Device For Optically Measuring An Object

Abstract

What is proposed is a device (1) for optically measuring an object, comprising an interferometer (2) having a measurement arm (21), wherein the measurement arm (21) is provided for optically measuring the object, and comprising a focusing element (3) arranged within the measurement arm (21). According to the invention, the device (1) comprises a first retardation element (4) arranged within the measurement arm (21) and downstream of the focusing element (3), wherein the first retardation element (4) has a movable displacement element (42), by means of which the optical path length of the beam path of the measurement arm (21) is variable.

Claims

1. A device (1) for optically measuring an object, comprising an interferometer (2) having a measurement arm (21), wherein the measurement arm (21) is provided for optically measuring the object, and a focusing element (3) arranged within the measurement arm (21), characterized in that the device (1) comprises a first retardation element (4) arranged within the measurement arm (21) and downstream of the focusing element (3), wherein the first retardation element (4) has a movable displacement element (42), by means of which the optical path length of the beam path of the measurement arm (21) is variable.

2. The device (1) as claimed in claim 1, characterized in that the interferometer (2) is embodied as a Michelson-Morley interferometer.

3. The device (1) as claimed in claim 1, characterized in that the first retardation element (4) comprises at least two deflection elements (40, 41), in particular prisms or mirrors, which are spaced apart from one another, wherein the deflection elements (40, 41), in addition to their being spaced apart, have an offset with respect to one another and the spacing of the deflection elements (40, 41) is variable by means of the movable displacement element (42).

4. The device (1) as claimed in claim 3, characterized in that the deflection elements (40, 41) are arranged in a manner rotated with respect to one another in such a way that the beam path of the first retardation element (4) extends outside a plane.

5. The device (1) as claimed in claim 1, characterized in that at least one area of the first retardation element (4) is at least partly reflectively coated in such a way that a light beam (400) passing through the first retardation element (4) is able to be returned at least partly to the interferometer (2).

6. The device (1) as claimed in claim 1, characterized in that said device comprises a sensor for detecting the movement of the movable displacement element (42).

7. The device (1) as claimed in claim 1 characterized in that said device comprises a beam splitter element (6) for splitting the measurement arm (21) into a first and second partial measurement arm (61, 62), wherein the beam splitter element (6) is arranged downstream of the first retardation element (4), and the partial measurement arms (61, 62) are provided for optically measuring the object.

8. The device (1) as claimed in claim 7, characterized in that a respective shutter (8) is arranged within the first and second partial measurement arms (61, 62).

9. The device (1) as claimed in claim 7, characterized in that said device comprises an optical retardation section (10) for increasing the optical path length of the first partial measurement arm (61) relative to the optical path length of the second partial measurement arm (62).

10. The device (1) as claimed in claim 9, characterized in that a material (12) having a refractive index of greater than 1, in particular greater than 1.4, is arranged within the optical retardation section (10).

11. The device (1) as claimed in claim 7, characterized in that the beam splitter element (6) is designed for splitting the measurement arm (21) into the first and second partial measurement arms (61, 62), and into a third and a fourth partial measurement arm.

12. The device (1) as claimed in claim 1, characterized in that said device comprises a second retardation element (5) and a beam splitter element (6) for splitting the measurement arm (21) into a first and a second partial measurement arm (61, 62), wherein the beam splitter element (6) is arranged upstream of the retardation elements (4, 5), and the first retardation element (4) is arranged within the first partial measurement arm (61) and the second retardation element (5) is arranged within the second partial measurement arm (62).

13. The device (1) as claimed in claim 12, characterized in that the optical path lengths of the retardation elements (4, 5) are variable together and/or separately from one another by means of the displacement element (42).

14. The device (1) as claimed in claim 12, characterized in that said device comprises an optical retardation section (10) for increasing the optical path length of the first partial measurement arm (61) relative to the optical path length of the second partial measurement arm (62).

15. The device (1) as claimed in claim 14, characterized in that a material (12) having a refractive index of greater than 1, in particular greater than 1.4, is arranged within the optical retardation section (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Further advantages, features and details of the invention are evident from the following exemplary embodiments described and also with reference to the drawing, in which, in a schematic fashion:

[0071] FIG. 1 shows a first configuration of a device according to the invention comprising a first retardation element;

[0072] FIG. 2 shows a configuration of the first retardation element;

[0073] FIG. 3 shows a second configuration of a device according to the invention comprising a first and a second partial measurement arm;

[0074] FIG. 4 shows a configuration of the device illustrated under FIG. 3;

[0075] FIG. 5 shows a further configuration of the device illustrated under FIG. 4;

[0076] FIG. 6 shows a third configuration of a device according to the invention comprising a first and a second retardation element;

[0077] FIG. 7 shows a configuration of the device illustrated under FIG. 6;

[0078] FIG. 8 shows a further configuration of the device illustrated under FIG. 6; and

[0079] FIG. 9 shows a further configuration of the device illustrated under FIG. 6.

