DE102005058220A1 - Interferometric sample measurement - Google Patents

Abstract

It describes a device for interferometric measurement a sample, in particular of the eye, with an interferometer arrangement, which a first measuring beam path, through the one measuring beam falls to the test and a first reference beam path through which a reference beam running, the with the measuring beam is brought to interference, wherein the interferometer arrangement a second measuring and / or second reference beam path whose optical path length differs from that of one of the first optical paths, wherein the path length according to one Distance between two measuring regions spaced apart in the depth direction of the sample chosen is.

Description

The The invention relates to a device for interferometric Measurement of a sample, in particular of the eye, with a short-coherence interferometer arrangement, which a measuring beam path, through the one measuring beam falls to the test and a reference beam path through which a reference beam running, superimposed with the measuring beam and is brought to interference. The invention further relates to a method for short coherence interferometric Measuring a sample, in particular of the eye, wherein by a first measuring beam path a measuring beam is directed to the sample and with a reference beam, which is a reference beam path goes through, superimposed and is brought to interference.

to interferometric measurement or measurement of samples is the optical Short coherence tomography (also known as OCT). With this principle can be with high sensitivity measuring optical sections in the material, with axial resolutions, d. H. resolutions along the optical axis of incidence of radiation, reached by a few microns become. The principle is based on optical interferometry and used for a resolution in the depth direction, d. H. along the optical axis, a partially coherent light source.

A well-known application for the optical short-coherence tomography is the measurement of the eye, especially the human eye. Carl Zeiss Meditec AG sells this under the name IOL-Master a machine, that, among other things, the eye length, d. H. the distance between corneal vertex and fundus, determined. This is during during measuring the path length changed the reference beam. Application finds the device especially in the context of cataract surgery. The refractive power of a Intraocular lens to be implanted is used in cataract surgery and refractive eye surgery from the initial refractive state of the eye, the acoustically or optically determined length of the Eye and an estimate determines the postoperative anterior chamber depth. So you need it before detailed knowledge of the procedure these parameters. The scanning process of the IOL master supplies at the interferometer output a signal from whose timing the lengths to be measured are determined. This scan takes time; Movements of the subject during the Measurement results in errors or inaccurate results.

Further For example, a Fourier-analyzing interference method is known. For the spatial resolution in Depth direction draws a spectrum of the interference pattern between reference beam and measuring beam on which backscattered at the sample has been. This recording can be done simultaneously by means of a spectrometer (with a suitable broadband light source) or sequentially (with tunable Sources). The inverse Fourier transform of the spectrum allows a reconstruction of the structure along the depth direction.

Of the The invention is therefore based on the object, a device of to improve the aforementioned type so that larger sections of the eye quickly can be measured.

These Task solves the invention in that the Interferometer arrangement for different, axially spaced sample areas in terms of lengths the reference beam paths is pre-agreed. Reference beam paths are spatially separated and different long, with the path length difference a distance of the measuring ranges pretending in the sample. The OCT measurement then only measures the deviation from preset distance. The radiation from the respective reference beam path is with the measuring beam independently overlaid and brought to detection.

The Invention thus uses the Fourier domain short-coherence interferometry (FD OCT), which is the wavenumber spectrum of the signal at the interferometer output recycled. This spectrum is z. B. by means of a spectrometer recorded, which is usually a dispersing element, for example a diffraction grating, and a focusing optic as well as a detector array, e.g. B. photodiode arrays or array cameras. The wavelength spectrum I (λ) registered by means of the detector array becomes, for example using the grid equation into the required signal spectrum or K-spectrum I (K) converted. That of typical photodiode arrays or array cameras electronically executed Scan is very fast, he needs a few milliseconds or fractions of a millisecond. The same applies to the tuning is more variable frequency Radiation sources when using spectrally non-selective detectors is working. This is the for Measurements of patients advantageous "one-shot" quality, in which the relevant measurement data obtained from a single or very short exposure of the eye be achieved.

The Fourier transform of the K spectrum provides a depth-dependent signal with signal peaks whose z-position is the path difference reference beam / measuring beam indicates.

The resolution Δz of the short-coherence interferometry depends on the half-width Δλ of the wavelength spectrum and its mean wavelength λ together. For a Gaussian spectrum one obtains:

worin ΔK die Bandbreite der benutzten optischen Strahlung im K-Raum ist. Die Meßfeldtiefe ist also

The measuring field depth z is limited by the number of pixels or number N of the array photodiodes in the dispersion direction of the spectrometer or by the number of recordings during the tuning. Here applies

where ΔK is the bandwidth of the used optical radiation in K-space. The measuring field depth is thus

she hangs linear from the pixel number of the spectrometer or the number of shots. Usual array pixel counts from N ≈ 1000 provide measuring field depths Z of about 5.3 mm. The origin of the measurement field is the "path difference zero position", that is that position in the measuring beam, for which the optical length of the measuring beam is equal to the reference beam.

The The invention can be realized by a device for interferometric Measurement of a sample, in particular of the eye, with a short-coherence interferometer arrangement, which a measuring beam path, through the one measuring beam falls to the test and a first reference beam path through which a reference beam running, superimposed with the measuring beam and to interference, the interferometer arrangement has at least one second reference beam path, the first reference beam path at least partially spatially separated extends and its optical path length differs from that of the first reference beam path, wherein the path length difference according to one Distance between two sample areas spaced in the depth direction of the sample chosen is and wherein a control device of the detected superimposed Beams by Fourier spectral analysis under consideration the path length difference the reference beam paths determined the distance of the sample areas. Analogously, the invention be realized by a method for short-coherence interferometric Measurement of a sample, in particular of the eye, wherein by a Meßstrahlengang a measuring beam is directed to the sample and with a reference beam, a first Traverses reference beam path, superimposed and is brought to interference, wherein at least a second reference beam path is provided, at least partially from the first reference beam path runs separately and its optical path length differs from that of the first reference beam path, wherein the path length difference according to one Distance between two sample areas spaced in the depth direction of the sample chosen is and the superimposed Radiation detected and from it by means of Fourier spectral analysis under consideration of path length the reference beam paths of Distance of the sample areas is determined.

In the interferometer arrangement, it is advantageous for the signal quality, the radiation from the two reference beam paths each separated with the reflected back from the sample measuring radiation to overlay and to prove. It is therefore provided in a development, that the Interferometeranordnung a superposition device having the reference beams separated from the two reference beam paths with the measuring beam superimposed from the Meßstrahlengang and the rays superimposed in this way then passes to a detector device for detection, which the spaced measuring ranges associated measuring signals generated. Analog is for the method provided that the Rays from the two reference beam paths separated with the measuring beam superimposed from the Meßstrahlengang, the superimposed so Detected separately beams and the spaced measuring ranges associated measuring signals be generated.

The Separation at overlay and proof can be done in a variety of ways. To the one is a temporal separation possible. The measuring beam is thus superimposed successively with the reference beams from the reference beam paths and proven. This has the advantage that only one detector unit is necessary, at the expense of a slightly longer measurement period. That only one spectral analysis device On the detection side is necessary, the effort and thus the cost reduce considerably. It is therefore in a variant of the invention provided that the superposition means a Switching mechanism for switching between the two reference beam paths, so that the overlay for the two reference beam paths is done sequentially. For the method is analogously provided that between the two reference beam paths sequentially is switched so that the measuring beam superimposed sequentially with radiation from the first and the second reference beam path is and the superimposed Rays are detected sequentially.

