METHOD AND DEVICE FOR MACHINING BY MEANS OF INTERFERING LASER RADIATION

Abstract

The invention concerns a method and an apparatus for processing an object (1) by means of interfering laser beams. It is the task of the invention to provide for an improved compensation of the aberrations accumulated over the beam path in such processes/apparatuses, since these are a substantial disturbing factor with respect to the precision in structuring the material. Furthermore, the influence of the period course, i.e. the spatial modulation of the period of the modification produced in the material of the object (1), shall be improved. The invention proposes that laser radiation is generated as a collimated laser beam (3). The intensity distribution and/or the phase progression is influenced over the cross-section of the laser beam (3) to correct aberrations. The laser beam (3) is divided into two partial beams (6, 7). Finally, the partial beams (6, 7) are deflected and focused so that the partial beams (6, 7) overlap in a processing zone (10) in the material of the object (1). The deflection and focusing of the partial beam (6, 7) is preferably performed by means of adaptive optics (11), which modify the phase and/or intensity profile over the cross section of at least one partial beam (6, 7) and thus adapt the intensity and/or period profile of a structure produced in the object (1) by the interfering partial beams (6, 7). Furthermore, the deflection and focusing of the partial beams (6, 7) preferably includes an aberration correction.

Claims

1. Method for processing an object (1) by means of interfering laser beams, comprising the following process steps: Generation of laser radiation as a collimated laser beam (3) Influencing the intensity distribution and/or the phase progression over the cross section of the laser beam Splitting the laser beam (3) into two partial beams (6, 7), and Deflection and focusing of the partial beams (6, 7) so that the partial beams (6, 7) are superimposed in a processing zone (10) in the material of the object (1).

2. Method according to claim 1, characterized in that the laser radiation is pulsed, wherein the pulse duration is 10 fs to 10 ps and the central wavelength is in the range from 150 nm to 10 m.

3. Method according to claim 1, characterized in that the deflection and focusing of at least one partial beam (6, 7) is effected by means of adaptive optics (11).

4. Method according to claim 3, characterized in that the adaptive optics (11) modify the phase and/or intensity profile over the cross-section of the partial beam (6, 7).

5. Method according to claim 1, characterized in that by modifying the phase and/or intensity profile over the cross-section of at least one partial beam (6, 7), the intensity and/or period profile of a structure generated in the object (1) by the interfering partial beams (6, 7) is adapted.

6. Method according to claim 1, characterized in that the influencing of the intensity distribution and/or the phase progression over the cross-section of the laser beam is effected by means of static or dynamic adaptive optical elements (4a, 4c).

7. Method according to claim 1, characterized in that the deflection and focusing of the partial beams (6, 7) comprises an aberration correction.

8. Apparatus for processing an object by means of interfering laser beams, comprising: a laser (2) which generates laser radiation as a collimated laser beam (3), a phase mask (4, 4a, 4c) which modifies the intensity distribution and/or the phase progression over the cross-section of the laser beam (3), a beam splitter (5) which splits the laser beam (3) into two partial beams (6, 7), and a deflection and focusing optics (8, 9) which superimposes the partial beams in a processing zone (10) in the material of the object (1).

9. Apparatus according to claim 8, characterized in that the deflection and focusing optics (8, 9) comprise at least one adaptive optical element (11).

10. Apparatus according to claim 9, characterized in that the at least one adaptive optical element (11) is a statically or dynamically adaptable reflective or transmissive element which modifies the phase and/or intensity profile over the cross-section of the partial beam (6, 7).

11. Apparatus according to claim 8, characterized in that by modification of the phase and intensity profile over the cross-section of at least one partial beam (6, 7), the intensity and period profile of a structure produced in the object (1) by the interfering partial beams (6, 7) can be adapted.

12. Apparatus according to claim 8, characterized in that a wavefront sensor is arranged downstream of the dynamically adaptable adaptive optical element (11) in the course of the partial beam (6, 7), a control unit (12) regulating the phase and/or intensity course over the cross-section of the partial beam (6, 7) on the basis of the output signal of the wavefront sensor.

13. Apparatus according to claim 8, characterized in that the deflection and focusing optics (8, 9) comprise an aberration correction.

14. Apparatus according to claim 8, characterized in that the phase mask (4) is integrated in the beam splitter (5).

15. Apparatus according to claim 8, characterized in that the deflection and focusing optics (8, 9) have a variable delay path associated with at least one of the partial beams (6, 7).

16. Apparatus according to claim 8, characterized in that at least one static or dynamic adaptive optical element (4a, 4c) modifies the intensity distribution and/or the phase response over the cross-section of the laser beam (3).

17. Apparatus according to claim 8, characterized by an imaging optics (4b) which is arranged in the beam path before the beam splitter (5).

Description

[0031] In the following, examples of the invention are explained in more detail using the figures. They show:

[0032] FIG. 1 schematic representation of an apparatus according to the invention;

[0033] FIG. 2 schematic representation of an apparatus according to the invention in a modified version;

[0034] FIG. 3 schematic representation of the deflection and focusing optics in the design example of FIG. 1.

