Device and method for the optical analysis of a test specimen

Abstract

Device for the optical analysis of a test specimen (2), comprising: - a beam source (1) for generating a test beam (P) which is directed onto the test object (2) during operation of the device and passes through it; - a beam splitter (3) for generating a plurality of partial beams (T1, T2, ..., T5) by splitting the test beam (P) after passing the test object (2) into the plurality of partial beams (T1, T2, ..., T5), wherein the beam splitter (3) comprises two beam-splitting surfaces (3a, 3b) which are designed in such a way that they each effect a beam splitting by reflection and transmission of a beam incident thereon; - a detector (5) for the spatially resolved detection of the plurality of partial beams (T1, T2, ..., T5), wherein the detector (5) comprises at least one detection surface (5a) onto which the plurality of partial beams (T1, T2, ..., T5) impinge, and wherein for each beam-splitting surface (3a, 3b) there is at least one detected partial beam (T1, T2, ..., T5), the generation of which involves at least one reflection at the respective beam-splitting surface (3a, 3b); - wherein the beam splitter (3) is designed such that the partial beams (T1, T2, ..., T5) travel different optical path lengths from the test object (2) until they impinge on the at least one detection surface (5a) and all detected partial beams (T1, T2, ..., T5) leave the beam splitter (3) via the same beam-splitting surface (3a, 3b) and then impinge on the at least one detection surface (5a), wherein at least one detected partial beam (T1, T2, ..., T5) arises from radiation which was reflected at the beam-splitting surface (3a, 3b) via which all detected partial beams (T1, T2, ..., T5) leave the beam splitter (3); - an evaluation unit (6) for determining a beam path of the test beam (P) after passing the test object (2) using the spatially resolved detection of the plurality of partial beams (T1, T2, ..., T5), wherein the evaluation unit (6) is set up to determine the beam path of the test beam (P) after passing the test object (2) by determining the angle of incidence (α) of the test beam on one of the beam-splitting surfaces (3a, 3b), wherein the angle of incidence (α) is determined from one or more distances (Δ) between the impact positions (PO1, PO2, ..., POn) of the partial beams (T1, T2, ..., T5) on the at least one detection surface (5a).

Description

[0001] The invention relates to a device and a method for the optical analysis of a test specimen.

[0002] Various methods for the optical analysis of materials or optical components are known from the prior art. Document DE 10 2007 003 681 A1 describes a method for analyzing an optical device. A test beam passes through the optical device, and the path of the test beam is determined via its impact positions in multiple detection planes. For this purpose, a planar intensity sensor is moved into the respective detection planes. The surface of the optical device can be scanned using the test beam, allowing properties of the optical device to be determined, such as the image quality by analyzing the wavefront after passing through the optical device.A disadvantage of the method described in this document is that a sensor with a corresponding detection layer must be moved to determine the beam path of the test beam, so that the measurement of the optical device is complex and takes a long time.

[0003] The document DE 10 2013 219 440 A1 discloses a device for the optical analysis of a test object. This device comprises a beam source for generating a test beam and a beam splitter for splitting the test beam into several partial beams after it has passed the test object to be analyzed. The impact position of the partial beams on a detection surface is detected by a detector. By using a beam splitter, which achieves different optical path lengths of the partial beams between the test object and the detection surface, the beam path of the test beam can be determined in just one detection plane. A disadvantage of this device is that the impact positions of the generated partial beams are far apart, so that larger deflections of the partial beams caused by the test object cannot be detected with conventional detectors due to a lack of a sufficiently large detection surface.The acceptance angle at which deflections of test beams can be detected is therefore small. Furthermore, the beam splitter used, consisting of several adjacent prisms, has a complex design and is large in size.

[0004] Document DD 2 86 420 A5 describes an optical probe for measuring technical surface profiles. The optical probe comprises a laser module that generates divergent light beams and an optical assembly that focuses these light beams onto a test specimen surface. The radiation reflected from the test specimen surface is split into partial beams by a prism, which are then detected by differential photodetectors.

[0005] The object of the invention is to provide a device and a method with which the optical analysis of a test specimen can be carried out in a simple manner.

[0006] This object is achieved by the device according to claim 1 and the method according to claim 15. Further developments of the invention are defined in the dependent claims.