On the other hand, a higher measuring speed is achieved if the superimposition is such that a parallel detection of the separately superimposed beams, ie the interference pattern generated for the different measuring ranges, takes place. A first approach uses polarization separation. Thus, for example, two reference beam paths are provided which lead to each other orthogonally polarized radiation. On the detection side, two detector units are then also provided, which also mutually orthogonal radiation components of Evaluate superimposed radiation. It is therefore expedient for this first variant that the superimposition device uses a polarization separation for the separate superimposition, so that the superimposition and the forwarding to the detector device for the two reference beam paths are separated according to polarization and at the same time. Further, it is expedient for the method that a separate polarization separation is used for separate superposition, so that the separate superposition and detection for the two reference beam paths separated by polarization and takes place simultaneously.

A further separation possibility results in a second variant through the use of different Wavelength ranges. The reference beam paths can then by dichroic division of the incident reference radiation be coupled to each other and a corresponding number of Detector means is also a corresponding dichroic Separation upstream. It is for Therefore, this second variant expedient that the superposition of the separate overlay a dichroic separation, so that the overlay and the forwarding to the detector device for the two reference beam paths spectrally separated and simultaneously. Analog is for the process provided that to separate overlay a dichroic separation is used so that the separate overlay and detection for the two reference beam paths spectrally separated and simultaneously.

A further separation, which allows simultaneous measurement, lies in a spatial Separation of the superimposed Radiation. In this third variant, the measuring radiation spatial guided apart and each with corresponding spatial superimposed separated reference beams from the reference beam paths. The spatial Separation can be realized in particular as a pupil division, why is provided in a development that the superposition device for separate overlay a pupil division begins, so that the overlay and the forwarding to the detector device for the two reference beam paths takes place in a divided pupil of the beam path.

The inventive concept used, as already mentioned, Short-coherence FD OCT. The required K spectrum with both spectrally sensitive detection and broadband Sources as well as spectrally non-resolving detection and tuning a narrowband source are generated. Of course, the detector effort is reduced if a spectrally tunable the interferometer arrangement dining Radiation source and a spectrally non-resolving detector device for Measurement are provided. The K spectrum becomes here from the data about the tuning together and then analyzed.

at FD OCT has so far been a problem that one with the available detector arrays with a given maximum number of pixels or shots per Time unit could either maximize the spectral resolution and thus the spatial resolution, or the covered spectral range, hence the measuring range. The inventive concept solve these opposing Coupling now in that several different long reference beam paths are used.

The measured distances are common related to the distance to the interferometer or to the aforementioned path difference zero position. In a further invention it is possible to use these measuring signals relate to each other. This is done by the reference beam path no longer the reflection on a static, in the interferometer built-in reflector, but one incident on the sample and reflected back from there or scattered beam used as a reference beam. It is for the beginning called interferometer arrangement therefore also provided according to the invention, that the Reference beam path comprises the sample, wherein reference beam and measuring beam against each other in the beam direction by a certain path length difference are offset and the reference beam at a first sample area and the measuring beam reflected at a second sample area of the sample and / or backscattered are and the interference between measuring beam and reference beam depends on the distance between the two sample areas, where a control device from the detected superimposed beams by means of Fourier spectral analysis taking into account the path length difference the reference beam paths determined the distance of the sample areas. Analog is for the process provided that the Includes reference beam path, Reference beam and measuring beam against each other in the beam direction by a certain path length difference are offset and, the reference beam at a first sample area and the measuring beam reflected at a second sample area of the sample and / or backscattered be and the distance between the two sample areas from the Interference between measuring and reference beam is determined, wherein the superimposed radiation detected and from this by means of Fourier spectral analysis under consideration the path length difference the reference beam paths the distance of the sample areas is determined.

When measuring the eye, it is of course useful to evaluate the back reflex of the anterior surface of the cornea, since then the eye length can be measured in a particularly simple manner. The autocorrelation function of the reference beam delivers a first Be in the evaluation zugspunkt and the superposition of the reference beam with the measuring beam a reference to this reference point second measuring point, for example, the signal for the fundus.

at the measurement of the eye, it is appropriate to a focusing element in one of the beam paths to provide a focus of the two beams both on to ensure the cornea as well as the fundus of the eye. The focusing element thus contributes thus the focusing effect of the eye bill, so that on the fund focused measuring beam as a parallel beam the eye invades, whereas the other reference beam already focuses on the anterior surface of the eye is. Naturally can the focusing element in Meßstrahlengang (expanding) or provided in the reference beam path (collimating) be. This procedure increases the signal strength considerably. It is therefore appropriate that the reference or the measuring beam path a preferably adjustable focusing element, in order for measurements on the eye the measuring beam to focus on the retina. For the analog method is it alike advantageous that for measurements at the eye of the reference beam by means of a preferably adjustable Focusing is focused on the cornea.

At the Passage through the eye can cause a dispersion influence, the disturbing can make noticeable. It is therefore expedient to have a corresponding dispersion compensation provided. Conveniently, is therefore ensured in the device that the Meßstrahlengang or the reference beam path is a dispersion compensating element has to for Measurements on the eye Dispersion influences of the eye on the measuring beam to influence. For the procedure applies analogously that for measurements on the eye of the reference or measuring beam by means of a preferably adjustable dispersion compensating Elementes is influenced in terms of dispersion influences of the eye.

There Focusing and dispersion correction are closely related stand together, it is convenient the adjustment of the focusing element and the adjustment of the dispersion-correcting Couple element together, for example by a mechanical or electrical coupling, so that a synchronous adjustment the dispersion compensating element and the focusing element is effected.

The The invention thus achieves an interferometer which has several sections measuring the eye at the same time, by a separate measurement of the separated measuring ranges takes place. Preferably is this separate measurement simultaneously by corresponding separate overlay of the measuring beam with radiation from different reference beam paths and separate proof of the superimposed Radiation performed. It can for the separate evidence separate spectrometer can be used when, as for some variants of the FD OCT, a spectrally selective detection takes place.

The inventive device or the inventive method are, as already mentioned, especially for the measurement of the human eye, but also other semi-transparent Objects can to be investigated.

extended The device is a scanning device, the beam across the Eye deflects, for example, by a parallel shift or a beam deflection, for example by means of scan mirrors, can be create a three-dimensional sample image.

With the principle of the invention can several Partial measurements at the same time as quasi "one-shot" recordings or measurement sequences with many fast consecutive single measurements, respectively consist of several partial measurements.

Conveniently, becomes the device according to the invention controlled by a corresponding control device in operation. This Control unit provides then the described operation and in particular the realization the described modes of operation safely. Advantageously the controller too suitably configured, for example by a computer and corresponding Program means to the Meßsignalaufbereitung from the electrical signals of the detector or detectors in particular those for FD OCT required Fourier transform.

The invention determines from at least two spaced-apart sample areas in a transparent and / or diffusive object, for. As in one eye, in a measuring time in the sub-second range, the distances of structures in the sample areas. For this purpose, an arrangement according to a Michelson interferometer is preferably used. Short-coherent radiation is used in the interferometer setup, wherein, for example, the short-coherent radiation emanating from a beam source is split up into a measuring beam and a reference beam. The radiation used for measuring beam and reference beams thus has a short coherence length compared to the sample area distances. The measuring beam irradiates the sample areas. The reference beam is split into at least two spatially separated reference beam paths which impose different propagation time changes on the reference beams guided therein, these runtime changes being pre-adjusted to the distance of the sample areas. The reflected reference beam len are then combined separately interfering with the reflected and / or backscattered measuring beam. The combined beams are detected and the detected signal, as already mentioned, Fourier-evaluated for distance measurement.

For measuring the distance of the measuring ranges in a transparent and / or diffusive sample, as it is necessary for distance, length, thickness and profile measurement, the sample is irradiated with a measuring beam, and a reference beam is provided for each sample area. The sample areas may be located at different locations in the direction of incidence of the optical radiation, as well as laterally offset from one another. The transit time difference of the reference beam paths corresponds to an optical distance of the sample areas with respect to the direction of incidence of the measurement beam, wherein at least one of the sample areas reflects and / or backscatters at least slightly (typically at least 10 ^-4 % of the radiation intensity). Of course, the beam configuration of the measuring beam can also be moved over the sample, in particular periodically, so that the sample is scanned transversely to the axis of incidence. Thus, profiles of the sample can be measured. Instead of having only one measuring beam incident along an optical axis, it is of course also possible to arrange several measuring beams next to each other at a distance in order to determine a surface profile more quickly.

