METHODS FOR CHARACTERIZING A LASER BEAM OF A LASER PROCESSING SYSTEM, DIAPHRAGM ASSEMBLY AND LASER PROCESSING SYSTEM

Abstract

The claimed embodiments relate to methods for characterizing a laser beam (24) of a laser processing system (30). The method includes a) providing an aperture arrangement (10) with a plurality of apertures (14) in a work plane (300) of the laser processing system (30) such that the apertures (14) extend within the work plane (300). The method also includes b) scanning the laser beam (24) along a scanning direction (200) parallel to the work plane (300) across the aperture arrangement (10) in such a way that the laser beam (24) at least partially sweeps over the apertures (14). The method also includes c) determining a respective energy of the laser beam (24) transmitted through the apertures (14) during the scanning process, and d) determining an extent of the laser beam (24) along the scanning direction (200) using the determined energy of the laser beam (24) transmitted through a first aperture (14a) of the plurality of apertures (14) and determining an energy parameter of the laser beam (24) on the basis of the determined energy of the laser beam (24) transmitted through a second aperture (14b) of the plurality of apertures (14). In this case, the first aperture (14a) has a predetermined extent along the scanning direction (200), which is smaller than the mean diameter of the laser beam (24) in the work plane (300). In addition, a second aperture (14b) has an extent that is larger than the laser beam (24) in the work plane (300) and is designed to transmit the laser beam (24) essentially completely.

Claims

1. A method for characterizing at least one laser beam (24) of a laser processing system (30), comprising: a) providing an aperture arrangement (10) with a plurality of apertures (14) in a work plane (300) of the laser processing system (30), in such a way that the apertures (14) extend within the work plane (300); b) scanning the laser beam (24) over the aperture arrangement (10) along a scanning direction (200) parallel to the work plane (300), in such a way that the laser beam (24) at least sweeps partly over the at least two of the apertures (14) successively in time; c) determining a respective energy of the laser beam (24) transmitted through the apertures (14) during the scanning procedure; d) determining an extent of the laser beam (24) along the scanning direction (200) on the basis of the determined energy of the laser beam (24) transmitted through a first aperture (14a) of the plurality of apertures (14) and determining an energy parameter of the laser beam (24) on the basis of the determined energy of the laser beam (24) transmitted through a second aperture (14b) of the plurality of apertures (14); the first aperture (14a) having a predetermined extent along the scanning direction (200) which is smaller than the mean diameter of the laser beam (24) in the work plane (300) and a second aperture (14b) having an extent which is greater than the laser beam (24) in the work plane (300) and which is designed to substantially fully transmit the laser beam (24).

2. The method as claimed in claim 1, wherein the aperture arrangement (10) further comprises a third aperture (14a) of the plurality of apertures (14) which has a predetermined extent along the scanning direction (200) which is smaller than the mean diameter of the laser beam (24) in the work plane (300) and which is arranged at a predetermined distance (100a, 100b) from the first aperture (14a) along the scanning direction (200), and wherein the method further comprises: determining an alignment parameter of the laser processing system (30) using the predetermined distance (100a, 100b) of the third aperture (14a) from the first aperture (14a).

3. The method as claimed in claim 2, wherein determining the extent of the laser beam (24) along the scanning direction (200) is further implemented on the basis of the determined energy of the laser beam (24) which has been transmitted through the third aperture (14a) and optionally comprises the calculation of a mean of the extents of the laser beam (24) determined on the basis of the first and the third aperture (14a).

4. The method as claimed in any one of the preceding claims, wherein the scanning of the laser beam (24) is implemented in a first scan portion and in a second scan portion, the scanning direction (200) in the first scan portion running along a first dimension parallel to the work plane (300) and the scanning direction (200) in the second scan portion running along a second dimension parallel to the work plane (300).

5. The method as claimed in claim 4, wherein the first aperture (14a) has the predetermined extent along the scanning direction (200) in the first scan portion and wherein the aperture arrangement (10) has an additional aperture (14a) of the plurality of apertures (14) which has a predetermined extent along the scanning direction (200) in the second scan portion which is smaller than the mean diameter of the laser beam (24) in the work plane (300).

6. The method as claimed in claim 5, wherein the plurality of apertures (14) comprise at least two apertures (14a) for each scan portion, the at least two apertures having a predetermined extent along the respective scanning direction which is smaller than the mean diameter of the laser beam (24) in the work plane (300) and being arranged at a predetermined distance (100a, 100b) from one another along the respective scanning direction (200).

7. The method as claimed in any one of the preceding claims, wherein the method is used to characterize the laser beam and further used to characterize a target laser beam of the laser processing system (30).

8. The method as claimed in any one of the preceding claims, further comprising a determination of a fluence and/or an intensity of the laser beam (30) in the work plane (300) using the determined extent of the laser beam (24) and the determined energy parameter of the laser beam (24).

9. The method as claimed in any one of the preceding claims, further comprising an adjustment of a laser parameter and a repeated implementation of steps b) to d) after the adjustment of the laser parameter.

10. An aperture arrangement (10) for characterizing a laser beam (24) of a laser processing system (30), the aperture arrangement (10) being arrangeable in a work plane (300) of the laser processing system (30) and comprising the following: a stop (12) with a plurality of apertures (14); a first aperture (14a) of the plurality of apertures (14) which has a predetermined extent along a scanning direction (200) of the laser beam (24) which is smaller than the mean diameter of the laser beam (24) to be tested in the work plane (300); a second aperture (14b) of the plurality of apertures (14) which has an extent which is greater than the laser beam (24) to be tested and which is designed to substantially fully transmit the laser beam (24); at least one photodetector (16) which is arranged such that at least a part of the laser beam (24) which has been transmitted through the apertures (14) in the work plane (300) is detectable by means of the photodetector (16).

11. The aperture arrangement (10) as claimed in claim 10, wherein the aperture arrangement (10) is designed to absorb and/or reflect a part of the laser beam (24) which is not transmitted through the apertures (14).

12. The aperture arrangement (10) as claimed in claim 10 or 11, wherein the first aperture (14a) is in the form of a slot and the predetermined extent corresponds to a predetermined width of the slot, and/or wherein the second aperture (14b) is in the form of a round hole and has an extent which substantially corresponds to the extent of the laser beam (24).

13. The aperture arrangement (10) as claimed in any one of claims 10 to 12, wherein the aperture arrangement (10) has a plurality of slot-shaped apertures (14a), which have a predetermined width which corresponds to the predetermined extent and which are respectively arranged in pairs at a predetermined distance (100a, 100b) from one another.

14. The aperture arrangement (10) as claimed in any one of claims 10 to 13, wherein the stop (12) and the photodetector (16) are designed to be located parallel above one another and, optionally, the stop (12) and a target laser detector are designed to be located parallel above one another.

15. A laser processing system (30) for processing an object in a work plane (300) by means of a laser beam (24), comprising: a laser source (32) for providing the laser beam (24); a deflection device (36) by means of which the laser beam (24) is movable in the work plane (300) perpendicular to the propagation direction of the laser beam; an aperture arrangement (10) as claimed in any one of claims 7 to 10, the aperture arrangement (10) for characterizing the laser beam (24) being arrangeable in the laser processing system (30) in such a way that the apertures (14) are arranged in the work plane (300).

16. The laser processing system (30) as claimed in claim 15, wherein the laser processing system (30) is configured: to scan the laser beam (24) over the aperture arrangement (10) along a scanning direction (200) parallel to the work plane (300) by using the deflection device (36) so that the laser beam (24) at least sweeps partly over the apertures (14); to use the photodetector (16) to determine a respective energy of the laser beam (24) transmitted through the apertures (14) during the scanning procedure; to determine an extent of the laser beam (24) along the scanning direction (200) on the basis of the determined energy of the laser beam (24) transmitted through the first aperture (14a); and to determine an energy parameter of the laser beam (24) on the basis of the determined energy of the laser beam (24) transmitted through the second aperture.

