EP0873565B1 - Condenser-monochromator arrangement for x-radiation - Google Patents

Description

The invention relates to a condenser monochromator arrangement for X-rays according to the characteristics in the preamble of Claim 1.

Significant progress has been made in the past few years X-ray microscopy in the wavelength range of about 0.2 - 5 nm made. X-ray microscopes were developed that were brilliant X-ray sources are operated. These X-ray sources include Electron storage rings, their deflection magnets and undulators Source locations of intense X-rays are; other x-ray sources So far there is no comparable brilliance. For transmission x-ray microscopes So far only the one generated by deflection magnets X-rays used.

To illuminate an object with X-rays Condensers used. Conventional condensers are as Mirror condensers or as condenser zone plates, further below are described, trained. The from OPTIK, Vol. 93, No. 3, May 1st 1993, pp. 95-102, G. Schmahl et al., "X-ray microscopy studies" (Fig. 6) and mirror condensers known from EP-A-0 475 098 have the shape of an ellipsoid of revolution and focus the Radiation from the X-ray source on the object to be examined. There as X-ray sources use pulsed plasma sources as line sources the condensers have no diffractive elements for one spectral decomposition.

Coming as high-resolution lenses in X-ray microscopes nowadays only micro zone plates are used. Microzone plates are rotationally symmetrical transmission circle grids with outwards decreasing lattice constants, typically have up to 0.1 mm Diameter and a few hundred zones. The numerical aperture of a Zone plate is generally determined by the diffraction angle, below the vertical and thus the finest zones Bend X-rays. The achievable spatial resolution of a Zone plate is determined by its numerical aperture. The numeric Aperture of the used X-ray lenses could in the last few years be significantly increased so that their resolution improved. This trend towards higher resolution will continue.

Generally, for X-ray microscopes, the zone plates are called Use X-ray lenses, a hollow cone-shaped object lighting needed. Otherwise, the image would also be at its center Radiation from the 0th and 1st diffraction order of the Overlay the condenser zone plate. This is because the overwhelming majority Proportion of radiation that is parallel or almost parallel to the optical axis the object falls, this and the following micro zone plate (the diffractive x-ray lens) penetrates undiffracted and turns out to be general diffuse underground in a straight line, i.e. in the center of the image field. For this reason, everyone uses Transmission X-ray microscopes, ring-shaped condensers and the The usable, non-diffusely overexposed area of the image field becomes even more so larger, the larger the inner, radiation-free solid angle range of the Is condenser.

From the theory of microscopy it is known that the numerical aperture of the illuminating condenser of a transmitted light microscope always approximately should be adapted to the numerical aperture of the microscope objective, order from incoherently radiating light sources also an incoherent Object lighting and thus an almost linear relationship between Obtain object intensity and image intensity. Is the aperture of the By contrast, the condenser is lower than that of the microscope objective a partially coherent mapping and the linear transformation between Object intensity and image intensity go for the important, the resolution of the Microscope determining high spatial frequencies lost.

So far, "large-area" condensers for X-rays have been used. annular zone plates used. (A. Schlachetzki, K. Dorenwendt: Quantitative microscopy and microstructuring, block seminar from 13. until September 14, 1995, Physikalisch Technische Bundesanstalt, Technical University of Braunschweig, published: PTB-Opt-50, Braunschweig, March 1996, pages 98-116, B. Niemann et al., "X-Ray Microscopy "(see Fig. 3); P.C. Cheng, G.J. Jan: X-ray Microscopy, Springerverlag Berlin Heidelberg 1987, pages 32-38, W. Meyer-llse et al., "Status of X-ray Microscopy Experiments at the BESSY Laboratory" (see Fig.3.1)). They focus the X-rays on the one with the X-ray microscope object to be examined. Such The size of the "condenser zone plate" is adapted to the Beam diameter at the end of the beam tube of a deflection magnet of an electron storage ring is typically up to 1 cm. Since the Condenser zone plate is annular, it catches about ¾ of this Beam diameter lying on radiation. Because the focal length is one Zone plate is reciprocal to the wavelength used, such acts Condenser zone plate together with a small so-called Monochromator pinhole located in the object plane around the object at the same time as a linear monochromator (Optics Communication 12, Pp. 160-163, 1974, "Soft X-Ray Imaging Zone Plates with Large Zone Numbers for Microscopic and Spectroscopic Applications ", Niemann, Rudolph, Schmahl). Only a narrow spectral range of the incident polychromatic radiation from an electron storage ring is transferred into the Pinhole focused and used to illuminate the object.

