Method, device and measuring system for measuring refractive index of optical sample

Abstract

The invention relates to a method for determining the refractive index of an optical sample (100), the sample comprising a first face (102) and a second face (104) arranged at a wedge angle (omega) to the first face (102), the method comprising the following steps: detecting a first reflected light beam (401) representing the light beam reflected on the first face (102), a second reflected light beam (402) representing the light beam reflected on the second face (102), and a third reflected light beam (413) representing the light beam reflected on the second face (102); the second reflected light beam (402) represents a light beam reflected on the second face (104) and the third reflected light beam (413) represents a light beam reflected at a mirror element (420), determining a first angle (alpha) between the first reflected light beam (401) and the second reflected light beam (402) and determining a second angle (beta) by means of the third reflected light beam (413), and calculating (315) the refractive index (n) using the first angle (alpha) and the second angle (beta).

Description

[0001] The invention relates to a method, a device and a measuring system for measuring the refractive index of an optical sample.

[0002] For measuring the refractive index of optical prisms or optical wedges with small prism angles, various methods are known to detect the back reflection inside the prism or wedge with the help of an autocollimator. For example, when the angle of incidence and the vertex angle are known, the refractive index of the wedge material can be determined with the help of Snell's refraction law. The methods described in the prior art have in common that the vertex angle is determined by a goniometer in the measurement preparation stage, which increases the overall measurement workload. Summary of the invention

[0003] In this context, the present invention proposes a method, a device and a measuring system for determining the refractive index of an optical sample according to the independent claims. Advantageous technical solutions are derived from the relevant dependent claims and the following description.

[0004] The invention has the advantage that the refractive index of a wedge-shaped sample can be measured without knowing the wedge angle or the top angle, thereby achieving simple measurement, saving time, or greatly simplifying the measurement process.

[0005] A method for measuring the refractive index of an optical sample is proposed, wherein the sample includes at least a first surface and a second surface arranged at a wedge angle with the first surface. The method includes the steps of detecting a first reflected light beam, a second reflected light beam and a third reflected light beam. The first reflected light beam represents a light beam reflected on the outer side of the first surface, the second reflected light beam represents a light beam reflected on the inner side of the second surface, and the third reflected light beam represents a light beam reflected on the reflector surface of a reflector element. The reflector element is interpreted as being arranged on the side of the sample opposite to the light source of the emitting light beam. The method further includes the steps of measuring a first angle by means of the first reflected light beam and / or the second reflected light beam and measuring a second angle by means of the third reflected light beam. In addition, the method also includes the step of calculating the refractive index using the first angle and the second angle.

[0006] By way of example, the method proposed herein allows the refractive index of at least partially wedge-shaped lenses or other optical elements, for example prism-shaped, to be measured. Accordingly, the sample may also be referred to below as a wedge lens or prism. In this case, in one method step, the reflection of a light beam emitted by a light source is detected. The first angle α is determined using these detected reflected light beams. This angle is the angle between two light beams reflected at different sample surfaces. Depending on the specific orientation of the sample, in one embodiment, the angle α can be determined only by the light beams reflected at the first sample surface. In this embodiment, the orientation of the sample should be monitored with the aid of an additional sensor. In this case, the first reflection can, for example, occur at the sample surface that is first hit by the incident light beam. The second reflection can occur on the inner side of the sample, which is opposite to the first sample surface and forms a wedge angle of the sample with the first sample surface. In addition, a second angle β is determined. This angle is the angle between the incident light beam and the light beam that is reflected at a reflector and passes through the sample for the second time, which reflector can be located below the sample. The position of the incident light beam should be determined in the measurement preparation phase by reflection at the reflector without a sample in the beam path. In this case, the mirror should be positioned approximately orthogonal to the incident beam. However, if the specimen is mounted so that it can rotate (which is the preferred measurement configuration), the reference measurement without the specimen can be omitted. In this case, the angle β can be determined directly from the diameter of the impact circle on the camera.

[0007] Finally, in a calculation step, the refractive index n of the sample material is calculated. For example, the refractive index can be determined using the following relationship for two angles: nAir represents the refractive index of the surrounding medium.

[0008] According to one embodiment, the method may include the step of emitting a collimated light beam from a light source toward the first surface. For example, the light beam may be emitted from a light source, such as a LED, and collimated, for example, by a collimator. For example, during the emission of the light beam, the light source and the collimator may be arranged in sequence with the sample or a support for fixing the sample and the reflector element. This may advantageously allow the sample to be optimally illuminated and produce a reflected light beam of maximum intensity.

[0009] Furthermore, in the emission step, the light beam may be emitted at an angle between 80 and 100 degrees, in particular at a right angle, relative to the first face of the sample. For example, the light beam or the plurality of collimated light beams may be emitted orthogonally to the outside of the first face. This has the advantage that the first angle and the second angle may be determined with high precision. This orientation is only a special case and is provided for reference only. The method is also effective when the outside of the first face is not orthogonal to the incident light beam.