With the device according to the invention and the method of the invention can measure a sample for distances or profiles become. Particularly preferred is the use in an optically transparent and / or diffusive sample, since then also the inner sample structure can be measured. The path length differences the spatially separated Reference beam paths becomes approximate so adjusted that they the expected distance, a thickness to be determined, etc. to corresponds to a certain tolerance. With FD OCT will then only by deviation of the unknown, yet to be determined distance determined from the preset value. Should z. B. the actual Length of one measured by the human eye, as one already knows before, that one optical length of 34 mm plus / minus 4 mm is expected. So you put the path length difference the reference beam paths on 34 mm, and the signal evaluation of the Fourier analysis determined the variation within the possible Range of 8 mm. Naturally is it for the device or the method generally useful if the path length difference between the reference beam paths while the measurement is adjustable or is set.

With the device according to the invention or the method according to the invention on the eye next to the eye - length (central, peripheral), also the Anterior chamber depth (central, peripheral), corneal thickness (central, peripheral), the tear film thickness (central, peripheral), the lens thickness (central, peripheral) and the vitreous thickness as well as corresponding surface profiles (Topographies) of the corneal anterior surface, the corneal posterior surface, the Lens front surface, the Lens back surface and the retina are measured. Furthermore, can be by suitable Scan mechanisms radii of curvature, z. B. the cornea front surface, the cornea's back surface, the Lens front surface and the lens back surface.

Of course you can a sample area also comprise several interesting subareas. So you can define a sample area such that he entire eye anterior chamber includes. For this purpose, the measuring beam focused at a location between the cornea front surface and the lens back surface. So then the reflection on the cornea's front surface, the Cornea back surface, the Lens front surface and the lens back surface within a sample area are detected. The distance between the cornea's back surface and Lens front surface is then the anterior chamber depth. The only condition is that the measuring range in the sample area is so big the existence Area of the cornea frontal area covered to the lens rear surface is.

The Inventors further realized that at a particular embodiment of Spektralanalyseeigenschaften the Fourier domain short-coherence interferometry is capable of the entire eye length of the human eye to record with a measurement if certain parameters adhered to the spectrometer become. As an essential parameter, the number of pixels or Number of sensitive cells of the detector array out. It is because of that in a further invention, an embodiment of the aforementioned Device provided in which a spectrometer arrangement superimposed Radiation detected, the one spectrally fanning the rays Element and a detector array that has at least 7000 individual having photosensitive cells. The one with such a detector array reached measuring range is for example at a wavelength between 700 and 900 nm and a spectral bandwidth of 10-30 nm of the radiation used so big that with it the eye length measurable is. Analog is therefore synonymous for the method of the aforementioned type provided that for detection the superimposed Blasting a spectrometer arrangement is used, which is a the rays spectrally fanning Element and a detector array that has at least 7000 individual having photosensitive cells.

Insofar as in the preceding or following description method steps, in particular signal evaluations, controls of ver In the devices according to the invention, these method steps can be carried out by the control device, which includes suitable operating means, for example a software control, for this purpose.

The Invention will now be described by way of example with reference to the drawings explained in more detail. It demonstrate:

1 an interferometric device for measuring an eye, measuring radiation being brought into interference spatially separated with radiation from three reference beam paths,

2 a representation similar to the 1 with a modified spectrometer unit,

3 a representation similar to the 1 but now using fixed optics instead of optical fibers,

4 a schematic diagram illustrating the effect of a diffraction grating of the interferometer of 1 - 3 .

5a -C embodiments of a split pupil optics, as used in the interferometers of 1 - 3 could be used,

6 another interferometer similar to the one of 1 , but with a different spatial separation of the superimposition of the measuring beam with the reference beams,

7 an interferometer similar to the one of 1 wherein the separate superimposition of the measuring beam with the reference beams is effected by a polarization separation,

8th and 9 Details of a possible design of the interferometer of the 7 .

10 an interferometer similar to the one of 10 , where the separation here is spectral,

11 a graph explaining the effect of the spectral separation,

12 and 13 Detailed views of components as used in the interferometer 10 can be used

14 an interferometer similar to the one of 7 , wherein the separate superimposition of the measuring beam with the reference beams takes place here sequentially,

15 an interferometer similar to the one of 7 , here a double jet is used as a measuring beam,

16 a modification of the interferometer of 15 with only one spectrometer,

17 a spectrometer similar to that of 15 , but without polarization separation but with double jet,

18 a fiber optic construction for the spectrometer of the 17 .

19 a simplified interferometer for the simultaneous detection of depth-spaced areas and

20 a simplified short-coherence Fourier-domain interferometer for measuring two or more depth-spaced regions.

1 shows a fiber optic implementations of an interferometer I. The reflected reflected radiation is registered simultaneously in a Michelson structure with several pupil-separated beam paths and respective reference beams for different eye structures. For this purpose, fiber optic couplers are used; other fiber optic or free-jet interferometer structures may also be used, for example with fiber optic circulators. In addition, the simultaneous measurement of three positions of the eye structure is performed (cornea anterior surface, anterior surface of the lens and fundus). You can also modify the interferometer to measure more or less than three positions. In the drawings, often only the beam axes are shown for the sake of simplicity. Also, in the following, sometimes simplistic is referred to as "ray", rather than "ray bundle" or "ray bundle".

From a short-coherence light source 1 For example, a superluminescent diode equipped with a "pig-tail" fiber or light coming from another short-coherence light source is made by a fiber coupler 2 on an interferometer measuring arm 3 and an interferometer reference arm 4 divided up. To three lying in different depths z of the eye structures, namely cornea 5 , Eye lens 6 and eye fundus 7 to capture by means of Fourier domain short-coherence interferometry, three reference beam paths R1, R2, R3 are used with corresponding beams simultaneously. These beam paths are from the reference arm fiber 4 separated by fiber couplers: a coupler 8th divides a fundus reference beam R1 into a fiber 9 from. The remaining radiation in a fiber 10 is from a coupler 11 in a fiber 12 for the cornea reference beam R2 and a fiber 13 for the eye lens reference beam R3 separated. The fiber lengths for these three reference beam paths are dimensioned such that on a photo-detector array 43 despite the short coherence length interference with the respective coming from the different object depths reflex beam, namely cornea 5 , Eye lens 6 and eye fundus 7 , occurs.

The at the exit point 20 from the fiber 3 emerging illumination radiation 21 is from an optics 22 , for example, a fiber collimator, collapses as a parallel illumination beam 24 a beam splitter 25 and lit, the eye 26 , One on the anterior surface of the cornea 5 reflected cornea reflex beam 27 comes virtually from a 1st Purkinje Sanson image 28 and an eye-lens reflex beam reflected from the lens front surface 29 comes virtually from a 3rd Purkinje Sanson image 30 , These two reflex beams diverge at different angles. In the 1 is to keep the overview, drawn only a smaller angle range. Another reflex comes from the fundus 7 and forms the reflected fundus reflex beam 31 ,

The reflected ray bundles on the eye 27 . 29 and 31 are thus present as a superimposed measuring beam M and are from the beam splitter 25 in a detection branch D and there on a relay optics 33 directed in front of a spectrometer S. The relay optics 33 fits the measuring beam M, which is a mixture of the three reflection beam bundles, to the following spectrometer S. This optics consists in the example of 1 from three partial optics 34 . 35 and 36 different focal lengths. The focal lengths are designed so that the three contained in the measuring beam M, reflected from different depths on the eye reflection beam in the same image plane 40 are focused in front of the spectrometer S; the focuses are from the spectrometer optics 41 ' and 41 '' over a diffraction grating 42 on a photo-detector array 43 for example, an array camera 44 displayed. The spectrometer optics 41 ' and 41 '' can also be combined into a single optics in front of or behind the diffraction grating 42 be set up.

