RETRO-INTERFEROMETER HAVING ACTIVE READJUSTMENT
[0001] The invention relates to an interferometer assembly, comprising [0002] Such an interferometer arrangement from the [0003] According to the genus interferometer arrangements may in particular in the FTIR (=Fourier transform infrared) - spectrometry are used. This is useful as a broadband infrared light (=lnfrarot) - light in an interferometer in two partial beams split into two arms and a speed difference between the partial beams impressed on interferometers, and then a useful light detector read out, the superimposed partial beams after interaction with the fall a sample to be tested. The reading of the useful light detector is repeated for different speed differences. In the superimposition of the partial beams if there is interference, the depending on the frequency of the IR light path difference and for decreasing or increasing the irradiance lead on useful light detector. The path difference of the useful light intensity data from the detector are subjected to a Fourier transform dependent, whereby a spectrum of the sample to be analyzed is obtained. [0004] It is important for this measurement method, the partial beams or pretend to follow exactly the path difference. It is known to, next to the broadband IR light for the actual measurement of the sample to a reference laser additionally, its narrow band light also passes through the interferometer, and from its constructive and destructive interference at a reference light detector to determine the phase difference of the interferometers arms correctly. [0005] The partial beams are generated with a beam splitter usually, on mirrors in the interferometers arms and again reflected in the beam splitter superimposed. [0006] From the [0007] From [0008] (Cube corner reflectors) are retroreflectors interferometers based on for example from the [0009] The invention is based on the, an interferometer arrangement based on retroreflectors provide, wherein a higher and more stable useful light intensity which can be evaluated can be ensured. [0010] This task is solved by a simple and effective manner interferometer arrangement of the aforementioned type, which is characterized, the reference light detector at least three detector surfaces, wherein the detector surfaces of a first pair of detector surfaces are lined up in a first direction, and the detector surfaces of a second pair of detector surfaces are lined up in a second direction, and wherein the first direction, the second direction of the reference light at the reference light detector and an average propagation direction linearly independently, in particular orthogonal to each other, are, and that the interferometer assembly further comprises [0011] With the invention it is possible interferometer arrangement, a lateral shear (offset transversely to the direction of propagation of the beam again so a mutual superimposed) between the two partial beams of the two arms of the interferometer arrangement interferometers to alter and rules, and in particular to stabilize. [0012] The position and orientation of the beam splitter and the retroreflectors interferometer arrangement can vary over time in a, in particular by thermal expansion effects temperature variations. These changes lead to an angle error of the superimposed portion not rays from the interferometric arms, but can lead to a lateral offset of the superimposed partial beams. With increasing lateral displacement is the useful light intensity due to less destructive interference which can be evaluated, and accordingly are the information about a sample to be investigated with the useful light less meaningful, and comparability of different measurements is deteriorating. [0013] The reference light is usually (and typically also the invention) used to, follow the path difference of the interferometers arms. Under the present invention is (also) to the reference light used, the lateral shear the reference light partial beams (the lateral shear of the useful light partial beams substantially corresponds to) and for detecting a stabilization, in particular minimizing, the lateral shear to evaluate. The lateral shear of reference corresponds substantially to the lateral shear of the useful light partial beams light partial beams, since this substantially the same beam path, in particular with the same retroreflectors and the same beam splitter, passing through. [0014] The required information about the quality of the instantaneous adjustment of the partial beams of the interferometric arms from the so-called Haidingerringen removed. This interference to obtain same inclination, the interferometric arrangement with the reference light is illuminated along its optical axis. This expansion of the reference light must a sufficiently large, about a sufficiently large divergence of the reference light or the reference light a sufficiently large angle difference between discrete partial beams, be ensured; therefor can be a scattering element (about a diverging lens) or a partition member (about a beamsplitter and wedge plate assembly -) between reference light source and beam splitter are arranged, or a reference light source with great divergence (about a VCSEL diode) inherently are chosen. By the corresponding beam components of different direction desired, different path differences generated; the path differences are visible by the interference pattern. In the resulting interference pattern on the collector element is infinite (Haidingerringe) on the reference light detector with the two pairs of detector surfaces mapped. [0015] In an optical path difference of zero (ZPD classpath in zero difference) is occurs lateral shear of reference light partial beams a strip-shaped interference pattern, wherein the strip perpendicular to the shear direction and their spacing is inversely proportional amount for shear. In this