The spectral resolution of such a linear monochromator is R = D / 2d if D and d are the diameters of the condenser zone plate and the monochromator pinhole and if the condenser zone plate shows the source area of the X-ray radiation in a greatly reduced manner. However, the relationship only applies if the image of the source - the so-called "critical lighting" - is not larger than the diameter d of the pinhole. If R is at least as large as the zone number n of the microzone plate of the X-ray microscope, the chromatic aberration of the microzone plate is negligible and it only insignificantly deteriorates the quality of the X-ray image. In order to meet this requirement for the spectral resolution R , a condenser zone plate is used which is not too small in diameter D , so that the permitted diameter d of the monochromator pinhole is larger than the image of the source.

Since the location of an X-ray microscope can never be brought close to the source of the X-rays of an electron storage ring for practical reasons and the distance is typically at least 15 m, the area illuminated by the beam cannot fall below certain values. Thus, the diameter D of a condenser zone plate that collects as much X-radiation as possible should not fall below these values. If the numerical aperture of the condenser zone plate is increased for these operating conditions, the focal length of the condenser zone plate inevitably decreases. This reduces the imaging scale with which the source is imaged in the object plane and the diameter of the illuminated object area decreases (in practice to a few µm diameter), which is disadvantageous. Only by other measures - for example, by rastering parallel movements of the condenser and monochromator pinhole - can it be ensured that a larger object area is illuminated homogeneously. In addition, the monochromator diaphragm and the condenser zone plate must remain precisely adjusted to one another during the movement.

Condenser zone plates are usually used in the first Diffraction order used, in which all realized so far Condenser zone plates have their highest diffraction efficiency. It is also for another reason explained below difficult to adapt the numerical aperture of the Condenser zone plate to that of the micro zone plate without new ones To achieve difficulties. In order to implement the adjustment, the lighting condenser zone plate on the outside the same fine Zones have themselves like the micro zone plate serving as an objective The brightest built microzone plates now have zone widths of only 19 nm (corresponding to 38 nm period of the zone structures). So far, zone plates with such fine zone structures can only be used Methods of electron beam lithography, in which the zones are in succession generated, manufactured. Holographic methods that Pattern of a zone plate in one step "parallel" and thus in a short time generate, are excluded because a suitably short-wave UV holography is not exists. Accordingly, condenser zone plates could also be used adapted numerical aperture only with methods of Electron beam lithography, which is serial and therefore slow Process to be referred to are manufactured. Such However, condenser zone plates necessarily have because of their large diameter typically many tens of zones. The Writing times with an electron beam lithography system are then in the order of magnitude of weeks, which is unrealistic for practical reasons, why Condenser zone plates using methods of electron beam lithography have not yet been manufactured.

For darkfield X-ray microscopy, they are even more powerful Condenser-monochromator arrangements necessary (unless a very absorbing ring to be precisely adjusted in the rear focal plane of the micro lens is placed). The periods of the zone structures suitable condenser zone plates would have to be less than 38 nm be.

A condenser monochromator arrangement is used for phase contrast X-ray microscopy an advantage that everything possible from the jet pipe provided X-ray light in an annular hollow cone aperture large aperture angle to the object.

In order to increase the resolution of the X-ray microscope, is currently worked on developing micro zone plates, the smallest Zone width of only 10 nm. This increases the apertures of the micro zone plates and accordingly the necessary numerical ones Apertures of the condensers to provide incoherent object lighting ensure and increase the difficulties already mentioned yourself further.

There are electron storage rings under construction worldwide and some. completed that Provide X-rays from undulators. This Undulators provide about 10 to 100 times higher X-ray radiation flow, which are fully used for X-ray microscopy can. In addition, the X-rays are much better collimated, typically the beam is at the end of a beam pipe at the location of a microscope only 1 - 2 mm in diameter and the ones used up to now and "large" condenser zone plates not adapted in their aperture can no longer be fully illuminated. In order to Condenser zone plates monochromatize the radiation sufficiently, would then either have arrangements with those already discussed above Disadvantages - smaller condenser zone plates with shorter focal lengths and correspondingly smaller monochromator pinholes - are used, or large condenser zone plates must be off-axis, i.e. in one Outskirts to be illuminated. Such off-axis arrangements but illuminate the object obliquely, resulting in an asymmetrical optical transmission function of the microscope and thus generated images are difficult to evaluate. Another way that has already been proposed is to beam with a additional zone plate in front of the condenser. This but has the disadvantage that this additional diffractive element Another loss of light occurs - the diffraction efficiency of Zone plates are in the range of only 10% to 20% - and also are then there are a total of three zone plates in the microscope, because of the wavelength dependency of their focal lengths much more difficult exactly can be adjusted to each other as two zone plates. It can also the adjustment of the apertures also in the last two cases disadvantageously only by adjusting the smallest zone widths of the condenser zone plate to that of the micro zone plate.

