Regenerative ring resonator

• US 8,014,432 B2
• Filed: 03/16/2010
• Issued: 09/06/2011
• Est. Priority Date: 03/27/2009
• Status: Expired

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Sandstrom, Richard L., Ye, Hong, Rafac, Robert J., Brown, Daniel J. W., Rokitski, Slava
• Primary Examiner(s): Nguyen; Dung T
• Application Number:
  US12/724,681
• Publication Number:
  US 20110069733A1
• Time in Patent Office: 539 Days
• Field of Search: 372/55, 372/61, 372/95, 372/99, 372/100
• US Class Current: 372/55
• CPC Class Codes: H01S 3/02 Constructional details housings or packages of fibre lasers H01S3/06704
• CPC Class Codes: H01S 3/0804 Transverse or lateral modes
• CPC Class Codes: H01S 3/0805 by apertures, e.g. pin-holes or knife-edges
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/08072 Thermal lensing or thermally induced birefringence; Compensation thereof
• CPC Class Codes: H01S 3/08081 Unstable resonators
• CPC Class Codes: H01S 3/0835 Gas ring lasers
• CPC Class Codes: H01S 3/10092 Coherent seed, e.g. injection locking
• CPC Class Codes: H01S 3/1053 Control by pressure or deformation
• CPC Class Codes: H01S 3/225 comprising an excimer or exciplex
• CPC Class Codes: H01S 3/235 Regenerative amplifiers
• CPC Class Codes: H01S 3/2366 comprising a gas as the active medium H01S3/10092, H01S3/2383 take precedence

Abstract

A laser includes a regenerative ring resonator that includes a discharge chamber having electrodes and a gain medium between the electrodes for producing a laser beam; a partially-reflective optical coupler, and a beam modification optical system in the path of the laser beam. The beam modification optical system transversely expands a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the laser and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at powers that induce thermal lenses in optical elements inside the regenerative ring resonator.

Claims

1. A laser comprising:

a regenerative ring resonator comprising;

a discharge chamber having electrodes and a gain medium between the electrodes;

an optical coupler that is partially reflective so that at least a portion of a laser beam impinging on the optical coupler from the discharge chamber is reflected back through the discharge chamber and at least a portion of the laser beam impinging on the optical coupler from the discharge chamber is transmitted through the optical coupler; and

a beam modification optical system in the path of the laser beam;

wherein the beam modification optical system transversely expands a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the laser and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at average output powers that induce thermal lenses in optical elements inside the regenerative ring resonator.

2. The laser of claim 1, wherein the beam modification optical system is between the optical coupler and a beam turning optical element placed on a side of the discharge chamber opposite to a side facing the optical coupler.

3. The laser of claim 1, wherein the beam modification optical system is configured to cause the laser beam at the exit of the regenerative ring resonator to have the same or a larger size of the transverse beam profile than the size of the transverse beam profile of the laser beam entering the regenerative ring resonator.

4. The laser of claim 1, wherein the beam modification optical system is configured to impart a negative curvature to the wavefront of the laser beam circulating within the regenerative ring resonator.

5. The laser of claim 4, wherein the beam modification optical system negatively alters the curvature along a transverse direction.

6. The laser of claim 4, wherein the beam modification optical system comprises a highly reflective mirror.

7. The laser of claim 6, wherein the optical system includes the highly reflective mirror that is convex.

8. The laser of claim 7, wherein the convex highly reflective mirror has a radius of curvature of between about 50 m and about 170 m.

9. The laser of claim 1, further comprising a beam turning optical element external to the discharge chamber and in the path of the laser beam on a side of the discharge chamber that is opposite to a side that faces the optical system.

10. The laser of claim 1, wherein the regenerative ring resonator remains marginally unstable if the size of the transverse profile of the laser beam increases as the laser beam travels through a portion of the regenerative ring resonator but the laser beam transverse profile size does not exceed the transverse size of any of the optical components within the regenerative ring resonator before being decoupled out of the regenerative ring resonator through the optical coupler.

11. The laser of claim 1, wherein the beam modification optical system comprises a set of prisms.

12. The laser of claim 11, wherein the prism set comprises first, second, and third prisms configured and arranged so that the first and third prisms reduce the transverse size of the profile of the laser beam travelling along a first direction through the beam modification optical system, and the third and second prisms increase the transverse size of the profile of the laser beam travelling along a second direction through the beam modification optical system.