17. The laser processing system (30) as claimed in claim 16, wherein the laser processing system (30) is in the form of a laser treatment system for ophthalmic surgery on an eye.

18. A method for characterizing a laser beam (24) of a laser processing system (30), comprising: a) providing an aperture arrangement with an aperture in a work plane of the laser processing system, in such a way that the aperture extends within the work plane, the aperture arrangement having at least two aperture edges which lie opposite one another at a predetermined distance and which extend parallel to one another, said aperture edges delimiting the aperture, and the aperture being larger than the laser beam in the work plane and being designed to substantially fully transmit the laser beam; b) scanning the laser beam over the aperture arrangement along a scanning direction parallel to the work plane, in such a way that the laser beam at least sweeps partly over a first aperture edge of the two aperture edges, the aperture and a second aperture edge of the two aperture edges successively in time; c) determining an energy of the laser beam transmitted through the aperture during the scanning procedure; d) determining an extent of the laser beam along the scanning direction on the basis of a transmitted energy curve when sweeping over the first and/or the second aperture edge by means of the laser beam and determining an energy parameter of the laser beam that has been substantially fully transmitted through the aperture; e) determining an alignment parameter of the laser processing system on the basis of the laser beam sweeping over the aperture edges arranged at the predetermined distance.

19. A method for characterizing a laser beam (1002) of a laser processing system (1000), the method comprising the steps of: determining an energy parameter of the laser beam (1002); providing a calibration device (1014) in a work plane (2000) of the laser processing system (1000) and having the laser beam (1002) impinge on the calibration device (1014) under the same conditions as are provided for the use of the laser beam (1002) for processing a processing object; determining a calibration parameter by means of the calibration device (1014) in the work plane (2000); providing the calibration device (1014) in a verification plane (2002) outside of the work plane (2000) and deflecting the laser beam (1002) in such a way that the laser beam (1002) impinges on the calibration device (1014) in the verification plane (2000); determining a verification parameter by means of the calibration device (1014) in the verification plane (2002); determining a deviation factor which characterizes a deviation between the calibration parameter and the verification parameter; characterizing the laser beam (1002) by means of the calibration device (1002) in the verification plane (2002) using the deviation factor.

20. The method as claimed in claim 19, wherein the calibration device (1014) comprises or is in the form of an aperture arrangement (10) as claimed in any one of claims 10 to 14.

21. The method as claimed in claim 19 or 20, wherein the calibration parameter and/or the verification parameter is determined using a method as claimed in any one of claim 1 to 9 or 18.

22. The method as claimed in any one of claims 19 to 21, wherein the calibration device (1014) provided in the verification plane (2002) is a calibration device (1014) that is formed separately from the calibration device (1014) provided in the work plane (2000) or wherein the same calibration device (1014) is provided for determining the calibration parameter in the work plane (2000) and is provided for determining the verification parameter in the verification plane.

23. The method as claimed in any one of claims 19 to 22, wherein the energy parameter is at least determined while the calibration parameter is determined and while the verification parameter is determined, and is optionally determined continuously.

24. The method as claimed in any one of claims 19 to 23, wherein the laser beam (1002) is only deflected by means of exactly one optical deflection element (1016).

25. The method as claimed in any one of claims 19 to 24, wherein the verification plane (2002) is arranged in such a way and/or the calibration device (1014) is provided in the verification plane (2002) in such a way that there is no spatial overlap between the calibration device (1014) provided in the verification plane (2002) and a processing object arranged in the work plane (2000).

26. The method as claimed in any one of claims 19 to 25, wherein the verification plane (2002) is at least partly arranged within the laser processing system (1000) and/or the calibration device (1014) is arranged within the laser processing system (1000), when provided in the verification plane (2002).

27. The method as claimed in any one of claims 19 to 28, wherein the energy parameter characterizes an energy of the laser beam (1002) and/or a power of the laser beam (1002) and/or an energy of a laser pulse and/or an energy of a series of laser pulses.

28. The method as claimed in any one of claims 19 to 27, wherein the determination of a calibration parameter comprises a determination of a fluence and/or an intensity of the laser beam in the work plane (2000) and/or wherein the determination of a verification parameter comprises a determination of a fluence and/or an intensity of the laser beam (1002) in the verification plane (2002).

29. The method as claimed in any one of claims 19 to 28, wherein the length of the optical path of the laser beam (1002) up to the work plane (2000) is substantially the same length as the optical path of the laser beam (1002) up to the verification plane.

30. A laser processing system (1000) for processing a processing object by means of a laser beam (1002), comprising: an energy sensor (1012) which is designed to determine an energy parameter of the laser beam (1002); a calibration device (1014) which is selectively arrangeable in a work plane (2000) of the laser processing system (1000) and being able to be impinged by the laser beam (1002) and which is selectively arrangeable in a verification plane (2002) outside of the work plane (2000) and being able to be impinged by the laser beam (1002); a deflection element (1016) which is arrangeable in the beam path of the laser beam (1002), in such a way that the deflection element (1016) deflects the laser beam, which is directed at the work plane (2000), into the verification plane (2002); the laser processing system (1000) being configured to arrange the calibration device (1014) in the work plane (2000) and determine a calibration parameter, to arrange the calibration device (1014) in the verification plane (2002) and determine a verification parameter, to determine a deviation factor which characterizes a deviation between the calibration parameter and the verification parameter, and to characterize the laser beam (1002) by means of the calibration device (1014) in the verification plane using the deviation factor.

31. The laser processing system (1000) as claimed in claim 30, wherein the calibration device (1014) in the arrangement in the verification plane (2002) is at least partly arranged within the laser processing device (1000).

32. The laser processing system (1000) as claimed in claim 30 or 31, wherein the laser processing system (1000) is designed to automatically switch the arrangement of the calibration device (1014) between the work plane (2000) and the verification plane (2002) and/or to automatically introduce the deflection element (1016) into the beam path of the laser beam (1002) and/or remove said deflection element from the beam path.

33. The laser processing device (1000) as claimed in any one of claims 30 to 32, wherein the calibration device (1014) comprises or is in the form of an aperture arrangement (10) as claimed in any one of claims 10 to 14.

34. A method for characterizing a laser beam (3022), comprising the steps of: having the laser beam (3022) impinge on a test object (3014), in such a way that the laser beam (3022) ablates some of the material of the test object (3014) at a test site (20) of the test object (3014); determining a change in the thickness of the test object (3014) at the test site (20) on account of the laser beam (3022) impinging thereon.

35. The method as claimed in claim 34, wherein the determination of the change in the thickness of the test object (3014) at the test site (3020) comprises a measurement of the thickness of the test object (3014) at the test site (3020) after the laser beam (3022) has impinged thereon and a comparison of the determined thickness with the thickness of the test object (3014) at the test site (3020) before the laser beam (3022) impinged thereon.

36. The method as claimed in claim 35, wherein the determination of a change in the thickness of the test object (3014) at the test site (3020) further comprises a measurement of the thickness of the test object (3014) at the test site (3020) before the laser beam (3022) impinges thereon.

37. The method as claimed in any one of claims 34 to 36, further comprising a configuration of the laser beam (3022) for ongoing and/or subsequent material processing by means of the laser beam on the basis of the determined change in the thickness of the test object (3014) at the test site (3020) on account of the laser beam (3022) impinging thereon.

38. The method as claimed in any one of claims 34 to 37, wherein the determination of the change in the thickness of the test object (3014) at the test site (3020) is implemented by means of an optical measurement of the thickness.

39. The method as claimed in claim 38, wherein the optical measurement comprises radiating optical radiation into the test object (3014) from a side of the test object (3014) that faces away from the direction of incidence of the laser beam and wherein the optical measurement optionally comprises a detection of a reflection and/or a scattering of the optical radiation at and/or in the test site (3020) of the test object (3014).