[0007] The device according to the invention comprises a beam source for generating a test beam, which is directed at the test object during operation and passes through it. The beam source can be, for example, a laser for generating a laser beam. The term "passing through the test object" includes both the passage of the test beam through the test object and the reflection of the test beam by the test object. The device is therefore suitable for the analysis of both reflective and transmissive test objects. Reflective test objects are directionally reflecting objects that deflect the test beam in a directed manner and do not (exclusively) scatter it.

[0008] The device according to the invention further comprises a beam splitter for generating a plurality of partial beams by splitting the test beam into the plurality of partial beams after it has passed the test object. The beam splitter comprises two beam-splitting surfaces which are designed such that they each effect a beam splitting by reflection and transmission of a beam incident thereon. In a preferred embodiment, three or more and in particular four or five or more partial beams are generated by the beam splitter. Each beam-splitting surface represents a continuous (i.e., without height jumps) surface which is preferably formed from a single-piece material. The beam-splitting surfaces can be realized, for example, by coatings with known dielectric materials.

[0009] The device according to the invention includes a detector for spatially resolved detection of the plurality of partial beams, the detector comprising at least one detection surface onto which the plurality of partial beams impinge, and for each beam-splitting surface there being at least one partial beam detected by the detector, the generation of which partial beam involves at least one reflection from the respective beam-splitting surface. According to the invention, the at least one detection surface is used to detect the impact positions of the plurality of partial beams in a fixed position of the detector, although this position can be changed if necessary for detection with a new test beam passing the test object at a different location. Preferably, the at least one detection surface is a flat or planar surface.

[0010] The beam splitter used in the device according to the invention is designed such that the partial beams travel different optical path lengths until they impinge on the at least one detection surface. Furthermore, an evaluation unit is provided for determining the beam path of the test beam after it has passed the test object using the spatially resolved detection of the multiple partial beams.

[0011] In the device according to the invention, the beam splitter is further configured such that all partial beams detected by the detector exit the beam splitter via the same beam-splitting surface and subsequently impinge on the at least one detection surface, wherein at least one detected partial beam arises from radiation that was reflected at the beam-splitting surface via which all detected partial beams exit the beam splitter. The beam splitter is thus configured and, in this sense, also arranged such that all detected partial beams exit the beam splitter via the same beam-splitting surface. The above term "exiting the beam splitter" is to be understood here and below to mean that a partial beam that exits the beam splitter does not re-enter the beam splitter before being detected.

[0012] Furthermore, the evaluation unit in the device according to the invention is configured to determine the beam path of the test beam after it has passed the test object by determining the angle of incidence of the test beam at one of the beam-splitting surfaces, wherein the angle of incidence is determined from one or more distances between the impact positions of the partial beams on the at least one detection surface. Preferably, the beam-splitting surface for which the angle of incidence is determined corresponds to a beam-splitting surface through which the test beam enters the beam splitter. A corresponding relationship between the angle of incidence of the test beam and the distances between the impact positions is known per se or can be derived by a person skilled in the art within the scope of their specialist knowledge. This relationship is specified in the specific description for one embodiment of the beam splitter.

[0013] According to the invention, the use of a single beam-splitting surface, through which all (subsequently) detected partial beams emerge and at which reflections of the partial beams also occur, allows the mutual spacing of the partial beams on the at least one detection surface to be reduced. This increases the acceptance angle of the device. Furthermore, the device can be implemented with a compact beam splitter. Furthermore, the device according to the invention has the advantage that the beam path of a test beam can be determined by simultaneous detection of several partial beams without having to move detection planes. In particular, the spatially resolved detection of the several partial beams corresponds to a spatially resolved detection of the test beam by several mutually offset detection planes.

[0014] In a preferred variant of the device according to the invention, multiple reflections from the beam-splitting surfaces are involved in generating one or more of the detected partial beams. This allows the detection of a large number of partial beams with a single detector.

[0015] In a further variant of the device according to the invention, the beam splitter is designed such that the test beam enters the beam splitters after passing the test object via one of the beam-splitting surfaces. "Entering the beam splitter" refers to the initial impact of the test beam on the corresponding beam-splitting surface after passing the test object. This embodiment allows for the realization of a device with a particularly compact beam splitter.

[0016] In a further, particularly preferred embodiment, the at least one detection surface is a single (continuous) detection surface. Alternatively, the detection surface can also comprise multiple detection surfaces arranged in the same plane.