DETAILED DESCRIPTION

[0080] Elements that are of identical type, equivalent and/or act identically may be provided with the same reference signs in one figure and/or in the figures.

[0081] FIG. 1 shows a schematic first configuration of a device 1 according to the invention comprising a first retardation element 4. The device 1 constitutes a device of the first type within the meaning of the description.

[0082] The device 1 comprises an interferometer 2, which is embodied by way of example as a Michelson-Morley interferometer. The interferometer 2 has at least one coherent light source 14, in particular a laser. Furthermore, the interferometer 2 comprises a plurality of lens elements and mirrors and at least one beam splitter. The beam splitter of the interferometer 2 is provided for splitting the light beam or the light of the coherent light source 14 into a measurement beam and a reference beam. The measurement beam corresponds to at least one measurement arm 21 of the interferometer 2.

[0083] The device 1 furthermore comprises a focusing element 3, which is a focusing lens element, for example.

[0084] Furthermore, the device 1 has, according to the invention, the first retardation element 4. The first retardation element 4 is arranged downstream of the focusing element 3 within the measurement arm 21 and has at least one displaceable or movable displacement element 42. By means of the displacement element 42, the optical path length of the light beam (measurement beam) associated with the measurement arm 21 within the first retardation element 4 is variable, adjustable, controllable, regulatable and/or adaptable.

[0085] The first retardation element 4 has a first and a second deflection element 40, 41. In the first exemplary embodiment illustrated, the deflection elements 40, 41 are formed in each case by a prism. In this case, the prisms 40, 41 are spaced apart with respect to the direction of the measurement arm 21 and are arranged with an additional offset with respect to one another. As a result, the light beam associated with the measurement arm 21 is reflected back and forth multiply between the prisms 40, 41 before it leaves the device 1 and impinges on the object to be measured (not illustrated) or the surface thereof.

[0086] The measurement beam is reflected for example at least four times within the first and second deflection elements 40, 41 (prisms). In this case, two reflections within the first deflection element 40, which in total bring about a change in direction of the light beam by approximately 180, are followed by respectively two comparable reflections within the second deflection element 41. In this case, the light beam associated with the measurement arm 21 extends approximately in a plane. In other words, the beam path associated with the measurement arm 21 is formed approximately in a plane.

[0087] By means of the displacement element 42 provided according to the invention, in the exemplary embodiment illustrated, the second deflection element 41 can be displaced in the direction of the measurement arm 21 or parallel to the direction of the beam path associated with the measurement arm 21. In the case of a displacement or movement of the displacement element 42, the spacing between the first deflection element 40 and the second deflection element 41 is increased or decreased, such that the optical path length of the light beam is varied within the first retardation element 4. As a result, the device 1 symbolically forms a type of optical trombone.

[0088] By virtue of the variable optical path length of the light beam within the first retardation element 4, the size of the measurement spot associated with the measurement beam can be adapted. In this case, the adaptation is carried out in such a way that the size of the measurement spot on the object remains approximately constant independently of the spacing between the device 1 and the object. In other words, the device 1 ensures a constant size of the measurement spot even upon a change in the spacing between the device 1 and the object to be measured.

[0089] In this case, the first retardation element 4 is preferably arranged downstream of the focusing element 3. In other words, the light beam generated by the coherent light source 14 is firstly split into a reference beam and a measurement beam by means of the interferometer 2. The interference between said reference beam and the measurement beam is used during the detection of a measurement signal which underlies the optical measurement of the object. The measurement beam corresponds to the measurement arm 21 of the device 1. A reference beam corresponds to the reference arm of the interferometer 2. The measurement beam is firstly guided through the focusing element 3, which brings about a focusing of the measurement beam. After said focusing, the measurement beam is guided to the first retardation element 4. Within the first retardation element 4, said measurement beam is multiply reflected back and forth, wherein at least one of the deflection elements 40, 41 is displaced by a displacement by means of the displacement element 42 and the optical path length of the measurement beam is thus varied within the first retardation element 4. After passing through the first retardation element 4, the measurement beam is projected onto the surface of the object to be measured. The change in the optical path length and thus the adaptation of the device 1 to a movement or a different spacing with respect to the object to be measured is represented by means of the dashed extension of the measurement arm 21. Furthermore, the movability of the displacement element 42 is identified by the arrow 101.

[0090] FIG. 2 illustrates a configuration of the first retardation element 4.

[0091] In the configuration illustrated, the first retardation element 4 comprises a first deflection element 40, a second deflection element 41, a third deflection element 43 and a fourth deflection element 44, which are embodied in particular in each case as a prism. The first and third deflection elements 40, 43 and the second and fourth deflection elements 41, 44 are respectively arranged alongside one another. Furthermore, the second deflection element 41 and the fourth deflection element 44 are coupled to the displacement element 42 in such a way that they are jointly movable.