40. The method as claimed in claim 38 or 39, wherein the optical measurement comprises a measurement of the thickness of the test object (3014) at the test site (3020) by means of at least one confocal-chromatic sensor (3016).

41. The method as claimed in any one of claims 34 to 40, wherein the laser beam (3022) is provided as a pulsed laser beam (3022), the laser beam (3022) optionally impinging on the test object (3014) in such a way that a first laser pulse sequence ablates the portion of the material of the test object (3014) at the test site (3020) of the test object (3014) and, optionally, a further laser pulse sequence in each case impinges on the test object (3014) at other test sites (3020).

42. The method as claimed in claim 41, wherein laser pulse sequences with different energy impinge on the various test sites (3020).

43. The method as claimed in any one of claims 34 to 42, wherein the test object (3014) is at least partly formed from PMMA and is optionally dimensioned such that one or more test sites (3020) can be arranged on the test object (3014).

44. The method as claimed in any one of claims 34 to 43, wherein the test object (3014) is at least partly formed from a biological tissue and/or a gel-like substance; and/or wherein the determination of the change in the thickness of the test object (3014) is implemented with a position and/or orientation of the test object that has not been changed from when the laser beam (3022) impinged on the test object (3014).

45. The method as claimed in any one of claims 34 to 44, wherein the laser beam (3022) is provided as a laser beam (3022) for refractive correction of the cornea and is optionally provided by an excimer laser.

46. The method as claimed in any one of claims 19 and 22 to 29, wherein the calibration parameter and/or the verification parameter is determined using a method as claimed in any one of claims 34 to 45.

47. An apparatus (3010) for characterizing a laser beam (3022), the apparatus comprising: a test object holder (3012) which is designed to provide a test object (3014) for the laser beam (3022) to impinge on the test object (3014) so that some of the material of the test object (3014) is ablatable from a test site (3020) of the test object (3014) by means of the laser beam (3022); a measuring device (3018) which is configured to determine a change in the thickness of the test object (3014) at the test site (3020) on account of the laser beam (3022) impinging thereon.

48. The apparatus (3010) as claimed in claim 47, wherein the measuring device (3018) has at least one confocal-chromatic sensor (3016).

49. The apparatus (10) as claimed in claim 47 or 48, wherein the apparatus (3010) is designed to provide the test object (3014) and/or to interchange the test object (3014) and/or to change a positioning and/or orientation of the test object (3014) relative to the laser beam (3022) in order to have the laser beam (3022) impinge on a different test site (3020).

50. The method as claimed in any one of claims 19 and 22 to 29, wherein the calibration device (1014) comprises or is in the form of an apparatus (3010) as claimed in any one of claims 47 to 49.

51. An excimer laser comprising an apparatus (3010) for characterizing the laser beam (3022) as claimed in any one of claims 47 to 49 and/or an aperture arrangement (10) for characterizing a laser beam (24) as claimed in any one of claims 10 to 14.

52. An apparatus for refractive correction of the cornea, comprising an excimer laser as claimed in claim 51 and/or an apparatus (3010) for characterizing a laser beam (3022) as claimed in any one of claims 47 to 50.

53. The laser processing system (1000) as claimed in any one of claims 30 to 32, wherein the calibration device (1014) comprises or is in the form of an apparatus (3010) as claimed in any one of claims 47 to 49.

Description

[0132] Further details and advantages of optional embodiments should now be explained in more detail on the basis of the following examples and optional embodiments with reference being made to the figures, in which:

[0133] FIG. 1A to 1D show schematic illustrations of stop arrangements according to optional embodiments.

[0134] FIGS. 2A and 2B show two cross-sectional views of an aperture arrangement according to an optional embodiment.

[0135] FIG. 3 shows an explanation of an optional embodiment for determining the extent of the laser beam.

[0136] FIG. 4 shows a processing system according to an optional embodiment.

[0137] FIG. 5 shows a schematic illustration of the aperture arrangement according to the embodiment from FIG. 2 with further explanations.

[0138] FIGS. 6A and 6B show a laser processing system 1000 according to an optional embodiment in two different modes of operation for characterizing the laser beam 1002.

[0139] FIGS. 7A and 7B show schematic illustrations of a processing head 1020 of a laser processing system 1000 according to an optional embodiment.

[0140] FIGS. 8A and 8B show an apparatus for characterizing a laser beam according to an optional embodiment.

[0141] FIG. 9 shows an apparatus according to an optional embodiment for characterizing the laser beam during refractive correction on a cornea.

[0142] FIGS. 10A to 10C show various optional embodiments of test objects.

[0143] The same or similar elements in the various embodiments are denoted by the same reference signs in the following figures for reasons of simplicity.

[0144] FIG. 1A shows, in plan view, a schematic illustration of an aperture arrangement 10 according to an optional embodiment. In particular, a stop 12 of the aperture arrangement 10, in which a plurality of apertures 14 have been formed, can be identified in the plan view. The apertures 14 include in particular slot-like apertures 14a, which are respectively formed in pairs at a predetermined distance 100a or 100b from one another and which each have a predetermined width. According to the illustrated embodiment, the apertures 14a respectively have the same thickness and the distances 100a and 100b are also dimensioned to be the same. However, this may be different according to other embodiments.

[0145] Further, the aperture arrangement 10 has a further aperture 14b, which is in the form of a round hole and which is arranged centrally in the stop 12 in accordance with the embodiment shown. The slot-like apertures 14a are arranged around the central, round aperture 14b.

[0146] A photodetector 16 whose detector area 16 overlaps with the apertures 14 is arranged below the stop 12 (and therefore not identifiable in FIG. 1A). According to the embodiment shown, the photodetector 16 has a round detector area, the circumferential boundary of which is indicated by the dashed line. The photodetector 16 is designed to detect a laser beam, that is to say a work laser beam, and to determine the energy radiated onto the photodetector by the laser beam. The photodetector 16 is therefore designed for the wavelength of the laser beam. If use is made of a laser beam with a wavelength in the ultraviolet spectral range, the photodetector 16 is optionally also designed for the ultraviolet spectral range or the corresponding wavelength of the work beam. A rasterization of the photodetector 16, that is to say a pixelation, is not mandatory in this case but possible by all means. Rather, it is sufficient for the energy of the laser beam transmitted through an aperture or the apertures 14 to be able to be detected by means of the photodetector and for the energy to be able to be determined.

[0147] The photodetector 16 and the aperture 12 are arranged over one another in this case such that all apertures 14 overlap with the photodetector 16. The energy transmitted through each of the apertures 14 when the laser beam sweeps over the respective aperture 14 is incident on the photodetector 16 and can be detected by the latter.

[0148] Moreover, the aperture arrangement 10 according to the shown embodiment has two further apertures 18 for the target laser beam, which likewise are in the form of a slot with a predetermined extent or width and which are arranged at the predetermined distance 100a from one another. Since the target laser beam typically has a different central wavelength to the work laser beam and therefore the photodetector 16 might not be designed to detect the target laser beam and/or determine the energy and/or power thereof, a separate target laser detector 20 is assigned to each aperture 18, each target laser detector being arranged below the associated aperture 18, as indicated on the basis of the dashed line. One of the two apertures 18 runs in the vertical direction and has a predetermined width in the horizontal direction whereas the other aperture 18 runs in the horizontal direction and has a predetermined width in the vertical direction. As a result, it is possible to determine the extent of the target laser beam in the work plane in both dimensions, referred to as horizontal and vertical in the present case.

[0149] As a result, the aperture arrangement allows both the laser beam and the target laser beam to be checked, even if these have entirely different central wavelengths.

