High brightness laser-sustained plasma broadband source

Patent metadata

Field	Value
Publication number	US-9865447-B2
Application number	US-201615285333-A
Country	US
Kind code	B2
Filing date	Oct 4, 2016
Priority date	Mar 28, 2016
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

The broadband light source includes a gas containment structure and a pump laser for generating a pump beam including illumination of a wavelength near that of a weak absorption line of a neutral gas contained in the gas containment structure. The broadband light source also includes anamorphic optics for focusing the pump beam into an elliptical beam waist positioned in or near the center of the gas containment structure. The broadband light source also includes collection optics for collecting broadband radiation emitted by the plasma in a direction aligned with a longer axis of the elliptical beam waist.

First claim

What is claimed:

1. A high brightness laser-sustained plasma broadband light source comprising:
a gas containment structure;
a pump laser configured to generate a pump beam including illumination of a wavelength at least proximate to a weak absorption line of a neutral gas contained in the gas containment structure;
one or more anamorphic illumination optics configured to focus the pump beam into an approximately elliptical beam waist positioned in or proximate to the center of the gas containment structure; and
one or more first collection optics configured to collect broadband radiation emitted by the plasma in a direction substantially aligned with a longer axis of the elliptical beam waist.

2. The light source of claim 1 , further comprising:
a plasma ignition device.

3. The light source of claim 2 , wherein the plasma ignition device comprises:
at least one of a set of electrodes or a pulsed laser.

4. The light source of claim 1 , wherein the gas containment structure comprises:
at least one of a plasma bulb, a plasma cell, or a plasma chamber.

5. The light source of claim 1 , wherein the gas comprises:
at least one of an inert gas, a non-inert gas, or a mixture of two or more gases.

6. The light source of claim 5 , wherein the gas comprises:
at least one of xenon, argon, or mercury.

7. The light source of claim 1 , wherein the pump laser comprises:
at least one of a fiber laser or a solid-state laser.

8. The light source of claim 1 , wherein the wavelength of light of the pump beam is approximately 1070 nm.

9. The light source of claim 1 , further comprising:
a second pump laser configured to generate a second pump beam including light of a wavelength not absorbed by the neutral gas, wherein the output wavelength of the second pump laser is absorbed by an ionized gas in the plasma.

10. The light source of claim 9 , wherein the wavelength of light of the second pump beam is between 515 nm and 540 nm.

11. The light source of claim 1 , wherein the one or more anamorphic illumination optics comprise:
at least one of an acylindrical lens or an aspheric lens.

12. The light source of claim 1 , wherein the one or more anamorphic illumination optics comprise:
an aberration compensator configured to compensate for aberration caused by at least one of a shape of the gas containment structure or the pump laser.

13. The light source of claim 1 , wherein the elliptical beam waist has a ratio of major axis to minor of at least 10.

14. The light source of claim 13 , wherein the one or more anamorphic illumination optics are configured to focus with a numerical aperture (NA) greater than 0.5 in the direction corresponding to the shorter axis of the elliptical beam waist, and with an NA less than 0.2 in the direction corresponding to the longer axis of the elliptical beam waist.

15. The light source of claim 13 , wherein the one or more anamorphic illumination optics are configured such that the minor axis of the elliptical beam waist is less than 5 μm and the major axis of the elliptical beam waist is between 50 μm and 500 μm.

16. The light source of claim 1 , wherein the first set of collection optics are configured to collect the broadband radiation in a direction substantially aligned with a longer axis of the elliptical beam waist.

17. The light source of claim 1 , further comprising:
a reflector placed on an opposite side of the gas containment structure from the first collection optics and configured to focus broadband radiation back to the plasma substantially overlapping the beam waist of the pump laser.

18. The light source of claim 1 , further comprising:
a reflector configured to reflect and focus unabsorbed pump laser illumination to the plasma substantially overlapped with the beam waist of the pump laser.

19. The light source of claim 1 , further comprising:
a second set of collection optics configured to collect illumination emitted by the plasma on an opposite side of the gas containment structure from the first set of collection optics.

20. A method to generate high brightness broadband light comprising:
providing a volume of gas in a gas containment structure;
igniting a plasma within the volume of the gas in the gas containment structure;
generating a pump laser beam including illumination having a wavelength at least proximate to a weak neutral absorption line of the gas in the gas containment structure;
shaping and focusing the pump laser beam with one or more anamorphic illumination optics to form an elliptical beam waist located at least proximate to the center of the gas containment structure; and
collecting broadband radiation emitted by the plasma in a direction substantially aligned with a longer axis of the elliptical beam waist.

21. The method of claim 20 , wherein the igniting a plasma within the volume of the gas in the gas containment structure comprises:
igniting a plasma within the volume of the gas in the gas containment structure with an a.c. discharge from a set of electrodes.

22. The method of claim 20 , wherein the igniting a plasma within the volume of the gas in the gas containment structure comprises:
igniting a plasma within the volume of the gas in the gas containment structure with a pulsed laser.

23. The method of claim 20 , wherein the provided gas comprises:
at least one of an inert gas, a non-inert gas, or a mixture of two or more gases.

24. The method of claim 23 , wherein the gas comprises:
at least one of xenon, argon, or mercury.

25. The method of claim 20 , wherein the pump laser beam is generated from at least one of a fiber laser or a solid state laser.

26. The method of claim 24 , wherein the wavelength of the pump beam is approximately 1070 nm.

27. The method of claim 20 , further comprising:
generating a second pump laser beam having an output wavelength that is not absorbed by the neutral gas, wherein the output wavelength of the second pump laser is absorbed by an ionized gas in the plasma.

28. The method of claim 27 , wherein the wavelength of light of the second pump laser beam is between 515 nm and 540 nm.

29. The method of claim 20 , wherein the one or more anamorphic illumination optics comprise:
at least one of an acylindrical lens or an aspheric lens.

30. The method of claim 20 , wherein the one or more anamorphic illumination optics comprise:
an aberration compensator configured to compensate for aberration caused by at least one of a shape of the gas containment structure or the pump laser.

31. The method of claim 20 , wherein the elliptical beam waist has a ratio of major axis to minor of at least 10.

32. The method of claim 31 , wherein the one or more anamorphic illumination optics are configured to focus with a numerical aperture (NA) greater than 0.5 in the direction corresponding to the shorter axis of the elliptical beam waist, and with an NA less than 0.2 in the direction corresponding to the longer axis of the elliptical beam waist.

33. The method of claim 32 , wherein the one or more anamorphic illumination optics are configured such that the minor axis of the elliptical beam waist is less than 5 μm and the major axis of the elliptical beam waist is between 50 μm and 500 μm.

34. The method of claim 20 , wherein t

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho Alex
• Lu Xiaoxu
• Liou Justin
• Fielden John

Classifications

• H05H1/24

  Generating plasma {(nuclear fusion reactors G21B1/00; gas-filled discharge reactors H01J37/32)} · CPC title

• H01J61/025 Primary

  Associated optical elements · CPC title

• H01J61/20

  mercury vapour · CPC title

• H01J61/16

  having helium, argon, neon, krypton, or xenon as the principle constituent · CPC title

• H01J65/042 Primary

  by an external electromagnetic field · CPC title