As in 4 is shown dispersing the diffraction grating 42 the different wavelengths of the incoming light in the x-direction on photodetectors 435 of the photo detector array 43 , In 4 is 140 one of the optics 41 ' and 41 '' (please refer 1 ) focused light beam of zero diffraction order of the grating 42 ; 141 and 142 are light beams of first diffraction orders of different wavelengths dispersed from the diffraction grating in the x-direction, that of the optics 41 ' and 41 '' on the photoreceptor of the array in a column 432 be focused. The light bundles of the first diffraction order are spectral components of the fundus 7 remittierten reflex beam 31 with the corresponding spectral components of the associated reference beam 53 superimposed from the reference beam R1. The cornea 5 and eye lens 6 remitted and also superimposed with reference light from the reference beam paths R2 and R3 reflex beam 27 and 29 be from the optics 41 ' and 41 '' on adjacent array columns 431 and 433 focused.

That at the exit point 50 from the fiber 9 emerging beam 51 is from an optics 52 collimated by a fiber collimator, passes through as a parallel reference beam 53 two dispersion compensation prisms 54 ' and 54 '' and is from a reflection prism 55 via a beam splitter 56 in the direction of an optical axis 19 of the reference arm 4 reflected in the interferometer I in the first reference beam input R1. The reference beam 53 here is only marked by its main ray. In the 1 is further indicated that this first reference beam 53 on the photo detector array 43 with the fundus 7 coming reflex beam 31 is superimposed. By adapting the optical length of the first reference beam path R1 from the coupler 2 to the beam splitter 25 to the optical length of the coupler 2 about the fundus 7 of the eye A and back to the beam splitter 25 interferences of the overlapping beams are ensured; this means that the origin of the relevant measuring field at the fundus 7 lies. This is by a suitable choice of the fiber lengths and / or the position of the reflection prism 55 set. For this purpose, an adjusting mechanism is preferably provided.

This can, for example, as in 1 be educated. The reflection prism 55 is on a table 57 a manually or electrically actuated displacement unit 57 ' assembled. An adaptation to different eye lengths and eye positions can also during a measurement sequence by a manual or electronically driven displacement of the reflection prism 55 by means of the displacement unit 57 ' respectively. The current position of the prism 55 can with the help of a pointer 58 and a scale 59 be determined. Alternatively, electronic position indicators can be used and their data can be sent directly to the computer 200 be entered. To compensate for the subject-dependent dispersion of the eye, the prisms 54 ' and 54 '' relative to each other in the direction of the double arrow 54 ''' be moved.

That at the exit point 60 from the fiber 12 emerging beam 61 is from an optics 62 of a fiber collimator and is used as a parallel reference beam 63 from a reflection prism 65 via a beam splitter 66 at an angle β to the optical axis 19 of the reference arm 4 in the second reference beam path R2 in the beam splitter 25 mirrored. In 1 is indicated that the second reference beam 63 on the photo detector array 43 with that of the cornea 5 coming reflex beam 27 is superimposed. By adapting the optical length of the second reference beam path R2 from the coupler 2 to the beam splitter 25 to the optical length of the coupler 2 over the cornea to the beam splitter 25 Short-coherence interference of these two superimposed light beams are ensured, or set the origin of the measuring field. This can also be done here by suitable choice of the fiber lengths and / or the position of the reflection prism 65 respectively. Again, preferably, an adaptation to different eye lengths and eye positions during a measurement, by a displacement of the reflection prism 65 by means of a manually or electrically operated displacement unit 67 ' , The position of the prism 65 can with the help of a pointer 68 and a scale 69 be determined. Alternatively, electronic position indicators can also be used here and their data can be sent directly to the computer 200 be entered.

That at the exit point 70 from the fiber 13 emerging beam 71 is from an optics 72 collimated by a fiber collimator and as a parallel reference beam 73 after reflection on a reflection prism 75 from a reflection prism 76 in the third reference beam R3 at the angle α to the optical axis 19 of the reference arm 4 mirrored into the interferometer I. In 1 is indicated that the third reference beam 73 on the photo detector array 43 with the from the front surface of the eye lens 6 or from the 3rd Purkinje-Sanson picture 30 coming reflex beam 29 superimposed. By adapting the optical length of the third reference beam R3 from the coupler 2 to the beam splitter 25 to the optical length of the coupler 2 over the front surface of the eye lens to the beam splitter 25 Short-coherence interference of the superimposed light beams are ensured, or set the position of the origin of this measuring field. This is also done here by suitable choice of the fiber lengths and / or the position of the reflection prism 75 , Even during a measurement sequence on the eye, an adaptation to different eye lengths and eye positions can preferably take place, namely by a displacement of the reflection prism 75 by means of a manually or electrically operated displacement unit 77 ' , Again, the position of the reflection prism 75 with the help of a pointer 78 and a scale 79 be determined. Alternatively, electronic position indicators can also be used here and their data can be sent directly to the computer 200 be entered.

In 3 Interferometer I is shown, which is essentially the interferometer of the 1 corresponds, why the same elements are provided with the same reference numerals. In contrast to 1 However, the interferometer is now executed in free-beam optics. One of the short-coherence light source 1 emitted source beam 101 , is of a look 102 collimates and hits a beam splitter as a parallel beam 103 , The beam splitter 103 divide the beam 101 on a Meßstrahlbündel 104 in the interferometer measuring arm 3 and a beam 105 in the interferometer reference arm 4 on. The beam 105 is again indicated by his main ray.

That of the beam splitter 103 reflected illumination beam 104 goes through the beam splitter 25 and illuminate the eye 26 , Running back a measuring beam M, which in turn contains a mixture of the following reflection beam bundles: reflected at the Corneavorderfläche reflex beam 27 comes virtually from the 1st Purkinje Sanson image 28 and the ocular lens reflex beam reflected from the lens front surface 29 comes virtually from the 3rd Purkinje Sanson image 30 , These two reflection beam bundles are divergent reflected and are expanded accordingly. In the 3 is drawn by these two reflex beam bundles again only a small angular range. Another reflex comes from the fundus 7 and forms the fundus reflex beam 31 , In that regard, identical conditions as in the interferometer I the 1 in front. This also applies to the detection of the superimposed beams in detection branch D.

For the three located in different depth areas of the eye structures, such as cornea 5 , Eye lens 6 and fundus 7 , as in the fiber optic interferometer I the 1 , three reference beams R1, R2, R3 used. These are here with the help of beam splitters 109 and 110 generated. Otherwise, the coupling and path length adjustment is unchanged.

In the interferometer I the 3 is for monitoring the position of the subject's eye 26 relative to the fundus reflex beam 31 another observation device consisting of a partially transparent mirror 130 and a look 131 arranged. The observation of the subject's eye can then directly ( 132 ), with the help of an eyepiece 133 or with the help of a camera 134 respectively. It may also be useful to the subject eye 26 additionally with an incoherent light source 135 to illuminate. Furthermore, for precise positioning of the subject's eye an image 136 a reticule 137 be used, which via partially transparent mirror 138 and 130 on the cornea 5 is projected.

At ametropia can the eye 26 collecting or dissipating auxiliary optics 140 be pre-set, which compensate the defective vision Sieren.