[0150] In this case, the aperture arrangement 10 is dimensioned and formed in such a way that it can be arranged in the work plane of a laser processing system. In particular, it is therefore advantageous to choose the dimensions of the aperture arrangement 10 in such a way that positioning in possibly tight conditions is possible at the location of the work plane.

[0151] FIG. 1B shows an aperture arrangement 10 according to a further optional embodiment. The aperture arrangement according to this optional embodiment has two slot-like or slot-shaped apertures 14a, which are arranged so as to run parallel to one another at a predetermined distance 100a from one another. In this case, the apertures 14a have a width that is significantly smaller than the mean diameter or the mean extent of the laser beam in the work plane. Moreover, the aperture arrangement 10 has a further aperture 14b, which is in the form of a round hole and which is larger than the laser beam in the work plane such that the laser beam can be transmitted substantially fully through the round hole-shaped aperture 14b. Further, the aperture arrangement 10 has a photodetector 16 which is arranged below the stop 12, the photodetector being able to register and detect the laser radiation of the laser beam passing through the aperture.

[0152] This stop arrangement 10 allows determination of the fluence of the laser beam in the work plane and a calibration of the scanner in one procedure. By way of example, this can be implemented by scanning the laser beam in a straight-lined movement over the aperture arrangement starting from the left, so that the laser beam initially sweeps over the left slot-like aperture 14a (sweeping over said aperture in a manner perpendicular to its longitudinal axis), then passes centrally through the round hole-shaped aperture 14b and subsequently also sweeps over the right slot-shaped aperture 14a. A scan of the laser beam in the opposite direction, that is to say from right to left, is equally suitable. The size or extent of the laser beam in the work plane can be determined on the basis of the first and/or second slot-like aperture 14a being swept over by the laser beam. The energy or power of the laser beam can be determined on the basis of the laser beam that passes centrally through the round hole-shaped aperture 14b, so that the fluence in the work plane can be determined from the determined information. Moreover, the scanner movement can be calibrated on the basis of the movement over the two slot-like apertures 14a, and so the laser beam can be characterized and the scanner can be calibrated in one procedure.

[0153] Optionally, the aperture arrangement may additionally have two further slot-like apertures 14a, which are arranged (shown using dashed lines) perpendicular to the other two slot-like apertures 14a. This can be used to determine the extent of the laser beam in the work plane along the other dimension (vertical in the figure) and also calibrate a scanner movement in this direction.

[0154] FIG. 1C shows an aperture arrangement 10 according to a further embodiment, which largely corresponds to the embodiment shown in FIG. 1B but deviates from the latter in the fact that only one vertically extending, slot-like aperture 14a is formed for the determination of the extent of the laser beam and, instead, a further vertically extending, slot-like aperture 18 is formed for determining the extent of the target laser. The slot-like aperture 18 accordingly also overlaps with a target laser detector 20 such that the radiation of this target laser beam passing through the aperture 18 can be detected and the extent of the target laser beam in the work plane can be determined. This embodiment facilitates a characterization of the fluence of the laser beam and a referencing of the target laser beam with the laser beam in the work plane in one procedure.

[0155] FIG. 1D shows a further optional embodiment of an aperture arrangement 10 which is distinguished in particular by its simplicity. The aperture arrangement 10 has only a single aperture 14, which is in the form of a rectangular hole with predetermined dimensions. Like in the case of the other embodiments as well, a photodetector 16 is arranged below the aperture 14 or the stop 12, the light of the laser beam passing through the aperture striking said photodetector. In particular, the aperture 14 is characterized in that it has two opposing, parallel edges that optionally extend in a straight line. By way of example, using an aperture arrangement 10 according to this embodiment, the laser beam can be characterized by virtue of the laser beam being guided in a straight-lined scanning movement over the aperture arrangement 10 in the work plane, in such a way that the laser beam sweeps over the aperture 14. In this case, sweeping is optionally implemented in such a way that the movement of the laser beam during the scan is implemented in perpendicular fashion over two opposing edges of the aperture 14. By way of example, such a scanning movement can be horizontal or vertical in the shown aperture. On the basis of sweeping over the edges of the aperture 14, it is possible firstly to determine the extent of the laser beam in the work plane and secondly to calibrate the scanner (on the basis of the predetermined spacing of the edges). In this case, the aperture 14 is dimensioned such that the laser beam is substantially fully transmitted when the latter passes through the aperture 14 in centered fashion. In this way, it is also possible to determine the energy or power of the laser beam by means of the photodetector 16. Consequently, the fluence of the laser beam in the work plane can be determined and the scanner can be calibrated in the same procedure even when an aperture according to this embodiment is used.

[0156] If moreover a target laser beam should be used, a further stop 18 with a photodetector 20 arranged therebelow is optionally also possible here, in order to calibrate processing laser beam and target laser beam with respect to one another, as already described above.

[0157] FIG. 2A shows the aperture arrangement 10 according to an optional embodiment in a schematic cross-sectional view along a cross-sectional line A-A′, as shown in FIG. 1. In this context, the aperture arrangement identifiably has a carrier element 22, on which the stop 12 is arranged lying on top. The carrier element 22 supports the stop 12 in the peripheral regions and forms a cavity within the carrier element 22 below the stop 12. The photodetector 16 is arranged in the cavity below the stop 12, in such a way that the photodetector or the detector area overlaps with the apertures 14a and 14b located thereover. If the laser beam sweeps over one of the apertures 14a and 14b, at least some of the energy of the laser beam is transmitted through the respective aperture 14a, 14b and is incident on the photodetector 16 located therebelow. In this context, the stop 14b is chosen in such a way in respect of shape and size that the laser beam can be substantially fully transmitted. The apertures 14a are significantly smaller than the mean diameter of the laser beam along the direction running horizontally in FIG. 2A, and so the size of the laser beam can be determined by means of sweeping over the respective aperture 14a.

[0158] FIG. 2B shows a further schematic cross-sectional view along a section line B-B′, as shown in FIG. 1. This cross section cuts the apertures 18 transversely and an aperture 14a longitudinally. Here, it is identifiable that a target laser detector 20 is arranged below the apertures 18 on each corresponding cantilever of the support element 22 such that some of the target laser beam is incident on the target laser detector 20 when sweeping over the respective aperture 18 and can be detected by said target laser detector. According to the embodiment shown, the target laser detectors 20 or the supporting cantilevers of the support element 22 overlap with the photodetector 16 arranged therebelow. However, this is irrelevant since the photodetector at the site shown only needs to detect the energy of the work laser beam transmitted through the aperture lying thereabove in any case, said energy being able to pass unimpeded through the aperture 14a and the cantilevers of the support element 22. In this way, it is possible to provide a particularly compact and space-saving stop arrangement 10, which is also attachable in work planes which have little space available.

[0159] As a result of the photodetector 16 being spaced apart from the stop 12, the photodetector is arranged in a recessed position relative to the stop 12 which is arranged in the work plane for the purposes of checking the laser beam. This may be advantageous, especially for embodiments where the laser beam is focused into the work plane, since the laser beam then already has a larger diameter in the plane of the photodetector 16 and accordingly strikes the photodetector 16 with a lower intensity. As a result, the load on the photodetector 16 may be reduced and/or use can be made of a photodetector 16 with a lower destruction threshold. Additionally, this recessed arrangement offers the advantage that the incident laser beam has a larger diameter and therefore the laser beam is detected by a larger sensor area, which can increase the accuracy and/or reduce the sensitivity in respect of local variations in the sensor sensitivity of the photodetector.

[0160] By contrast, the target laser detectors 20 are arranged closer to the stop 12 and therefore closer to the work plane. However, since the target laser beam typically has a significantly lower power than the work laser beam, damage of the target laser detectors 20 need not be feared even in the case of an arrangement close to the work plane.