particular case an infinitely large radius have the Haidingerringe. [0016] Wherein uniform feed of the sinusoidal electrical signals to the detector-interferometer are the faces. A superimposed, strip-shaped interference pattern results in a phase difference between the signals of the detector surfaces of a respective pair. The phase difference is a direct measure for the shearing of the reference light partial beams toward these two detector surfaces, and thus a measure of the Dejustierung interferometer arrangement with respect to the direction of array of the detector surfaces. With the signals of the two pairs of detection surfaces the adjusting position of the interferometer arrangement can therefore be grasped. The phase differences by driving the actuators can, in a closed loop about, are used, so as to compensate for a desired adjustment position or the-interferometer Dejustage be followed precisely. It allows a high and stable useful light intensity be ensured. [0017] The interferometer arrangement is typically used according to the invention, a FTIR spectrum receive a sample. The sample is typically between the beamsplitter and a useful light detector (the at or downstream of the output light is arranged for user) arranged. The reference light typically happens not the sample. The reference light is (additionally for driving the actuators) also usually used, the path difference of the interferometers follow arms. [0018] The interferometric arrangement can own a useful light source, in particular a broadband IR light source, comprise, on useful light input their payload provides the light. It can also be an external utility light source, in particular broadband IR useful light source, are used, for example the sun. The useful light detector can be configured in particular as an IR detector. [0019] An adjustment of the at least two actuators can interferometer arrangement carried out in a manner, that mutual, orthogonal to the optical axis can be compensated for lateral displacement of the retroreflectors. The two degrees of freedom can in particular a mutual displacement of the partial beams of the interferometric arms perpendicular to the beam direction and within the interferometric plane, from the apex of the two the retroreflectors, at the beam splitter mirror image and said optically active center of its generated beam splitter is spanned, and a displacement perpendicular to the beam direction and perpendicularly to this plane be. Typically being the actuators or at the beam splitter arranged on one of the retroreflectors; but it is also possible for example, a reflection mirror between the beamsplitter and a retroreflector arrange, and the deflecting mirror to adjust with the actuators. If the actuators are arranged on a retroreflector, this is preferably not movable (relative to the optical path difference of the interferometers arms) formed. If both retroreflectors are movable, about on a common pendulum, the actuators are preferably arranged at the beam splitter. [0020] The reference light source comprises typically a He-Ne laser or a diode laser. The reference light detector (also referred to as a reference light detector arrangement can be) can be realized with a total component, on which the at least three detector (about with a quadrant detector) are surfaces; alternatively the reference light detector comprising a plurality of separate individual components can be formed, on which the at least three detector surfaces are formed individually (about with three separate individual detectors). [0021] In a preferred embodiment of the interferometer arrangement is provided according to the invention, that the interferometric arrangement is arranged, the reference light source to said beamsplitter that a reference light at the beam splitter in the blocking a minimum MSP expansion, in particular arranged by a minimum divergence angle of the reference light or a minimum between MZWMDIV of discrete partial beams of the reference light, comprises, and that MSP ≥ 2 mrad, preferably MSP ≥ 5 mrad, in particular wherein the arrangement comprises [0022] Wherein a retro interferometers is output side shear the reference light partial beams twice the lateral shift of the two vertices each other retroreflectors, measured orthogonal to the optical axis. A divergence angle of the reference light source fully Div, measured in radians, in the light of the reference light detector a radial angle alpha of focal plane coordinate Div± 2/from. At a given SHEAR shear the reference light partial beams, measured in units of the wavelength of the reference light, wherein the order n of the strip-shaped interference pattern ZPD applies for [0023] These considerations apply in a similar way for the minimum angle when using three or four discrete partial beams between MZW, generated from the reference light with a partition member. In this embodiment the scattering element is omitted and the reference light source should have the lowest possible divergence. Wherein one of the three discrete partial beams is discrete partial beams (this typically on the optical axis) in both pairs of detector surfaces or the associated detector surface used for the first pair and second pair of detector for belongs to both surfaces. By the concentration of the reference light power on only three or four discrete partial beams is a particularly low noise allows determination of the phase differences. [0024] Preferably is also an embodiment, wherein the reference light detector a quadrant diodes, in particular a silicon quadrant diodes, comprises, preferably wherein the quadrant diode for each of the electronic control unit a current-voltage converter is connected downstream of the detector surface used. This assembly is cost-effective and proven in practice. [0025] Advantageously is also an embodiment, wherein the two linear actuators by means of the beam splitter