[0010] Another advantageous embodiment of the invention is that the sample is initially oriented such that the orientations of the first and second faces are interchanged. In this case, the first angle α can be measured with the aid of the first reflected light beam without passing through the sample material. The second angle β remains unchanged. For example, the refractive index n can be determined in this case using the following formula: The advantage of this slightly modified formula is that it can reduce the measurement error of high refractive indices, which will be explained later.

[0011] To implement this variant, it is necessary to know the degree of inclination of the side surface resting on the sample stage relative to the optical axis of the incident light beam. For this purpose, the measuring device is expanded with a sensor which detects the inclination of the bottom side of the sample by means of the light beam reflected at the bottom side of the sample, so that the inclination can be calculated within the measuring range.

[0012] According to another embodiment, the method may comprise the step of orienting a mirror surface of the mirror element orthogonally to the incident light beam. For example, the mirror element may be formed with a planar reflective mirror surface. In the orienting step, the mirror surface may be approximately or substantially orthogonal to the incident light beam, wherein the mirror surface may, for example, be oriented parallel to the first face of the sample. If the refractive index measurement is performed without rotating the sample, it is necessary to pre-calibrate the mirror without the sample (determine the zero position).

[0013] According to another embodiment, the first reflected light beam, the second reflected light beam and the third reflected light beam can be detected simultaneously in the detection step. For example, a collimated light beam can be emitted in the direction of the sample or a reflector element arranged behind the sample starting from the light source, and the reflections of these light beams can be detected simultaneously. This has the advantage that the method proposed in this article can be implemented in a time-saving manner.

[0014] According to another embodiment, the detection step, the determination step and the calculation step can be repeated, wherein the reflected light beam is interpreted as a reflection of different wavelengths during the repeated detection step. For example, the refractive index can be measured successively at a plurality of different wavelengths. For this purpose, the light source can be implemented as a polychromatic light source, for example as a white light LED. In order to adjust one or more measuring wavelengths, the autocollimator or the light source unit can have a replaceable optical filter. The objective lens of the autocollimator can be designed to be able to be linearly moved to compensate for longitudinal chromatic aberrations. This has the advantage that the refractive index can be determined particularly accurately.

[0015] According to another embodiment, the method may include a step of controlling the sample to rotate around an axis of rotation parallel to the light beam. The rotating step may be performed simultaneously with the detecting step. As a supplement or alternative, the rotating step may also be performed simultaneously with the step of emitting light from the light source. For example, the sample may be rotated around an axis parallel to the incident collimated light beam by a corresponding support. This has the advantage that the second angle can be determined directly from the diameter of the impact circle generated by the rotation without the need to orient the reflector element.

[0016] The method can be implemented, for example, in the form of software or hardware or a combination of software and hardware, for example in a control device.

[0017] The present invention further provides a device, which is designed to execute, control or realize the steps of the variants of the method proposed herein in a corresponding device. This device helps to achieve the purpose of the present invention quickly and efficiently.

[0018] For this purpose, the device can have at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or actuator for reading in sensor signals from the sensor or outputting data signals or control signals to the actuator and / or at least one communication interface for reading in or outputting data embedded in the communication protocol. The computing unit can be, for example, a signal processor, a microcontroller or the like, wherein the memory unit can be a flash memory or a magnetic storage unit. The communication interface can be designed to read in or output data wirelessly and / or wired, wherein a communication interface capable of reading in or outputting wired data can, for example, output these data electrically or optically from a corresponding data transmission line or input them into a corresponding data transmission line.

[0019] In this context, a "device" may be understood as an electrical device that processes sensor signals and outputs control signals and / or data signals accordingly. The device may have interfaces, which may be designed in hardware and / or software. In a hardware-based design, these interfaces may, for example, be part of a so-called system ASIC, which contains the various functions of the device. However, these interfaces may also be self-contained integrated circuits or at least partially consist of discrete components. In a software-based design, these interfaces may be software modules that are present on a microcontroller, for example, together with other software modules.

[0020] In addition, a measuring system for measuring the refractive index of an optical sample is proposed, wherein the measuring system comprises a variant of the aforementioned device. The device is designed to control a light source of the measuring system, and additionally or alternatively to control a receiving element of the measuring system, and additionally or alternatively to control a reflector element of the measuring system. In addition, the measuring system also comprises a light source for emitting a light beam, a receiving element for receiving the sample, and a reflector element, wherein the reflector element is arranged on a side of the receiving element opposite to the light source. The advantage of the measuring system described herein is that the aforementioned method can be implemented in an optimal manner.