[0161] FIGS. 3A and 3B are used below to schematically explain how the extent of the laser beam 24 is determined according to an optional embodiment. FIG. 3A shows a plan view of an aperture 14a and a laser beam 24, the cross-sectional area of which is symbolically represented by a dotted line and which sweeps over the aperture 14a along a scanning direction 200. In this case, the scanning direction 200 runs perpendicular to the longitudinal axis of the slot-shaped aperture 14a. Along the scanning direction 200, the aperture 14a has a dimension, that is to say a width, that is significantly smaller than the mean diameter of the laser beam 24. Accordingly, when sweeping over the aperture 14a along the scanning direction 200, different amounts of the energy or power of the laser beam are transmitted through the aperture 14a at different times and for different relative positions of the laser beam 24 relative to the aperture 14a, while the remaining amount is absorbed or reflected by the stop 12.

[0162] In an exemplary diagram, FIG. 3B plots the detector signal of the photodetector 16 arranged below the aperture 14a, said detector signal being proportional to the transmitted energy. The detector signal in arbitrary units on the y axis is plotted against the relative position x of the laser beam 24 vis-à-vis the central axis of the aperture 14a on the x-axis. When the laser beam reaches the aperture 24, the detector signal initially increases in the subsequent measurement points until a maximum has been reached at the position x0, at which the center of the laser beam 24 is located on the central axis of the aperture 14a. The detector signal reduces again if the laser beam is moved further along the scanning direction 200. In order to reliably determine the extent of the laser beam in the scanning direction, the scanning direction must run perpendicular to the longitudinal axis of the aperture 14a. Accordingly, the detector signal follows a curve that is symmetric about the position x0, that is similar to a Gaussian bell curve and that corresponds to a convolution of the laser beam profile with the slot width along the scanning direction, and that facilitates the determination of the beam profile along the dimension of the scanning direction. Deviations of the detector signal from the actual extent of the laser beam 24 or from an ideal Gaussian curve arises for apertures 14a with a finite width. Therefore, accurate knowledge of the extent or width of the aperture 14a is required for the determination of the extent of the laser beam. Subsequently, the extent of the laser beam can be determined as a sum of error functions erf(x). Further, FIG. 3B plots the mean diameter (FWHM) and denotes the latter by d.

[0163] FIG. 4 shows a laser processing system 30 according to an optional embodiment for refractive surgery on an eye. The laser processing system 30 is designed as treatment equipment and serves for example to carry out, using a laser beam or processing laser beam 24, a refractive error correction on an eye of a patient (not shown) by means of a method for refractive surgery. To this end, the laser processing system 30 comprises a laser or a laser source 32, which emits the laser beam 24. The laser beam 24 is designed to act on the cornea of an eye in order to modify the refractive power of the cornea.

[0164] The laser beam 24 or the processing beam 24 emitted by the laser 32 along an optical axis A1 is incident on a beam splitter 34 in the process, the latter guiding the laser beam 24 to a deflection unit 36 in the form of a deflection device 36. The deflection unit 36 has two scanning mirrors 38 and 40 which are rotatable about mutually orthogonal axes such that the deflection unit 36 deflects the laser beam 24 in two dimensions. For processing purposes, an adjustable projection optical unit 42 focuses the laser beam 24 onto the processing object or onto or into an eye to be treated. In this case, the projection optical unit 42 has two lens elements 44 and 46.

[0165] The eye to be treated is arranged in the work plane 300 for treatment purposes so that the laser beam can be focused thereon. However, an aperture arrangement 10 is arranged in the work plane 300 in FIG. 4 and can be used to check the focused laser beam. To treat the eye, the checking of the laser beam by means of the aperture arrangement 10 can be completed first, the aperture arrangement 10 can then be removed and the treatment of the eye in the work plane can subsequently be started. In this way, the aperture arrangement 10 can be used to examine the laser beam at the position where the eye is also processed or treated by means of the laser beam.

[0166] Further, the laser processing system has a control unit 48. The control unit 14 optionally determines the relative position of the focus 50, both perpendicular to the optical axis A1 (by the scanning mirrors 38 and 40) and in the direction of the optical axis A1. Further, the control unit 14 reads a detector 52 which, for example, acts as a co-observation unit and which serves to monitor the processing procedure. Additionally, the laser processing system 30 may have further sensors and/or detectors, in particular an internal energy sensor or energy detector, but these are not shown in the figure. By way of example, the energy sensor may be arranged behind the beam splitter 38 in order to determine the energy of the energy transmitted through the beam splitter. Further, the control unit 48 is connected to the aperture arrangement 10 and designed to read especially the photodetector 16 and optionally the target laser detectors 20 and/or to monitor these. Provided the aperture arrangement 10 is designed and arranged in movable fashion such that, for instance, the laser beam can sweep over the apertures by virtue of the aperture arrangement 10 being displaced in the work plane, it may be advantageous for a corresponding displacement unit also to be connected to the control unit 48 and to be controlled and/or regulated by the latter.

[0167] A method for checking a laser beam of a laser processing system is described in exemplary fashion below, without the claimed embodiments however being restricted to this example.

[0168] The calibration of the laser system or the checking of the laser beam is implemented in a plurality of steps, but these may also be combined in one scanning pattern in the case of a sufficiently parameterizable laser control:

a) calibrating the deflection device for the generation of the scanning movement;
b) determining the diameter of the laser beam and calculating a target value for the fluence of the laser beam in the work plane for this diameter;
c) measuring the laser energy of the processing laser beam and calculating the fluence from the independent quantities of mean diameters of the laser beam and energy of the laser beam. Comparing target value and actual value;
d) adjusting the energy and repeating b) and c);
e) calibrating a laser beam offset which describes a beam position of the laser beam in the work plane in the case of a neutral position of the scanner mirrors or the deflection device;
f) calibrating a target laser beam offset;
g) calibrating an eye tracker offset.

[0169] The following explanations are provided with reference to FIG. 5, which corresponds to an aperture arrangement according to the embodiment in FIG. 2.

[0170] For a better overview, unique labels were assigned to the individual apertures, as is made evident in FIG. 5.

[0171] Step 1) The aperture arrangement comprising a stop, a photodetector and two target laser detectors is adjusted in terms of position and alignment in the work plane such that the aperture arrangement is positioned in the work plane, perpendicular to the direction of incidence of the laser beam. The alignment can be implemented using typical adjustment aids of the processing laser. By way of example, these are distance lasers, camera images/video overlays and/or distance sensors.

[0172] Step 2) The laser beam is successively driven over the slots or apertures ExH1 and ExH2 with a known increment ds. This yields a respective approximately Gaussian curve for each scan over one of the apertures. The following quantities are derived for both apertures by fitting the known convolution function of intensity curve or detector signal and stop geometry: center x0, mean diameter d (FWHM). Optionally, the amplitude A and the offset y0 of the detector signal are recorded for consistency checks, even though they are not necessarily used further.

[0173] Step 3) The comparison of the quantity Distance_H_actual=x0(ExH2)−x0(ExH1) is compared to the known spacing of the slots ExH1 and ExH2 of the stop (distance 100a in FIG. 1), and hence the gain factor gain_H=Distance_Hactual/Distance_H_target of the scanner or deflection device is checked for the horizontal deflection. If there is a deviation between the new and old gain which exceeds a certain tolerance range, the gain factor should be adjusted and steps 1-3 should be repeated.

[0174] Step 4) The quantity Offset_Ex_H=x0(ExH2)+xO(ExH1) describes the offset between the position of the centroid of the processing laser beam in the scanner neutral position and a stop center of the stop. The latter is compared to a tolerance range. In the case of deviations, the position of the sensor should be checked using the means from step 1). If the latter is correct, there is a decentration of the scanner or deflection device and the calibration should be terminated.

[0175] Step 5) The mean diameters of the laser beam d(ExH1) and d(ExH2) are individually compared to their tolerance range and specified value. A mean value dH is formed for the further calculations. The target fluence F.sub.target can be adjusted using the value dH.