It should be mentioned that in order to avoid disturbing reflections and to optimize the beam intensities on the beam splitter 25 meeting lighting beams 104 by means of a polarizer 120 can linearly polarize and the beam splitter 25 can form as a polarizing beam splitter. Using other polarization optical components such as λ / 4 plates in the positions 121 and 122 According to the state of the art, reflection losses of the reference and reflection beam bundles can be largely avoided during multiple passes through the beam splitter. Such methods known in technical optics can also be used for the beam splitters 56 and 66 to be used.

The observation device described above, consisting of the partially transmissive mirror 130 and the optics 131 as well as the auxiliary optics 140 to compensate for ametropia of the subject 's eye, can also in the interferometer I the 1 be used. Likewise, it can also be there to avoid disturbing reflections and to optimize the beam intensities on the beam splitter 25 meeting measuring beam 24 by means of the polarizer 120 be linearly polarized, the beam splitter 25 be formed as a polarizing beam splitter, and λ / 4 plates in the positions 121 and 122 to be ordered.

The relay optics 33 can in the simplest case of three circular partial optics 131 . 132 and 133 be constructed of different refractive powers, as in the 5a is indicated. 131 ' . 132 ' and 133 ' are the puncture positions of the associated optical axes. The sub-optics are to be arranged so that their optical axes lie in the yz-plane, corresponding to the fanning out of the reference beams in the yz-plane. Alternatively, these three partial optics can also be composed of parts of larger circular optics having different refractive powers in order to increase their light conductance, as in US Pat 5b outlined. The optics 131 . 132 and 133 of the 5a here correspond the partial optics 141 . 142 , and 143 ; the puncture points of the optical axes 141 ' and 143 ' can also be outside of the associated partial optics. Finally, the three partial optics can also be composed of central sections of larger circular optics of different powers, as shown in FIG 5c is shown. Here are optics 151 . 152 and 153 executed as central sections of larger optics (as for 151 with the circle 151 '' indicated). 151 ' . 152 ' and 153 ' the positions are the puncture points of the associated optical axes.

Basically, the sub-optics of the relay optics 33 also at different z-positions of the optical interferometer axis 19 be positioned. It must then be ensured only by appropriate choice of their focal lengths, that the three reflex beam 27 . 29 and 31 in a common plane 40 be focused in front of the spectrometer.

The Fourier domain short-coherence interferometer I must be calibrated because of the separate reflection beams. The Fourier domain short-coherence interferometry gives as measurement result the optical distance of the object measuring point relative to the "path difference zero position" (for this the optical length of the measuring beam is equal to that of the reference beam.) The distances between the origins of the independent reflex beam paths Reference beams R1, R2, R3 must therefore be defined, and the measuring range is limited in the depths, for example to approximately 5.3 mm for the parameters assumed at the outset, and the interferometer I must therefore be coarsely preconcentrated to the expected eye distances For example, as a basic setting, a plane mirror can be positioned as an object in the measuring beam path at the expected position of the cornea, and then all the reflection prisms ( 55 . 65 and 75 ) are positioned so that all associated reference beams 53 . 63 . 73 Show short-coherence interference with the light beam reflected from this plane plate. Starting from this basic adjustment, for example, the positions of each of a reference mirror in the expected positions of the lens front surface to be measured 6 and the fundus 7 be set. By reading the executed displacements by means of the measuring devices 58 . 59 such as 68 . 69 and 78 . 79 or the corresponding electronic position signals you have a base value for lengths to be measured. The optical measurement now gives the distance of the actual position of the reflection points in the eye relative to the base position. If you add these to the base value, you have the required distance in high accuracy.

The three reflected ray bundles remitted by the eye 27 . 29 and 31 illuminate next to the associated partial optics 34 . 35 and 36 also the respective other partial optics and are defocused by these on the detector array 43 to meet. This leads to false light and thus to an undesirable background. Since this false light with the focused there reference beams 53 . 63 . 73 is not adjusted with respect to path difference, arise at the detector array very high modulation frequencies that are not resolved by the detector array.

Nevertheless, in addition to the increased noise due to aliasing, additional false signals can occur. It is therefore advantageous to suppress this stray light as much as possible. This is due to a spatial filtering in the image plane 40 possible. For this purpose, a pinhole mask is in this level 80 attached, with three openings at the locations of the bundle foci. However, the positions of the bundle foci depend on the position of the eye, with the exception of the fundus focus 26 from. The eye must therefore be positioned by means of the above-described device for observing the position of the subject's eye. So can the reflex beam from Fundus 7 and cornea 5 be well discriminated against.

The 1 and 3 show the measurement of the positions of cornea anterior surface, anterior lens surface and fundus. As already mentioned, however, other positions of eye structures can be measured simultaneously, for example, the lens back surface with the help of the 4th Purkinje-Sanson image virtually remitted light or the position of the cornea back surface with the help of the 2nd Purkinje-Sanson virtually remitted light. It requires corresponding additional reference beam and relay sub-optics ( 33 ) as well as additional openings in the pinhole mask 80 and further array columns. However, it can be assumed at Meßfeldtiefen to the 5 mm east of the fact that the two cornea positions are present in the measurement signal simultaneously.

Finally, the described interferometers can also be modified to measure other positions, such as the lens back surface. For this purpose z. B. the reference beam 53 be shortened accordingly and the focal length of the optics 35 be downsized.

It should be noted that the use of an array 43 with only three ( 431 . 432 and 433 ) or four columns without limitation. Commercially available array cameras often have several hundred columns. These can be used in two ways: on the one hand, you can leave several unused gaps between the columns to be read and thus prevent optical and electronic crosstalk. However, it is also possible to interconnect the row elements of several adjacent columns by binning in order to increase the measurement sensitivity.

2 shows a modification of the interferometer I of 1 ; unchanged or functionally identical 1 Therefore, adopted elements are identified by the same reference numerals and will not be explained again here. The difference between the design of the 1 and 2 essentially lies in the fact that the spectrometer S no longer uses a two-dimensional photo-detector array, but three single-row photo-detector arrays 531 . 532 and 533 , For the division of z. B. by pupil separation spatially separated with the reference beams 53 . 63 . 73 superimposed reflex rays bundles 31 . 29 . 27 are in the detection branch D two suitable mirror 540 . 541 provided, the two of the reference beams superimposed reflex beam to two perpendicular to the optical axis photo detector array lines 531 and 533 redirect.

A further modified interferometer I is in 6 shown. Again, unchanged or functionally identical 1 taken over components provided with the same reference numerals, so that the repetition of the description is unnecessary. The interferometer I the 6 uses one opposite the 1 different type of spatial separation. The separation of the measuring beam M and the superposition with the three reference beams 53 . 63 . 73 takes place here by beam splitter. Components whose function or structure corresponds to that of 1 are denoted by the same reference numerals, optionally with a suffix .1, 2 or .3 was appended to distinguish the components for the three individual overlay. The component 42.3 For example, corresponds to the component 42 of the 1 However, it is in the presentation of the 6 only effective for superposition with the reference beam R3.

The separate superimposition of the reflex beam 27 . 29 . 31 in the measuring beam M takes place in the construction of the 6 now not by a shared pupil provided with relay optics 33 but by deflecting elements 33.1 such as 33.2 that the reflex beam 27 and 29 decouple from the beam. The deflecting elements 33.2 and 33.1 can be performed for example as a spectrally neutral beam splitter.

The deflecting element 33.2 directs a portion of the measuring beam M from the beam, that of the beam splitter 25 was separated, and makes it to overlay with the second reference beam 63 ready to be separated via a beam splitter 66 is coupled. The downstream optics essentially corresponds to the optics of the detector branch D of 1 , with the difference that there is no spatially separated pupil; the beam path after the beam splitter 33.2 does not lead to spatially separated rays anymore. Accordingly, the photo-detector array must 43.2 also not be carried out in two dimensions.

The same applies to the photo detector array 43.3 at the end of the beam path to the department through the beam splitter 33.3 lies.

