Diffractive optical beam shaping element

Patent metadata

Field	Value
Publication number	US-10620444-B2
Application number	US-201715599623-A
Country	US
Kind code	B2
Filing date	May 19, 2017
Priority date	Nov 19, 2014
Publication date	Apr 14, 2020
Grant date	Apr 14, 2020

Abstract

A diffractive optical beam shaping element for imposing a phase distribution on a laser beam that is intended for laser processing of a material includes a phase mask that is shaped as an area and is configured for imposing a plurality of beam shaping phase distributions on the laser beam incident on to the phase mask. A virtual optical image is attributed to at least one of the plurality of beam shaping phase distributions, wherein the virtual image can be imaged into an elongated focus zone for creating a modification in the material to be processed. Multiple such elongated focus zones can spatially add up and interfere with each other, to modify an intensity distribution in the material and, for example, generate an asymmetric modification zone.

First claim

What is claimed is:

1. A diffractive optical beam shaping element for imposing a phase distribution on a laser beam that is intended for laser processing of a material, which is essentially transparent for the laser beam, comprising
a phase mask that is configured for imposing a plurality of beam shaping phase distributions on the laser beam incident on to the phase mask;
wherein a virtual optical image is attributed to at least one of the plurality of beam shaping phase distributions, the virtual optical image being imageable into an elongated focus zone for creating a modification in the material to be processed.

2. The diffractive optical beam shaping element of claim 1 , wherein the phase mask is configured such that at least one of the plurality of beam shaping phase distributions forms a ring structure, a ring segment structure limited to an azimuthal angular range, and/or a local maximum in a transverse output intensity distribution.

3. The diffractive optical beam shaping element of claim 1 , wherein
the phase mask is configured such that at least one of the plurality of beam shaping phase distributions transfers an incident laser beam having a Gaussian intensity distribution into at least one divergent beam area attributed to the virtual optical image, the divergent beam area comprising downstream of the diffractive optical beam shaping element a transverse intensity distribution, which decreases from the inside to the outside, and/or
the phase mask is configured such that at least one of the plurality of beam shaping phase distributions transfers an incident laser beam into at least one divergent beam area attributed to the virtual optical image, the divergent beam area comprising downstream of the diffractive optical beam shaping element a transverse intensity distribution that comprises a section of a step-shaped intensity increase, which comprises a steep flank facing radially to the inside.

4. The diffractive optical beam shaping element of claim 3 , wherein the transverse intensity distribution is present before a far field focal length attributed to a focusing action of the phase mask.

5. The diffractive optical beam shaping element of claim 1 , wherein
a virtual optical image is respectively attributed to several phase distributions of the plurality of beam shaping phase distributions and the virtual optical images are configured for being imaged in respective focus zones in order to shape in combination the modification in the material to be processed.

6. The diffractive optical beam shaping element of claim 1 , wherein
the focus zones are superposed with respect to each other and/or spatially complement each other.

7. The diffractive optical beam shaping element of claim 1 , wherein
the phase mask is configured such that the phase distributions of the plurality of beam shaping phase distributions image the respective virtual optical images in an asymmetric transverse intensity distribution in the material to be processed.

8. The diffractive optical beam shaping element of claim 7 , wherein the asymmetric transverse intensity distribution in the material to be processed is based on an asymmetry of a focus zone itself and/or on the asymmetric arrangement of multiple focus zones with respect to each other.

9. The diffractive optical beam shaping element of claim 1 , further comprising at least one of
a separate far field optical element and
a far field optical phase imposing integrated into the phase mask,
wherein the far field optical element and/or the far field optical phase imposing is configured to perform a focusing action on the laser beam, in order to form the output intensity distribution for the at least the one virtual optical image in a respective focal plane.

10. The diffractive optical beam shaping element of claim 1 , wherein
the phase increase generated by a section of the phase mask, which is configured areally, is a combination of phase contributions, which are respectively attributed to the plurality of beam shaping phase distributions.

11. The diffractive optical beam shaping element of claim 1 , wherein
at least two images of the virtual optical images are superposed while interfering or form a common elongated focus zone.

12. An optical system for beam shaping of a laser beam for processing a transparent material by modifying the material in a focus zone that is elongated in a common propagation direction, the optical system comprising
the diffractive optical beam shaping element of claim 1 ; and
a near field optical element, which is arranged downstream of the diffractive optical beam shaping element at a beam shaping distance and configured to focus the laser beam into the focus zone, wherein
at least one imposed phase distribution of the plurality of beam shaping phase distributions is such that a virtual optical image of an elongated focus zone is attributed to the laser beam, the virtual optical image being located before the diffractive optical beam shaping element, and
the beam shaping distance corresponds to a propagation length of the laser beam within which the plurality of beam shaping phase distributions transform the transverse input intensity profile into a transverse output intensity profile in the region of the near field optical element.

13. The optical system of claim 12 , wherein the transverse output intensity profile has, in comparison with the input intensity profile, at least one local maximum lying outside of a beam axis.

14. The optical system of claim 12 , wherein
the diffractive optical beam shaping element is arranged to be rotatable around a beam axis of the incident laser beam to set an asymmetric transverse intensity distribution in the workpiece in its orientation with respect to a preferred direction.

15. The optical system of claim 12 , wherein an imaging system attributes to the beam shaping element an image plane downstream of a longitudinal center of the image of the virtual optical image, and a transverse beam profile of the laser beam is present at the beam shaping element in the image plane.

16. The optical system of claim 15 , 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.

17. The optical system of claim 12 , wherein only a central area of the incident laser beam contributes to a downstream end of the focus zone attributed to the virtual optical image, so that a change of the beam diameter of the incident laser beam does not result in an essentially longitudinal displacement of the downstream end of the focus zone.

18. A laser processing machine for processing a material, which is to a large extent transparent for the laser beam, with a laser beam by modifying the material in a focus zone, which is elongated in a common propagation direction of the laser beam, comprising
a laser beam source;
an optical system of claim 12 ; and
a control unit for setting operation parameters.

19. The laser processing machine of claim 18 , wherein the control unit is configured for orienting a transverse asymmetric intensity distribution with respect to a preferred direction.

20. The laser processing machine of claim 18 , wherein the control unit is configured for setting a rotation angle of the diffractive optical beam shaping element with respect to the beam axis of the incident laser beam.

21. A diffractive optical beam shaping element for impos

Assignees

• Trumpf Laser & Systemtechnik Gmbh

Inventors

• Kumkar Malte
• Grossmann Daniel
• Flamm Daniel

Classifications

• B23K26/066

  by using masks · CPC title

• B23K26/064

  by means of optical elements, e.g. lenses, mirrors or prisms · CPC title

• G02B27/0944 Primary

  Diffractive optical elements, e.g. gratings, holograms (gratings per se G02B5/18; holograms used as optical elements per se G02B5/32) · CPC title

• B23K26/0624

  using ultrashort pulses, i.e. pulses of 1 ns or less · CPC title

• G02B27/425

  in illumination systems (mask illumination systems in photolithographic systems G03F7/70158) · CPC title