Optical system for beam shaping

Abstract

An optical system for shaping a laser beam includes a beam shaping element configured to receive the laser beam having a transverse input intensity profile and to impose a beam shaping phase distribution onto the laser beam. The optical system further includes a near field optical element, arranged downstream of the beam shaping element at a beam shaping distance and is configured to focus the laser beam into the focus zone. The imposed phase distribution results in a virtual optical image of the elongated focus zone located before the beam shaping element. The beam shaping distance corresponds to a propagation length of the laser beam within which the imposed phase distribution transforms the transverse input intensity profile into a transverse output intensity profile at the near field optical element.

What is claimed is: 
     
         1 .- 19 . (canceled) 
     
     
         20 . An optical system for modifying a shape of a laser beam that processes a material in a focus zone elongated in a propagation direction, the optical system comprising:
 a beam shaping element arranged to receive the laser beam having a transverse input intensity profile, wherein the beam shaping element is configured to impose a beam shaping phase distribution over the transverse input intensity profile of the laser beam; and   a near field optic arranged downstream of the beam shaping element at a beam shaping distance, wherein the near field optic is configured to focus the laser beam into the focus zone so that a virtual optical image of the elongated focus zone appears at a position before the beam shaping element, and   wherein the beam shaping distance corresponds to a propagation length of the laser beam within which the imposed phase distribution transforms the transverse input intensity profile into a transverse output intensity profile in the region of the near field optic, and the transverse output intensity profile has, in comparison with the input intensity profile, a local maximum lying outside of a beam axis.   
     
     
         21 . The optical system of  claim 20 , wherein the optical system is an imaging system comprising a demagnifying imaging ratio for imaging the virtual optical image and for generating the elongated focus zone. 
     
     
         22 . The optical system of  claim 21 , wherein the beam shaping element is configured to impose onto the laser beam a spherical phase distribution with focusing action such that imaging of the virtual optical image onto the elongated focus zone is performed by both the imposed spherical phase distribution of the beam shaping element and the focusing of the near field optic. 
     
     
         23 . The optical system of  claim 21 , wherein the optical system comprises a far field optic arranged adjacent to the beam shaping element such that imaging of the virtual optical image onto the elongated focus zone is performed by both focusing of the far field optic and focusing of the near field optic. 
     
     
         24 . The optical system of  claim 20 , wherein a transverse beam profile of the laser beam is present at the beam shaping element in an image plane downstream of a longitudinal center of the image of the virtual optical image. 
     
     
         25 . The optical system of  claim 24 , wherein there is in the region of the image plane a change, which changes fast in longitudinal direction, from a lateral beam profile, which is given in the focus zone, to a lateral beam profile having a dark center, the latter for an lateral Gaussian beam profile of the laser beam and with respect to beam portions of the incident laser beam, which generate a divergent beam area that is attributed to the virtual optical image. 
     
     
         26 . The optical system of  claim 20 , wherein the optical system is configured such that only a central area of the laser beam contributes to a downstream end of the virtual optical image of the focus zone, so that a change of the beam diameter of the laser beam does not result in an longitudinal displacement of the downstream end of the focus zone. 
     
     
         27 . The optical system of  claim 20 , wherein the laser beam comprises a Gaussian intensity distribution, and wherein the beam shaping phase distribution is configured to generate, for a portion of the laser beam, a divergent beam area comprising, downstream of the optical beam shaping element, a transverse intensity distribution decreasing from an inner region to outer region. 
     
     
         28 . The optical system of  claim 28 , comprising a far field optic, wherein the transverse intensity distribution is present upstream of a downstream focal plane of the far field optic, and
 wherein a phase imposed beam area comprises a lateral intensity distribution having a section of a step-shaped increase of intensity, which comprises a radially inward facing flank in the region between the beam shaping element and a focal plane, which is attributed to at least one of the near field optic, the far field optic and the beam shaping element.   
     
     
         29 . The optical system of  claim 28 , wherein the lateral intensity distribution comprises a radially outward facing flank in the region between the focal plane and the focus zone. 
     
     
         30 . The optical system of  claim 28 , wherein the phase distribution is such that at least one of an inverse quasi-Bessel beam-like beam profile or an inverse quasi-Airy beam-like beam profile is formed, for which only a central area of the laser beam provides contributions to a downstream end of the elongated focus zone. 
     
     
         31 . The optical system of  claim 20 , wherein the beam shaping element is configured to induce phase-modulation without amplitude modulation. 
     
     
         32 . The optical system of  claim 20 , wherein the beam shaping element comprises a hollow cone axicon-lens or mirror system, a reflective axicon-lens or mirror system, or a programmable diffractive optical element. 
     
     
         33 . The optical system of  claim 20 , wherein the beam shaping element is configured to impose a linear phase distribution, so that a spatial separation of a usable beam portion from a disturbing beam portion is achieved by a lateral beam deflection of the usable beam portion. 
     