[0176] Step 6) Steps 2-4 are repeated for the vertical direction on the basis of the apertures ExV1 and ExV2. This supplies the values of dV, Offset_Ex_V and gain_V.

[0177] Step 7) In a scanner neutral position or a small region surrounding the latter, the processing laser beam is steered through the central aperture (14b in FIG. 1), which is in the form of a round hole, and the transmitted energy is measured. This supplies the measurement value E.sub.Mess. The measurement value can be converted using a sensor-inherent calibration factor to the actual value of the energy. This supplies the value E.sub.ist.

[0178] Step 8) The actual fluence f.sub.ist is calculated from the values of E.sub.ist, dH, dV. It is compared with the target fluence F.sub.soll. In the case of deviations between actual and target fluence, the energy of the processing laser is adjusted and steps 2-7 are repeated with a new setting for the laser energy.

[0179] Step 9) Determining the offset of the central aperture ExL (14b in FIG. 1) in the form of a round hole by means of an eyetracker in the vertical and horizontal direction and determining the parameters of Offset_Tracker_V, Offset_Tracker_H. Comparing the offsets with the tolerance ranges defined therefor.

[0180] Step 10) Scanning the target laser over the structure VisH and evaluating the position of the centroid x0.sub.ist(VisH). Since the scanners are calibrated in terms of gain factor from step 3, a difference between actual and target position of the beam centroid arises purely from the offset of the target laser beam: Offset_Vis_H=xO(VisH)−x0.sub.target(VisH). Comparing Offset_Vis_H with the tolerance range defined therefor.

[0181] Step 11) Repeating step 10 for the vertical direction. ->Offset_Vis_V.

[0182] In schematic illustrations, FIGS. 6A and 6B show a laser processing system 1000 according to an optional embodiment in two different modes of operation for characterizing the laser beam 1002.

[0183] In this case, the laser processing system 1000 has a laser source 1004 which emits the laser beam 1002, the latter subsequently initially running through a beam shaping device 1006, in which the laser beam 1002 is brought into the desired shape. After the beam shaping device 1006, the laser beam propagates through a deflection device 1008 or scanning device, by means of which the laser beam 1002 is deflectable in such a way that the laser beam 1002 is movable into a work plane 2000 or into a verification plane 2002 in order to carry out the desired processing of a processing object, for instance the treatment of an eye. Optionally, the beam shaping device 1006 is configured to focus the laser beam 1002 into the work plane 2000 or verification plane 2002.

[0184] A beam splitter 1010 is arranged in the beam path of the laser beam 1002 between the beam shaping device 1006 and the deflection device 1008, said beam splitter branching off a small part of the laser beam 1002 or laser energy and supplying this to an internal energy sensor 1012. By way of example, the beam splitter 1010 may be designed such that the latter reflects approximately 10% of the energy of the laser beam and transmits the remaining energy, beam splitters with a different ratio also being able to be used for as long as sufficient energy is transmitted for the treatment or processing in the work plane. On the basis of the supplied portion of the laser beam, the energy sensor 12 determines an energy parameter, from which it is possible to derive the energy and/or power of the entire laser beam. Optionally, the laser processing system is configured to use the energy sensor 1012 to carry out a continuous and/or regular determination of the energy parameter during the operation of the laser processing system 1000.

[0185] FIG. 6A shows the laser processing system in a first mode of operation for characterizing the laser beam 1002, in which a calibration device 1014 is arranged in the work plane 2000 and determines a calibration parameter for the characterization of the laser beam 1002. In this case, the calibration parameter renders it possible to determine the fluence of the laser beam 1002 in the work plane 2000.

[0186] FIG. 6B shows the laser processing system 1000 in a second mode of operation for characterizing the laser beam 1002, in which the calibration device 1014 is arranged in the verification plane 2002. In this case, the verification plane 2002 and also the calibration device 1014 are located within the laser processing system 1000. In the process, a verification parameter is determined in the verification plane 2002 by means of the calibration device 1014, said verification parameter optionally being determined in identical fashion to the calibration parameter, the difference being that the verification parameter is not determined in the work plane 2000 but in the verification plane 2002. In this case, the verification parameter renders it possible to determine the fluence of the laser beam 1002 in the verification plane 2002. In the process, the laser beam 1002 is deflected by a deflection element 1016 such that said laser beam is incident not on the work plane 2000 but on the verification plane 2002. By way of example, to this end, the deflection element 1016 may be in the form of a mirror and can be moved into the beam path of the laser beam 1002 by the laser processing system 1000. By way of example, the deflection element may be arranged in displaceable or pivotable fashion in order to be able to be moved into and out of the beam path. Once the determination of the verification parameter has been completed, the deflection element 1016 may be moved out of the beam path again such that the laser beam 1002 can propagate into the work plane again.

[0187] Optionally, the verification parameter is determined directly after the determination of the calibration parameter in order to minimize the risk of intervening changes.

[0188] Then, the laser processing system 1000 can determine a deviation factor on the basis of the calibration parameter and the verification parameter, it being possible to relate the two parameters or measurement values based thereon, for instance the determined fluence values, to one another using said deviation factor.

[0189] Subsequently, the laser processing system 1000 may perform a verification of the laser beam 1002 by virtue of only determining the verification parameter, comparing the latter to a target value and carrying out a check on the basis of the energy parameter as to whether the energy of the laser beam 1002 also corresponds to the target value. As a result, the laser beam 1002 can even be checked if the work plane is not accessible for a determination of the calibration parameter.

[0190] In a processing mode, in which a processing object is processed by means of the laser beam, the deflection element 1016 is likewise arranged outside of the beam path, for example as shown in FIG. 6A, but in the processing mode it is not the calibration device 1014 that is arranged in the work plane 2000, but a processing object (not shown).

[0191] In schematic illustrations, FIGS. 7A and 7B show a processing head 1020 of a laser processing system 1000 according to an optional embodiment in two modes of operation for the characterization of the laser beam 1002.

[0192] In this case, the processing head 1020 is designed to emit the laser beam 1002 such that the latter propagates along the optical axis A1 and is incident either in the work plane 2000 or in the verification plane 2002.

[0193] Further, on the processing head 1020, the laser processing system 1000 has an arrangement for being able to choose an arrangement of the calibration device 1014 in the work plane 2000 and in the verification plane 2002 and for being able to choose a positioning of the deflection element 1016 within or outside of the beam path or optical axis A1 of the laser beam 1002. To this end, the arrangement has a drive 1022 and a guide 1024 in order to bring the deflection element 1016 from a position outside of the beam path (FIG. 7A) into a position in the beam path (FIG. 7B), and vice versa.

[0194] Further, the laser processing system 1000 has a pivoting device for pivoting the calibration device 1014 from the work plane 2000 into the verification plane 2002, and vice versa. By way of example, to this end the calibration device 1014 may be fastened to a pivot joint 1026 by way of an arm 1024, the arm 2024 being able to be pivoted about said pivot joint, as indicated by the curved arrow 2004. Naturally, the arrangement is formed and/or arranged in such a way that the laser beam is not impeded or blocked by the arrangement or any one of its components in all of the modes of operation.

[0195] In a mode of operation for processing a processing object or for treating an eye, the calibration device 1014 for example may be pivoted into the verification plane and the deflection element 1015 may be arranged outside of the beam path. A calibration of the laser beam 1002 of a laser processing system 1000 is described below on the basis of an example, without the claimed embodiments being restricted to the following example.

[0196] In particular, the following explanation relates to linking the calibration with the calibration device in the work plane (external position) with the verification by means of the calibration device in the verification plane (internal position).