[0017] In a further, particularly preferred embodiment, the at least one detection surface is arranged on the beam-splitting surface through which the detected partial beams exit the beam splitter. Preferably, the at least one detection surface is adjacent to this beam-splitting surface. This results in a particularly compact design of the device with a large acceptance angle.

[0018] In a further preferred variant, the beam splitter comprises a body made of material that is transparent (i.e. at least partially permeable) to the test beam and the partial beams, wherein the beam-splitting surfaces are formed on two opposite boundary surfaces of the body, e.g. by means of a coating made of dielectric material that is known per se. The transparent material can be, for example, glass or a plastic, such as, for example, PMMA (polymethylacrylate) or PC (polycarbonate). According to this embodiment, the beam splitter has a particularly simple construction. However, the beam splitter can also be constructed differently, provided that it is ensured that the beam splitter fulfills the features of the beam splitter of the device according to claim 1. In particular, the beam splitter can, for example, also be realized by two opposite and preferably parallel plates or another resonator.

[0019] In a further preferred embodiment, the beam-splitting surfaces of the beam splitter are flat or planar surfaces. These beam-splitting surfaces can run parallel to one another or, if appropriate, also obliquely to one another.

[0020] In a particularly preferred embodiment, the evaluation unit is configured to determine properties of the test object based on the beam paths of several test beams that pass the test object at different positions.

[0021] In particular, the properties of the test object can be determined as the shape of at least one surface of the test object and / or the optical wavefront after passing through the test object and / or quantities that depend on the shape of the at least one surface or on the optical wavefront (e.g., the gradient field of the wavefront). Such properties can be determined from the beam paths of the test beams using methods known per se. For example, zonal or modal integration can be performed, or the methods described in the document DE 10 2007 003 681 A1 (e.g., Zernike polynomials) can be used.

[0022] In a variant of the embodiment just described, the evaluation unit is configured to determine, as properties of the test object, the shape of several surfaces of the test object and / or quantities that depend on the shape of the several surfaces. For this purpose, several beam paths of the same test beam are determined. These several beam paths differ in that the test beam was reflected from a different surface of the several surfaces. This variant of the invention has the advantage that two surfaces of the test object can be measured in parallel.

[0023] In a further variant, the device according to the invention is designed such that the test beam passes through the beam splitter before passing the test object and re-enters the beam splitter after passing the test object. The division of the test beam into several partial beams is then used to determine the beam path of the test beam. This allows a particularly compact design of the device to be achieved, which design is particularly suitable for the analysis of reflective test objects. Nevertheless, the device can also be designed such that the test beam enters the beam splitter for the first time after passing the test object. This variant is particularly suitable for the analysis of transmissive test objects, such as lenses.

[0024] To ensure rapid measurement of the test object, the device according to the invention preferably comprises an actuator for changing the relative position of the test beam with respect to the test object in one or more directions, which change the impact position of the test beam on the test object. The actuator preferably causes a relative displacement between the test object and the assembly comprising the beam source, beam splitter, and detector. Depending on the design, the actuator can displace only the assembly, only the test object, or both the assembly and the test object.

[0025] The detector used in the device according to the invention can be based on different technologies. In particular, it can comprise a CCD sensor and / or a CMOS sensor and / or a PSD sensor (PSD = Position Sensitive Device). PSD sensors include, for example, photodiodes or 4-quadrant photodiodes. All of these sensor types are known from the prior art and will therefore not be explained in detail.

[0026] In addition to the device described above, the invention relates to a method for the optical analysis of a test specimen using the device according to the invention or one or more preferred variants of the device according to the invention. In the method according to the invention, the test beam is directed onto the test specimen, wherein the test beam impinges on the beam splitter after passing the test specimen. Partial beams split by the beam splitter impinge on the at least one detection surface of the detector and are detected there with spatial resolution, wherein all detected partial beams leave the beam splitter via the same beam splitting surface and at least one detected partial beam arises from radiation that was reflected by the beam splitting surface via which all detected partial beams leave the beam splitter.By means of the evaluation unit of the device according to the invention, the beam path of the test beam is determined after it has passed the test object using the spatially resolved detection of the plurality of partial beams, wherein the evaluation unit determines the beam path of the test beam after it has passed the test object by determining the angle of incidence of the test beam at one of the beam-splitting surfaces, wherein the angle of incidence is determined from one or more distances between the impact positions of the partial beams on the at least one detection surface. Preferably, the method according to the invention is used to determine properties of the test object based on the beam paths of several test beams that pass the test beam at different positions. In particular, the properties already described above can be determined, in particular the shape of the surface of the test object or the optical wavefront after it has passed the test object orQuantities that depend on the shape of the surface or the optical wavefront.