[0021] According to one embodiment, the measuring system may have a collimator including a light source, wherein the collimator may include a plurality of replaceable optical filters for filtering the light beam. The measuring system may, for example, include an automatic collimator for irradiating the sample and for detecting reflections occurring on each sample surface. For example, the light source and the graticule may be arranged on an illumination arm of the automatic collimator. Therein, the light source may, for example, be implemented as a multicolor, such as a white light LED. The automatic collimator or the light source unit may have replaceable optical filters so that one or more measuring wavelengths can be advantageously set. As a supplement or alternative, the objective lens of the automatic collimator may be designed to be capable of linear movement to compensate for longitudinal chromatic aberration.

[0022] According to another embodiment, the reflector element may have an adjustable aperture stop. For example, the reflector may have an additional adjustable aperture stop for limiting the light beam. This has the advantage that the contrast between the detected reflections can be adjusted by varying the intensity of the reflected light beam. Furthermore, the reflectivity of the reflector surface may advantageously be of the same order of magnitude as the reflectivity of the sample surface, so that reflections on various surfaces can be detected without adjusting the camera integration time.

[0023] According to another embodiment, the accommodation element can be mounted in a rotatable manner. For example, the accommodation element can be mounted in a rotatable manner around a rotation axis parallel to the optical axis of the autocollimator, so that the tilt between the rotation axis of the sample holder and the surface of the reflector or the tilt of the reflector relative to the optical axis of the autocollimator can be advantageously compensated in a mathematical manner. As an alternative, the sample can also be placed on the sample table. If this embodiment is adopted, the autocollimator will advantageously be located below the sample, the reflector will be located above the sample, and the wedge mirror will preferably be placed on the sample table in a way that one of its long sides is against the sample table.

[0024] According to another embodiment, the light source and the reflector element can be rotated about a common axis. For example, as an alternative to rotating the sample holder, the autocollimator can also be rotated together with the reflector about a corresponding common axis. In this case, the sample and the holder can remain stationary. This variant can also advantageously compensate mathematically for the tilt between the rotation axis of the sample holder and the reflector surface or the tilt of the reflector relative to the optical axis of the autocollimator. Without rotating the receiving element, the reflector surface should be oriented towards the autocollimator in a preparation step or a residual error of the tilt of the reflector surface relative to the optical axis of the autocollimator should be determined. This preparation step is carried out without a sample.

[0025] According to another embodiment, the receiving element can be designed to receive a liquid and additionally or alternatively to receive a solid. For example, the measuring system can also be advantageously used to measure the refractive index of a liquid. To this end, the liquid to be measured should be stabilized in a suitable manner. For example, the liquid can be clamped between two plane-parallel plates so that it assumes a wedge shape. This allows advantageous measurements similar to those of solids. In this case, the sample should remain stationary and the autocollimator should rotate together with the reflector. In addition, it must be ensured that the plane-parallel plates have excellent flatness.

[0026] Also advantageous is a computer program product or a computer program with a program code, which can be stored on a machine-readable carrier or storage medium, such as a semiconductor memory, a hard disk memory or an optical memory, and is used to implement, realize and / or control the steps of a method according to one of the above-described embodiments, in particular when the program product or the program is executed on a computer or a device.

[0027] Embodiments of the present invention are illustrated in the accompanying drawings and will be described in detail in the following description. Figure 1 is a schematic diagram of an optical specimen according to an embodiment; Figure 2 A schematic diagram of an optical specimen and a measurement method are provided; Figure 3 A flow chart of a method for measuring the refractive index of an optical sample according to one embodiment; Figure 4a is a schematic diagram of an embodiment of an optical specimen; Figure 4b is a schematic diagram of an embodiment of an optical specimen; Figure 4c A schematic diagram of an embodiment for measuring the refractive index of an optical sample; Figure 4d A schematic diagram of an embodiment for measuring the refractive index of an optical sample; Figure 4e is a graph showing the relationship between the refractive index change and the ratio of the two angles α and β; Figure 5 A flow chart of a method for measuring the refractive index of an optical sample according to one embodiment; Figure 6a A schematic diagram of an embodiment of a measuring system for measuring the refractive index of an optical sample; Figure 6b A schematic diagram of an embodiment of a measuring system for measuring the refractive index of an optical sample; Figure 7a is an exemplary camera image of the reflection detected when the rotation amplitude (azimuth angle) of the specimen is 0°; Figure 7b is an exemplary camera image of the reflection detected when the sample is rotated by 180° (azimuth angle); and Figure 8 The figure is a schematic cross-sectional view of an embodiment of a containing element for containing a liquid sample.

[0028] In the following description of advantageous embodiments of the present invention, elements illustrated in the various figures and having similar functions will be provided with the same or similar reference numerals, and these elements will not be described repeatedly.