13. The laser of claim 12, wherein the one or more first, second, and third prisms are adjusted so that the transverse size of the profile of the laser beam travelling along the second direction through the beam modification optical system and exiting the prism set is greater than the transverse size of the profile of the laser beam travelling along the first direction from the optical coupler to the prism set.

14. The laser of claim 1, wherein the laser beam output from the regenerative ring resonator has an average irradiance of at least about 5 W/cm².

15. The laser of claim 1, wherein the laser beam output from the regenerative ring resonator has an irradiance of at least about 10 W/cm².

29. The laser of claim 1, wherein the laser beam output from the regenerative ring resonator has an average output power of greater than 40 W.

16. A method of modifying a laser beam of an electric discharge gas laser, the method comprising:

directing a laser beam through an optical coupler of a regenerative ring resonator;

directing the laser beam that passes through the optical coupler through a discharge chamber and back to the optical coupler such that at least some of the light impinging on the optical coupler from the discharge chamber is reflected back through the discharge chamber and at least some of the light impinging on the optical coupler from the discharge chamber is transmitted through the optical coupler; and

transversely expanding a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the laser and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at powers that cause thermal lensing of elements within the regenerative ring resonator.

17. The method of claim 16, wherein transversely expanding the profile of the laser beam comprises:

compressing a profile of the laser beam by passing the laser beam from the optical coupler through first and third prisms of a prism set before directing the laser beam through the discharge chamber; and

expanding a profile of the laser beam after it has passed through the discharge chamber by passing the laser beam through the third prism and through a second prism of the prism set before reaching the optical coupler.

18. The method of claim 17, wherein expanding the laser beam profile includes expanding the laser beam profile to a size that is larger than the profile of the laser beam input to the prism set.

19. The method of claim 16, wherein the regenerative ring resonator remains marginally unstable if the size of the transverse profile of the laser beam increases as the laser beam travels through at least a portion the regenerative ring resonator but the laser beam transverse profile size does not exceed the transverse size of any of the optical components within the regenerative ring resonator before being decoupled out of the regenerative ring resonator through the optical coupler.

20. The method of claim 16, wherein transversely expanding the profile of the laser beam includes imparting a negative curvature to the wavefront of the laser beam circulating within the regenerative ring resonator.

21. A regenerative ring resonator in the path of a laser beam, the resonator comprising:

a discharge chamber having electrodes and a gain medium between the electrodes;

an optical coupler that is partially reflective so that at least some of the light impinging on the optical coupler from the discharge chamber is reflected back through the discharge chamber and at least some of the light impinging on the optical coupler from the discharge chamber is transmitted through the optical coupler; and

a beam modification optical system in the path of the laser beam;

wherein the beam modification optical system is configured to transversely expand a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the resonator and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at powers that cause thermal lensing of elements inside of the regenerative ring resonator.

22. The resonator of claim 21, wherein the beam modification optical system is between the optical coupler and a beam turning optical element placed on a side of the discharge chamber opposite to a side facing the optical coupler.

23. The resonator of claim 21, wherein the beam modification optical system is configured to impart a negative curvature to the wavefront of the laser beam circulating within the regenerative ring resonator.

24. The resonator of claim 23, wherein the beam modification optical system comprises a highly reflective convex mirror.

25. The resonator of claim 21, wherein the regenerative ring resonator remains marginally unstable if the size of the transverse profile of the laser beam increases as the laser beam travels through at least a portion of the regenerative ring resonator but the laser beam transverse profile size does not exceed the transverse size of any of the optical components within the regenerative ring resonator before being decoupled out of the regenerative ring resonator through the optical coupler.

26. The resonator of claim 21, wherein the beam modification optical system comprises a set of prisms.

27. The resonator of claim 26, wherein the prism set comprises first, second, and third prisms configured and arranged so that the first and third prisms reduce the transverse size of the profile of the laser beam travelling along a first direction through the beam modification optical system, and the third and second prisms increase the transverse size of the profile of the laser beam travelling along a second direction through the beam modification optical system.

28. The resonator of claim 27, wherein the one or more first, second, and third prisms are adjusted so that the transverse size of the profile of the laser beam travelling along the second direction and exiting the prism set is greater than the transverse size of the profile of the laser beam travelling along the first direction from the optical coupler to the prism set.