Series of stacked confocal pulse stretchers for speckle reduction

Patent metadata

Field	Value
Publication number	US-12166327-B2
Application number	US-202017765193-A
Country	US
Kind code	B2
Filing date	Oct 14, 2020
Priority date	Oct 16, 2019
Publication date	Dec 10, 2024
Grant date	Dec 10, 2024

Abstract

An extended optical pulse stretcher is provided that combines confocal pulse stretchers in combination to produce, for example, 4 reflections, 4 reflections, 12 reflections, and 12 reflections per optical circuit configuration. The inclusion of the combination of different mirror separations and delay path lengths can result in very long pulse stretching, long optical delays, and minimal efficiency losses. Also, in the extended optical pulse stretcher, at least a beam splitter can be positioned relative to the center of curvature of the mirrors to “flatten” each of the circuits to enable the beam to propagate in the same plane (e.g., parallel to the floor). Also, the curvatures and sizes of the individual mirrors can be designed to position the beam splitter closer to one of the banks of mirrors to allow the optical pulse stretchers to properly fit in an allocated location in a laser system.

First claim

What is claimed is:

1. An optical pulse stretcher configured to receive a laser beam and generate an output pulse stretched laser beam, the optical pulse stretcher comprising:
a first stage optical pulse stretcher comprising two or more first mirrors forming at least a first confocal resonator and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;
a second stage optical pulse stretcher comprising four or more second mirrors forming at least a second confocal resonator and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam, the four or more second mirrors distinct from the two or more first mirrors; and
a third stage optical pulse stretcher comprising four or more third mirrors forming at least a third confocal resonator and configured to receive a portion of the second pulse stretched laser beam and generate the output pulse stretched laser beam, the four or more third mirrors distinct from the two or more first mirrors and the four or more second mirrors.

2. The optical pulse stretcher of claim 1 , wherein the two or more first mirrors of the first stage optical pulse stretcher, the four or more second mirrors of the second stage optical pulse stretcher, and the four or more third mirrors of the third stage optical pulse stretcher comprise concave mirrors.

3. The optical pulse stretcher of claim 1 , wherein the first stage optical pulse stretcher is configured to generate the first pulse stretched laser beam by reflecting the portion of the laser beam four times using the two or more first mirrors of the first stage optical pulse stretcher.

4. The optical pulse stretcher of claim 1 , wherein the second stage optical pulse stretcher is configured to generate the second pulse stretched laser beam by reflecting the portion of the first pulse stretched laser beam twelve times using the four or more second mirrors of the second stage optical pulse stretcher.

5. The optical pulse stretcher of claim 1 , further comprising:
a first beam splitter corresponding to the first stage optical pulse stretcher and configured to receive the laser beam and direct the portion of the laser beam to the two or more first mirrors of the first stage optical pulse stretcher.

6. The optical pulse stretcher of claim 5 , wherein the first beam splitter is positioned relative to a center of curvature of the two or more first mirrors to flatten the first stage optical pulse stretcher and to enable the portion of the laser beam to propagate in the first stage optical pulse stretcher in a same plane.

7. The optical pulse stretcher of claim 5 , further comprising:
a second beam splitter corresponding to the second stage optical pulse stretcher and configured to receive the first pulse stretched laser beam and direct the portion of the first pulse stretched laser beam to the four or more second mirrors of the second stage optical pulse stretcher.

8. The optical pulse stretcher of claim 7 , further comprising:
a third beam splitter corresponding to the third stage optical pulse stretcher and configured to receive the second pulse stretched laser beam and direct the portion of the second pulse stretched laser beam to the four or more third mirrors of the third stage optical pulse stretcher.

9. The optical pulse stretcher of claim 8 , wherein the third beam splitter is positioned relative to a center of curvature of the four or more third mirrors of the third stage optical pulse stretcher to flatten the third stage optical pulse stretcher and to enable the portion of the second pulse stretched laser beam to propagate in the third stage optical pulse stretcher in a same plane.

10. The optical pulse stretcher of claim 8 , wherein:
the second beam splitter is positioned closer to a first pair of the four or more second mirrors of the second optical pulse stretcher,
the second beam splitter is a D shape beam splitter,
the third beam splitter is positioned closer to a first pair of the four or more third mirrors of the third optical pulse stretcher, and
the third beam splitter is a D shape beam splitter.

11. The optical pulse stretcher of claim 1 , wherein:
the laser beam received by the first stage optical pulse stretcher comprises a pulse stretched laser beam generated by an orthogonal stage optical pulse stretcher, and
the orthogonal stage optical pulse stretcher is positioned outside of and approximately perpendicular to the optical pulse stretcher.

12. A laser source, comprising:
an optical pulse stretcher configured to receive a laser beam and generate an output pulse stretched laser beam, the optical pulse stretcher comprising:
a first stage optical pulse stretcher comprising two or more first mirrors forming at least a first confocal resonator and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;
a second stage optical pulse stretcher comprising four or more second mirrors forming at least a second confocal resonator and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam, the second mirrors being distinct from the first mirrors; and
a third stage optical pulse stretcher comprising four or more third mirrors forming at least a third confocal resonator and configured to receive a portion of the second pulse stretched laser beam and generate the output pulse stretched laser beam, the third mirrors being distinct from the first mirrors and the second mirrors.

13. A lithographic apparatus, comprising:
an illumination system configured to condition a radiation beam;
a support structure configured to support a patterning device;
a substrate table configured to hold a substrate; and
a projection system configured to project a pattern imparted to the radiation beam by the patterning device onto a target portion of the substrate,
wherein the illumination system comprises a laser source, the laser source comprising an optical pulse stretcher configured to receive a laser beam and generate an output pulse stretched laser beam, the optical pulse stretcher comprising:
a first stage optical pulse stretcher comprising at least a first confocal resonator and configured to receive a portion of the laser beam and generate a first pulse stretched laser beam;
a second stage optical pulse stretcher comprising at least a second confocal resonator distinct from the at least first confocal resonator, and configured to receive a portion of the first pulse stretched laser beam and generate a second pulse stretched laser beam; and
a third stage optical pulse stretcher comprising at least a third confocal resonator distinct from the at least first confocal resonator and the at least second confocal resonator, and configured to receive a portion of the second pulse stretched laser beam and generate the output pulse stretched laser beam.

14. The lithographic apparatus of claim 13 , wherein:
the first stage optical pulse stretcher has a first optical delay,
the second stage optical pulse stretcher has a second optical delay equal to or greater than the first optical delay, and
the third stage optical pulse stretcher has a third optical delay equal to or greater than the second optical delay.

15. The lithographic apparatus of claim 13 , wherein:
the first stage optical pulse stretcher is configured to generate the first pulse stretched laser beam by reflecting the portion of the laser beam four times,
the second stage optical pulse stretcher is configured to generate the second pulse stretched laser beam by reflect

Assignees

• Cymer LLC

Inventors

• Mason Eric Anders
• Zhao Zhong Quan
• Ye Hong

Classifications

• H01S3/225

  comprising an excimer or exciplex · CPC title

• H01S3/0071

  Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction · CPC title

• G03F7/70025

  by lasers · CPC title

• G02B27/145

  having sequential partially reflecting surfaces · CPC title

• G02B17/004

  Systems comprising a plurality of reflections between two or more surfaces, e.g. cells, resonators (multipass arrangements for optical cuvettes G01N21/031; laser resonators H01S3/05) · CPC title