[0029] Figure 1 Schematic diagram of an optical sample 100 according to an embodiment is shown. The sample 100 shown here is formed as a wedge prism for example only, including a first face 102 and a second face 104 arranged at a wedge angle ω with respect to the first face 102. The wedge angle ω can also be generally referred to as the vertex angle A. When the sample 100 is irradiated with a light beam 110 from the side of the first face 102, the light beam is generally deflected under the action of a prism or a wedge mirror. The deflection δ of the light beam 110 depends on the refractive index n and the wedge angle ω. The deflection δ can be expressed by the following formula: δ=(n–n 空气 )ω Figure 2 Schematic diagram of an optical sample 100 according to an embodiment is shown. The sample 100 shown here is the same or similar to the sample described in the previous figure. The measurement method shown in this figure is consistent with the prior art, that is, the back reflection inside the prism / wedge lens can be detected by an automatic collimator 200. This method can determine the refractive index of the wedge lens material with the help of Snell's refraction law when the incident angle i and the vertex angle A are known.

[0030] A disadvantage of the measurement method according to the prior art illustrated here is that the vertex angle A or the wedge angle ω is determined by means of a goniometer in preparation for the refractive index measurement, which increases the overall measurement effort.

[0031] Figure 3A flow chart of a method 300 for determining the refractive index of an optical sample according to one embodiment is shown. The method illustrated here is applicable to the sample described in the previous figures, assuming that the sample has at least a first surface and a second surface arranged at a wedge angle to the first surface.

[0032] The method 300 includes a step 305 of detecting a first reflected light beam, a second reflected light beam, and a third reflected light beam. The first reflected light beam represents a light beam reflected on the outside of the first surface, the second reflected light beam represents a light beam reflected on the inside of the second surface, and the third reflected light beam represents a light beam reflected on a reflector surface of a reflector element. The reflector element is interpreted as being arranged on a side of the sample opposite to a light source emitting the light beam.

[0033] The method 300 further includes step 310 of determining a first angle between the first reflected light beam and the second reflected light beam and determining a second angle via the third reflected light beam.

[0034] In addition, the method 300 further includes a step 315 of calculating a refractive index using the first angle and the second angle.

[0035] The method 300 described herein is based on the following realization: the refractive index of a wedge-shaped sample can be measured without knowing the wedge angle and the top angle, which means that there is no need to perform multi-step measurement or the measurement procedure will be greatly simplified.

[0036] Figure 4a and Figure 4b Schematic diagrams of an embodiment of an optical sample 100 are shown respectively, on which the above-mentioned Figure 3 The refractive index determination method described in . Figure 4a shows the determination of the first angle α, Figure 4b The determination of the second angle β is shown.

[0037] In one embodiment, the sample 100 is illuminated during the measurement with collimated light, which is shown here as light beam 110. In an advantageous embodiment, the first face 102 (ie the sample surface) of the sample 100 is oriented orthogonally to the incident light beam, which is shown only by way of example.

[0038] exist Figure 4aIn the first measurement step shown, a first angle α can be determined. The first angle is between a first reflected beam 401 and a second reflected beam 402, wherein the first reflected beam 401 represents the beam 110 reflected on the outer side 405 of the first surface 102 and the second reflected beam 402 represents the beam 110 reflected on the inner side 410 of the second surface 104. In other words, the first angle α is the angle between two beams reflected on different sample surfaces 102, 104. The first reflection occurs on the sample surface that is first hit by the incident beam. The second reflection occurs on the inner side of the sample 100, which is opposite to the first sample surface and forms a wedge angle ω with the first sample surface.

[0039] In one embodiment, the first angle α may be calculated using the following formula: α*n 空气 =2nω exist Figure 4b In the second measurement step shown, a second angle β can be determined. The second angle is between the incident light beam 110 and the third reflected light beam 413, wherein the third reflected light beam 413 represents the light beam reflected on the reflector surface 415 of the reflector element 420. In the present figure, the reflector element 420, which can also be simply referred to as a reflector, is arranged on the side of the second face 104 of the sample 100, so that the reflector surface 415 is parallel to the first face 102 and opposite to the light source 225 that emits the light beam 110. In addition, the incident light beam 110 is orthogonal to the reflector surface 415. Accordingly, the second angle β is the angle between the light beam reflected at the reflector located below the sample 100 in the figure and passing through the sample for the second time and the light beam reflected at the above-mentioned reflector when the sample is not in the light path. However, the method is also effective when the first sample face 405 and the reflector surface 415 are not parallel to each other and are not orthogonal to the incident light beam 110. In other words, angle β is the angle between light beam 413 and a reference reflected light beam generated at the reflector surface 415 when the sample is not in the light path. For the sake of clarity, the reference reflected light beam is not shown here because it coincides with the incident light beam 110 when the reflector is orthogonal to the incident light beam 110. In a preferred application example where the sample rotates, it is not necessary to perform a reference measurement without the sample. When the sample rotates, the reflected light beam 413 forms an impact circle on the detection surface. From the diameter of this impact circle, the angle β can be directly calculated. This relationship will be explained in detail later in conjunction with Figure 7. In summary, the angle β can be determined with the help of the reflected light beam 413.