to independent axes, in particular mutually orthogonal axes and to a normal of the beam splitter, is tilted. This embodiment can in particular be chosen, if both retroreflectors are movable for changing the speed difference (about on a common pendulum); in this case the tilting of the beam splitter for compensating lateral shear structurally particularly simple. [0026] In another advantageous embodiment by means of the actuators is one of the retroreflectors linearly independent directions along two, in particular mutually orthogonal directions and the optical axis, displaceable. This design can in particular be chosen, if only one of the retroreflectors is movable for changing the speed difference. The actuators can then (with respect to the speed difference) on solid retroreflector engage, in turn perform what is structurally simple. The actuators are formed as piezo-actuators typically, since the required operating range typically in the 10 micron ranges. [0027] Into the framework of the present invention is also a method for operating an interferometer arrangement, in particular a above described, interferometer arrangement according to the invention, wherein a coherent reference light from a reference source at a beam splitter to a first interferometer-poor having a first and a second retroreflector with a second retroreflector interferometer-poor is divided, and the reference light from the two interferometers arms superimposed on a reference light detector at the beam splitter again and is detected, wherein at least one of the retroreflectors in repeating cycles of motion and thereby the optical path difference of the interferometers arms is moved is changed, characterized in, wherein the reference light is focused behind the beam splitter, in particular with a collecting element between beam splitter and reference light detector, the reference light detector at least three detector surfaces, wherein the detector surfaces of a first pair of detector surfaces are lined up in a first direction, and the detector surfaces of a second pair of detector surfaces are lined up in a second direction, and wherein the first direction, the second direction of the reference light at the reference light detector and an average propagation direction linearly independently, in particular orthogonal to each other, are, at least a portion of the movement cycles that each [0028] According to the invention by the readjustment may many movement cycles phase differences, especially over many receptacles of useful light interferograms, or permanently held approximately constant (or at least for different movement cycle blocks are held in known manner identical or running). The phase differences are usually solid phase difference values readjusted. By the process of the invention is the interferometric arrangement particularly stable or can provide very good reproducible measurement results. [0029] In an optical path difference of zero during the at a lateral shear reference light partial beams on the reference light detector gives a strip-shaped interference pattern, the optical path difference increases resulting a zusammenschnürendes, annular interference pattern, its center is shifted to the situation without such a shear. The phase differences are therefore depend from the speed difference, so that the phase differences to a certain path difference usefully (preferably zero, the zero differenceZPD classpath) are based. It is also possible, but difficult, the course of the phase differences against the optical path difference in the scope of this regulation to detect, because the exact course of the illumination of the reference light detector depends only and near ZPD substantially independently of the illumination is. Preferably takes place at least a readjustment at each hundredth movement cycle, preferably at each movement cycle. On the other hand is sufficient in many cases, such as temperature variations only slow, an occasional readjustment, about at each fifth cycle of movement or rare. The movement cycles typically run at a frequency of 0.3 - 40 hz, usually 1 - 5 hz, from. [0030] The adjustability of the interferometer arrangement with the two actuators with respect to the (at least) (at least) two degrees of freedom is so arranged, that lateral displacement of the optical axis can be compensated orthogonally retroreflectors. This is typically one of the retroreflectors displaced in two directions about two axes tilted or beam splitter; but it is also possible, a reflection mirror between the beamsplitter and a retroreflector arrange, and the deflecting mirror (tilting and/or displacement) to adjust. The two degrees of freedom can in particular a mutual displacement of the partial beams of the interferometric arms perpendicular to the beam direction and within the interferometric plane, from the apex of the two the retroreflectors, at the beam splitter mirror image and said optically active center of its generated beam splitter is spanned, and a displacement perpendicular to the beam direction and perpendicularly to this plane be. [0031] The readjustment of the interferometer arrangement can during or after a cycle of movement (or optionally an associated receiving a interferograms), with the phase determination was made, are carried out. Preferably takes place according to the readjustment movement cycle, particularly preferably in a reverse phase of the drive. [0032] In a preferred embodiment according to the invention is provided, from the reference light source to said beamsplitter that the passing light at a minimum reference beam splitter MSP expansion, in particular arranged by a minimum divergence angle of the reference light or a minimum between MZWMDIV of discrete partial beams of the reference light, comprises, and that MSP ≥ 2 mrad, preferably MSP ≥ 5 mrad, in particular wherein [0033] In one advantageous variant