The after the beam splitters 33.2 and 33.3 still existing proportion of the measuring beam M is with the reference beam 53 superimposed and on the photo-detector array 43.1 detected after previous spectral separation.

The interferometer of the 6 So has three spectrometers, S1 for the superposition of the remaining measuring beam M with the reference beam 53 from reference beam R1, the spectrometer S2 im through the beam splitter 33.2 separated part of the beam path, in which the reference beam 63 is coupled, and the spectrometer S3, the beam splitter 33.3 is downstream and the separated radiation superimposed with the reference beam 73 prove.

The spatial separation by beam splitter has the advantage that the pinhole 80.1 . 80.2 and 80.3 can be designed much more effectively on the Falschichtunterdrückung. Also, a separate focusing by means of now easier independently adjustable partial optics 36.1 . 36.2 and 36.3 possible without any effort, whereby the signal-to-noise ratio is improved for the object areas separated at depth.

7 shows an interferometer I, which, like the interferometer described above, also pursues the principle of independently superimposing and detecting reference beams guided in differently long reference beam paths R1, R2 with a measuring beam M. The details realized on the basis of the previously described figures are therefore also possible without restriction for the variants described below. Also matching elements are provided with the same reference numerals, so that your explanation can be omitted here. Likewise, in the following figures, by appending a corresponding suffix .1, .2, etc., a distinction is made with regard to the reference beams and their beam paths or superimpositions.

The interferometer I the 7 makes a separation of the reference beam paths with respect to the polarization. For this, the radiation of the light source 1 by means of a polarizer 300 circularly polarized before moving to the beam splitter 25 and from there a sample P falls. Alternatively, a circularly polarized light emitting beam source is used. In the reference beam R, the circularly polarized radiation by means of a pole divider 301 divided into two perpendicular polarized beams. The pole divider can be designed, for example, as a Wollaston prism. Adjustable gray filters 303.1 respectively. 303.2 allow adjustment of the intensity of the radiation in the two reference beam paths R1, R2, which is advantageous for optimizing the measurement signal. The reference beams in R1 and R2 become reflectors 304.1 respectively. 304.2 reflected. Every reflector 304 is on a sledge 305 slidably mounted, so that the path length of the reference beam path is individually adjustable. This can be under the control of the computer 200 respectively. The adjustment mechanism can in particular the basis of 1 ff described structure. The superimposed measuring beam M with the reference beams, in the return reflection direction of the reference beam path R1 and R2 to the pole divider 301 are superposed in the detection branch D.

In it, the superimposed rays are again through a pole splitter 302 split, so that superimposed rays 306.1 and 306.2 is present, in which the measuring beam M is superimposed with the reference beam of R1 or R2. The different path length of the reference beam paths R1 and R2 causes, as already described above, a corresponding depth selection in the sample P, which in turn may be the human eye A, for example. The thus separated according to their polarization superimposed rays 306 are then detected separately in a spectrometer S.

For spatial measurement of the sample P is finally still a scanner 307 provided with suitable optics, the abscant the sample with the incident radiation.

The possible construction of the spectrometer S is in 8th exemplified. The pole divider 302 For example, each is a polarization manipulator 308.1 respectively. 308.2 downstream, with which you can rotate or set the polarization direction of the rays so that sets a maximum yield in the downstream beam path. The polarization-separated beams 306.1 and 306.2 fall after passing through the polarization manipulator 308.1 respectively. 308.2 on the diffraction grating 42.1 respectively. 42.2 , Reflection diffraction grating. The spectral split thus obtained then becomes detector array lines 43.1 respectively. 43.2 demonstrated.

The spectrometer S is made up of two partial spectrometers S1 and S2, which are the polarization-divided superimposed radiation 306 individually prove.

The in the 1 - 6 Separation and detection realized by spatial separation is in the construction of the 7 achieved by polarization separation.

As mentioned, FD OCT can work in two ways. On the one hand, a short-coherent beam source which has been described above can be used. Then a spectral separation of the superimposed radiation is required. On the other hand, a tunable short-coherent radiation source can be used. If you tune the spectral range of this source, no spectral analysis of the radiation must be done more; instead, a spectrally insensitive detector can be used. The sample structure can in both cases by forming the inverse Fourier transform of the spectral interference pattern to be obtained. Of course, the previously and also explained below interferometer I can be adapted for one of the two modes of operation. The necessary modifications are in 9 exemplary for the interferometer I der 7 shown. The polarization beam splitter 302 Instead of the spectrometers S1 and S2 now only individual detectors 309.1 and 309.2 nachordnen who make no spectral analysis of the incident radiation. The construction of the 7 can in the variant according to 9 can also be used for TD OCT. Here only a synchronized adjustment of the path length of the reference beam paths R1, R2 is required and the tuning of the light source 1 eliminated.

10 shows a modification of the construction of 7 , in which the spatial separation of the reference radiation R1 and R2 and the corresponding superposition now does not take place according to the polarization, but by spectral separation. There are therefore two sources of light 1.1 and 1.2 provided that emit radiation at a different wavelength, as in 11 is shown. In the spectrum applied there, the left-hand wavelength distribution is, for example, the light source 1.1 assign the right wavelength distribution is in the radiation of the light source 1.2 given. The construction of the interferometer I of 10 otherwise corresponds to the interferometer the 7 , with the difference that now the polarizers are no longer required, but propagate two spectrally separated beams through the interferometer. The sake of clarity drawn spatial separation must necessarily be present in the entire beam path, if necessary, suitable non-dichroic divider can be used. The structure can then essentially that of 7 correspond, wherein the pole divider 301 and 302 replaced by corresponding dichroic dividers and the polarizer 300 is exchanged against a corresponding superposition unit of the spectrally different rays.

12 shows the structure of the spectrometer S, which contains the two spectrally separated beams 306.1 and 306.2 prove. Again, for clarity, a spatial distance between the rays 306.1 and 306.2 drawn, which does not have to be given. The diffraction grating 42 Divide the two superimposed, spectrally different rays in different solid angles, so that they on separate photo detector arrays 43.1 such as 43.2 can be directed. In the construction of the 12 is to expand the beam path additionally a deflection mirror 310 intended.

In the event that the light sources 1.1 and 1.2 be tuned, the spectral analysis can be omitted and it is only the spectrally insensitive detectors 309.1 respectively. 309.2 needed. For this purpose, the superimposed rays 306.1 and 306.2 however, be spatially separated by suitable means known to those skilled in the art.

Of course, instead of two separate light sources 1.1 and 1.2 Also, a light source can be used, which emits two chromatically different rays simultaneously. 14 shows a further modification of the spectrometer of 1 - 10 , but now no simultaneous measurement with superimposition of the reference beam paths R1, R2, etc. takes place, but a sequential overlay and measurement. The structure corresponds essentially to that of 7 but no polarization-effective elements are used.

The reference beam R has instead a plurality of beam splitters 311 on, which divide the beam path into a plurality of reference beam paths R1, R2, ..., each in corresponding reflectors 304 end up. Every reflector 304 is on a sled 305 attached. In the exemplary embodiment, three different reference beam paths R1, R2, R3 are formed. The beam splitters 311.1 . 311.2 respectively. 311.3 is a aperture wheel 312 downstream, which implements a selection means which determines which of the reference beam paths R1, R2, R3 is active. The others are switched off. In the presentation of the 14 the reference beam R1 is active, ie its reference beam is at the mirror 304.1 reflected. By switching the aperture wheel 312 Thus, in each case a differently long reference beam path is switched active, so that the superimposed beam 306 always a superposition of the measuring beam M is formed with the reference beam from the correspondingly activated reference beam path. The spectrometer S then detects the corresponding signal. The length of the reference beam paths R1, R2, R3 (of course, any number of reference beam paths can be used) causes, as already mentioned, the depth selection of the object area in the sample P.