[0040] As an alternative, the sample can also be illuminated from the bottom side. In this case, the reflector is located above the sample.

[0041] The second angle β can be calculated, for example, using the following formula: β*n 空气 =2(nn 空气)ω Furthermore, in one embodiment, the measurement is designed so that all reflections are detected simultaneously, so that two angles α, β can be measured simultaneously.

[0042] The refractive index of the sample material can now be determined using the following relationship for the two angles α, β: In this case, it should be noted that the absolute angle does not need to be measured. Since the numerator and denominator of the formula contain angles, the calibration coefficient of the angle measurement system is omitted during the measurement.

[0043] The test specimen 100 is designed merely as an example so that the value of the wedge angle ω is less than 1° or less than 0.5°.

[0044] A further advantage of the measurement method described here is that no calibration of the measurement system is necessary, since only the ratio of the two angles α and β is decisive for the measurement of the refractive index.

[0045] Figure 4c A schematic diagram showing an embodiment of measuring the refractive index of an optical sample 100, on which the aforementioned Figure 3 The refractive index was determined by the method described in Figure 4a and Figure 4b The difference shown is that the sample is oriented with the side surface 104 facing upward, so that the incident light beam 110 is now reflected at the side surface 104 at an angle α. The angle α can now be determined with the aid of the first reflected light beam 401 according to the following relationship: Α=2ω The angle β is then subject to the above relationship. For this embodiment to be effective, the sample surface 102 must be as perpendicular as possible to a reference axis, such as the optical axis of the incident light beam 110. If there is an inclination angle δ between the side surface 102 and the reference axis (such as the optical axis of the incident light beam 110), this inclination angle should be determined. This inclination angle can be calculated as part of the measurement.

[0046] This inclination angle δ can be obtained, for example, Figure 4c The sensor 430 is measured by a sensor not shown in the figure, which emits a sensor beam 430 to the side 102 of the sample 100, detects the corresponding sensor reflected beam 435 on the opposite side and determines its direction. Knowing the direction of the sensor beam 430 and the sensor reflected beam 435, the tilt angle δ and / or the position of the sample 100 relative to this sensor can be determined or detected. When the side 102 of the sample 100 is oriented at a 90° angle to the optical axis of the incident light beam 110, it can be assumed that the first angle α=2·ω. The second angle β represents or reflects the angle of light transmitted through the sample 100, and the relationship is β=2·(n-nA)·ω / nA. If these two equations are solved according to n, the following relationship is obtained: Figure 4d A schematic diagram showing an embodiment of measuring the refractive index of an optical sample 100, on which the aforementioned Figure 3 The refractive index was determined by the method described in Figure 4c The difference in the illustrated approach is that now also a rotation of the specimen 100 by 440° is taken into account. This means that the relationship for the first angle α and the second angle β is α=4·ω and β= 4·(n-nA)·ω / nA. Regardless of the orientation of the sample, rotation of the sample has the effect of introducing a factor of 2 in the equations for the angles α and β. Rotation has no effect on the calculation of the refractive index. However, from a measurement technology point of view, rotation is advantageous because it increases the amount of data, especially when measuring a complete impact circle. In addition, adjustment errors of the measuring system lead to angular measurement errors, which can be more easily identified and corrected by moving the impact circle.

[0047] Figure 4e A graph 450 is shown showing the relationship between the refractive index change and the ratio ν of the two angles α and β to illustrate the background of the measurement configuration. In the graph 450, the ratio ν = β / α of the two angles α and β is plotted on the horizontal axis, and the refractive index η of the sample 100 when the refractive index of air is ηair is plotted on the vertical axis. Figure 4a and Figure 4b The refractive index η of the sample 100 is measured by the second graph 460. Figure 4c and Figure 4d The refractive index η of the sample 100 measured in the embodiment of FIG. The measurement error of the refractive index is related to the slope of the curve. Therefore, especially in the case of high refractive index, Figure 4c and Figure 4d The processing method proposed in the paper helps to reduce or minimize the impact of measurement errors.

[0048] Figure 5 FIG. 3 is a flow chart showing a method 300 for determining the refractive index of an optical sample according to an embodiment. The method 300 illustrated here is similar to the method described above. Figure 3 The methods shown are the same or similar, except that the method 300 in the embodiments described herein includes additional and / or optional steps.

