Laser-operated light source

• US 9,678,262 B2
• Filed: 09/19/2014
• Issued: 06/13/2017
• Est. Priority Date: 09/20/2013
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: Qioptiq Photonics GmbH & Company KG (Excelitas Technologies Holdings LLC)
• Inventors: Grtz, Bjrn, Frerking, Dieter, Thni, Thomas, Spruch, Claus
• Primary Examiner(s): TSO, LAURA K
• Application Number:
  US14/491,079
• Publication Number:
  US 20150085517A1
• Time in Patent Office: 998 Days
• Field of Search: 362553, 362259
• CPC Class Codes: G02B 6/0006 Coupling light into the fibre in general G02B6/4298
• CPC Class Codes: G02B 6/4206 Optical features G02B6/4207, G02B6/421 take precedence
• CPC Class Codes: G02B 6/4296 coupling with sources of high radiant energy, e.g. high power lasers, high temperature light sources
• CPC Class Codes: G02B 6/4298 coupling with non-coherent light sources and/or radiation detectors, e.g. lamps, incandescent bulbs, scintillation chambers
• CPC Class Codes: G06F 30/00 Computer-aided design [CAD]

Abstract

A laser-operated light source encompasses a chamber for accommodating an ionizable gas and an ignition source for ionizing the gas in the chamber for generating a plasma. The light source encompasses a laser for inputting laser energy into the plasma such that, under the impact of the laser radiation, the plasma emits useful light, which forms the output signal of the light source, wherein provision is made for means for coupling the useful light into a transferring optical fiber. An optical system for imaging the plasma onto the end of the optical fiber, which faces the optical system, is arranged between the chamber and the transferring optical fiber, wherein the optical system is corrected for reducing the chromatic aberration.

Claims

1. A laser-operated light source, comprising:

a chamber for accommodating an ionizable gas and a plasma formed by energizing the ionizable gas, the chamber further comprising an output window selected from the group consisting of a flat output window and a spherical output window;

a laser for inputting laser energy into the plasma such that, under the impact of the laser radiation, the plasma emits useful light out of the output window, which forms the output signal of the light source;

means for coupling the useful light into a transferring optical fiber; and

an optical system arranged between the chamber output window and the transferring optical fiber, configured to balance a correction of aberrations of the output window and image the plasma onto the end of the optical fiber facing the optical system, wherein the optical system is configured to correct chromatic aberration.

2. The light source according to claim 1, wherein the optical system further comprises collimating optics and focusing optics arranged downstream from the collimating optics.

3. The light source according to claim 1, further comprising an ignition source for ionizing the gas in the chamber for generating the plasma.

4. The light source according to claim 1, wherein the optical system is corrected for more than two wavelengths of the useful light.

5. The light source according to claim 1, characterized in that, with reference to its magnification, the optical system is configured such that the imaging of the plasma in the inlet plane of the optical fiber equals the diameter of the light-guiding core of the optical fiber or is larger than it.

6. The light source according to claim 1, characterized in that, with reference to its magnification, the optical system is configured such that the imaging of the plasma in the inlet plane of the optical fiber is smaller than the diameter of the light-guiding core of the optical fiber.

7. The light source according to claim 1, characterized in that the numerical aperture of the optical system and the numerical aperture of the optical fiber are adapted to one another such that the opening angle of the optical system at the image side is adapted to the acceptance angle of the optical fiber.

8. The light source according to claim 1, characterized in that the light source emits useful light within the visible wavelength range.

9. The light source according to claim 1, wherein the optical system is further configured to correct spherical aberration.

10. The light source according to claim 1, wherein the optical system is further configured to correct comatic aberration.

11. The light source according to claim 2, wherein the optical system further comprises filtering optics.

12. The light source according to claim 11, wherein the filtering optics is disposed between the collimating optics and the focusing optics.

13. An optical system for use between a laser excited plasma chamber comprising an output window and a transferring optical fiber, comprising:

collimating optics configured to receive and collimate a plasma image from the plasma chamber via the output window; and

focusing optics configured to receive and focus a collimated image from the collimating optics onto an input plane of the transferring optical fiber,

wherein the output window is selected from the group consisting of a flat output window and a spherical output window, the collimating optics and focusing optics are configured to correct aberration introduced by at least one of the output window, the collimating optics, and the focusing optics, and the aberration comprises at least one of the group consisting of chromatic aberration, spherical aberration, and comatic aberration.

14. The optical system according to claim 13, wherein the collimating optics further comprise a plurality of lenses.

15. The optical system according to claim 13, wherein the focusing optics further comprise a plurality of lenses.

16. The optical system according to claim 13, wherein the optical system further comprises filtering optics disposed between the collimating optics and the focusing optics.

17. A method for designing an optical system for receiving light from a laser excited plasma chamber comprising an output window selected from the group consisting of a flat output window and a spherical output window and a transferring optical fiber, comprising the steps of:

determining an aberration imparted to light exiting the chamber via the output window;

designing collimating optics configured to collimate light received from the output window;

designing focusing optics configured to receive and focus a collimated image from the collimating optics onto an input plane of the transferring optical fiber;

modeling an optical train comprising the output window, the collimating optics, and the focusing optics;

configuring the optical train to balance a correction for aberrations of the output window; and

determining whether the modeled optical train introduces an optical aberration to light at the input plane of the transferring optical fiber, the aberration comprising at least one of the group consisting of chromatic aberration, spherical aberration, and comatic aberration; and

updating the design of the collimating optics and/or focusing optics to reduce the aberration.

18. The method of claim 17, wherein the collimating optics and modeling optics are configured to correct aberration achromatically.

19. The method of claim 17, wherein the collimating optics and modeling optics are configured to correct aberration apochromatically.

20. A laser-operated light source, comprising:

a chamber for accommodating an ionizable gas and a plasma formed by energizing the ionizable gas;

a laser for inputting laser energy of the plasma such that, under the impact of the laser radiation, the plasma emits useful light, which forms the output signal of the light source;

means for coupling the useful light into a transferring optical fiber;

an optical system arranged between the chamber and the transferring optical fiber, configured to image the plasma onto the end of the optical fiber facing the optical system, wherein the optical system is configured to correct chromatic aberration for more than two wavelengths of the useful light.

21. The light source according to claim 20, wherein the optical system further comprises collimating optics and focusing optics arranged downstream from the collimating optics.

22. The light source according to claim 20, further comprising an ignition source for ionizing the gas in the chamber for generating the plasma.

23. The light source according to claim 20, characterized in that, with reference to its magnification, the optical system is configured such that the imaging of the plasma in the inlet plane of the optical fiber equals the diameter of the light-guiding core of the optical fiber or is larger than it.

24. The light source according to claim 20, characterized in that, with reference to its magnification, the optical system is configured such that the imaging of the plasma in the inlet plane of the optical fiber is smaller than the diameter of the light-guiding core of the optical fiber.

25. The light source according to claim 20, characterized in that the numerical aperture of the optical system and the numerical aperture of the optical fiber are adapted to one another such that the opening angle of the optical system at the image side is adapted to the acceptance angle of the optical fiber.

26. The light source according to claim 20, characterized in that the light source emits useful light within the visible wavelength range.

27. The light source according to claim 20, wherein the optical system is further configured to correct one of the group consisting of spherical aberration and comatic aberration.

28. The light source according to claim 21, wherein the optical system further comprises filtering optics.

29. The light source according to claim 28, wherein the filtering optics is disposed between the collimating optics and the focusing optics.