[0092] A light beam that enters the first retardation element 4 is reflected twice here within each of the deflection elements 40, 41, 43, 44, such that the measurement beam experiences in total a change in direction by 180 in each deflection element 40, 41, 43, 44.

[0093] An arrow 101 once again indicates the movability of the displacement element 42.

[0094] FIG. 3 illustrates a second configuration of a device according to the invention comprising a first and a second partial measurement arm 61, 62. FIG. 3 shows a configuration of the device illustrated under FIG. 1 inter alia with a first retardation element 4 in accordance with FIG. 2. In this case, the device 1 illustrated in FIG. 3 comprises the same elements as already in FIG. 1 and FIG. 2, respectively. Consequently, the statements made in respect of FIG. 1 and/or FIG. 2 can be applied directly to FIG. 3.

[0095] Supplementarily to FIG. 1 or FIG. 2, the device 1 illustrated in FIG. 3 has a beam splitter 6. The device 1 shown thus constitutes a device of the second type within the meaning of the description.

[0096] The beam splitter can be embodied as a polarization beam splitter and/or a mirror. By means of the beam splitter 6, the measurement arm 21 downstream of the first retardation element 4 is split into the first partial measurement arm 61 and a second partial measurement arm 62. In other words, the measurement beam downstream of the retardation element 4 is split into the first partial measurement beam 61 and the second partial measurement beam 62. The splitting can be on equal terms, that is to say that the beam splitter 6 is embodied in particular as a symmetrical 50/50 beam splitter. An asymmetrical splitting deviating therefrom can be provided.

[0097] The partial measurement arms 61, 62 extend in diametrical directions with respect to one another. An advantageous measurement of diameters or internal diameters of the object can be carried out as a result.

[0098] Shutters 8 are provided for differentiation of the partial measurement arms 61, 62 in an evaluation. Each of the partial measurement arms 61, 62 has one of the shutters 8. Switching between the partial measurements arms 61, 62 can advantageously be carried out as a result. A temporally separate or temporally spaced measurement of the object by means of the first partial measurement arm 61 or by means of the second partial measurement arm 62 is made possible as a result.

[0099] An end face 63 of the beam splitter 6 is reflectively coated in this case.

[0100] A retardation section 10 can be provided for improved separation or differentiation of the partial measurement arms 61, 62. A simultaneous measurement by means of the partial measurement arms 61, 62 is made possible as a result. A corresponding configuration of the device according to the invention which makes this possible is illustrated in FIG. 4.

[0101] FIG. 4 shows a configuration of the device illustrated under FIG. 3. Supplementarily to FIG. 3, the retardation section 10 is provided downstream of the beam splitter 6. In order to form the retardation section 10, the previously (see FIG. 3) reflectively coated end face 63 of the beam splitter 6 is arranged in a manner spaced apart therefrom. As a result, the first partial measurement beam 61 has an increased optical path length relative to the second partial measurement beam 62. In other words, the first partial measurement beam 61 is retarded relative to the second partial measurement beam 62. The beam axes of the partial measurement arms 61, 62 can advantageously be adjusted as a result. Furthermore, measurement deviations, for example as a result of a tilting of the device 1, can be reduced.

[0102] Furthermore, by means of a light reflected from the beam splitter 6 back into the retardation section 10, it is possible to determine the refractive index of the ambient medium of the device 1, as described above.

[0103] FIG. 5 illustrates a further configuration of the device illustrated under FIG. 4, which enables a distinguishability of the partial measurement arms 61, 62 by means of a material 10 arranged within the retardation section 10. In this case, the material 10 has a refractive index of greater than 1, in particular greater than 1.4, in particular greater than 1.5, in particular greater than 1.6, preferably greater than 2.0. The material 10 can preferably extend approximately over the entire retardation section 10. The material 10 can be embodied as a glass block.

[0104] Together with the material, the retardation section 10 leads to a frequency shift between the measurement signals associated with the partial measurement arms 61, 62. As a result, the partial measurement arms 61, 62 or their associated measurement signals can be separated in an improved manner in the frequency domain, that is to say with regard to their beat frequency, as a result of which a differentiation between the first and second partial measurement arms 61, 62, in particular in the case of simultaneous measurement, is made possible.

[0105] For the rest, FIG. 5 shows the same elements as already shown by FIG. 4. In particular, the refractive index of the ambient medium of the device 1 can be determined as already in FIG. 4.