Using a broadband light source for the interferometers previously or subsequently described 1 the spectrometer or S are preferably realized in the so-called Czerny-Turner structure. If the sample P or the eye A is illuminated with a plurality of spots or with an illumination line, which is possible for all constructions described here, spectrometers S are equipped with corresponding detector arrays which record the spectral interference pattern on different detector array lines.

In a tuned light source 1 offer instead of the spectrometer S, as already mentioned, photodiodes or monochromators, which for the tuned spectral range of light source 1 usually the most sensitive. If several spots or one line or line in the sample P are illuminated here, the detector is in turn equipped with the appropriate number of photodiodes or pixels. Basically, the photodetector must record the interference pattern synchronized to tune the light source. This is done by appropriate control of the computer 200 , which is an exemplary implementation of a controller that controls the operation of the interferometer I.

The control unit allows in particular a fully automatic two- or three-dimensional image acquisition.

15 shows a variant of the spectrometer of 7 , where the eye is now illuminated with a double beam. Elements already in 7 are therefore not described again here. The double beam provides two measuring beams M1 and M2 polarized perpendicular to one another, these beams running coaxially and offset from one another. The interferometer I the 15 So uses two measuring beams M1 and M2 and two reference beams R1 and R2. Thus, two simultaneous measurements are easily possible, for example, position of the cornea and position of the fundus. The division of the double jet by means of pole dividers 313 . 314 and deflecting mirrors 315 . 316 allows further to make a separate focus for the two measuring beams M1 and M2. For this purpose, only a focus element in the Umlenkweg between the pole dividers 313 and 314 be switched. Thus, for example, the measuring beam M1 can be focused on the frontal surface of the eye, whereas the measuring beam M2 is incident parallel and thus focused through the eye lens in the fundus. The eye length L is obtained as the sum of the offset (= the path difference) of the two measuring beams M1 and M2 due to the beam splitting by the beam splitters 313 and 314 , plus the path difference of the reference beams R1 and R2, plus a remaining optical path difference resulting from the difference in positions of the signal peaks of the two Fourier transforms of the two K spectra.

16 shows a modification of the interferometer I of 15 , in which now only one spectrometer S is provided for the two measuring beams M. For this purpose, the sum of the path differences between the two measuring beams M1 and M2 and the associated reference beams R1 and R2 is suitably set to values smaller than the measuring field depth z. The eye length then results, as for 15 already described; the difference in the positions of the two signal peaks of the two Fourier transforms is read on the computer monitor. This adjustment can be effected by adjusting the path differences by an adjustment mechanism, for example a displacement mechanism of the type previously described for other interferometers, either at the respective measuring beam or reference beam.

A Alternative is to use a measuring beam as a reference beam to use and the optical path length of the rays suitable so adjust that again two measuring signals, So the autocorrelation function (AKF) of the reference beam and the Interference signal, to be displayed on the computer monitor. Well results the eye length as the sum of the path difference between the two beams plus am Monitor read position difference of the two Fourier transform. The device is thus insensitive to movements of the measurement object.

For the measurement of the eye length, it is advantageous to relate the interference pattern with regard to the path length difference on the cornea front surface. This can be achieved in that the reference beam uses a reflex of the cornea, so the reference beam is reflected at the cornea. An appropriate structure is in 17 shown. Components that have been taken over by the previously described Interferometer I unchanged or functionally identical, here again provided with the same reference numerals and will not be explained again.

The ray path of the 17 is that of a short-coherence interferometer I, which is a double beam of two beams 400 . 401 , which are coaxial with each other and offset from each other, aimed at the eye. The anticipatory ray 401 acts as a reference beam, which is reflected at the Corneavorderfläche. The path length difference between the rays 400 and 401 is doing over mirror 318 and 319 set using a beam splitter 317 be charged. The path length difference corresponds essentially to the expected eye length L. The preset path length difference ensures that the reference beam 401 together with the measuring beam reflected at the fundus 400 interferes, so that a beam splitter 322 downstream spectrometer records a corresponding interference signal. A Fourier evaluation of the signal then shows, on the one hand, the autocorrelation function of the reference beam 400 , which interferes with itself, and on the other hand a corresponding distance for the superposition of the reference beam 401 with the measuring beam 400 , In addition, the path length difference Z, which was set externally, must be taken into account. The length L of the eye A thus results from the sum of the measurement result of the optical measurement plus the mechanically set path length difference between 400 and 401 , The presetting allows the FD analysis with simple means, with a comparatively small measuring range.

The interferometer of the 17 is an Bei play, in which the reference beam is reflected on the sample. As a result, an automatic relative measurement is achieved and the distance is not determined by the difference between two absolute measuring points. Locations of the sample are negligible.

18 shows a fiber optic design of the interferometer I of 17 , Again, unchanged or functionally identical components are provided with the same reference numerals. The formation of the rays 400 . 401 now takes place using a coupler 323 feeding two fibers that the reference beam 401 and the measuring beam 400 submit. The reference beam 400 is adjustable with respect to the path length by a displacement mechanism, as he previously already, for example, based on 1 was explained. In addition, on the shift mechanism but still the optics 320 arranged so that automatically with the shift also a suitable focus on the cornea 5 results. Next are the dispersion compensation prisms 54 ' and 54 '' involved in the displacement mechanism such that a change in length of the light path automatically has a corresponding adapted, ie dynamic dispersion compensation result. Otherwise, the structure corresponds functionally to the 17 ,

In addition, for clarification still after the evaluation by the computer 200 displayed monitor image 201 shown. Also is 18 can be seen that the measuring beam M1, which also acts as a reference beam R, is focused on the cornea front surface. It is thus achieved a dynamic focus that can be adapted to different eye lengths. Due to the adjustable optics 325 is the measuring beam M2 collimated so that the optical effect of the eye A the measuring beam M2 at the fundus 7 focused.

With reduced signal quality requirements, one can simplify the beam separation devices. Then one has several measurement signals simultaneously on the array and in the Fourier transform. Corresponding beam paths are in the 19 and 20 displayed. It is about simplifications of the beam paths of the construction according to 16 , The reference mirror 304.2 is now in both arrangements on a translation table 304.4 assembled. By moving this displacement table, it can be seen from the synchronous movement of the associated signal peak of the Fourier transform, to which sample surface it belongs.

In the 20 is the reference mirror 304.1 through a partially transparent mirror 304.3 replaced. It can be between the beam splitter 25 and the reference mirror 304.2 even more semitransparent reference mirror can be arranged. Thus, two or more reference beams in the reference beam path can be used at the same time and a plurality of measuring areas spaced at a depth can be detected. These other reference mirrors can be mounted on translation tables to increase measurement flexibility.

The construction of the 20 can be further modified. Then, the spectrometer S has a detector array 43 with at least 7000 pixels on, z. B. 8000. It is then worked with only one measuring beam, and the partially transmissive mirror 304.3 eliminated. As a result, only one reference beam path R is present in the interferometer I. The eye length measurement is carried out by the pixel-rich array 43 in combination with appropriate spectral fanning by the diffraction grating 43 in one measurement.