• die eine ringförmige Beleuchtungspupille besitzt,
• mit der eine hohe numerische Apertur erzeugt werden kann, die den hohen Aperturen eines modernen Röntgenobjektivs mit Mikrozonenplatten zur Erzeugung einer hohen Auflösung entsprechend angepaßt ist und
• mit der auch ein einfallendes enges Strahlenbündel mit nur wenigen Millimetern Durchmesser vollständig genutzt werden kann.

It is the object of the invention to provide a condenser-monochromator arrangement for quasi-monochromatic object illumination in an X-ray microscope and for incoherent image recording.

• which has an annular lighting pupil,
• with which a high numerical aperture can be generated, which is adapted to the high apertures of a modern X-ray objective with micro zone plates in order to produce a high resolution and
• with which even an incident narrow beam of rays with a diameter of only a few millimeters can be fully used.

This object is achieved by the in the license plate of the specified features solved. Beneficial Refinements and developments of the invention result from the subclaims.

The invention is based on the knowledge that an incoherent image recording is obtained if an object to be imaged is illuminated successively from different directions during the exposure time of an image. A condenser-monochromator arrangement is used, which consists of an off-axis zone plate, a plane mirror, a monochromator pinhole on the optical axis and a mechanical holder for the off-axis zone plate and the plane mirror. The holder can be rotated around the optical axis of the microscope. This rotation creates lighting from different directions.

The condenser-monochromator arrangement requires only a small amount Beam cross section of the incident X-rays only one diffractive optical element and this contains coarser and therefore one overall fewer number of diffractive structures than in previously used optical elements. Which especially compared to the fine structures the microzone plate of the lens very coarse structures of the diffractive Elements of the condenser-monochromator arrangement can be used with the help of electron beam lithography in significantly shorter times. In addition, the lighting aperture of the condenser monochromator arrangement can can be set variably without another diffractive optical element is needed. The usable area of the image field is enlarged, because the lighting only from a very "thin-walled Hollow cone jacket "exists.

In the following, schematically illustrated embodiments of the Invention explained with reference to the drawing.

1 shows a condenser monochromator consisting of an off-axis Transmission zone plate and a subordinate plane mirror.

2 shows a condenser monochromator consisting of an off-axis Transmission zone plate, one upstream and one subordinate plan table.

3 shows a condenser monochromator consisting of an off-axis Transmission zone plate and two upstream plane mirrors.

4 shows a condenser monochromator consisting of an off-axis Transmission zone plate and an upstream plane mirror.

5 shows a condenser monochromator consisting of a Condenser zone plate and two upstream plane mirrors.

6 shows a condenser monochromator consisting of an off-axis Reflection zone plate and a subordinate plane mirror.

7a shows a condenser monochromator consisting of a Reflection plan grating and a subordinate focusing mirror.

7b shows a condenser monochromator consisting of a Transmission plan grid and a subordinate focusing Mirror.

8 shows a condenser monochromator consisting of an off-axis Reflection zone plate and an upstream plane mirror.

9 shows a condenser monochromator consisting of an off-axis Reflection zone plate, an upstream and a downstream Plane mirror.

10 shows a condenser monochromator consisting of an off-axis Reflection zone plate and two upstream plane mirrors.

11 shows a condenser monochromator consisting of an off-axis Transmission zone plate and two downstream plane mirrors.

Fig. 12. shows a condenser monochromator consisting of an off-axis Transmission zone plate and three downstream plane mirrors.

Fig. 13 shows a condenser monochromator that has an off-axis Transmission zone plate made of two segments different Focus and two pairs of plane mirrors.

Fig. 14. shows a condenser monochromator that has an off-axis Transmission zone plate made of two segments different Focus and two pairs of plane mirrors.

15 shows a condenser monochromator consisting of a Focuser with ring focus and a downstream concave mirror.

Fig. 16 shows a condenser monochromator consisting of a Focuser with ring focus and two downstream concave mirrors.

1 shows a condenser-monochromator arrangement which contains two optical elements. The incident X-ray radiation 1 hits on a diffractive and at the same time imaging optical element 7 and is focused by this and bent in the direction of a plane mirror 2.