     
         34 . The optical system of  claim 20 , wherein the elongated focus zone comprises an aspect ratio of at least 10:1. 
     
     
         35 . The optical system of  claim 20 , wherein the elongated focus zone is an inverse Bessel beam-like beam focus zone, an inverse Airy beam-like beam focus zone, or a combination therefore. 
     
     
         36 . The optical system of  claim 20 , comprising a scan unit configured to scan the elongated focus zone with respect to the material. 
     
     
         37 . The optical system of  claim 20 , comprising a beam preparation unit configured to adapt at least one of the transverse input intensity profile of the laser beam, an input divergence of the laser beam, and a polarization of the laser beam. 
     
     
         38 . An optical system for modifying a shape of a laser beam that processes a material, the optical system comprising:
 a beam shaping element arranged to impose a beam shaping profile onto the laser beam, wherein the beam shaping profile comprises an inverse quasi-Bessel beam-like beam profile, an inverse quasi-Airy beam-like beam profile, or a combination thereof; and   a near field optic arranged downstream of the beam shaping element, wherein the near field optic focuses the laser beam onto which the beam shaping profile is imposed into a focus zone elongated in propagation direction of the laser beam, wherein only a central region of the laser beam makes contributions to a downstream end of the elongated focus zone.   
     
     
         39 . A laser processing machine comprising:
 a laser beam source;   an optical system according to  claim 20 ; and   a workpiece positioning unit for positioning the material as a workpiece.   
     
     
         40 . The laser processing machine of  claim 39 , comprising:
 a control unit configured perform a control operation, wherein the control operation comprises:   i) setting a downstream end of the elongated focus zone with respect to a workpiece positioning unit;   ii) setting an elongation parameter of the laser beam and the optical system, wherein the elongation parameter specifies an elongation of the elongated focus zone in an upstream direction, wherein at the same time the position of the downstream end of the elongated focus zone is maintained with respect to the workpiece positioning unit without a follow-up correction of a distance of a near field optics to the workpiece positioning unit; or   iii) a combination of i) and ii).   
     
     
         41 . The laser processing machine of  claim 39 , wherein the laser beam source is configured to generate a laser beam that modifies the material by nonlinear absorption. 
     
     
         42 . The laser processing machine of  claim 41 , wherein the laser beam source is further configured to focus laser pulses to a fluence of 2 J/cm 2  within the elongated focus zone. 
     
     
         43 . A method for beam shaping a laser beam, the method comprising:
 imposing a beam shaping phase distribution onto a transverse input intensity profile of a laser beam, wherein the imposed phase distribution is such that a virtual optical image of the elongated focus zone is produced;   propagating the laser beam over a beam shaping distance after which the imposed phase distribution has transferred the transverse input intensity profile into a transverse output intensity profile, so that the transverse output intensity profile, in comparison to the input intensity profile, comprises a local maximum located outside of a beam axis of the laser beam; and   focusing the laser beam into the focus zone to form a near field based on the transverse output intensity profile.   
     
     
         44 . The method of  claim 43 , wherein imposing the beam shaping phase distribution onto the transverse input intensity profile is performed together with at least one other step, wherein the at least one other step comprises:
 imposing a spherical phase distribution onto the laser beam;   imposing a linear phase distribution onto the laser beam;   filtering out a beam portion of the laser beam;   filtering out a central non-modulated beam portion of the laser beam; or   filtering out beam portions of higher diffraction order from the laser beam.   
     
     
         45 . A method for processing a material with a laser beam, the method comprising:
 applying a phase modulation to the laser beam to generate at least one of an inverse quasi-Bessel beam-like laser beam profile or an inverse quasi-Airy beam-like laser beam profile with a focus zone, wherein the focus zone is elongated in a propagation direction; and   positioning the focus zone at least partly in the material to be processed.   
     
     
         46 . A method for laser material processing of a material with a laser beam, the method comprising:
 applying a phase modulation to the laser beam to generate at least one of an inverse quasi-Bessel beam-like laser beam profile or an inverse quasi-Airy beam-like laser beam profile with a focus zone, wherein the focus zone is elongated in a propagation direction, wherein applying the phase modulation comprises:   passing the laser beam through a beam shaping element configured to impose a beam shaping phase distribution over a transverse input intensity profile of the laser beam;   subsequently focusing the laser beam into a focus zone with a near field optic arranged downstream of the beam shaping element at a beam shaping distance,   wherein the imposed beam shaping phase distribution is such that a virtual optical image of the focus zone is located before the beam shaping element, and   wherein the beam shaping distance corresponds to a propagation length of the laser beam within which the beam shaping phase distribution transforms the transverse input intensity profile into a transverse output intensity profile in a region adjacent to the near field optic, and the transverse output intensity profile has, in comparison with the input intensity profile, a local maximum lying outside of a beam axis;   positioning the focus zone at least partly in the material to be processed.   
     
     
         47 . The method of  claim 46 , comprising:
 setting a position of a downstream end of the focus zone with respect to a workpiece positioning unit.