DOUBLE-MIRROR SHEAR INTERFEROMETER

Abstract

A measuring arrangement for non-destructive measurement of an object surface by interferometric measuring methods, wherein light strikes the measuring arrangement as a light beam reflected from the surface, including a diaphragm with an aperture; mirror arrangement with two mirrors having mirror surfaces; a camera lens and camera; wherein the incoming light beam passes the diaphragm and diffracts before hitting the mirror arrangement and splits and deflects into two partial beams, which reach and interfere in the camera; wherein the light beam passes the camera lens in front of the camera in beam direction; and wherein one mirror of the mirror arrangement is rotatable relative to the other; and wherein the camera includes a camera chip with a local sampling frequency and the diaphragm diffracts the incoming light beam as it passes through such that its spatial frequency corresponds at most to the maximum camera chip local sampling frequency during detection.

Claims

1-15. (canceled)

16. A measuring arrangement for non-destructive measurement of the surface of an object by means of interferometric measuring methods, wherein light strikes the measuring arrangement as a light beam reflected from the surface, comprising a diaphragm with an aperture; a mirror arrangement with two mirrors each having a mirror surface, one of which is a partially transparent partial mirror and one of which is a full mirror which is arranged behind the partially transparent partial mirror in the direction of radiation (S); a camera lens and a camera; wherein the incoming light beam passes the diaphragm and is diffracted in the process before it hits the mirror arrangement and is split and deflected therein into two partial beams, which subsequently reach the camera and interfere in the camera; wherein the light beam passes the camera lens in front of the camera in beam direction (S); and wherein one of the mirrors of the mirror arrangement is rotatable relative to the other mirror such that the two mirrors include a non-zero angle Q in a plane normal to the mirror surfaces; and wherein the camera comprises a camera chip with a local sampling frequency and the diaphragm is designed such that the incoming light beam is diffracted as it passes through the diaphragm such that its spatial frequency f_.sub.light corresponds at most to the maximum local sampling frequency of the camera chip f_.sub.max_camera during detection on the camera chip.

17. The measuring arrangement according to claim 16, wherein one of the mirrors of the mirror arrangement is aligned in such a manner that the light beam incident on the mirror arrangement is reflected by an angle in the direction of the camera and impinges the camera, the angle being at least 70.

18. The measuring arrangement according to claim 17, wherein the angle is at least 80.

19. The measuring arrangement according to claim 17, wherein the angle is 90.

20. The measuring arrangement according to claim 17, wherein the angle is at most 110.

21. The measuring arrangement according to claim 17, wherein the angle is at most 100.

22. The measuring arrangement according to claim 16, wherein the two mirror surfaces of the mirrors of the mirror arrangement have a distance x between them, wherein the distance x is the distance between the mirror surfaces of the two mirrors directed towards the incident light beam orthogonal to the mirror surface, and the distance x is greater than or equal to 70% of the width of the aperture of the diaphragm and less than seven times the aperture of the diaphragm.

23. The measuring arrangement according to claim 16, wherein the angle lies in a range between 0.001 and 20.

24. The measuring arrangement according to claim 16, wherein the angle lies in a range between 0.01 and 10.

25. The measuring arrangement according to claim 16, wherein the angle lies in a range between 0.1 and 5.

26. The measuring arrangement according to claim 16, wherein the angle lies in a range between 0.2 and 1.

27. The measuring arrangement according to claim 16, wherein the angle lies in a range between 0.5 and 1.

28. The measuring arrangement according to claim 16, wherein the full mirror of the mirror arrangement is rotatable relative to the partial mirror.

29. The measuring arrangement according to claim 16, wherein the camera lens is arranged in front of the diaphragm in beam direction (S) or between the mirror arrangement and the camera.

30. The measuring arrangement according to claim 16, wherein the diaphragm comprises a slit with a slit width b, the maximum slit width b being less than or equal to the product of wavelength of the light beam, focal length f.sub.lens of the camera lens and maximum local sampling frequency of the camera chip f_.sub.max_camera.

31. The measuring arrangement according to claim 16, wherein the diaphragm has a circular aperture with a diameter d, the maximum diameter d being less than or equal to the product of 1.22 times the wavelength of the light beam, focal length f.sub.lens of the camera lens and maximum local sampling frequency of the camera chip f_.sub.max_camera.

32. The measuring arrangement to claim 16, wherein the diaphragm is a grating diaphragm or the diaphragm comprises a polarization filter or a frequency filter.

33. The measuring arrangement according to claim 16, wherein the partial mirror is designed to be polarizing, so that a first partial beam is reflected and an orthogonally polarized second partial beam is transmitted, the second partial beam being reflected at the full mirror before it reaches the camera.