[0027] Embodiments of the invention are described in detail below with reference to the attached figures.

[0028] They show: Fig. 1 is a schematic perspective view of a first embodiment of the device according to the invention; Fig. 2 a top view of the detection surface of the detector Fig. 5 with corresponding impact positions of partial beams; Fig. 3 is a side sectional view of a second embodiment of a device according to the invention; and Fig. 4 is a sectional view illustrating the determination of several surface shapes according to a variant of the invention.

[0029] The Fig. The embodiment of the device according to the invention shown in Figure 1 serves to analyze a reflective test specimen 2 having a corrugated reflective surface O. The device comprises a beam source 1 with which a test beam P is generated. The beam source can be, for example, a laser source for generating a laser beam. The test beam generated by the beam source 1 strikes a beam splitter which consists of a material which is transparent to the test beam and has a thickness d. The top side of the beam splitter 3 represents a beam-splitting surface 3a. Likewise, the underside of the beam splitter 3 is a beam-splitting surface 3b. The beam-splitting surfaces are realized in a manner known per se, for example via a coating of dielectric material. Each beam-splitting surface reflects part of the test beam and transmits part of the test beam.In particular, the respective beam-splitting surfaces can be designed as semi-transparent mirrors.

[0030] The test beam originating from beam source 1 initially strikes the beam-splitting surface 3a. The portion of the test beam transmitted through surface 3a passes through the beam splitter and reaches the beam-splitting surface 3b. The portion of the test beam transmitted via this beam-splitting surface finally strikes the surface O of the test piece 2 at position PO. The test piece is arranged in a predetermined measurement plane ME, for which a Cartesian coordinate system K with corresponding x, y, and z axes is defined. This impact position PO is given in this Cartesian coordinate system by the coordinates x_m, y_m, and z_m.

[0031] The beam incident at position PO is reflected by surface O and returns to the beam-splitting surface 3b of beam splitter 3. The test beam is then split into partial beams T1, T2, T3, and T4. The individual partial beams differ in how often they were reflected by the beam-splitting surface 3a. In particular, partial beam T1 arises from the beam originating from surface O solely through a reflection by the beam-splitting surface 3b, i.e., no reflection by the beam-splitting surface 3a was involved in the generation of partial beam T1. In contrast, partial beam T2 arises from a single reflection by the beam-splitting surface 3a, whereas partial beam T3 was generated by two reflections, and partial beam T4 by three reflections by the beam-splitting surface 3a.

[0032] The individual partial beams T1 to T4, which decrease in intensity with an increasing number of reflections, run essentially parallel to a detector 5, to which an evaluation unit 6 in the form of a computer is connected via a data line 7. The partial beams impinge on a detection surface 5a of the detector. This detection surface can be realized, for example, by a CCD sensor. The impact positions of the individual partial beams T1 to T4 are determined via the detector 5 in a local Cartesian coordinate system of the detection surface 5a, as described below using Fig. 2 is explained.

[0033] Fig. Figure 2 shows a top view of the detection surface 5a of the detector 5. The two-dimensional positions on the detection surface are described by the local Cartesian coordinate system with the axes x_s and y_s. If n partial beams fall on the detector, in the embodiment described here they impinge on the detection surface 5a at mutually offset, evenly spaced positions PO1, PO2, PO3, ..., POn. The even spacing of the impingement positions results from the fact that the two beam-splitting surfaces 3a and 3b run essentially parallel. As the beam-splitting surfaces diverge, the distance between the individual positions increases continuously.

[0034] The determination of the impact positions PO1 to POn preferably proceeds by measuring the intensity distribution of the incident partial beams through the detection surface 5a and determining the center of gravity of this intensity distribution. This center of gravity is equated with the corresponding impact position. The impact positions can be determined by digital or analog electronics of the detector 5 or, if necessary, by the evaluation unit 6.

