Y of the frequency comb laser 1b. The object 19 is moved in the measuring process with a speed of 172.2 microns / s in the depth. The integration period of the CCD camera 23 is here ΔtD = 2.5 ms. By exact synchronization of the clock of the CCD camera 23 for oscillation of the frequency comb laser 1b and the depth scan of the object 19 by the electronic system 26 for system control, images are respectively taken and stored in a stack of images. Thus, the phase angle φ in the interference image on the CCD camera 23 practically does not change in every fourth camera image, namely, when the retardation length Y and the optical retardation x_O increase by at least approximately the same amount, respectively, and the interference image becomes almost nearly every fourth camera image quiet. An image is always stored here when the oscillation process of the frequency comb laser 1b is in the rise range Ai-2, Ai-1, Ai .... From a first image to a fifth image, ie from the rise area Ai-2 to the rise area Ai-1, the change in the optical path difference in the object-imaging interferometer is approximately Δx_O = 2.1-λ_S = 2.1 * 820 nm = 1722 nm For example, the change of the phase angle in the pixels is approximately 756 degrees from a first image to a fifth image, each in the phase of a rise range Ai-2, Ai-2, Ai. This leads to a subsampling of the interference signals and provides over the depth scan of the object 19 in the pixels of the CCD camera 23 for each detected object point in each case a comparatively low-frequency wavelet. FIG. 23 shows the voltage curve U which results in the electronic system 26 for system control at the output of the camera amplifier, for example for the pixel 23a, over a long scan. The wavelet evaluation takes place here in each case via a center of gravity determination or a determination of the modulation maximum and thus leads to the depth position z of each detected object element of the object 19.

The triple reflector 126 and the lens 127 are each as mirror systems educated. The dispersion in the beam splitter plate 109, which is formed as a high-precision plane-parallel plate is the same in the two arms of the object-imaging interferometer, so that a nearly complete compensation of the dispersion in the object-imaging interferometer is given and advantageously no disturbing chirp effect occurs in the interference signal. Another advantage of this arrangement is that no mechanical vibrations due to short scans can occur in the object-imaging interferometer, since these take place in the frequency comb laser 1b arranged spatially remote from the object-imaging interferometer.

Figure 24 illustrates the magnification of the optical retardation x_O versus the time of an interferometer long scan when, as shown in Figure 22, the object 19 in Figure 20 is advanced in depth in a long scan at a constant speed. In FIG. 23, the dotted line also shows the difference between the optical path difference x_O and the delay length Y of the frequency comb laser 1b over time. In the one interferometer long scan several short scans are temporally embedded. In the time of each short scan Δt_kurz_fc, the increase of this difference, that is, x_O -Y, is significantly reduced, and in these times of short scans, the CCD camera 23 is read out each time with the integration period ΔtD. From short-scan to short-scan, the increase in the optical retardation is 2.1 centroid wavelengths λ_S. According to the actual difference of the optical path difference x_O to the delay length Y, the phase angle φinterference is also modulated. This results in a variable change of the phase angular velocity dφ / dt over time. In the minima of the phase angle velocity, where the intensity in the interference image changes only comparatively slowly or not at all, the intensity is detected at the times t_i-2, t_i-1, t_i with the integration time ΔtD by means of the CCD camera 23 These voltage values U_t i-2, U_t i-1 and U_t i thus obtained are at the output of the camera amplifier of the CCD camera 23 on a long-periodic wavelet. This is shown in FIG. 25 for a part of the signal U which is obtained by means of pixels 23a. The full voltage signal over the time t resulting in the interferometer long scan U detected by the pixel 23a is shown in FIG. 26.