[0197] 1) Initially, the calibration or characterization of the laser beam is carried out by means of the calibration device in the work plane (determining a calibration parameter) without an additional optical element or deflection element. Moreover, an energy parameter is determined in this case as a reference value for the internal energy sensor (Eint,0) according to a calibration method, and the laser energy is adjusted until the actual fluence F.sub.actual_external is within the tolerances of the target fluence (F.sub.target, external).

[0198] 2) Immediately subsequently, the test is carried out on the same calibration device, but in a verification plane within the laser processing apparatus, optionally at a constant work distance in relation to the aperture of the laser source, and a verification parameter is determined. By way of example, this may be realized by a rigid pivoting mechanism or by mechanical or magnetic stops. In this case, an additional optical element is used as a deflection element, in order to fully steer the laser beam onto the internal position of the calibration device in the verification plane. The additionally introduced deflection element is arranged downstream of the last optical element of the beam path (in the beam direction).

[0199] This determination of the verification parameter by means of an internal fluence measurement (this measurement is explicitly not a calibration) is carried out at a fixed energy setting in respect of the energy found in step 1), that is to say at E.sub.int,0, and supplies a fluence value F.sub.actual,internal.

[0200] This value differs from the fixed value F.sub.target,external on account of the properties of the additional deflection element, for instance the reflectivity of the deflection element in the form of a mirror. This is used to determine a deviation factor, by means of which these effects can be calculated:

R=F.sub.actual,internal/F.sub.target,external.

[0201] 3) The characterization of the laser beam or the calibration of the laser system can subsequently be carried out exclusively by way of the internal position (that is to say, without the necessity of arranging the calibration device in the external position), that is to say by way of the verification parameter, with the target value of the fluence being calculated by way of the deviation factor R determined in 2):

F.sub.target,internal=R*F.sub.target,external.

[0202] 4a) The calibration interval for determining the deviation factor R (steps 1 & 2) can be defined in such a way that a degradation of the additional deflection element does not influence the calibration accuracy (e.g., by defining adequate time intervals/number of tests).

[0203] 4b) Ideally, a possible degradation of the deflection element, for instance a waning reflectivity, can be checked by continuously monitoring the verification parameter relative to that of the energy sensor in the laser arm, that is to say of the energy parameter: Optionally, this is implemented by continuous comparison of the measurement signals F.sub.actual,internal and E.sub.int,current (cross-calibration of the calibration device with the current measurement value of the internal energy sensor in the case of a calibration device with continuous measurement value).

[0204] 4c) Independently thereof, a possible degradation of the deflection element may be monitored in a different spectral range to that of the processing laser. To this end, a transmission or reflectivity measurement of the deflection element can be carried out regularly. Since a degradation of an optical element at this position, that is to say as a last optical element in front of the work plane, may typically arise by surface damage on the coated side (by the treatment laser) or by contamination, for example by droplets of the rinsing fluid used in refractive surgery, a degradation may also be determined in a different spectral range. By way of example, a degradation may be implemented by means of an illumination device and a camera and/or by using the scanned target lasers typically present in such systems.

[0205] However, degradation only can be determined in this way; a quantification can be attained by means of the method presented in 4b) or in step 1)-2). However, the determination alone may serve to deactivate the laser processing system and/or terminate a treatment and/or output an appropriate notification that a check is required.

[0206] FIG. 8A shows an apparatus 3010 for characterizing a laser beam (see FIG. 8B) in a schematic illustration. The apparatus 3010 has a test object holder 3012, which holds a test object 14 in a specified position. The test object holder 3012 is configured in such a way here that a laser beam can be incident on a surface on the top side 3014a of the test object 3014 from the side distant from one of the test object holders 3012.

[0207] A sensor 3016 of a measuring device 3018 (not shown) is arranged below the test object 3014, that is to say on the side facing the test object holder 3012. In addition to the sensor 3016, the measuring device 3018 may comprise even further elements, for instance a control and/or evaluation unit.

[0208] The sensor 3016 is designed as a confocal-chromatic sensor which is designed and arranged such that the latter radiates electromagnetic radiation in the visible and/or infrared spectral range along the optical axis 3100 of the sensor 3016 into the test object 3014 via the lower side 3014b, said electromagnetic radiation being referred to as measurement light below. As is conventional for confocal-chromatic sensors, the radiated-in measurement light is focused in such a way that different wavelengths or different spectral components are focused at different focal lengths and accordingly differ in terms of their penetration depth into the test object 3014.

[0209] Typically, the shorter wavelength spectral components are focused with a shorter focal length while the longer wavelength components are focused with a longer focal length, even though other embodiments may likewise also be suitable. The light cone of the focused measurement light is represented in exemplary fashion by the dotted line.

[0210] By means of the sensor 3016, it is possible to measure the thickness of the test object 3014 by virtue of detecting, evaluating and comparing the components of the measurement light reflected and/or scattered at the lower side 3014b and at the top side 3014a. On account of the different penetration depths of the various spectral components, the two reflections or scatterings at the top side 3014a and lower side 3014b are different from one another such that the distance of the reflection plane or scattering plane from the sensor 3016 can be determined from the different spectral composition of the two reflections or scatterings, and the thickness of the test object 3014 can be determined therefrom.

[0211] It is self-evident that the test object 3014 needs to be at least partly, ideally virtually completely transparent to the measurement light. By way of example, the test object 3014 is formed from PMMA since PMMA has a suitable transparency to the measurement light and moreover is processable by means of UV laser radiation.

[0212] The site of the test object 3014 which is measured by the sensor 3016 or at which the thickness of the test object 3014 is determined is referred to as test site 3020. To also determine the thickness of the test object 3014 at other positions of the test object 3014 or at other test sites 3020, the test object 3014 can be at least partly scanned by means of a relative movement between the test object 3014 and the sensor 3016. In this case, the thickness of the test object 3014 is the spatial extent of the test object 3014 parallel to the optical axis 3100. The thickness may vary at different sites of the test object 3014. To measure the thickness at a plurality of test sites 3020, the sensor 3016 and/or the test object holder 3012 may be moved in one or preferably two dimensions perpendicular to the optical axis 3100, as indicated by arrows 3200 and 3300.

[0213] FIG. 8B shows the apparatus of the embodiment according to FIG. 8A, a laser beam 3022 additionally being shown, the latter being used or having been used to ablate material from the top side 3014a of the test object 3014. Optionally, the laser beam 3022 has a central wavelength in the ultraviolet spectral range, for example at 193 nm. Optionally, the laser beam 3022 is provided by an ArF excimer laser, even though other laser sources may also be suitable for providing a suitable laser beam 3022.

[0214] According to the shown embodiment, the laser beam 3022 is incident on the test object 3014 along the optical axis 3102, the optical axis 3102 of the laser beam 3022 being parallel to the optical axis 3100 of the sensor 3016. According to other embodiments, the laser beam may also be incident under a different angle.

[0215] The test object 3014 at least partly consists of a material that is suitable to at least partly absorb the laser radiation. This facilitates material ablation of the test object 3014 by means of the laser beam 3022. As already explained above, the test object is optionally formed from PMMA since the latter has a high optical density in the ultraviolet spectral range and further is sufficiently transparent to the measurement light. The thickness of the test object 14 is optionally chosen in such a way here that, even after material ablation for the characterization of the laser beam 3022, the thickness of the test object 14 is sufficient to avoid the laser radiation passing through to the sensor 3016. As a result, damage to the sensor as a result of the laser beam 3022 can be avoided.

[0216] If the position of the sensor 3016 and its axis 3100 relative to the focus position of the laser beam 3022 and its axis 3102 are known or specified, for example by way of a suitable stop on the laser by way of the test object holder 3012, the acceptable position of the test site 3020 relative to the laser beam 3022 can be ensured before the thickness measurement, for example to the effect of the test object 3014 having been inserted correctly into the specimen holder 3012.