[0035] In the evaluation unit 6, which is connected to the detector 5 via the data line 7, the impact positions of the partial beams T1 to T4 are appropriately processed. The beam path of the test beam after reflection at the surface O of the test object 2 is determined from the impact positions. In other words, the angle of the test beam with respect to the surface normal of the beam-splitting surface 3b is determined. From this, the inclination of the surface normal at the surface position PO can be determined from the known position of the measuring plane ME and the likewise known position of the beam splitter 3. By detecting test beams that are reflected at many different surface positions, further surface parameters can then be derived, as explained further below.

[0036] The Fig. The device shown in Figure 1 has an actuator (not shown) with which the test beam P and the test object 2 can be displaced relative to one another along the measurement plane ME. In the embodiment described here, the assembly comprising beam source 1, beam splitter 3, and detector 5 are arranged fixedly relative to one another, but can be displaced relative to the test object 2. As part of the analysis of the test object 2, a plurality of positions on the surface O of the test object are approached via the actuator, and the corresponding beam paths of the test beams and, from this, the surface normal at the approached surface position are determined. Using a reconstruction algorithm known per se, the shape of the surface is then reconstructed via zonal or modal integration. This surface shape is given by corresponding height positions according to the z-coordinate of the Cartesian coordinate system K for corresponding x- and y-coordinates of this coordinate system.

[0037] Fig. 3 shows a sectional view of a modification of the embodiment of the Fig. 1. In contrast to Fig. 1, the test beam P from the beam source 1 hits the test object 2 directly without passing through the beam splitter 3. The beam splitter 3 is analogous to the beam splitter of the Fig. 1, whereby the beam-splitting surfaces 3a and 3b run parallel to the measuring plane ME, whereas these surfaces in the embodiment of the Fig. 1 are inclined to the measuring surface. Furthermore, the detector 5 is now arranged on the side of the upper surface 3a. The detection surface 5a runs parallel to the surface 3a and is arranged in the immediate vicinity of it. In a preferred variant, the detection surface 5a rests on the beam-splitting surface 3a, thereby achieving a particularly compact design.

[0038] In the device of the Fig. 3 are in contrast to Fig. 1, the impact positions of five partial beams T1 to T5 on the detection surface 5a are recorded. The individual partial beams differ in the number of reflections at the beam-splitting surface 3b. In other words, partial beam T1 was not reflected at all by the reflection surface 3b, whereas partial beam T2 results from one reflection, partial beam T3 from two reflections, partial beam T4 from three reflections, and partial beam T5 from four reflections at the beam-splitting surface 3b.

[0039] The following is an example of Fig. Figure 3 explains the determination of the angle of incidence α of the test beam P onto the beam-splitting surface 3b. The following explanations are also applicable to other beam splitter arrangements and designs by adapting the corresponding calculation rules. Appropriate adaptation of the calculation rules is within the scope of expert practice.

[0040] As explained above, the impact positions of the individual partial beams on the detection surface 5a are first determined. From this, the distance Δ between the individual adjacent partial beams is calculated. Due to the parallelism of the surfaces 3a and 3b, these distances differ only slightly. Since in the embodiment of the Fig. 3 If several such distances are determined, the calculation continues with the mean value of these distances, which keeps corresponding errors in the distance determination small.

[0041] Based on the law of reflection, the following relationship arises between the angle of incidence α and the distance Δ between adjacent partial rays: sin α=nβ1+β2 with β=Δ2d

[0042] The parameter d is the thickness of the beam splitter 3, and the parameter n corresponds to the refractive index of the beam splitter material. Using the above formula, the angle of incidence and, from this, the surface normal at the corresponding surface position at which the test beam P was reflected can be determined. The shape of the surface of the test specimen is determined using zonal or modal integration.

[0043] When surfaces 3a and 3b are inclined to each other, the distances Δ between the partial beams change. In this case, a function can be defined depending on the measured change in the distances Δ. This function depends not only on the change in the distances but also on the relative inclination of surface 3a to surface 3b, the angle of incidence α, the refractive index n, and the thickness d. Since the relative inclination, the refractive index n, and the thickness d are known, and the change in the distance Δ is measured, the angle of incidence α can be determined using this function.

[0044] Fig. Figure 4 shows a modified embodiment of the device according to the invention. For reasons of clarity, the beam source as well as the detector arranged adjacent to the beam-splitting surface 3a and the evaluation unit connected to it have been omitted. With the embodiment of the Fig. 4, a test specimen 2 is measured, which consists of a transparent material and comprises an upper surface O1 and a lower surface O2. The upper surface O1 is beam-splitting, whereas the lower surface O2 is an at least partially reflective surface.

