Beam characterization by wavefront sensor

• US 5,936,720 A
• Filed: 07/07/1998
• Issued: 08/10/1999
• Est. Priority Date: 07/10/1996
• Status: Expired due to Term

• Current Assignee: AMO Development LLC (Johnson & Johnson)
• Original Assignee: Amo Wavefront Sciences LLC (Johnson & Johnson)
• Inventors: Neal, Daniel R., Alford, W. J., Gruetzner, James K.
• Primary Examiner(s): MANUEL, GEORGE C
• Application Number:
  US09/111,620
• Time in Patent Office: 399 Days
• Field of Search: 430/321, 359/573, 359/559, 359/566, 359/619, 359/846, 359/847, 359/848, 359/849, 365/106, 365/127, 356/121, 250/201.9, 250/208.1
• US Class Current: 356/121
• CPC Class Codes: G01J 11/00 Measuring the characteristics of individual optical pulses or of optical pulse trains
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 3/0025 Machining, e.g. grinding, polishing, diamond turning, manufacturing of mould parts
• CPC Class Codes: G02B 3/0056 arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085
• CPC Class Codes: G02B 3/0075 characterized by non-optical structures, e.g. having integrated holding or alignment means
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1885 Arranged as a periodic array

Abstract

An apparatus and method for characterizing an energy beam (such as a laser) with a two-dimensional wavefront sensor, such as a Shack-Hartmann lenslet array. The sensor measures wavefront slope and irradiance of the beam at a single point on the beam and calculates a space-beamwidth product. A detector array such as a charge coupled device camera is preferably employed.

Claims

1. An apparatus for characterizing an energy beam comprising

a lenslet array for separating the energy beam to a plurality of spots;

detection means for converting a pattern of said spots to electronic signals; and

computing means for determining wavefront slope distribution and beam wavefront and irradiance distribution.

2. The apparatus of claim 1 wherein said apparatus comprises a Shack-Hartmann wavefront sensor.

3. The apparatus of claim 1 additionally comprising means for integrating wavefront slope distribution to produce information selected from the group consisting of wavefront information and phase information.

4. The apparatus of claim 1 wherein said computing means determines wavefront slope distribution and beam wavefront and irradiance distribution of the beam at a single location along the beam.

5. The apparatus of claim 1 additionally comprising means for calculating a space-beamwidth product.

6. The apparatus of claim 5 wherein said means for calculating a space-beamwidth product comprises gradient method calculation means.

7. The apparatus of claim 5 wherein said means for calculating a space-beamwidth product comprises curvature removal method calculation means.

8. The apparatus of claim 5 wherein said means for calculating a space-beamwidth product comprises Fourier propagation method calculation means.

9. The apparatus of claim 1 wherein said apparatus characterizes a laser beam.

10. The apparatus of claim 1 wherein said detection means comprises a detector array.

11. The apparatus of claim 10 wherein said detector array comprises a device selected from the group consisting of charge coupled/device cameras, charge inductive device cameras, and CMOS cameras.

12. The apparatus of claim 10 wherein said lenslet array is rigidly mounted directly in front of said detector array.

13. The apparatus of claim 12 additionally comprising shims for adjusting spacing between said lenslet array and said detector array.

14. The apparatus of claim 13 additionally comprising means for computing shim size and placement to properly adjust said spacing.

15. The apparatus of claim 1 additionally comprising means for calibrating said apparatus.

16. The apparatus of claim 15 wherein the calibrating step comprises comparing against a known optically induced wavefront characteristic selected from the group consisting of curvature and tilt.

17. The apparatus of claim 16 wherein said means for computing one or more spot positions comprises a means selected from the group consisting of center-of-mass computation means, matched filter means, and correlation means.

18. The apparatus of claim 15 wherein said means for calibrating comprise means for generating a reference beam and means for computing one or more spot positions.

19. A method for characterizing an energy beam comprising the steps of:

a) separating the energy beam to a plurality of spots using a lenslet array;

b) converting a pattern of the spots to electronic signals; and

c) determining wavefront slope distribution and beam wavefront and irrandiance distribution.

20. The method of claim 19 wherein the method employs a Shack-Hartmann wavefront sensor.

21. The method of claim 19 additionally comprising the step of integrating wavefront slope distribution to produce information selected from the group consisting of wavefront information and phase information.

22. The method of claim 19 wherein the determining step comprises determining wavefront slope distribution and beam wavefront and irradiance distribution of the beam at a single location along the beam.

23. The method of claim 19 additionally comprising the step of calculating a space-beamwidth product.

24. The method of claim 23 wherein the calculating step comprises gradient method calculation.

25. The method of claim 23 wherein the calculating step comprises curvature removal method calculation.

26. The method of claim 23 wherein the calculating step comprises Fourier propagation method calculation.

27. The method of claim 19 additionally comprising the step of characterizing a laser beam.

28. The method of claim 19 wherein the separating step comprises using a detector array.

29. The method of claim 28 wherein using a detector array comprises using a device selected from the group consisting of charge coupled device cameras, charge inductive device cameras, and CMOS cameras.

30. The method of claim 28 additionally comprising the step of rigidly mounting the lenslet array directly in front of the detector array.

31. The method of claim 30 additionally comprising employing shims to adjust spacing between the lenslet array and the detector array.

32. The method of claim 31 additionally comprising the step of computing shim size and placement to properly adjust the spacing.

33. The method of claim 19 additionally comprising the step of calibrating.

34. The method of claim 33 wherein the calibrating step comprises comparing against a known optically induced wavefront characteristic selected from the group consisting of curvature and tilt.

35. The method of claim 33 wherein the calibrating step comprises generating a reference beam and computing one or more spot positions.

36. The method of claim 33 wherein the computing step comprises a step selected from the group consisting of center-of-mass computation, matched filter computation, and correlation computation.