[0217] On account of the material ablation by the laser beam 3022, the thickness of the test object 3014 has changed at the processed sites. The change of the thickness can be determined by means of the sensor 3016, for example by virtue of the thickness being determined before and after and/or before and during the processing with the laser beam 3022. On account of the high sensitivity of the confocal-chromatic sensor 16, a change in the thickness above 100 nm or even less can optionally already be determined.

[0218] The material ablation by the laser beam 3022 is optionally implemented with a predetermined shot number or laser pulse number for each test site 3020. Therefore, the material ablation per pulse or shot can be determined from the change in the thickness of the test object 3014 since the number of shots or pulses that impinged on the test site 3020 is known. Additionally, other test sites 3020 can each have a different number of pulses or shots impinging thereon in order to obtain further measurement data by comparing the material ablation or the change in thickness at the different test sites, and in order to be able to determine the change in the thickness even more reliably.

[0219] FIG. 9 shows a further embodiment, in which the laser beam (not shown) is characterized during the application to the cornea 3024 of a human eye 3026. Expressed differently, the cornea 3024 adopts the function of the test object 3014 according to this optional embodiment and should therefore likewise be considered a test object 3014 within the meaning of this patent application.

[0220] According to this optional embodiment, the cornea 3024 is subjected to refractive correction by means of the laser beam (not shown), for the purposes of which the laser beam is incident on the cornea 3024 along the optical axis 3102 as indicated by the arrow 3104.

[0221] In the beam path of the laser beam, that is to say in the optical axis 3102, a beam splitter 3028 is arranged in front of the cornea 3024, said beam splitter being tilted by 45° with respect to the optical axis 3102 according to this embodiment, with other angles also being possible according to other embodiments. Optionally, the beam splitter 3028 is virtually completely transparent at the central wavelength of the laser beam such that the laser beam can pass through the beam splitter virtually unimpeded, without having to accept noteworthy power losses.

[0222] By contrast, the beam splitter 3028 is optionally highly reflective to the wavelengths of the measurement light emitted by the confocal-chromatic sensor 3016. Alternatively or in addition, the beam splitter 3028 may also be designed as polarization splitter which merges differently polarized processing laser and measurement light. According to an optional embodiment, the beam splitter 3028 is in the form of a measurement light reflector which is able to be intermittently pivoted in in order to realize measurements or characterizations of the laser beam 3022 between individual pulses or pulse sequences of the laser beam 3022.

[0223] According to this embodiment, the optical axis 3100 of the sensor 3016 is arranged here at right angles to the optical axis 3102 of the laser beam. In this case, the measurement light is directed at the beam splitter 3028 which deflects the measurement light to the test site 20 on the cornea 3024 which is processed by the laser beam.

[0224] The light reflected and/or scattered at the test site 3020 or cornea 3024 is likewise reflected by the beam splitter and cast back to the sensor 3016. Thereupon, the sensor 3016 can detect the cast-back measurement light. The measuring device 3018 which also has a control and evaluation unit 3032 in addition to the sensor determines the change in the thickness of the cornea 3024 at the test site 3020 on the basis of the data determined by the sensor and can characterize the laser beam on the basis thereof. A check of the position of the corneal surface in relation to the sensor 3016 and/or focus of the laser beam 3022, which is also possible, is advantageous for realizing correct processing and thickness measurements. Should in the case of a fault the cornea move out of a predefined work range on the axis 3100, the laser processing and thickness measurement can be readjusted and/or terminated and/or at least be interrupted.

[0225] Not shown is an alternative optional embodiment in which the sensor 3016 is positioned laterally to the incident laser beam 3022 in order to be able to measure test sites 3020 processed by the laser beam 3022 without needing the light of the sensor 3016 and the laser beam 3022 to be overlaid by means of optical components, for example by virtue of the axes 3100 and 3102 forming an angle so as to intersect at a test site 3020, or even without an overlap by virtue of the sensor 3016 being successively laterally displaced in order to measure a test site 3020 previously processed by the laser beam 3022.

[0226] According to an optional embodiment, the measuring device is also connected to a control device (not shown) of the laser source and can if necessary intervene in the closed-loop and/or open-loop control of the laser source using the data from the characterization of the laser beam, for example in order to increase and/or reduce the power of the laser beam.

[0227] Using the shown embodiment it is therefore possible to carry out a real-time characterization of the laser beam, which may be used for closed-loop control of the laser beam for example.

[0228] FIGS. 10A to 10C show various optional embodiments for the provision of test objects 3014 in schematic illustrations.

[0229] According to the embodiment in FIG. 10A, a plurality of block-like test objects 3014 are arranged on a substrate 34. By way of example, the substrate 3034 can be in the form of a flexible film. By way of example, such an embodiment facilitates an automated supply of test objects 3014 to the test object holder by virtue of the substrate 3034 being moved by way of rollers, for example.

[0230] According to the embodiment shown in FIG. 10B, the test object 3014 itself is in the form of a film 36. Different parts of the film can be used as test sites 3020 by way of suitable repositioning of the film 36. In this case, the film 3036 should be chosen to be sufficiently thick to prevent the laser beam 3022 from passing through the film 3036 and prevent the laser beam from being incident on a sensor 3016 possibly arranged below the film.

[0231] According to the embodiment shown in FIG. 10C, the test object 3014 is in the form of a disk 3036, the disk being substantially larger than an individual test site 3020. By displacing and/or rotating the disk 36 it is subsequently possible to select different sites on the disk 3036 for impingement by the laser beam such that a multiplicity of test sites 3020 are able to be housed on the test object 3014 or on the disk 3028, optionally more than 1000 test sites 3020.

LIST OF REFERENCE SIGNS

[0232] 10 Stop arrangement [0233] 12 Stop [0234] 14, 14a, 14b Aperture for the work laser beam [0235] 16 Photodetector [0236] 18 Aperture for the target laser beam [0237] 20 Target laser detector [0238] 22 Carrier element [0239] 24 Laser beam [0240] 30 Laser processing system [0241] 32 Laser source [0242] 34 Beam splitter [0243] 36 Deflection device [0244] 38 Scanning mirror [0245] 40 Scanning mirror [0246] 42 Projection optical unit [0247] 44 Lens [0248] 46 Lens [0249] 48 Control unit [0250] 50 Focus [0251] 52 Detector for monitoring the processing procedure [0252] 100a, 100b Predetermined distance between two apertures 14a [0253] 200 Scanning direction [0254] 300 Work plane [0255] 1000 Laser processing system [0256] 1002 Laser beam [0257] 1004 Laser source [0258] 1006 Beam shaping device [0259] 1008 Deflection device [0260] 1010 Beam splitter [0261] 1012 Energy sensor [0262] 1014 Calibration device [0263] 1016 Deflection element [0264] 1018 Arrangement for moving the deflection element [0265] 1020 Processing head [0266] 1022 Drive [0267] 1024 Guide [0268] 1026 Pivot joint [0269] 1028 Arm [0270] 2000 Work plane [0271] 2002 Verification plane [0272] 2004 Pivoting movement [0273] 3010 Apparatus for characterizing a laser beam [0274] 3012 Test object holder [0275] 3014 Test object [0276] 3014a Top side of the test object [0277] 3014b Lower side of the test object [0278] 3016 Sensor [0279] 3018 Measuring device [0280] 3020 Test site [0281] 3022 Laser beam [0282] 3024 Cornea [0283] 3026 Eye [0284] 3028 Beam splitter [0285] 3032 Control and evaluation unit [0286] 3034 Substrate [0287] 3036 Film [0288] 3038 Disk [0289] 3100 Optical axis of the sensor [0290] 3102 Optical axis of the laser beam [0291] 3200 Movement direction of the sensor [0292] 3300 Movement direction of the test object holder [0293] A-A′ Indicators of the cross-sectional profile [0294] B-B′ Indicators of the cross-sectional profile [0295] A1 Optical axis of the laser beam