34. The measuring arrangement according to claim 33, wherein a depolarization element is arranged between the mirror arrangement and the camera in order to render the two orthogonally polarized partial beams of the light capable of interference for the camera.

35. The measuring arrangement according to claim 16, wherein the partial mirror has a reflectance which is different from the transmittance, the transmittance being greater than the reflectance.

36. The measuring arrangement according to claim 16, wherein a control and evaluation unit receives and processes measurement signals generated by the camera, so that a measurement variable characteristic of the surface of the object to be measured is determined from the measurement signals of the interfering partial beams, which measurement variable permits a statement to be made about properties of the surface.

37. A measuring system with a measuring arrangement according to claim 16 and with an evaluation unit which receives and processes measuring signals generated by the camera, so that a measured variable characteristic of the surface of the object to be measured is determined from the measuring signals of the interfering partial beams, which allows a statement to be made about properties of the surface.

38. A method for non-destructive measurement of the surface of an object by interferometric measurement techniques and for determining a property of the surface of an object, comprising the following steps: providing a measuring arrangement with a diaphragm, a mirror arrangement arranged behind the diaphragm with two mirrors each with a mirror surface, one of which is a partially transparent partial mirror and one of which is a full mirror arranged behind the partially transparent partial mirror in the direction of radiation (S), a camera lens and a camera with a camera chip with a local sampling frequency; generating a light beam and irradiating the surface of the object to be measured; guiding the light beam reflected from the surface through the diaphragm and directly onto the mirror arrangement arranged behind it; adjusting a desired angle 3 between the partial mirror and the full mirror by rotating one of the mirrors in such a manner that the light beam is split into two partial beams, both of which are directed to the camera; recording of the two partial beams by means of the camera and generating a measurement signal of the interferometric superposition; adjusting the diaphragm in such a manner that the incoming light beam is diffracted as it passes through the diaphragm in such a way that its spatial frequency f_.sub.light corresponds at most to the maximum local sampling frequency of the camera chip f_.sub.max_camera during detection on the camera chip; evaluating the measurement signal and determining a measured variable characteristic of the surface of the object to be measured, which allows a statement to be made about the properties of the surface.

Description

[0048] FIG. 1 a measuring arrangement according to the invention with a diaphragm and a mirror arrangement;

[0049] FIG. 2 a measuring system for measuring the surface of an object comprising a measuring arrangement, a light source and an evaluation and control unit.

[0050] A measuring arrangement 10 according to the invention comprises a diaphragm 20 with an aperture 21, a mirror arrangement 30 with two mirrors 32, a camera 40 and a camera lens 42.

[0051] One mirror 32 of the mirror arrangement 30 is designed as a partially transparent partial mirror 34, while the second mirror 32 is a full mirror 36. The full mirror 36 is arranged behind the partial mirror 34 in the direction of radiation (arrow) S of the incident light beam 100. In the embodiment shown here, the partial mirror 34 is rotated by an angle relative to the full mirror 36, so that the two mirrors 32 are no longer arranged in parallel. The two mirrors 32 are spaced apart from each other and have a distance x. The distance x is the distance between the mirror surfaces 38 of the mirrors 32 when the two mirrors 32 are arranged parallel to each other.

[0052] When a light beam 100 hits the measuring arrangement 10, it first passes the diaphragm 20 and is then directed straight onto the mirror arrangement 30. This is preferably done without interposing any other optical elements. The light beam 100 hits the mirror surface 38 of the partial mirror 34 and is partially reflected there into a first partial beam 110, which is deflected in the direction of the camera. The partial beam 110 passes through the camera lens 42 to the camera 40, where it strikes a camera chip not shown here.

[0053] A part of the light beam 100 is transmitted through the partial mirror 34 and then impinges the mirror surface 38 of the full mirror 36. This part of the light beam 100 is now reflected and reaches the camera 40 as the second partial beam 120. The two partial beams 110 and 120 interfere with each other in the camera 40, whereby the two partial beams do not strike the camera 40 parallel to each other. The carrier frequency required for the spatial phase shift is generated by the distance x between the two mirrors 32. This results in a lateral shift to the beam direction. By rotating one of the mirrors 32 and the distance between the two mirrors, the shear angle of the two mirror planes to each other is also changed at the same time. The adjustment for a measurement can therefore be made very sensitively and is variable or possible in small steps. Fine adjustment of the arrangement can be carried out easily.