of the beam splitter with respect to the degrees of freedom comprise two linearly independent axes tilting, in particular mutually orthogonal axes and to a normal of the beam splitter. This is simply set up, especially if the two retroreflectors are arranged on a common pendulum. [0034] Preferably is also a variant, wherein the degrees of freedom with respect to two linearly independent directions of the retroreflectors shifts, in particular mutually orthogonal directions and the optical axis, comprise. This is also structurally simple, particularly if the retroreflector is fixed with respect to the establishment of the speed difference between the interferometric arms. [0035] Preferably is a variant, wherein a respective phase difference by measuring the time interval of the zero crossings of two electrical detector signals, are sent to the reference light determined proportions, relative to their periods are determined length. The phase differences are then particularly easy to determine. In particular the zero crossings with the condition can for the signal of the respective detector surface "instantaneous value - cumulative average=0" are determined. The moving average can be determined for example 100 signal periods. [0036] At a preferred variant is provided, for the determination of phase differences that only a portion of the movement cycle is used always the same, in particular less than 1000 wavelengths of the reference light wherein the portion comprises, an optical path difference between the interferometric arms and that the portion contains from zero, in particular wherein the portion symmetrically around the optical path difference of zero is selected. In the area around the path difference is zero the influence of adjustment of the Refeferenzlicht ray path on the lowest stage. [0037] Preferably is a variant, wherein the readjustment of the actuators by means of a digital PI control takes place, preferably wherein the PI controller is connected downstream of a high voltage amplifier per actuator. This has proved in practice. If the directions, in which the reference light detector surfaces are lined up and the directions, in which the actuators are effective, are not collinear, the scheme must additionally performing a coordinate transformation. Pi (=proportional integral) control avoids overshoot in the readjustment of the actuators -. Piezo actuators are typically with 100v to 1000v operated. [0038] In an especially preferred variant is provided, for receiving a useful light interferograms that [0039] Preferably is a further development of this variant, wherein a plurality of useful light interferograms for a total measurement are received one behind the other, and in that the useful light optical path difference of the useful same amplitude individual measurements of each of the total measuring light interferograms are summed up. Typically 10 or more useful light interferograms belonging to a total measurement, or 1000 or more useful light interferograms also, in successive movement cycles are typically the received. An improved signal-to-noise ratio by the summation is obtained. Within the overall measurement according to the invention especially stable measurement conditions are obtained. A total measurement with a single sample typically is total instead. The accumulated useful light amplitude individual measurements of the total measurement are typically subjected to a Fourier transformation, a spectrum, in particular infrared spectrum, to obtain a sample. [0040] Provided it is further advantageous, that a determination of the first and second phase difference and a corresponding readjustment of the at least two actuators wherein each at least one hundredth of the total useful light interferogram is measured, preferably at each measurement of the total useful light interferogram. By a frequent readjustment of the phase difference at the interferometer arrangement can especially stable ratios are obtained. Only slow temperature fluctuations and a frequency of received light interferograms of typically 1 - 5 hz satisfies an occasional useful however readjustment, approximately in the range of once every 5 seconds. [0041] Advantageously is also a refinement, provides, according to one exchange or a reinstall a component of the interferometer arrangement, in particular of the beam splitter or one of the retroreflectors, position and/or orientation of the component is determined first an optimal, in particular so that a maximum intensity of useful light on useful light detector is obtained, the optimum position and/or orientation of the component that to an associated first initial phase difference value and an associated second initial phase difference value are determined for the reference light components, and that during a subsequent measurement operation, in which the useful light interferograms are received, the first phase difference and the second phase difference on the determined first initial phase difference value and the determined second initial phase difference value being readjusted. By this approach can a high and stable useful light intensity are obtained. Measurements of samples are particularly significant. [0042] Additional advantages of the invention result from the description and the drawing. The above and still further features can also exported individually or in any desired combinations according to the invention for more used. The illustrated and described embodiments are not to be understood as a final list, but rather have exemplary character for the description of the invention. [0043] The invention is represented in the drawing and is explained in more detail with reference to embodiments. It show: [0044] The FTIR spectroscopy with two retroreflectors are often interferometer for equipped, since a possible tilting mirror for changing the optical path difference this during their