Claims

Applicant: University of Stuttgart
"Method and apparatus for interferometry"
Our Ref .: S 9863WO - ds / hb
claims
1. Method for interferometry comprising:
Generating an electromagnetic measurement signal;
Splitting the measuring signal into a scanning beam component and a reference beam component;
Irradiating at least one object point with at least a portion of the scanning beam component;
Generating an interference signal by superimposing a portion of the scanning beam component reflected by the at least one object point on the reference beam component, wherein the portion of the scanning beam component reflected by the at least one object point in the interference signal has an optical retardation x_O relative to the reference beam component depending on the position of the object point, the measurement signal f_Signal the individual frequency components is generated with a frequency comb spectrum with the same frequency comb intervals and / or wherein the interference signal is filtered by means of a frequency comb filter such that the filtered interference signal only one frequency comb spectrum with the same frequency comb intervals [delta] f_Signal the having individual frequency components; and wherein the method further comprises:
 temporal change of the frequency comb distances [Delta] f_Signal in the frequency comb spectrum and / or the optical path difference x_O such that the frequency comb distances [delta] f_Signal at least temporarily equal to an integer multiple of the quotient c / x_O from the speed of light c and the optical path difference x_O ; and
Detecting an intensity and / or intensity change of the interference signal for a plurality of frequency comb distances [delta] f_Signal and / or for a plurality of optical path differences x_O.
2. The method of claim 1, wherein a section of a spatially resolving detector, in particular a detector array or detector array, is used with a plurality of optical detector elements as the optical detector element.
3. The method of claim 1, wherein generating the electromagnetic measurement signal comprises:
Generating an electromagnetic output signal having a continuous spectrum; and
Filtering the output signal by means of a tunable multi-beam interferometer for generating the electromagnetic measurement signal with a frequency comb spectrum such that the frequency comb distances [Delta] f_Signal of the measurement signal in a modulation interval ([[Delta] f_Signal_min; [Delta] f_Sig [eta] aLmax]) of the frequency comb Intervals are changed over time.
4. The method according to claim 1, further comprising determining a frequency comb modulation distance [Delta] f_Source_Mod from the detected values of the intensity and / or intensity changes of the interference signal, the frequency comb modulation distance [Delta] f_Source_Mod being the frequency comb distance [Delta] f_Signal at the maximum modulation of the detected waveform of the interference signal; and / or as the frequency comb distance [Delta] f_Signal at the maximum signal in the detected waveform of the interference signal and / or; is determined as frequency comb distance [Delta] f_Signal in the signal center of gravity of the detected signal waveform of the interference signal.
5. The method according to claim 4, further comprising determining a value of the optical path difference x_O from the frequency-comb modulation distance [delta] f_Source_Mod according to x_O = c / [delta] f_Source_Mod with the speed of light c.
6. The method according to any one of the preceding claims, comprising: a first scan such that while the frequency comb intervals [Delta] f_Signal be changed continuously; and a second scanning process carried out repeatedly during the first scan in such a way that the optical retardation x_O is continuously changed such that the continuous change in the quotient c / x_Q caused by it is at least temporarily the continuous change in the frequency comb distances effected in the first scan [Delta] f_Signal, whereby the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scanning process.
7. The method according to any one of claims 1 to 5, comprising: a first scan such that thereby the optical path difference x_O is changed continuously; and a second scan performed repeatedly during the first scan, such that the frequency comb intervals [delta] f_signal are continuously changed such that the change in the frequency comb intervals [delta] f_signal follows the sign, at least temporarily, of the continuous scan caused by the first scan Changing the quotient c / x_O corresponds, wherein the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scan.
8. The method according to any one of claims 1 to 5, which comprises: a first scan, that while an optical delay length or path length Y of the signal path in the measuring signal source is changed continuously; and a second scanning operation carried out repeatedly during the first scan in such a way that the optical delay length or path length Y of the signal path in the measurement signal source is continuously changed in such a way that the change in the optical delay length due to the second scan follows the sign after at least the change of the optical path Delay length by the first scan is opposite, wherein the detection of an intensity and / or intensity change of the interference signal takes place during the second scan.
The method of any of claims 6 to 9, wherein detecting an intensity and / or intensity change occurs during a detector integration period [delta] tD during which the phase in the interference signal changes by no more than 180 degrees in magnitude.
10. The method according to any one of claims 6 to 9, wherein the second scan a sawtooth curve of the optical path difference x_O or the reciprocal 1 / [delta] f_Signal the frequency comb intervals [delta] f_Signal or the optical delay length Y in the measuring signal source on the Time and wherein the detection of an intensity and / or intensity change of the interference signal during the long edge of the sawtooth occurs.
11. The method according to claim 6, wherein the second scanning process takes place in the form of a harmonic of the optical transition pitch x_O or of the reciprocal value 1 / [delta] f_signal of the frequency comb intervals [delta] f_signal over time, and wherein the detection an intensity and / or intensity change of the interference signal takes place in a period which contains the passage of the harmonic oscillation through the point of inflection of the spatial oscillatory motion in which the change of the frequency comb distances [delta] f_signal corresponds to the sign after the change of the quotient c / x_O ,