The plane mirror 2 stands a few cm before the focal point of the X-ray radiation and reflects this into the monochromator pinhole 11 on the object 4, which is on the optical axis 6 of the X-ray microscope 5 is located. The plane mirror 2 is grazing Incidence with a few degrees of incidence so that total reflection occurs (Matter has a refractive index for soft X-rays, which is is less than one) and a high reflectivity is achieved. To the Surface quality of the plane mirror 2 must with respect to the Angle tangent error is not a particularly high requirement (an angular tangent error of better than 10 arc seconds sufficient), since the plane mirror 2 is only a few cm in front of the illuminating object 4 is located. This allows the Angle tangent error only the illuminated image field by scattering expand insignificantly. Since the plane mirror 2 is relatively close to the focal point the X-rays and the beam cross-section is already small here, The plane mirror 2 advantageously only needs to be a few cm long.

Together as a unit, the two described optical form Elements 2,7 with the monochromator aperture 11 a condenser-monochromator arrangement. The optical elements 2,7 are rotatable around the optical axis 6 of the X-ray microscope 5 is mounted. You can do this they are attached in a mechanical holder, not shown here. The holder has a coincident with the optical axis 6 Axis of rotation about which they are together with the optical elements 2.7 can turn. The optical axis 6 of the X-ray microscope 5 is in Direction of propagation of the incident X-rays 1 aligned. The entire structure is due to the high absorption of the used soft x-rays in a vacuum chamber.

The diffractive and imaging optical element 7 can be an off-axis zone plate. An off-axis zone plate is understood here to mean a zone plate which consists only of a small, asymmetrical zone region which is asymmetrical and far from the center of the zone plate. For this reason, the structures within this zone area are generally not rotationally symmetrical. The zone area is so large that it can capture an X-ray beam with a cross-sectional area of a few mm ^2. It can be used in transmission as an off-axis transmission zone plate 7 according to FIG. 1, or in reflection as an off-axis reflection zone plate 3 according to FIG. 6 . Since an off-axis zone plate laterally deflects the X-rays, the plane mirror 2 is absolutely necessary in order to reflect the X-rays back onto the optical axis 6.

Now, during the exposure of a microscopic image, the is typically a few seconds, the mechanical bracket with the optical elements 7.2 (Fig.1) exactly one turn around optical axis 6 rotated, this describes obliquely on the object 4th incident light cone 8 a hollow cone, which is the effective Aperture of the lighting determined. The opening angle 10 this Hollow cone can be the reflection angle 9 of the plane mirror 2nd can be set. For this purpose, the distance of the plane mirror 2 from the optical axis 6 and the position of the off-axis transmission zone plate 7 (or the off-axis reflection zone plate 3 in FIG. 6) along the Optical axis 6 can be readjusted so that the focus is exactly back on the optical axis 6 lies in the object 4. The location of the axis of rotation of the Bracket must remain stable except for a few, what with Spindle ball bearings or play-free ball guides can be achieved.

Since the aperture adjustment is carried out with the plane mirror 2, there are no special requirements with regard to the strength of the beam deflection by diffraction at the off-axis zone plate 7.3. The off-axis zone plate 7, 3 only has to generate an image of the X-ray source of a suitable size in the object plane and spectrally split the X-ray radiation. Since undulators have very small source sizes - they are significantly smaller than the source sizes in the deflection magnets used to date - a small scale of reduction and thus an off-axis zone plate 7.3 with typically at least twice the focal length than that of the condenser zone plates mentioned in the introduction can be used be used to illuminate the object in so-called "critical lighting". The result of this is that not only an off-axis reflection zone plate 3 (FIG. 6, also also FIG. 8 -10) used under grazing incidence, which has coarser zones from the outset, can be used, but that an off already -axis transmission zone plate 7 (Fig.1, also Fig.2-4, 11-14) is sufficient, which has coarser and therefore fewer zones than the condenser zone plate discussed above, which corresponds to the prior art in a condenser-monochromator arrangement is the only optical element at all and is always used in transmission for quasi-monochromatic lighting. In addition, the area to be structured for applications on undulators is typically 10 times smaller than in the condenser zone plate for radiation from deflection magnets described in the introduction because of the better focused beam. In addition, the zone widths of an off-axis zone plate 7.3 are almost constant, so that they advantageously have an almost uniformly high dispersion over their entire area .

