Spot size and distance characterization for a laser tool

• US 6,667,458 B1
• Filed: 04/19/2001
• Issued: 12/23/2003
• Est. Priority Date: 04/19/2000
• Status: Expired due to Term

• Current Assignee: Optimet, Optical Metrology Ltd. (MKS Instruments Incorporated)
• Original Assignee: Optimet, Optical Metrology Ltd. (MKS Instruments Incorporated)
• Inventors: Sirat, Gabriel Y.
• Primary Examiner(s): Heinrich, Samuel M.
• Application Number:
  US09/838,536
• Time in Patent Office: 978 Days
• Field of Search: 219/121.6, 219/121.67, 219/121.68, 219/121.69, 219/121.63, 219/121.72, 219/121.83, 219/121.85
• US Class Current: 219/121.83
• CPC Class Codes: B23K 26/04 Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• CPC Class Codes: B23K 26/043 along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus

Abstract

A system and method for maintaining a specified distance between the focus of a laser tooling beam of a laser machining system and a workpiece. The system includes an optical assembly for focusing the tooling beam substantially onto a spot on the surface of the workpiece and a beam splitter for deflecting light retro-reflected from the workpiece and through the optical assembly. The system also includes a distance-measuring apparatus, such as a conoscope, for receiving the retro-reflected beam and for determining the distance to the spot on the surface of the workpiece relative to a fiducial reference as well as a controller for governing the location of the workpiece relative to the focus of the optical assembly based on the measured distance of the spot.

Claims

1. A method for maintaining a specified distance between the focus of an optical assembly of a laser machining system having a tooling beam and a workpiece having a surface disposed at a location relative to the focus of the optical assembly, the method comprising:

a. focusing a light output of a light source co-aligned with the tooling beam through the optical assembly substantially onto a single spot on the surface of the workpiece, the light source being characterized by a spectrum;

b. deflecting light of the light source retro-reflected from the workpiece and through the optical assembly onto a distance-measuring apparatus;

c. measuring the distance to the spot on the surface of the workpiece relative to a fiducial reference; and

d. governing the location of the workpiece relative to the focus of the optical assembly based on the measured distance of the spot.

2. A method according to claim 1, wherein the step of focusing the light output of a light source includes focusing the light output of a light source that is identical to a source of optical power used for at least one of welding and ablating the workpiece.

3. A method according to claim 1, wherein the step of focusing the light output of a light source includes focusing the light output of a light source characterized by a spectrum substantially identical to the spectrum of the source of optical power used for welding or ablating the workpiece.

4. A method according to claim 1, wherein the step of measuring the distance to the spot on the surface of the workpiece includes measuring the distance with a conoscopic holography apparatus.

5. A method according to claim 1, wherein the step of measuring the distance to the spot on the surface of the workpiece includes measuring the distance with an autofocus apparatus.

6. A method according to claim 1, wherein the step of measuring the distance to the spot on the surface of the workpiece includes measuring the distance with a Shack-Hartmann wavefront sensor.

7. A system for maintaining a specified distance between the focus of a laser tooling beam of a laser machining system and a workpiece having a surface disposed at a location relative to the focus of the tooling beam, the system comprising:

a. an optical assembly for focusing the output of a light source co-aligned with the tooling beam substantially onto a spot on the surface of the workpiece;

b. a beam splitter for deflecting light retro-reflected from the workpiece and through the optical assembly;

c. a distance-measuring apparatus for receiving the retro-reflected beam and for determining the distance to the spot on the surface of the workpiece relative to a fiducial reference; and

d. a controller for governing the location of the workpiece relative to the focus of the optical assembly based on the measured distance of the spot.

8. A system according to claim 7, wherein the distance-measuring apparatus is a conoscopic holography apparatus.

9. A system according to claim 7, wherein the distance-measuring apparatus is an autofocus apparatus.

10. A system according to claim 7, wherein the distance-measuring apparatus is a Shack-Hartmann wavefront sensor.

11. A system according to claim 7, wherein the light source is identical to a source of optical power used for at least one of welding and ablating the workpiece.

12. A system according to claim 7, wherein the spectrum of the light source is substantially identical to the spectrum of the source of optical power used for welding or ablating the workpiece.