[0049] In this embodiment, there is an emission step 500 before the detection step 305. In the emission step 500, a collimated light beam is emitted from a light source toward the first surface of the sample.

[0050] In this embodiment, the light beam is emitted at a right angle to the first surface of the sample in the emission step 500. In another embodiment, the light beam may be emitted at an angle between 80 and 100 degrees relative to the first surface of the sample.

[0051] Furthermore, in this embodiment, method 300 further comprises an optional step 505 of orienting the mirror surface of the mirror element orthogonally to the light beam. Orienting the mirror surface is always required when rotation of the wedge-shaped specimen or the autocollimator is technically impossible. The orientation step is performed without a specimen in the light path.

[0052] In this embodiment, as an example only, the detection step 305 is performed after the emission step 500. In this embodiment, a control step 510 is further performed simultaneously with the detection step. In the control step 510, as an example only, the sample is controlled to rotate around a rotation axis parallel to the light beam, so as to detect the reflected light beam at different rotation positions of the sample.

[0053] In this case, as an example only, the first reflected light beam, the second reflected light beam and the third reflected light beam are detected simultaneously in the detection step 305 .

[0054] Furthermore, in one embodiment, the detecting step 305 , the determining step 310 , and the calculating step 315 are repeatedly performed, wherein when the detecting step 305 is repeated, the reflected light beam is interpreted as a reflection of a different wavelength.

[0055] In other words, this figure and the above Figure 3 The illustrated method 300 for measuring the refractive index of a wedge-shaped specimen can be described as follows: First, a collimated light beam is emitted to a first side of the sample, and in an optional preparatory step, the mirror surface of the mirror element is oriented orthogonally to the incident collimated light beam, without the sample being in the light path. In this case, purely by way of example, the incident collimated light beam strikes the first side of the sample at an angle of about 90°. In one embodiment, the sample is rotated during this process about an axis parallel to the incident collimated light beam. In this case, the mirror surface orientation step is omitted.

[0056] Subsequently, a first light beam reflected at a first surface of the sample is detected. In addition, a second light beam reflected at an inner side of a second surface of the sample is detected, wherein the second surface forms a wedge angle with the first surface. A first angle α is determined between the first reflected light beam and the second reflected light beam.

[0057] In addition, a third light beam reflected by a reflector sequentially arranged behind the second surface of the sample along the light beam direction is detected, and before that, the third light beam passes through the sample again after being reflected on the reflector surface. The second angle β is determined by means of the third reflected light beam. In one embodiment, the detection of the first, second and third reflected light beams is performed simultaneously.

[0058] Then the refractive index of the wedge-shaped sample is calculated according to the first and second angles. In one embodiment, the refractive index is measured sequentially at a plurality of different wavelengths.

[0059] Figure 6aSchematic diagram of an embodiment of a measuring system 600 for measuring the refractive index of an optical sample 100 is shown. The measuring system 600 includes a light source 225 for emitting a light beam 110, a receiving element 610 for receiving the sample 100, a reflector element 420, and a device 620, which is designed to control the refractive index of the optical sample 100 as described above. Figure 3 and Figure 5 The method for measuring the refractive index of the optical sample 100.

[0060] In one embodiment, the light source 225 is designed as part of the autocollimator 200 for collimating the light emitted by the light source 225 and directing it to the specimen 100. In this case, the autocollimator includes an exemplary polychromatic light source 225 and a plurality of replaceable and optional optical filters in the optical path for filtering the light emitted by the light source 225.

[0061] The reflector element 420 is arranged on the side of the accommodation element 610 opposite to the light source 225. In other words, the autocollimator, the sample holder and the reflector are arranged in sequence. In this embodiment, the accommodation element 610 is designed as a mechanical holder for the wedge-shaped sample 100, and a rotatable mounting method is only used as an example. Similarly, in one embodiment, the autocollimator 200 with the light source 225 and the reflector element 420 can also rotate around a common axis 630.

[0062] By way of example only, the reflector element 420 may be brought into the light path by a moving device and may optionally include an adjustable aperture diaphragm. Furthermore, the surface of the reflector and the surface of the sample may be designed to have similar degrees of reflection. However, it is important to ensure that the reflection occurring on the sample surface can be distinguished from the reflection occurring on the reflector surface so that the detected signal can be assigned to the corresponding light beam. For this purpose, it is helpful to know the reflectivity of the sample for the desired wavelength. With the aid of an adjustable aperture diaphragm, the intensity of the light reflected by the reflector surface can be adjusted, which helps to distinguish the light beams detected by the detector.

[0063] In one embodiment, in addition to outputting light through the light source, the device 620 is also only exemplarily designed to control the objective lens of the autocollimator to perform an exemplary movement parallel to its optical axis. As a supplementary solution or alternative solution, the rotation of the accommodating element 610 or the rotation of the autocollimator 200 and the reflector element 420 can also be controlled.