As already mentioned, arrangements with off-axis are in principle Transmission and reflection zone plates can be used. An off-axis Transmission zone plate 7 for an X-ray radiation with 2.4 nm Wavelength has e.g. Germanium zones 50 nm wide and 300 nm high - what is currently technologically producible. One in its optical Properties equivalent off-axis reflection zone plate 3, which at In contrast, angles of incidence of a few degrees are approximately 10 up to 50 times larger zone widths and at the same time significantly smaller Zone height. Therefore, the off-axis reflection zone plate 3 is technological much easier to implement than the equivalent off-axis Transmission zone plate 7.

In contrast to an off-axis transmission zone plate 7, the self-supporting with fine support structures or on a very thin one Support film is produced, an off-axis reflection zone plate 3 on a stable, solid substrate. Because of the extremely weird In the case of X-rays, this substrate is thermally resilient and coolable.

Even with several plane mirrors 2, both the off-axis Transmission zone plate 7 as well as the off-axis reflection zone plate 3 can be arranged in different ways, which is exemplified in the 2, 3 and 9-14 is shown.

Thus, according to FIG. 2 and also according to FIG. 9, the incident one X-ray radiation 1 first with a plane mirror 2 from it Original direction deflected towards an off-axis zone plate 7.3. Behind the off-axis zone plate 7.3, a second plane mirror 2 the diffracted and converging radiation towards the optical Axis 6 mirrored, the aperture through this second plane mirror 2 the lighting can be adjusted. According to Figure 2, an off-axis Transmission zone plate 7 and, according to FIG. 9, an off-axis Reflection zone plate 3 used. The arrangement of both plane mirrors 2 and the off-axis zone plate 7.3 is used during the exposure time X-ray image rotated one revolution around the optical axis 6. Of the Illuminating cone 8 incident obliquely on the object describes one Hollow cone that determines the effective aperture of the lighting. The desired aperture adjustment is done with the second in Beam path arranged behind the off-axis zone plate 7.3 Plane mirror 2 by appropriately setting the reflection angle 9.

According to Figure 3 and also according to Figure 10, the incident X-ray radiation 1 first with a plane mirror 2 from it directed in the original direction and meets a second plane mirror 2. From there it reaches an off-axis according to FIG Transmission zone plate 7 or, according to FIG. 10, on an off-axis Reflection zone plate 3. The off-axis zone plate 7.3 focuses that X-ray light in the object 4. The described arrangement of the two Flat mirror 2 and the off-axis zone plate 7.3 is not using a shown mechanical holder during the exposure time of the X-ray microscope 5 rotated one revolution around the optical axis 6. The illumination cone 8, which falls obliquely onto the object 4, describes a hollow cone that determines the effective aperture of the lighting. The The desired aperture adjustment is done with the second one in the beam path shortly before the off-axis zone plate 7,3 arranged plane mirror 2 by the reflection angle 9 is set appropriately.

4 shows a condenser-monochromator arrangement with an off-axis Transmission zone plate 7 and an upstream plane mirror 2. Die Off-axis transmission zone plate 7 focuses the X-ray light at an angle back to object 4 on the optical axis 6. The off-axis Transmission zone plate 7 and the upstream plane mirror 2 are during the exposure time of the X-ray microscope 5 one revolution rotated about the optical axis 6. The one that falls obliquely onto the object Illumination cone 8 describes a hollow cone, which is the effective one Aperture of the lighting determined. However, with this arrangement no more flexible aperture adjustment possible.

In Figure 5 an embodiment is shown in which as a diffractive Element an annular described in the introduction Condenser zone plate 14 is used. In front of it in the beam path itself for beam deflection two plane mirrors 2, which during the Exposure time of an X-ray microscopic image using a rotatable mechanical holder once around the optical axis 6 be rotated so that the deflected beam covers the entire annular condenser zone plate 14 sweeps once. The Condenser zone plate 14 therefore does not need to be rotated. Of the Illuminating cone 8 incident obliquely on the object 4 describes one Hollow cone that determines the effective aperture of the lighting.

6 shows a condenser monochromator arrangement in which the incident X-rays 1 on an off-axis reflection zone plate 3 hits, which bends the X-rays 1 in reflection and at the same time focused. The plane mirror 2 directs the diffracted X-rays onto the Object 4. The off-axis reflection zone plate 3 and Plane mirror around the optical axis 6. Under the description of Fig.1 is the mode of operation has already been explained in detail.