[0106] The additional material 10 relative to FIG. 4 enables the separation of the partial measurement arms 61, 62 by way of their beat frequency. Furthermore, a tilting of the end mirror 63 provided at the end of the retardation section 10 makes it possible to reduce a tilting of the first and/or second partial measurement arm 61, 62 or of their associated beam axes or measurement axes.

[0107] FIG. 6 illustrates a third configuration of a device according to the invention comprising a first and a second retardation element 4, 5. The device 1 as shown constitutes a device of the third type within the meaning of the description.

[0108] In comparison with the devices illustrated under FIGS. 1 to 5, the device 1 illustrated comprises a first and a second retardation element 4, 5. Furthermore, the device 1 comprises a beam splitter 6 arranged upstream of the retardation elements 4, 5. The beam splitter 6 splits the measurement arm 21 into a first and a second partial measurement arm 61, 62. In other words, the splitting of the measurement arm 21 into the first and second partial measurement arms 61, 62 takes placein contrast to the device in FIGS. 3, 4 and 5upstream of the retardation elements 4, 5. The first retardation element 4 is arranged within the first partial measurement arm 61 and the second retardation element 5 is arranged within the second measurement arm 62. As a result, the device 1 symbolically forms an optical double trombone.

[0109] The further elements of the device 1 illustrated in FIG. 6 correspond to the elements in FIGS. 1 to 5.

[0110] Further deflection elements, in particular mirrors, for example as illustrated, can be provided for further deflection or alignment of the beam paths of the partial measurement arms 61, 62.

[0111] The retardation elements 4, 5 respectively have a displacement element 42, which are not coupled to one another here, such that the retardation elements 4, 5 are movable and variable with regard to their optical path length differently than one another. This enables in each case an approximately constant size of the measurement spot in different directions.

[0112] The changes in the optical path lengths are indicated symbolically by the arrows 101, 102.

[0113] Furthermore, the optical path length of the second partial measurement arm 62 is increased relative to the optical path length of the first partial measurement arm 61 upstream of the retardation elements 4, 5 by means of a retardation section 10. The retardation section 10 can be formed by means of mirrors, for example as illustrated. A spectral separation of the first and second partial measurement arms 61, 62 or of their associated beat frequencies or measurement signals can be effected by the retardation section 10. That is the case since the frequency shift of the beat frequencies that are assigned to the partial measurement arms 61, 62 is proportional to the retardation. As a result, the first and second partial measurement arms 61, 62 can advantageously be operated temporally in parallel. Furthermore, with regard to the retardation section 10, reference should be made to the explanations in respect of FIG. 5.

[0114] FIG. 7 shows a configuration of the device illustrated under FIG. 6.

[0115] The device illustrated in FIG. 7 shows substantially the same elements as the device under FIG. 6.

[0116] In comparison with FIG. 6, the retardation elements 4, 5 here have a common displacement element 42. As a result, the optical path lengths of the retardation elements 4, 5 can be jointly varied or adapted.

[0117] By means of the further deflection elements, for example mirrors, which are arranged downstream of the retardation elements 4, 5, a diametric measurement is made possible via the coupled partial measurement arms 61, 62.

[0118] FIG. 8 shows a further configuration of the device illustrated under FIG. 6 or FIG. 7. Here the retardation elements 4, 5 from FIG. 7 are replaced in each case by a retardation element configured in accordance with FIG. 2. In other words, each of the retardation elements 4, 5 has at least four deflection elements 40, 41, 42, 43, which are embodied in particular in each case as a prism.

[0119] FIG. 9 shows a further configuration of the device illustrated under FIG. 6 or FIG. 8.

[0120] In contrast to FIG. 8, the retardation elements 4, 5 are movable separately from one another. In other words, each of the retardation elements 4, 5 has at least one displacement element 42, which can be operated and thus moved separately from one another. For the rest, FIG. 9 shows the same elements as already shown by FIG. 6 or FIG. 8.

[0121] If the devices in FIGS. 6 to 9 have an additional beam splitter having an end face comparable to the devices in FIGS. 4 and 5 within the partial measurement arms 61, 62, then in the partial measurement arms it is possible to determine the respective refractive index of the ambient medium in the partial measurement arms 61, 62. It is thereby possible to determine a difference in the refractive index of the ambient medium in the partial measurement arms 61, 62 such that said difference can be taken into account in the measurement.

[0122] The present invention provides a type of optical trombone or double trombone by means of which an object can be measured in accordance with the basic principle of a laser radar. A major advantage of the present invention is that by means of the displacement of the at least one displacement element, said displacement being comparable to a trombone or double trombone, a constant size of the measurement spot on the surface of the object is achievable independently of the spacing between the object and the device.

[0123] Although the invention has been more specifically illustrated and described in detail by means of the preferred exemplary embodiments, nevertheless the invention is not restricted by the examples disclosed and other variations can be derived therefrom by the person skilled in the art, without departing from the scope of protection of the invention.