Claims (28)

Apparatus for the interferometric measurement of a sample (P), in particular of the eye (A), having a short-coherence interferometer arrangement (I) which has a measuring beam path through which a measuring beam is incident on the sample (P) and a first reference beam path (R) through which passes a reference beam which is superimposed with the measuring beam and brought to interference, characterized in that the interferometer arrangement (I) has at least one second reference beam path (R2) whose optical path length differs from that of the first reference beam path (R1), wherein the path length difference is determined according to a distance of two sample regions spaced apart in the depth direction of the sample (P) ( 5 . 6 . 7 ) and wherein a control device ( 200 ) from the detected superimposed beams by means of Fourier spectral analysis taking into account the path length difference of the reference beam paths (R1, R2), the distance of the sample areas ( 5 . 6 . 7 ). Device according to Claim 1, characterized in that the interferometer arrangement (I) has an overlay device ( 25 . 322 ) having the reference beams ( 53 . 63 . 73 ) separated from the reference beam paths (R1, R2) with the measuring beam (M) from the Meßstrahlengang superimposed and then the superimposed beams then to a detector device (S) for detection forwards. Apparatus according to claim 2, characterized in that the overlay device comprises a switching mechanism ( 322 ) for switching between the two reference beam paths (R1, R2), so that the superposition for the two reference beam paths (R1, R2) is effected sequentially. Apparatus according to claim 2, characterized in that the superposition device ( 25 ) for separate superposition uses a polarization separation, so that the superposition and the Forwarding to the detector device (S) for the two reference beam paths (R1, R2) separated according to polarization and takes place simultaneously. Apparatus according to claim 2, characterized in that the superposition device ( 25 ) for separate superimposition uses a dichroic separation, so that the superposition and forwarding to the detector device (S) for the two reference beam paths (R1, R2) is spectrally separated and simultaneously. Apparatus according to claim 2, characterized in that the superposition device ( 25 ) spatially separates the measuring beam (M) into measuring beam bundles for separate superimposition and the separated measuring beam bundles each with one of the reference beams ( 53 . 63 . 73 ) is superimposed on one of the reference beam paths (R1, R2, R3), a pupil division being used in particular for the spatial separation. Device according to one of the above claims, characterized in that at least one spectrometer (S) is provided, which spectrally analyzes the superimposed beams and sends measuring signals to the control device (S). 200 ). Device according to one of Claims 1 to 6, characterized in that a spectrally tunable radiation source (FIG. 1 ) and a spectrally non-resolving detector device (S) are provided for the measurement, wherein the detector device (S) measuring signals to the control device ( 200 ), which, taking into account the tuning of the radiation source ( 1 ) performs the Fourier spectral analysis. Method for short-coherence interferometric measurement a sample, in particular of the eye, wherein by a Meßstrahlengang a measuring beam is directed to the sample and with a reference beam, the one passes through the first reference beam path, superimposed and for interference is brought, characterized in that at least one second reference beam path is provided, whose optical path is different from that of the first Reference beam path is different, with the path length difference according to one Distance between two sample areas spaced in the depth direction of the sample chosen is and the superimposed Radiation detected and derived therefrom by means of Fourier spectral analysis the path length difference the reference beam paths the distance of the sample areas is determined. Method according to claim 9, characterized that the Rays from the two reference beam paths separated with the measuring beam superimposed from the first measuring beam path, the superimposed so Radiated detected and associated with the spaced sample areas measuring signals be generated. Method according to claim 10, characterized in that that between the two reference beam paths is switched sequentially, so that the measuring beam sequentially with radiation superimposed from the first and the second reference beam path is and the superimposed Rays are detected sequentially. Method according to claim 10, characterized in that that to separate overlay a polarization separation is used, so that the separate superposition and detection for the two reference beam paths separated according to polarization and carried out simultaneously. Method according to claim 10, characterized in that that to separate overlay a dichroic separation is used so that the separate overlay and detection for the two reference beam paths spectrally separated and simultaneously. Method according to claim 10, characterized in that that to separate overlay a spatial Separation of the measuring beam takes place in Meßstrahlbündel and the separated Meßstrahlbündel respectively be superimposed with one of the reference beams, being to the spatial Separation in particular a pupil division is used. Method according to one of the above method claims, characterized characterized in that the superimposed Radiation spectrally selectively detected. Method according to one of claims 9 to 14, characterized that the Radiation spectrally tuned and the superimposed beams brought spectrally non-resolving be detected. Apparatus for the interferometric measurement of a sample (P), in particular of the eye (A), having a short-coherence interferometer arrangement (I) which has a measuring beam path through which a measuring beam is incident on the sample (P) and a reference beam path (R), through which passes a reference beam which is superimposed with the measuring beam and brought to interference, characterized in that the reference beam path (R) comprises the sample (P), reference beam ( 401 ) and measuring beam ( 400 ) are offset from each other in the beam direction by a certain path length difference and the reference beam ( 401 ) at a first sample area ( 5 ) and the measuring beam ( 400 ) at a second sample area ( 7 ) of the sample (P) are reflected and / or backscattered and the interference between the measuring beam ( 400 ) and reference beam ( 401 ) of the distance between the two sample areas ( 5 . 7 ), whereby a control device ( 200 ) from the superimposed detected beams by Fourier spectral analysis taking into account the path length difference the distance of the sample areas ( 5 . 7 ). Apparatus according to claim 17, characterized by a short-coherent beam source ( 1 ) emitting radiation from which the measuring beam ( 400 ) and the reference beam ( 401 ) are obtained, wherein measuring beam and reference beam coaxially incident on the sample (P) and are mutually offset by more than the coherence length. Apparatus according to claim 17 or 18, characterized in that the reference and / or Meßstrahlengang a preferably adjustable focusing element ( 320 ) for measurements on the eye (A), the beam passing through the reference or Meßstrahlengang beam to the retina ( 7 ) or the cornea ( 5 ) to focus. Device according to one of Claims 17 to 19, characterized in that the measuring beam path or the reference beam path is a dispersion-compensating element ( 54 ' . 54 '' ) for measurements on the eye (A) with respect to the influence of the influence of the eye (A) on the 400 ) to compensate. Device according to Claims 19 and 20, characterized in that the dispersion-compensating element ( 54 ' . 54 '' ) and the focusing element ( 320 ) are each adjustable, wherein a mechanical or electrical coupling is provided which a synchronous adjustment of dispersion-compensating element ( 54 ' . 54 '' ) and focusing element ( 320 ) causes. Method for short-coherence interferometric measurement a sample, in particular of the eye, wherein by a Meßstrahlengang a measuring beam is directed to the sample and with a reference beam, the one Traverses reference beam path, superimposed and brought to interference, characterized in that the reference beam path the sample comprises the reference beam and measuring beam against each other in the beam direction by a certain path length difference are offset and, the reference beam at a first sample area and the measuring beam reflected at a second sample area of the sample and / or backscattered be and the distance between the two sample areas from the Interference between measuring and reference beam is determined, wherein the superimposed radiation detected and from this by means of Fourier spectral analysis under consideration the path length difference the distance of the sample areas is determined. Method according to claim 22, characterized in that that for measuring and reference beam radiation from a short-coherent Beam source is used, wherein measuring beam and reference beam be directed coaxially and offset from one another to the sample. Method according to claim 22 or 23, characterized that for measurements on the eye the measuring beam and / or reference beam by means of a preferably adjustable Focusing is focused on the retina or the cornea. Method according to one of claims 22 to 24, characterized that for measurements on the eye the measuring beam or the reference beam by means of a preferably adjustable Dispersion compensating element with respect to dispersion influences of Eye on the measuring beam is compensated. Process according to Claims 24 and 25, characterized that this dispersion compensating element and the focusing element synchronously be adjusted. Device for the interferometric measurement of a Sample (P), in particular of the eye (A), with a short-coherence interferometer arrangement (I), which a Meßstrahlengang (M), through which a measuring beam falls to the test and a reference beam path (R) through which a reference beam is running, the superposed with the measuring beam and to interference, characterized in that a spectrometer arrangement the superimposed ones Radiation detected, which is a spectrally fanning the radiation elements and a detector array comprising at least 7000 individual photosensitive Comprising cells. Method for short-coherence interferometric measurement a sample, in particular of the eye, wherein by a Meßstrahlengang a measuring beam is directed to the sample and with a reference beam, the one Traverses reference beam path, superimposed and to interference, characterized in that for detection the superimposed Blasting a spectrometer arrangement is used, the one the Rays spectrally fanning Element and a detector array that has at least 7000 individual having photosensitive cells.