An exemplary embodiment is shown in FIG Element used a reflection plan grating 15a with variable line density becomes. The line density of the reflection plan grating 15a varies such that the X-ray radiation after diffraction at the reflection plan grating 15a is the same Beam divergence has as before the reflection plan grating 15a. This Technology is well known and is already being used. According to the invention but there is also a focusing one in the further beam path Mirror 16 and together with the reflection plan grating 15 around the optical axis 6 rotated. The focusing mirror 16 focuses the X-ray radiation on the object 4, the rotation being a Aperture of the illuminating hollow cone is formed.

It is of course also possible, instead of the reflection plan grating 15a Use suitable short-wave X-rays - a crystal under Use Bragg reflection.

The Fig.7b differs from Fig.7a only in that as a diffractive optical element a transmission plan grating 15b instead of Reflection plan grating 15a is used. The transmission plan grid 15b diffracts the incident X-rays 1 in transmission and retains them their parallelism even after diffraction. Only the focusing one Mirror 16, which together with the transmission plan grid around the optical axis 6 rotates, the X-ray radiation focuses on the object 4.

8 shows a condenser-monochromator arrangement with an off-axis Reflection zone plate 3 and an upstream plane mirror 2. The off-axis The reflection zone plate 3 focuses the X-ray back at an angle to object 4 on the optical axis 6. The off-axis reflection zone plate 3 and the upstream plane mirror 2 are during the Exposure time of the X-ray microscope 5 one revolution optical axis 6 rotated. The one that falls obliquely onto the object Illumination cone 8 describes a hollow cone, which is the effective one Aperture of the lighting determined. However, with this arrangement no more flexible aperture adjustment possible.

When using suitable short-wave X-rays, it is natural also possible to place a crystal under the plane mirror 2 in Fig.8 Use Bragg reflection.

Likewise, when using suitable short-wave X-rays instead of the off-axis reflection zone plate 3 in FIG. 8, a curved one Crystal in the so-called "Rowland arrangement" and using the Bragg reflection can be used.

The condenser-monochromator arrangements according to FIG. 9 and FIG. 10 with in each case two plane mirrors 2 and an off-axis reflection zone plate 3, the Rotate around the optical axis 6 are already in the text for the sake of analogy to Fig.2 and. Fig.3 described.

It should be mentioned that these have been found so far Solutions with transmission and reflection zone plates 7.3 also for Radiation of longer wavelengths, for example for UV radiation and visible ones Radiation. In particular, with these rotating optics Object lighting for incoherent image recording also with coherent Light sources, e.g. when illuminated with lasers. Corresponding systems are considered as systems with "dynamic coherence Aperture ". They embody the special case very obliquely and rotating lighting. For this is in the visible spectral range known that the transfer function at high spatial frequencies compared to almost incoherent lighting a condenser circular pupil, so that an improved Contrast transmission is achieved. When using monochromatic Laser radiation is of course enough, the steel deflection only by mirrors to make, i.e. in Fig.6 and in Fig.8-10 can on the monochromatizing properties of the off-axis reflection zone plate 3 can be dispensed with and replaced by a focusing mirror become. For the same reason, the off-axis can then be shown in Fig. 1-4 Transmission zone plate 7 to be replaced by a lens in a Part is used far from the center of the lens.

In Fig. 11 the e.g. Plane mirror 2 shown in FIG. 1 by two successive individual plane mirror 2 replaced. Both steer Flat mirror 2 the X-rays in the same direction. But it is also possible that the two plane mirrors 2 the X-rays distract in the opposite direction. An arrangement with two successive plane mirrors 2 rotating about the optical axis 6 (as they are also shown in Fig. 3 and Fig. 10) in any case, that the image of the x-ray source despite rotating off-axis Transmission zone plate 7 and the rotating plane mirror 2 are not is rotated. This has the advantages discussed below Applications with elliptical radiation sources and it can Accuracy requirements for the game of the axis of rotation of the mirror and Reduce the zone plate bracket.

In Fig.12. is a condenser monochromator consisting of an off-axis Transmission zone plate 7 and three downstream plane mirrors 17, 18, 19 shown. In this arrangement only the two need each other downstream plane mirror 17.18 around the optical axis 6 of X-ray microscope 5 to rotate. The off-axis transmission zone plate 7 and the plane mirror 19 can remain fixed in space. This arrangement has the advantage that the off-axis transmission zone plate 7 generated image of the x-ray source because of the double Reflection on the rotating mirrors 17, 18 is not rotated. If an electron beam undulator is used as the X-ray source, it generally has a strongly elliptical source area from which the off-axis transmission zone plate 7 generates an image. The Dispersion direction of the off-axis transmission zone plate 7 can now do so be placed so that it falls in the direction of the small axis of the ellipse. The only slightly curved zones of the off-axis run here Transmission zone plate 7 essentially "parallel" to the large one Ellipse axis of the picture. Because the image of the x-ray source due to double reflection on the two rotating, Downstream mirrors 17, 18 does not rotate, therefore, in this way a relatively homogeneously illuminated "band" the width of the large one Diameter of the image ellipse are generated, its intensity in Dispersion direction varies only slowly.