movement completely compensated and the quality of the adjustment (i.e. the modulation efficiency) is not affected. Another perturbation, namely lateral displacement of the optical axis orthogonal to the mirror, is not compensated. This displacement generates a shear of the output beams and the interferometer (i.e. reduced its modulating efficiency) dejustiert. More precisely the modulation efficiency decreases the interferometer, at the beam splitter of the apex of the picture when the mirrored with respect to the apex of the other opposing reflection a lateral displacement comprises opposing reflection, measured perpendicular to the optical axis. The displacement in the bearing or thermal drift of the components e.g. by inaccuracies can arise. The effect is an order of magnitude smaller than the wherein tilting of the mirror in a plane mirror interferometer effect occurring, but disturbs and especially in use longer measurement series (of NIR, visible or UV range) significantly shorter wavelengths. They can fully compensate Dejustierung the interferometer, by one of the two in two axes perpendicular to the optical axis shifts retroreflectors, or the beam splitter into two orthogonal angle tilted degrees of freedom. Both methods are optically equivalent (Dejustierung decreases). In the state of the technique a basic adjustment of the interferometer typically only once or before a measurement series or upon changing of optical components, but not during operation. [0045] The invention provides, lateral displacement of the retroreflectors measurement to detect and technically in a closed control circuit via actuators, the shearing of the output beams influence, the initial alignment state of the interferometer to obtain over a longer period, especially during sustained longer measurement series. The process of the invention is also well suited, to automatically change the interferometer beam splitter according to the initial alignment state again to adjust. [0046] Figures each show schematic all, not scale-representations. In particular beam divergences are and the size of optical elements exaggeration, to make this clearer. [0047] The 1 shows schematically a first embodiment according to the invention in plan view interferometer arrangement 1. [0048] From a light source is not shown useful input by an input light along the optical axis 2a 3 a beam of useful light for user 4 (here by a broadband IR light) into the interferometer arrangement 1 irradiated. Along the optical axis is also input with a reference light source 2a 5, here a HeNe laser, coherent, narrow-band light irradiated reference 6. [0049] The reference light 6 from the He-Ne laser is spread apart, in the configuration shown by means of a dispersing element 7, here a scattering lens, conically widened, so that a divergence of at least 2 mrad, preferably at least 5 mrad, is ensured, see MDIV minimum divergence. In an alternative design can replace the dissipation member such as a beam splitter and wedge plate assembly - 7 are, for example four discrete partial beams on the reference light 6 divide, in pairs (corresponding to the pairs of detector surfaces 19a, 19b, they make on) an intermediate angle of at least 2 mrad, preferably at least 5 mrad, include (not shown - and wedge plate assembly beam splitter, see but the edge beams of the reference light into 6/17 1 and 2, the discrete partial beams can describe), minimum angle between the (average) propagation directions MZW see between the discrete partial beams. The reference light 6 (with thin lines represented) and the useful light 4 are directed to a beam splitter 8 (represented with thick lines). [0050] The beam splitter 8 is by means of two actuators 9, 10, as piezo-actuators are formed here, about two mutually orthogonal axes tilted (see also 3); the mounting of the actuators 9, 10 is closer to simplify not represented. The beam splitter 8 is substantially flat, plate-shaped and semi-transparent, so that it transmits a first portion of the incident light thereon, and a second portion of the reflected light incident on it. For simplification is only the beam-splitting plane effectively represented, but not the beam splitter substrate. [0051] At the beam splitter 8 corresponding to the reference light is on two reference light partial beams 6 11, 12 divided. The reference light partial beam propagated in a first interferometer-poor 11 13 15 and a retroreflector is reflected there. The reference light partial beam propagated in a second interferometer-poor 12 14 16 and to a retroreflector is reflected there. The retroreflectors 15, 16 each have three mutually perpendicular oriented mirror surfaces on, corresponding to the inner corner of a cube. The of the retroreflectors 15, 16 reference light partial beams reflected back 11, 12 are partially reflected back to the beam splitter 8 and take on it and partially transmitted, so that having an average propagation direction along a output side optical axis behind the beam splitter 8 an output-side reference light 17 2b is obtained. This reference light is reflected back from the superimposition of the reference light part 17 beams 11, 12 obtained. [0052] The exit-side reference light 17 (in the alternative design in the form of discrete partial beams) with a collection member 18, here of a convex lens, on a reference light detector 19 focused, the diode is formed as a quadrant detector here four surfaces (these are just two detector surfaces 19a, 19b into 1 to see). A first pair of detector surfaces 19a, 19b it is lined up in a first direction, and a second pair of detector surfaces is in a second direction (perpendicular to the plane of the drawing) of Zr lined up; the two directions it, of Zr are perpendicular to the optical axis. output side optical axis output 2b 2b is given by mirroring the upstream optical axis 2a at the beam splitter 8. [0053] The useful light