Laser processing

Patent metadata

Field	Value
Publication number	US-11008250-B2
Application number	US-201514738839-A
Country	US
Kind code	B2
Filing date	Jun 13, 2015
Priority date	Jun 25, 2014
Publication date	May 18, 2021
Grant date	May 18, 2021

Abstract

A laser processing method comprises generating a laser beam comprising laser pulses having a duration less than 1000 ps, focussing the laser beam to form a focal region inside a transparent material and varying the position of at least one of the focal region and the transparent material so as to provide a pulse-to-pulse overlap of between 45% and 99%, thereby to form a smooth material modification inside the transparent material.

First claim

The invention claimed is:

1. A laser processing method, comprising:
forming a watermark in a glass material, wherein the watermark comprises a patterned volumetric grating which varies in visibility to the naked eye with changes in a viewing direction and/or an illumination direction, forming the watermark comprising forming a smooth refractive index modification inside the glass material, wherein forming the smooth refractive index modification comprises:
generating a laser beam comprising laser pulses having a duration within the range of 2 ps to 1000 ps;
focussing the laser beam to form a focal region inside the glass material; and
varying the position of at least one of the focal region and the glass material so as to provide a pulse-to-pulse overlap of between 45% and 99%.

2. A laser processing method as claimed in claim 1 , wherein the fluence in the focal region is less than the bulk damage threshold of the glass material.

3. A laser processing method as claimed in claim 1 , wherein the laser pulses have a duration within the range of 2 ps to 30 ps.

4. A laser processing method as claimed in claim 1 , wherein the focal region has a 1/e 2 spot size diameter within the range of 2 μm to 100 μm.

5. A laser processing method as claimed in claim 4 , wherein the focal region has a 1/e 2 spot size diameter within the range of 5 μm to 10 μm.

6. A laser processing method as claimed in claim 1 , wherein the laser pulses have a wavelength within the near-infrared, near UV, or visible region of the electromagnetic spectrum.

7. A laser processing method as claimed in claim 1 , wherein forming the watermark comprises said varying the position of at least one of the focal region and the glass material to provide a pulse overlap of between 45% and 99%, thereby to form a plurality of regions defined by smooth, laser-induced modification of refractive index, wherein said plurality of regions are arranged to cause light propagating in the illumination direction to be redirected such that the mark is visible when viewed in the viewing direction.

8. A laser processing method as claimed in claim 7 , wherein said plurality of regions define a plurality of layers.

9. A laser processing method as claimed in claim 1 , wherein the smooth refractive index modification comprises a diffractive area.

10. A laser processing method as claimed in claim 1 , wherein the position of at least one of the focal region and glass material is varied so as to provide a pulse-pulse overlap of between 50% and 90%.

Assignees

• Fianium Ltd
• Nkt Photonics As

Inventors

• Gerke Timothy

Classifications

• C03C23/0025 Primary

  by a laser beam · CPC title

• B23K26/53

  for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks · CPC title

• B41M5/267 Primary

  Marking of plastic artifacts, e.g. with laser · CPC title

• B23K26/50

  Working by transmitting the laser beam through or within the workpiece · CPC title

• B23K26/0626

  Energy control of the laser beam (B23K26/0622 takes precedence) · CPC title