At the same time, this arrangement is relatively insensitive to Tilting and translations of the axis of rotation of the mirror arrangement, since two rotating plane mirrors 2 are used.

In Fig.13 is a condenser monochromator arrangement with a off-axis transmission zone plate 7, which in two off-axis Transmission zone plate segments 20a, 20b is divided, and with two Pairs downstream and each distracting Flat mirror 2 shown. Here the X-rays from two off-axis Transmission zone plate segments 20a, 20b of the same focal length captured. The off-axis transmission zone plate segments 20a, 20b are identical in structure, but rotated 180 ° against each other, see above that the two associated foci face each other, symmetrical to optical axis 6. With one pair of plane mirrors each, the rays reflected back on the optical axis 6, so that the two Overlay focal points in object 4. This type of lighting is strict mirror-symmetrical and leads to different imaging properties than that "Single sideband imaging" with one-sided and extreme bright field oblique lighting. In particular, with this type of lighting further enlargement of the illumination angle in the object plane Dark field microscopy are operated. Then they are always complementary diffracted rays present in the image plane, which are with each other can interfere. This is a necessary requirement if the Limit resolution should be achieved in the dark field.

In the embodiment according to FIG. 13 rotate with the off-axis Transmission zone plate 7 and the 2 pairs of plane mirrors 2 several beam-deflecting optical elements around the optical axis 6. This is also the case for the exemplary embodiment shown in FIG. 14.

In Fig. 14. is a condenser monochromator arrangement with an off-axis Transmission zone plate 7 and with two pairs each rectified distracting plane mirrors 2 shown. The off-axis Transmission zone plate 7 is like that according to FIG. 13 of two segments 20a, 20b composed, which have the same focal length but with - based on the optical axis 6 - opposite focal points. However, due to the radiation-deflecting plane mirror 2, they overlap the otherwise separate focal points in a focal point in object 4. The the principle of operation is the same as that shown in Fig. 13 described.

Finally, according to FIG. 15, it is also possible to specify equivalent systems for quasi-monochromatic object illumination with incoherent image recording that do not require the entire system to rotate about the optical axis 6 during the exposure time of an image. In this case, as is generally the case in optical microscopy, a condenser monochromator is used which generates an illumination wave with a high numerical aperture. A special diffractive element with a mirror can be used. The diffractive element is a so-called focuser 13 with a ring focus, which instead of a focal point generates a sharply focused ring concentric to the optical axis 6. Such focusers 13 can be produced in the same way as off-axis zone plates 7, 3 with the aid of electron beam lithography. They have parameters and laws very similar to the previously described off-axis zone plates 7 in transmission, in particular they only need to have "coarse" diffractive structures as in the cases described above. Another advantage of the focuser 13 is that it is well suited for highly collimated radiation. All the radiation from the central beam diffracts and focuses the focuser 13 into a ring of larger diameter, which is concentric about the optical axis 6 (Fig. 15). The following mirror system consists of one or two concave mirror 12 connected in series. It is arranged at a suitable distance behind the focuser 13 and in front of the ring focus. As a result, a point-like focus on the optical axis 6 is obtained instead of a ring focus. If a small pinhole 11 is placed around this "focal point", the arrangement of the focuser 13, the hollow cone mirror 12 and the pinhole 11 acts as a monochromator.

Fig. 16 shows a condenser monochromator arrangement with a focuser 13 with ring focus and two downstream hollow cone mirrors 12. The advantage of a system with two hollow cone mirrors 12 is that in such a system the so-called "kink surface" of the radiation deflection is almost perpendicular to the optical axis 6 lies (the kinked surface is the surface on which the reflected rays extended in the beam direction and the reflected rays elongated to the rear intersect). It is known that in these optical systems, the aberrations that occur when the system is tilted - that is, for example, in the case of incorrect adjustment - are lower than in systems whose kink surface is almost parallel to the optical axis 6. The latter is the case when using a system with only one concave cone mirror 12, for which the reflecting surface and the kinked surface have to match and which has to be adjusted much more precisely.