[0045] With the construction of the Fig. 4, the surfaces O1 and O2 are measured simultaneously. For this purpose, a test beam P is used, which is positioned at various positions on the test object by means of an actuator. At each position of the test beam P, two beam paths are recorded, one resulting from a reflection at surface O1 and the other from a reflection at surface O2. This is shown in Fig. 4. The test beam P generated by the beam source is split at the surface O1 into a partial beam P1 and a partial beam P'. The beam path of the beam P' reflected directly at the surface O1 is determined via the impact positions of the resulting partial beams. At the same time, the beam path of the beam P'' is again determined via the corresponding impact positions of partial beams. The beam P'' originates from the beam P2, which was created by the reflection of the beam P1 at the surface O2. The beam P1 represents the part of the original test beam P transmitted across the surface O1.

[0046] According to the embodiment of the Fig. 4 thus results in both distances of the partial rays resulting from a reflection at the surface O1 and distances of partial rays resulting from a reflection at the surface O2.

[0047] The partial beams can be differentiated, for example, by their intensity, since the intensity of the partial beams resulting from a reflection at surface O2 is lower than the intensity of the partial beams resulting from a reflection at surface O1. With the embodiment just described, the shapes of both surfaces O1 and O2 of test piece 2 can be determined simultaneously in a single measurement process.

[0048] The embodiments described above offer a number of advantages. In particular, a compact device is created with which even larger deflections of a test beam on a test object can be detected via a detector. In other words, the device has a large acceptance angle. Furthermore, the device enables the detection of a large number of partial beams, which can increase measurement accuracy, e.g., by averaging the distances between the partial beams.

[0049] Furthermore, the beam paths of test beams can be determined in a simple manner without having to move a detector with its associated detection surface into different positions. Instead, the test beam is split into partial beams using a beam splitter, each with different optical path lengths between the test object and the detection surface. This simulates the impact positions of the test beam in offset detection planes, which in turn enables the beam path of the test beam to be determined. The device according to the invention ensures significantly faster measurement of test objects, because only one measurement with a stationary detection surface or stationary detector is required to determine a beam path, whereas the prior art requires at least two measurements in different detector positions.