[0035] In the following figure description the same reference signs and the same terms are used for the same elements.

[0036] FIG. 1 shows an example of an apparatus for processing an object 1 by means of interfering laser beams. The object 1 can be made of transparent, partially transparent or absorptive material, in each case related to the wavelength of the laser radiation used. The apparatus comprises a laser 2, which emits pulsed laser radiation with a pulse duration of, for example, 100 fs, whereby the central wavelength is, for example, 1550 nm. The laser 2 emits the laser radiation as a collimated laser beam 3. The laser beam 3 passes through a phase mask 4, which modifies the intensity distribution and the phase response over the cross section of the laser beam 3. Deviations from the ideal beam path caused by non-idealities of the optical components are compensated by the phase mask 4. Next, the laser beam 3 passes through a beam splitter 5, which splits the laser beam 3 into two partial beams 6 and 7. In each of the partial beams 6, 7 a deflection and focusing optics 8 and 9 respectively is provided. The deflecting and focusing optics 8, 9 cause the partial beams 6, 7 to overlap in a processing zone 10 (diamond-shaped in the design examples) in the material of the object 1. In alternative configurations, the two partial beams 6, 7 can enter the object 1 via the same surface. In the same way, the partial beams 6, 7 can, in extreme cases, run in opposite directions. Any beam geometry is conceivable in which the two partial beams 6, 7 overlap in the volume of object 1 or on its surface. The two deflection and focusing optics 8, 9 each comprise at least one adaptive optical element, which is a statically or dynamically adaptable reflective or transmissive element that modifies the phase and/or intensity profile over the cross-section of the respective partial beam 6, 7. The adaptive optical elements allow a control of the intensity and wavefront progression in the focal interference region 10. In this way the intensity envelope of the respective partial beam 6, 7 as well as the center period and the period progression of the modifications to be generated in the material of the object 1 can be controlled and influenced. According to the invention, adaptive optics is combined with an aberration correction to correct imaging errors due to aberrations.

[0037] The version of FIG. 2 is largely identical to that of FIG. 1, except for the two adaptive optical elements 4a, 4c for phase and intensity modification and the imaging optics 4b arranged in the beam path in front of the beam splitter 5. The problem of compensation of the system-inherent aberrations and the interactions between diffraction and focusing by high numerical apertures can be solved in a particularly efficient way by the approach illustrated in FIG. 2. By using an imaging optics 4b with aberration correction for a given configuration (e.g. modified prism or several prisms to increase the working distance, mirrors) a large part of the imaging errors can be compensated compared to a spherical optics (e.g. cylindrical lens). The adaptive optical elements 4a, 4c allow additional control of the imaging quality. Again, deflection and focusing optics 8, 9 are used to generate the interference rhombus 10 in the material of the object 1. This allows a large working distance from the phase mask 4a, 4c and additionally a large modulation range. The imaging optics 4b act on both partial beams 6, 7, whereas the deflection optics 8, 9 interact individually with only one partial beam 6, 7. Thus, unwanted aberrations of the individual partial beams (e.g. of the individual diffraction orders in a diffraction-based beam splitter 5) can be addressed by the use of static or dynamic-adaptive mirrors. Furthermore, phase and intensity distribution manipulations can be performed in order to adjust the intensity envelope as well as the central period and the period course of the modifications generated in object 1 in a well-defined manner in the interference region 10.

[0038] FIG. 3 shows an example of the design of the deflection and focusing optics 8 schematically. For the deflection of the partial beam 6, this comprises a dynamically adaptive mirror 11, which is controlled by an external control unit 12. The adaptive mirror 11 makes it possible to influence the wavefront of the partial beam 6. In this way, unwanted aberrations accumulated by the partial beam 6 over its course can be individually addressed and compensated. In addition, the influence of the wavefront by means of the adaptive mirror 11 allows the generation of a periodic structure in the material of the object 1. The periodic course can be variably modulated by appropriate adaptation of the surface shape of the mirror 11. A focusing optic 13 features an aberration correction. An imaging lens with an additional lens for aberration correction is provided for this purpose. The aberration correction largely compensates for the spherical aberration that occurs. A particular advantage is that the combination of dynamic compensation by means of adaptive optics with static aberration correction allows the wavefront progression in the focus of the partial beams 6, 7 to be adjusted particularly precisely and variably in order to generate the desired intensity and period progressions in the material of the object in a variable manner.

[0039] Optionally, a wavefront sensor (not shown) can be arranged behind the adaptive mirror in the design example of FIG. 2 in the course of the partial beam 6. This sensor can be connected e.g. via a beam splitter between mirror 11 and focusing optics 13. The wavefront sensor detects the phase and/or intensity profile via the beam cross section, and the control unit 12 regulates the wavefront accordingly to a target profile.