on the interferometric 8 at the beam splitter 4 is also arms 13, 14 on beneficial light partial beams divided, the retroreflectors at 15, 16 are reflected, and behind the beam splitter 8 to a useful light output 20 superimposing. The useful light output side 20 passes a light output for user 21 on a useful light detector (not shown) and is detected. [0054] The two retroreflectors 15, 16 are mounted on a common pendulum here 22, 23 can oscillate about a rotary axis; the optical path difference of the interferometers arms 13 can thereby, 14 are changed. By successive movement cycles can be established swing. The pendulum 22 is provided with a drive 24, here comprising a permanent magnet and a stationary electromagnetic coil arranged on the pendulum 22. By a the coil with electric current can be deflected the pendulum 22. [0055] Due to bearing tolerances or due to temperature variations can also the orientation of the beam splitter 8 and the lateral alignment of the retroreflectors 15, 16 for the associated optical axis 2a, 2b (i.e. the alignment transversely of the optical axis) change, resulting in a lateral shear of the superimposed partial beams from the beam splitter 8 can lead behind the interferometric arms, in essentially the same manner as in the reference light by a light useful in 20 of the beam splitter 17.8 9 with the actuators tilting, 10, controlled via the phase shifts of reference light portions measured at the reference light detector 19 or its detector surfaces 19a, 19b, may be eliminated or corrected lateral shear (see therefor 6). [0056] The 2 shows the interferometer array of 1 in a side view, wherein the useful light is not shown for simplification. [0057] The input-side reference light propagates in a lower region of the measuring structure from 6 first, while the output-side reference light 17 passes through the measuring structure in an upper region. In the central portion of the measuring structure for the useful light is available. [0058] At the beam splitter 8, in 3 in a lateral supervision is represented, in an upper and lower part 25 for the vaporizations can therefore reference light (laser light) are arranged, and a steaming for the useful light in a central part 26 (broadband IR radiation). [0059] The beam splitter 8 is mounted at a pivot point 27, and by means of the actuators 9 can, 10 perpendicular to the beam splitter plane (the plane of the drawing into the 3 corresponds) are deflected. Actuation of the actuator 9 thereby producing a tilting of the beam splitter 8 ua1 about a first axis, and actuation of the actuator 10 generates a tilting of the beam splitter 8 about a second axis. the linearly independent axes ua2 ua1, extend orthogonal to each other and orthogonal to the normal ua2 here also plane beam splitter. [0060] The 4 shows a second embodiment according to the invention in a schematic supervision interferometer arrangement 1; this embodiment resembles the embodiment of 1, so that only the essential differences are explained here. For simplification only the reference light in turn is also represented. [0061] In this embodiment is the retroreflector 15 along the optical axis with a not shown drive movable 2a, the path difference of Interferomaterarme 13, 14 to change ("movable retroreflector"). The retroreflector 16 by means of two actuators 9 can further, 10 are deflected, any lateral shear between the superimposed partial beams 11 a, 12 from the interferometric arms 13, 14 balance. With the actuator 9 can the retroreflector 16 along the direction r1 (into the plane of the drawing of 4) 2b process are perpendicular to the optical axis, and with the actuator 10 can the retroreflector 16 toward r2 (extends perpendicular to the plane of 4) perpendicular to the optical axis are also 2b method. The retroreflector is 2b along the optical axis 16 but not movable ("immovable retroreflector"). The beam splitter 8 in this variant is not adjustable. [0062] The 5 shows an overall survey to the interferometer arrangement 1 of 4. [0063] In the representation of the 5 the useful light source 30 is evident, their broadband IR light, see useful light 4, at a lens 31 is afterstretching. After passing through the interferometric arms 13, 14 is the useful light output side 20 at a further lens 32 to the useful light detector 33 focused; between the further lens 32 and the useful light detector 33 is the sample to be investigated 34 arranged, by transmission is the radiates. [0064] The from the reference light source 5 and a scattering element 7 expanded reference light 6 is generated after passing the interferometric arms 13, 14 as an output-side reference light part with a collecting element on the reference light detector 17 18 19, near the useful light detector 33 here, registered, in part to the further reference light detector 19', in the vicinity of the useful light source 30 is arranged here. It is possible thereby, altering a direction of the gear difference of the interferometers arms 13, 14 when moving the retro reflector 15 to determine. The retroreflector is 16 by means of the actuators according to the invention 9, 10 2b displaceable transversely of the optical axis, to compensate for lateral shear stanchions. On the reference light detector 19, of the at least three detector surfaces, phase differences between the reference light beam are therefor determined proportions (see 6). The further reference light detector 19' is formed as a single element. [0065] The signal obtained on useful light detector 33, 34 contains information about the sample, to an amplifier 35 is reinforced, and an a/d converter 36 and a not shown supplied digitized evaluation computer. The useful light output signal to a display 37 can additionally. [0066] In the in the 5 the reference light detector 19 embodiment shown on the opposite side for reference is light source 5 disposed, and the further reference light