Claims

[1] Device for the optical analysis of a test specimen (2), comprising: - a beam source (1) for generating a test beam (P) which is directed onto the test object (2) during operation of the device and passes through it; - a beam splitter (3) for generating a plurality of partial beams (T1, T2, ..., T5) by splitting the test beam (P) after passing the test object (2) into the plurality of partial beams (T1, T2, ..., T5), wherein the beam splitter (3) comprises two beam-splitting surfaces (3a, 3b) which are designed in such a way that they each effect a beam splitting by reflection and transmission of a beam incident thereon; - a detector (5) for the spatially resolved detection of the plurality of partial beams (T1, T2, ..., T5), wherein the detector (5) comprises at least one detection surface (5a) onto which the plurality of partial beams (T1, T2, ..., T5) impinge, and wherein for each beam-splitting surface (3a, 3b) there is at least one detected partial beam (T1, T2, ..., T5), the generation of which involves at least one reflection at the respective beam-splitting surface (3a, 3b); - wherein the beam splitter (3) is designed such that the partial beams (T1, T2, ..., T5) travel different optical path lengths from the test object (2) until they impinge on the at least one detection surface (5a) and all detected partial beams (T1, T2, ..., T5) leave the beam splitter (3) via the same beam-splitting surface (3a, 3b) and then impinge on the at least one detection surface (5a), wherein at least one detected partial beam (T1, T2, ..., T5) arises from radiation which was reflected at the beam-splitting surface (3a, 3b) via which all detected partial beams (T1, T2, ..., T5) leave the beam splitter (3); - an evaluation unit (6) for determining a beam path of the test beam (P) after passing the test object (2) using the spatially resolved detection of the plurality of partial beams (T1, T2, ..., T5), wherein the evaluation unit (6) is set up to determine the beam path of the test beam (P) after passing the test object (2) by determining the angle of incidence (α) of the test beam on one of the beam-splitting surfaces (3a, 3b), wherein the angle of incidence (α) is determined from one or more distances (Δ) between the impact positions (PO1, PO2, ..., POn) of the partial beams (T1, T2, ..., T5) on the at least one detection surface (5a). [2] Device according to claim 1, characterized by that several reflections at the beam-splitting surfaces (3a, 3b) are involved in the generation of one or more of the detected partial beams (T1, T2, ..., T5). [3] Device according to claim 1 or 2, characterized bythat the beam splitter (3) is designed such that the test steel (P) enters the beam splitter (3) via one of the beam-splitting surfaces (3a, 3b) after passing the test piece (2). [4] Device according to one of the preceding claims, characterized by that the at least one detection surface (5a) is a single detection surface or comprises several detection surfaces arranged in the same plane. [5] Device according to one of the preceding claims, characterized by that the at least one detection surface (5a) is arranged on the beam-splitting surface (3a, 3b) via which the detected partial beams (T1, T2, ..., T5) leave the beam splitter (3), wherein the at least one detection surface (3a) preferably rests on this beam-splitting surface (3a, 3b). [6] Device according to one of the preceding claims, characterized bythat the beam splitter (3) comprises a body made of material transparent to the test beam (P) and the partial beams (T1, T2, T3, T4, T5), the beam-splitting surfaces (3a, 3b) being formed on two opposite boundary surfaces of the body. [7] Device according to one of the preceding claims, characterized by that the beam-splitting surfaces (3a, 3b) of the beam splitter (3) are flat surfaces which run parallel to one another or obliquely to one another. [8] Device according to one of the preceding claims, characterized by that the evaluation unit (6) is designed to determine properties of the test object (2) based on the beam paths of several test beams (P) which pass the test object (2) at different positions (PO). [9] Device according to claim 8, characterized bythat the evaluation unit (6) is designed to determine, as properties of the test object (2), the shape of at least one surface (O, O1, O2) of the test object (2) and / or the optical wavefront after passing the test object (2) and / or quantities which depend on the shape of the at least one surface (O, O1, O2) or on the optical wavefront. [10] Device according to claim 9, characterized by that the evaluation unit (6) is set up to determine, as properties of the test object (2), the shape of a plurality of surfaces (O, O1, O2) of the test object (2) and / or sizes which depend on the shape of the plurality of surfaces (O, O1, O2), wherein for this purpose a plurality of beam paths of the same test beam (P) are determined, wherein the plurality of beam paths differ in that the test beam (P) was reflected on a different surface of the plurality of surfaces (O, O1, O2). [11] Device according to one of the preceding claims, characterized by that the device is designed such that the test beam (P) passes through the beam splitter (3) before passing the test specimen (2) and re-enters the beam splitter (3) after passing the test specimen (2), wherein the division of the test beam (P) into several partial beams (T1, T2, ..., T5) is then used to determine the beam path of the test beam (P). [12] Device according to one of claims 1 to 10, characterized by that the device is designed such that the test steel (P) enters the beam splitter (3) for the first time after passing the test piece (2). [13] Device according to one of the preceding claims, characterized by that the device comprises an actuator for changing the relative position of the test beam (P) with respect to the test piece (2) in one or more directions which change the impact position (PO) of the test beam (P) on the test piece. [14] Device according to one of the preceding claims, characterized by that the detector (5) comprises a CCD sensor and / or a CMOS sensor and / or a PSD sensor. [15] Method for the optical analysis of a test specimen (2) with a device according to one of the preceding claims, characterized by , that - the test beam (P) is directed onto the test piece (2) and, after passing the test piece (2), falls onto the beam splitter (3); - partial beams (T1, T2, ..., T5) split by the beam splitter (3) impinge on the at least one detection surface (5a) of the detector (5) and are detected there in a spatially resolved manner, wherein all detected partial beams leave the beam splitter (3) via the same beam-splitting surface (3a, 3b) and at least one detected partial beam (T1, T2, ..., T5) arises from radiation which was reflected at the beam-splitting surface (3a, 3b) via which all detected partial beams (T1, T2, ..., T5) leave the beam splitter (3); - by means of the evaluation unit (6), the beam path of the test beam (P) is determined after passing the test object using the spatially resolved detection of the plurality of partial beams (P), wherein the evaluation unit determines the beam path of the test beam (P) after passing the test object (2) by determining the angle of incidence (α) of the test beam on one of the beam-splitting surfaces (3a, 3b), wherein the angle of incidence (α) is determined from one or more distances (Δ) between the impact positions (PO1, PO2, ..., POn) of the partial beams (T1, T2, ..., T5) on the at least one detection surface (5a).

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