The advantages of the invention are summarized again below. With a single structure, the apertures of all can be closed Available microzone plates for brightfield, phase contrast and Dark field microscopy can be adjusted. The aperture of one Ring pupil is created by rotating an oblique illumination through 360 ° obtained, the angle of the oblique lighting for example over a Plane mirror 2 can be set over a wide range. Of the Flat mirror 2 is very small, typically a few cm long and therefore inexpensive. For operation on well collimated beams from undulators beam expansion is not necessary. The wavelength can be very wide Areas are changed. The condenser-monochromator arrangement contains an off-axis zone plate 7.3 with zone widths that are significantly larger and are therefore easier and faster to manufacture than those available standing microzone plates, which are used as X-ray lenses. The wavelength can be changed over a wide range. Alternatively, a ring pupil can also be generated by a focuser 13 be, then a concave mirror 12 for focusing the Radiation on the optical axis 6 is used.

Reference list

1

incident x-rays

2nd

Plane mirror

3rd

off-axis reflection zone plate

4th

object

5

X-ray microscope

6

optical axis of the x-ray microscope

7

off-axis transmission zone plate

8th

obliquely incident lighting cone

9

Angle of reflection

10th

half opening angle of the hollow cone lighting

11

Monochromator pinhole in the object plane

12th

Concave mirror

13

Focuser with ring focus

14

annular condenser zone plate

15a

Reflection grid

15b

Transmission plan grid

16

focusing mirror

17th

Plane mirror

18th

Plane mirror

19th

Plane mirror

20a

off-axis zone plate segment

20b

off-axis zone plate segment

Claims (10)

1. Condenser monochromator arrangement for x-rays for the quasi-monochromatic, hollow-conically shaped illumination and incoherent image recording of an object (4) in an imaging x-ray microscope (5) with refracting and reflecting optical elements (2, 3, 7, 12, 13, 15a, 15b, 16, 17, 18, 19, 20a, 20b) and with a monochromator aperture (11), which is arranged in the optical axis (6) of the x-ray microscope (5) and in the plane of which the object (4) is arranged on the optical axis (6), characterised in that a refracting optical element (3, 7, 13, 14, 15a, 15b, 20a, 20b), which causes the spectral dissection of the x-rays, and at least one reflecting optical element (2, 12, 16, 17, 28, 19) are provided, wherein the aperture angle (10) of the produced illumination cone (8) and the position of the focal point of the illumination cone (8) on the optical axis (6) at the location of the object (4) are determined by the reflecting element (2, 12, 14, 17, 18, 19) in combination with the refracting element (3, 7, 13, 14, 15a, 15b, 20a, 20b).
2. Condenser monochromator arrangement according to claim 1, characterised in that the refracting element (3, 7, 15a, 15b, 20a, 20b) and one or more reflecting elements (2, 18, 19) are borne to be rotatable about the optical axis (6) of the x-ray microscope (5).
3. Condenser monochromator arrangement according to claim 2, characterised in that the refracting element (3, 7, 15a, 15b, 20a, 20b) is constructed as off-axis zone plates (3, 7) in reflection or transmission or as plane grating (15a, 15b) crystal in Bragg reflection.
4. Condenser monochromator arrangement according to claim 1, characterised in that two reflecting elements (2, 17, 18) are borne to be rotatable about the optical axis (6) of the x-ray microscope (5).
5. Condenser monochromator arrangement according to claim 4, characterised in that an off-axis zone plate (3, 7) is spatially arranged in the ray path.
6. Condenser monochromator arrangement according to claim 4, characterised in that an annular condenser zone plate (14) is spatially arranged in the ray path.
7. Condenser monochromator arrangement according to one of the preceding claims, characterised in that the reflecting elements are planar mirrors (2, 17, 18, 19) or focussing mirrors (16).
8. Condenser monochromator arrangement according to claim 7, characterised in that the focussing mirror (16) is a curved crystal used in Rowland arrangement.
9. Condenser monochromator arrangement according to one of the preceding claims, characterised in that the refracting and reflecting optical elements (2, 3, 7, 12, 13, 15a, 15b, 16, 17, 18, 19, 20a, 20b) are displaceable and tiltable for the variable setting of the aperture angle (10).
10. Condenser monochromator arrangement according to claim 1, characterised in that the refracting optical element is a focussing device (13) with an annular focus, behind which at least one hollow cone mirror (12) is arranged in the ray path as reflecting optical element.

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