detector 19 'on the same side as the reference light source 5. see, for example that an inverse arrangement is also possible, wherein the reference light detector 19 on the same side as the reference light source 5 is arranged, and the further reference light detector 19' on the opposite side to the reference light source 5. [0067] The 6 the electronic control unit for driving the actuators 38 explained 9, 10 interferometer arrangement according to the invention a closer. [0068]Areference light detector 19 is here with a quadrant form of a Zener diode, the detector has a total of four surfaces 19a - 19d, of which three detector surfaces 19a, 19b, 19c invention needed for driving. The pair of detector surfaces 19a, 19b it is lined up in a first direction, and the pair of detector surfaces 19a, 19c is lined up in a second direction of Zr. The two directions it, of Zr are orthogonal to each other and orthogonal to the incidence direction of the light to be detected also an average reference (perpendicular to the plane of the drawing). The surfaces are of different directions of the reference light detector 19a - 19d (i.e. different reference light proportions, in differing directions) behind the beam splitter illuminated and thus different see, local regions of the Haidingerringe; the proportion of the detector surface 19a is preferably in the optical axis direction 2b. [0069] Within a movement cycle is the retardation between the interferometric arms changed, thereby to constructive and destructive interference of the reference light comes in temporal succession; wherein uniform feed of the difference are output to the detector surfaces 19a, 19b, 19c after amplification by a respective current-voltage converter 44a - 44c approximately sinusoidal signals S.A., self, as a function of the time T obtained by SC. The signal at the detector surface 19a is a common reference signal for S.A. here both pairs 19a/19b and 19a/19c. [0070] Depending on the lateral shear of the superimposed light component beams behind the beam splitter 8 is a reference phase difference between the signals and between the signals to comprise a self SA and SA and. [0071] In the illustrated variant is the period of the reference signal determined first Tperiod S.A., the time interval of adjacent passages by da1, da2 by the average signal magnitude ("cumulative average" or "zero-crossing") this signal waveforms sa is determined. [0072] For the signal Sb is the position of the passage through the intermediate signal magnitude decibels then this signal determined, and the time interval [0073] To control the actuators 9, 10 are the phase X and the phase Y is determined repeatedly (typically only during a certain part of a cycle of movement, about a path difference of "zero" around, ZPD=classpath in zero difference) and with associated, stored desired values compared. Wherein deviations from the desired values are the actuators 9, 10 readjusted. [0074] Will preferably a digital proportional integral control (proportional controllers) 40 used, the phases X, Y is evaluates. Their output signals are converted into analog signals by a D/A converter 41, into high-voltage amplifiers 42, 43 to the actuators (piezo actuators here) amplified and 9, 10 applied. In the interferometric arrangement on constant phase differences between the signals can the detector surfaces 19a/19b and 19a/19c are adjusted, and thus a constant (and typically minimum) lateral shear are achieved. [0075] The stored reference values for the phase differences, the values of phase X and Y is therefore stage, are generally at a first start-up of the interferometer arrangement determined. It is an adjustment position of the retroreflectors visited, with a maximum intensity of useful light on useful light detector is obtained; this adjustment position corresponds to a minimum lateral shear usually. The wherein maximum light intensity measured values for phase X is, stage Y are the future, to in-regulate setpoint values. See, that these nominal values of phase X is, Y is usually differ from 0° stage, usually in the range of + / - 35° and can be found. The phase determining should always in a same portion of a cycle of movement around a path difference of "zero", take place, since the phasing over a cycle of movement and usually only in the vicinity of ZPD varies substantially independently of the illumination of the reference light detector is. [0076] The 7 shows a simulated intensity distribution (light/low Punktdichte=high intensity; high/low intensity=dark Punktdichte) on a reference light detector, is formed with a Quadtrantendiode (see therefor 6), wherein an extremely strong Dejustage the retroreflectors by lateral shear in both directions X and Y, here at a ZPD-position (zero path difference). Because of the large plurality of adjustment are, from left top to right bottom (with four light-dark transitions) interference fringes extending to see; the associated phase differences here are greater than 360 °, so that the phase relation on the signals of the detector surfaces is not more clearly. [0077] The 8 shows a simulated intensity distribution at the reference light detector (cf. 6), wherein in the X and Y is a far lower Dejustage, again at a ZPD-position. The phase difference is 180° about here in X and Y each can and the signals of the detector surfaces are determined well. It is only a light-dark transition to see, from left to right above wherein a bright fringe extends downwardly. In practice the Dejustage the retroreflectors is even smaller, and then the phase differences are observed even smaller corresponding to (but not in Figures to identify what would be more). [0078] In the 7 and 8 is shown, as the phase differences of the signals of the various detector surface pairs of the reference light detector by the degree of lateral shear Dejustage depend, and thus adjusting the phase differences