12. The method of claim 9, wherein the second scanning is in the form of a harmonic of the optical delay length Y in the measurement signal source over time and wherein the detection of an intensity and / or intensity change of the interference signal in a period of time, the passage of the includes harmonic vibration through that inflection point of the spatial vibration motion in which the change of the optical delay length Y by the second scan is opposite to the sign after the change of the optical delay length Y by the first scan.
13. An apparatus for interferometry comprising: a measurement signal source for generating an electromagnetic measurement signal; an interferometer arrangement configured to split the measurement signal into a sample beam component and a reference beam component; to irradiate at least one object point with at least a portion of the scanning beam component; and generate an interference signal by superimposing a portion of the scanning beam component reflected from the at least one object point on the reference beam component, wherein the portion of the scanning beam component reflected in the interference signal by the at least one object point has an optical retardation x_O relative to the reference beam component depending on the position of the object point;
 wherein the measurement signal source is adapted to generate the measurement signal with a frequency comb spectrum with equal frequency comb intervals [delta] f_signal of the individual frequency components and / or wherein the apparatus further comprises a frequency comb filter which is adapted to filter the interference signal such that the filtered interference signal only one frequency comb spectrum with the same frequency comb intervals [delta] has f_Signal the individual frequency components; and wherein the device further comprises:
 a control device for temporally changing the frequency comb distances [Delta] f_Signal in the frequency comb spectrum and / or the optical path difference x_O such that the frequency comb distances [delta] f_Signal at least temporarily an integer multiple of the quotient c / x_O from the speed of light c and the optical Path difference x_O correspond; and at least one detector element for detecting an intensity and / or intensity change of the interference signal for a plurality of frequency comb distances [delta] f_Signal and / or for a plurality of optical path differences x_O.
14. The apparatus of claim 13, wherein the interferometer arrangement comprises a Fizeau interferometer and / or a Michelson interferometer and / or a TwymanGreenlnterferometer and / or a Mirau interferometer and / or a Linnik interferometer and / or a Mach-Zehnder interferometer.
15. The apparatus of claim 13 or 14, wherein the measuring signal source comprises a tunable frequency comb laser.
16. The apparatus of claim 13 or 14, wherein the measurement signal source comprises: a radiation source for generating an electromagnetic
Output signal with a continuous spectrum; and a frequency comb filter for filtering the output signal to generate the electromagnetic measurement signal having a frequency comb spectrum such that the frequency comb distances [delta] f_signal of the measurement signal are time-changeable in a modulation interval ([[delta] f_signal_min; [delta] f_signal_max]) of the frequency comb intervals are.
17. Device according to one of claims 13 to 16, comprising an optical waveguide for transmitting the measuring signal from the measuring signal source to the interferometer.
18. Device according to one of claims 13 to 17, wherein the control device is designed to control a first and a second scan so synchronously that in the first scan, the frequency comb intervals [delta] f_Signal be changed continuously; and in the second scan repeatedly executed during the first scan, the optical retardation x_O is continuously varied such that the continuous change in the quotient c / x_O caused by this, following at least the continuous scan in the first scan, causes the frequency comb distances [Delta] f_Signal corresponds, and wherein the control device is designed to control the at least one detector element such that the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scanning operation.
19. Device according to one of claims 13 to 17, wherein the control device is designed to control a first and a second scan so synchronously that in the first scan, the optical path difference x_O is changed continuously; and in the second scan repeatedly executed during the first scan, the frequency comb distances [Delta] f_Signal are continuously changed such that the change in the frequency comb distances [Delta] f_Signal follows the sign, at least temporarily, of the continuous change in the quotient caused by the first scan c / x_O corresponds, and wherein the control device is designed to control the at least one detector element such that the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scanning process.
20. Device according to one of claims 13 to 17, wherein the measuring signal source comprises: a first signal scanning means for performing a first scan such that while an optical delay length or path length Y of the signal path is continuously changed in the measuring signal source; and a second signal scanning device for carrying out a second scan repeatedly executed during the first scan in such a way that the optical delay length or
 Path length Y of the signal path in the measurement signal source is continuously changed such that the change of the optical delay length by the second signal scanning opposite in the sign at least temporarily the change of the optical delay length by the first signal scanning, and wherein the control means is designed to control at least one detector element such that the detection of an intensity and / or intensity change of the interference signal takes place in each case during the second scanning process.
EP09741220A 2008-10-10 2009-10-12 Method and device for interferometry Withdrawn EP2347215A1 (en)

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