[0064] Figure 6b FIG. 6 is a schematic diagram showing an embodiment of a measurement system 600 for measuring the refractive index of an optical sample 100. Figure 6a The illustrated embodiment of the measurement system 600 is different. Figure 6b The measuring system 600 shown is also provided with a sensor 650 for detecting the tilt angle δ, the result of which is also considered or processed in the device 620 as described above. Figure 6b The measuring system 600 shown is expanded by way of example with the following features, namely: the first angle α is determined with the aid of a first light beam reflected on the hypotenuse of the sample, and the measuring device is expanded with an additional sensor 650 (referred to herein as a tilt sensor), which is used to detect the tilt of the side 102 relative to the reference axis (optical axis) of the light beam 110.

[0065] In other words, the measurement system 600 introduced herein and the methods that can be implemented using the system can be described as follows: The measuring system 600 comprises an autocollimator for illuminating the sample 100 and for detecting reflections occurring on each sample surface. A graticule which can be designed as a pinhole or a cross is provided on the illumination arm of the autocollimator. The detection arm comprises, for example, a CMOS camera or a CCD camera. The light source 225 is, for example, multi-color and is implemented as a white light LED. In order to adjust one or more measurement wavelengths, the autocollimator or the light source unit may have a replaceable optical filter. The objective lens 210 of the autocollimator may be designed to be able to move linearly to compensate for longitudinal chromatic aberration.

[0066] The sample 100 is fixed on a suitable support. The support can optionally be mounted so that it can be rotated about an axis of rotation parallel to the optical axis of the autocollimator, so that the tilt between the rotation axis of the sample support and the mirror surface or the tilt of the mirror relative to the optical axis of the autocollimator can be mathematically compensated. As an alternative to rotating the sample support, the autocollimator can also be rotated together with the mirror about the corresponding common axis 630. Without rotating the sample support, the mirror surface should be oriented towards the autocollimator in a preparation step or the residual error of the tilt of the mirror surface relative to the optical axis of the autocollimator should be determined. This preparation step is carried out without the sample 100.

[0067] As an alternative, the sample 100 can also be placed on a sample stage. If this embodiment is adopted, the autocollimator will be advantageously located below the sample, the reflector is located above the sample, and the wedge mirror is preferably placed on the sample stage in a manner that one of its long sides is against the sample stage.

[0068] In addition, the reflector can be rotated into or out of the light path by means of a movable bracket.

[0069] Furthermore, the reflectivity of the mirror surface should advantageously be of the same order of magnitude as the reflectivity of the sample surface, so that reflections on each surface can be detected without adjusting the camera integration time. The mirror can optionally be equipped with an adjustable aperture diaphragm for limiting the light beam. This allows the contrast between the detected reflections to be adjusted by varying the intensity of the reflected light beam.

[0070] Figure 7aThe first camera image of the three reflected beams 401, 402, 413 is shown by way of example. The corresponding detection signals are denoted by the symbols 701, 702, 713. From the distance between the signals 701 and 702, the angle α in this example can be determined. In this case, if the angle β is to be determined, the mirror must be oriented orthogonally to the optical axis of the autocollimator. The angle β can then be determined from the distance between the signal 713 and a reference signal (not shown), which is detected without a sample in the light path.

[0071] Figure 7b The second camera image of the reflected light beam is shown by way of example. In this case, the rotation angle (azimuth) of the sample is 180°. In addition to the signals 701, 702, 713, additional signals 701', 702' and 713' are detected on the circular trajectory of each impact circle. As shown in the figure, the angle β can be determined by means of the connection of the signals 713 and 713', which connection represents the diameter of the impact circle. The mirror is tilted only to linearly displace the impact circle of diameter 713-713' on the detector without changing the diameter and the angle β.

[0072] Figure 8 A schematic cross-sectional view of an embodiment of a receiving element 610 for receiving a liquid sample 100 is shown. The receiving element 610 shown here is consistent with or similar to the receiving element described in the aforementioned Fig. 6. In this embodiment, the receiving element 610 is designed to receive a sample 100, which is merely a liquid.

[0073] The measurement system described in FIG. 6 or the measurement system described in FIG. Figure 3 and Figure 5 The method described in can also be used to measure the refractive index of liquids. To this end, as shown in the figure, the liquid to be measured should be stabilized in an appropriate manner. For example, the liquid is clamped between two plane parallel plates of the accommodating element 610 so that the liquid is wedge-shaped. In this way, measurements similar to those of solids can be performed. In this case, the sample 100 should remain stationary, while the autocollimator should rotate together with the reflector. In addition, it must be ensured that the plane parallel plates have excellent flatness.

[0074] When an embodiment includes an “and / or” relationship between a first feature and a second feature, it should be understood that the embodiment has the first feature and the second feature according to one embodiment, and has either only the first feature or only the second feature according to another embodiment.