to a respective desired value by a constant adjustment position with respect to the lateral shear can be achieved. The present invention relates to an interferometer assembly (1), comprising an input for useful light (3), a beam splitter (8), two reflectors (15, 16) for establishing two interferometer arms (13, 14), a drive (24) for moving at least one of the retroreflectors (15, 16) in order to modify an optical path difference between the interferometer arms (13, 14), a reference light source (5) for coherent reference light, an output for useful light (21), and a reference light detector (19), said interferometer assembly being characterised in that the reference light detector (19) comprises at least three detector faces (19a-19d), the detector faces of a first pair of detector faces (19a, 19b) being lined up in a first direction (ER) and the detector faces of a second pair of detector faces (19a, 19c) being lined up in a second direction (ZR), and the first direction (ER), the second direction (ZR) and a central propagation direction of the reference light (17) on the reference light detector (19) being linearly independent, and in that the interferometer assembly (1) also comprises - a collector element (18) for reference light (17), arranged between the beam splitter (8) and the reference light detector (19), for focusing the reference light (17) from the beam splitter (8), - at least two actuators (9, 10) for modifying a lateral shearing between two reference light partial beams (11, 12), which are reflected back from the interferometer arms (13, 14) and are superposed again at the beam splitter (8), in at least two degrees of freedom, - and control electronics (38) for controlling the actuators (9, 10) on the basis of signals (Sa-Sc) at the detector faces (19a-19d) of the reference light detectors (19). The invention provides an interferometer assembly based on retroreflectors, by means of which assembly a greater degree of evaluatable and more stable useful light intensity can be ensured. 1. Interferometer arrangement (1), comprising an input for commercial light - (3), - a beam splitter (8), - two retroreflectors (15, 16) for establishing two interferometers arms (13, 14), - a drive (24) for moving at least one of the retroreflectors (15, 16), is an optical path difference between the interferometric arms (13, 14) to change, - a reference light source (5) for coherent reference light, in particular a reference laser, - an output for commercial light (21), - and a reference light detector (19), characterized, that the reference light detector (19) at least three detector surfaces (19a - 19d) has, wherein the detector surfaces of a first pair of detector surfaces (19a, 19b) are lined up in a first direction (it), and the detector surfaces of a second pair of detector surfaces (19a, 19c) in a second direction (of Zr) are lined up, and wherein the first direction (it), the second direction and an average propagation direction of the reference light (of Zr) (17) on the reference light detector (19) independently linearly, in particular orthogonal to each other, are, and in that the interferometer arrangement (1) further comprises - a collection member (18) for reference light (17), preferably a collection lens, disposed between the beam splitter (8) and the reference light detector (19), for focusing the reference light (17) from the beam splitter (8), - at least two actuators (9, 10) for changing a lateral shear between the two interferometers arms (13, 14) and back reflected at the beam splitter (8) reference light partial beams superimposed again (11, 12) in at least two degrees of freedom, in particular arranged at the beam splitter (8) or on at least one of the retroreflectors (15, 16), - and an electronic control unit (38) for driving the actuators (9, 10) in response to the detector signals (sa to SC) surfaces (19a - 19d) of the reference light detector (19). 2. Arrangement (1) according to 3. Arrangement (1) according to 4. Arrangement (1) according to one of 5. Arrangement (1) according to one of 6. A method of operating an interferometer arrangement (1), in particular a interferometer arrangement (1) according to one of 7. The method 8. The method 9. The method 10. Method according to one of 11. Method according to one of 12. Method according to one of 13. The method 14. The method 15. Method according to one of The purpose of the invention
Brief description of the invention
Preferred embodiments of the invention
Process of the invention
and that a plurality of useful light interferograms are received. Wherein the receiving of the useful light interferograms is a sample to be investigated in the beam path of the useful light (and not in the path of the reference light typically) arranged, preferably between beam splitter and useful light detector. (Successively) receptacles of the more useful during the interferometric arrangement by means of the invention light interferograms can be stabilized readjustment of the actuators, so that for the plurality of measurements are obtained same measurement conditions. The more useful light interferograms can be included with different samples, or in each case some useful light interferograms ("total measurement", see below) with the same sample. Useful light and reference light are parallel or anti-parallel to each other in the interferometer arrangement typically guided. A movement cycle of the at least one retro-reflector both for the determination of phase differences in the reference light can also be used as the useful light amplitude individual measurements. See, that the invention also can take place according to rules of the actuators (and should), if not just useful light interferograms are included, next to the interferometric arrangement for measurements to stably hold.Figures list
Overview of the invention
Explanation of Figures
List of reference symbols