[0054] The measuring arrangement shown in FIG. 1 provides for the partial mirror 34 to be rotated relative to the full mirror 36. In the embodiment shown here, the light beam 100 incident on the full mirror 36 is reflected by an angle at the full mirror 36 and reaches the camera 40 as a second partial beam 120. In the example shown here, the angle is equal or almost equal to 90.

[0055] Alternatively and particularly preferably, the partial mirror 34 is fixed and the full mirror 36 can be rotated, so that the angle between the light beam 100 incident on the partial mirror 34 and the reflected first light beam 110 is in the range between 7 and 110, preferably 902, due to the suitable arrangement of the partial mirror 34.

[0056] FIG. 2 shows a measuring system 12 with the measuring arrangement 10 of FIG. 1, a housing 14 for the measuring arrangement 10, a light source in the form of a laser 16 and a control and evaluation unit 18, which on the one hand can control and regulate the laser 16 and on the other hand receives measuring signals from the camera 40 and processes them into measured variables characteristic of the surface of the object 22 to be measured.

[0057] A light beam generated by the laser 16 is directed onto a surface 24 of the object to be measured and reflected here in the direction of the measuring arrangement. The reflected light beam 100 enters the housing 14 through an opening 15 and first passes the diaphragm 20 of the measuring arrangement 10 before the light beam 100 hits the mirror arrangement 30. Here, the light beam 100 is split into a first partial beam 110 and a second partial beam 120 in the manner described above, whereby both partial beams do not hit the camera 40 parallel to each other and interfere with each other there. By rotating the two mirrors 32 relative to each other and by the offset caused by the distance x between the two mirrors 32, the necessary shear is generated, which is required for the shearographic evaluation.

[0058] The present measuring arrangement therefore has the advantage that it is very inexpensive and simple in design. Apart from the camera 40 with the camera lens 42, only a diaphragm and a double-mirror arrangement with a partially transparent partial mirror 34, for example a semi-transparent half mirror, and a full mirror 36 are required. Since one of the mirrors 32, for example, as shown here, the partial mirror 34, is tilted by an angle relative to the full mirror 36, a shear is generated, which is necessary for shearography. In the present embodiment example, the partial mirror is therefore rotated out of the 45 position in which the full mirror 36 is located. The two reflected components (first partial beam 110 and second partial beam 120 of the partial mirror 34 or full mirror 36) are merged on their way to the camera, but at the latest in the camera, so that the desired interference occurs. The resulting interference pattern is imaged in the camera so that a shearographic measurement can be carried out. The lateral offset (distance x) between the two mirrors creates a virtual double slit from the camera's point of view. As a result, the superposition of the two light components (first partial beam, second partial beam) contains an additional carrier frequency that is used for spatial phase shifting.

[0059] As only a few components are used, a very small and compact design is possible. The measuring arrangement as a whole is very robust and also mobile and can be used easily in many different locations.

[0060] FIG. 2 shows an optional filter 44, which is arranged in the beam path in front of the diaphragm 20. The filter 44 is an optical filter and can, for example, be a color filter or polarization filter. It can also optionally be positioned between the diaphragm 20 and the mirror arrangement 30 or between the mirror arrangement 30 and the camera 40. However, there must be no component between the diaphragm and the mirror arrangement that diffracts, splits or reflects the measuring light. The measurement light is the laser light reflected by the measurement object, which is interferometrically superimposed in the camera.

[0061] The invention has been comprehensively described and explained with reference to the drawings and description. The description and explanation are intended to be exemplary and not limiting. The invention is not limited to the disclosed embodiments. Other embodiments or variations will become apparent to those skilled in the art upon use of the present invention and upon detailed analysis of the drawings, the disclosure and the following claims.

[0062] In the claims, the words comprising and with do not exclude other elements or steps. The indefinite article a or an does not exclude a plurality. A single element or unit may fulfill the functions of several items recited in the claims. An element, a unit, a device, and a system may partially or completely be implemented by corresponding hardware and/or software. The mere fact that certain measures are recited in several different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0063] Reference signs in the patent claims are not to be understood restrictively.

REFERENCE SIGNS

[0064] 10 Measuring arrangement [0065] 12 Measuring system [0066] 14 Housing [0067] 15 Opening [0068] 16 Laser [0069] 18 Control and evaluation unit [0070] 20 Diaphragm [0071] 21 Aperture [0072] 22 Object [0073] 24 Surface [0074] 25 Mirror arrangement [0075] 32 Mirror [0076] 34 Partial mirror [0077] 36 Full mirror [0078] 38 Mirror surface [0079] 40 Camera [0080] 42 Camera lens [0081] 44 Filter [0082] 100 Light beam [0083] 110 First partial beam [0084] 120 Second partial beam [0085] S Direction of the light beam [0086] X Distance