Claims

1. A method (300) for determining the refractive index of an optical sample (100), wherein the sample (100) is assumed to include at least a first surface (102) and a second surface (104) arranged at a wedge angle (ω) with respect to the first surface (102), wherein the method (300) comprises the following steps (305, 310, 315): Detecting (305) a first reflected light beam (401), a second reflected light beam (402), and a third reflected light beam (413), wherein the first reflected light beam (401) represents a light beam reflected at an outer side (405) of the first surface (102), the second reflected light beam (402) represents a light beam reflected at an inner side (410) of the second surface (104), and the third reflected light beam (413) represents a light beam reflected at a reflective mirror surface (415) of a reflective mirror element (420), wherein the reflective mirror element (420) is interpreted as being arranged at a side of the sample (100) opposite to a light source (225) emitting the light beam (110); Determining (310) a first angle (α) by means of the first reflected light beam (401) and / or the second reflected light beam (402) and determining a second angle (β) by means of the third reflected light beam (413); and calculating (315) the refractive index using the first angle (α) and the second angle (β), It is characterized in that A step (510) of controlling the sample (100) to rotate around a rotation axis parallel to the light beam (110), wherein the rotating step (510) is performed simultaneously with the detecting step (305).

2. The method (300) according to claim 1, characterized in that: The method comprises the step (500) of emitting a collimated light beam from the light source (225) toward the first surface (102). Specifically, in the emitting step (500), the light beam (110) is emitted at an angle between 80 degrees and 100 degrees, specifically at a right angle, relative to the first surface (102) of the sample (100).

3. The method (300) according to claim 2, characterized in that: In the detection step (305), the tilt angle (δ) of the second surface (104) relative to the incident direction of the light beam (110) is detected, and in the calculation step (315), the refractive index is calculated taking into account the tilt angle (δ).

4. The method (300) according to any one of the preceding claims, characterized in that The step (505) of orienting a reflector surface (415) of the reflector element (420) substantially orthogonal to the light beam (110) is included.

5. The method (300) according to any one of the preceding claims, characterized in that In the detection step (305), the first reflected light beam (401), the second reflected light beam (402) and the third reflected light beam (413) are detected simultaneously.

6. The method (300) according to any one of the preceding claims, characterized in that The detecting step, the determining step and the calculating step (305, 310, 315) are repeatedly performed, wherein when the detecting step (305) is repeatedly performed, the reflected light beams (401, 402, 413) are interpreted as reflections of different wavelengths.

7. The method (300) according to any one of the preceding claims, characterized in that In the emitting step (500), the light beam (110) is emitted at an angle between 80 and 100 degrees, in particular at a right angle, relative to the first face (102) of the sample (100).

8. An apparatus (620) designed to execute and / or control the steps (305, 310, 315) of the method (300) as claimed in any one of the preceding claims in a corresponding unit.

9. A measuring system (600) for measuring the refractive index of an optical sample (100), characterized in that: The measurement system (600) has the following features: Device (620) designed to perform and / or control the steps (305, 310, 315) of the method (300) as claimed in any one of the preceding claims in a corresponding unit, wherein the device (620) is designed to control a light source (225) and / or a receiving element (610) and / or a reflector element (420) of the measuring system (600), wherein the device (620) is designed to control a rotation of the sample (100) around a rotation axis parallel to the light beam (110), wherein the rotation is performed simultaneously with the detection step; The light source (225) for emitting a light beam (110); The containing element (610) is used to contain the sample (100); and The reflector element (420) is arranged on a side of the accommodating element (610) opposite to the light source (225).

10. The measuring system (600) according to claim 9, characterized in that An automatic collimator (200) comprising the light source (225) is provided, wherein the automatic collimator (200) comprises a plurality of replaceable optical filters for filtering the light beam (110), and in particular, wherein the automatic collimator (200) has at least one optical element (210) which is movable parallel to the optical axis of the automatic collimator (200).

11. The measuring system (600) according to any one of claims 9 or 10, characterized in that The reflector element (420) has an adjustable aperture stop, and / or wherein the reflector element (420) is pivotable into the optical path of the light beam (110).

12. The measuring system (600) according to any one of claims 9 to 11, characterized in that The accommodating element (610) is installed in a rotatable manner.

13. The measuring system (600) according to any one of claims 9 to 12, characterized in that The light source (225) and the reflector element (420) are rotatable about a common axis (630).

14. The measuring system (600) according to any one of claims 9 to 13, characterized in that The receiving element (610) is designed to receive liquid and / or solid.

15. A computer program adapted to perform and / or control the steps of the method (300) as claimed in any one of the preceding claims 1 to 7 when the computer program is executed on a computer or a device.

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