CW far-UV laser system with two active resonators

Coherent light generators – Particular beam control device – Nonlinear device

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C372S092000

Reexamination Certificate

active

06567434

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to ultraviolet (UV) lasers. It relates, in particular, to a laser in which radiation at a wavelength between about 200 and 280 nanometers (nm), generated by a first active laser-resonator, is mixed, in an optically-nonlinear crystal located in a second active laser-resonator, with radiation generated by the second laser resonator and having a wavelength between about 900 and 1080 nm, thereby generating radiation having a third wavelength corresponding to the sum-frequency of the first and second wavelengths and having a wavelength between about 175 and 215 nm.
DISCUSSION OF BACKGROUND ART
Optical systems are used in optical lithography for patterning or “writing” on photoresist for lithographic masking operations. The resolution of these optical systems is inversely related to the wavelength used for the patterning or writing. In so-called direct-writing systems, where photoresist coated wafers are directly patterned by an optically-steered, focussed, beam of radiation rather than being exposed through a mask. The, the quality of the beam is as important as the wavelength of the beam for obtaining highest possible resolution, and, accordingly smallest possible feature size. Smaller features, of course, lead to higher component packing densities. One particularly useful light source for direct writing operations is an intracavity frequency-doubled argon ion-laser, having an output wavelength of 244 nm. Such a laser is used in a direct writing system manufactured by Etec, Inc., of Hayward, Calif.
Because of a continuing demand for ever smaller and faster semiconductor devices, there is a similar need for a laser system having a shorter wavelength than the 244 nm of existing direct-writing systems. Such a laser system, of course, should have a beam-quality comparable to existing 244 nm laser systems and provide sufficient power such that exposure times are not unacceptably protracted.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a laser system comprises first and second active laser-resonators. The first laser-resonator delivers laser-radiation at a first wavelength, and the second laser-resonator is arranged to generate laser-radiation therein at a second wavelength.
The second laser-resonator includes an optically-nonlinear crystal. The first and second laser-resonators and the optically-nonlinear crystal are cooperatively arranged such that first-wavelength radiation delivered by the first laser-resonator is mixed in the optically-nonlinear crystal with the second-wavelength radiation generated in the second laser-resonator, thereby generating radiation having a third-wavelength corresponding to the sum frequency of the first and second wavelengths.
In another aspect of the present invention, radiation having a wavelength between about 200 and 280 nanometers (nm), generated by a first active laser-resonator, is mixed, in an optically-nonlinear crystal located in a second active laser-resonator, with radiation generated by a second laser resonator and having wavelength between about 900 and 1080 nm, thereby generating radiation having a third wavelength corresponding to the sum-frequency of the first and second wavelengths and having a wavelength between about 175 and 215 nm.
In one embodiment of a laser system in accordance with the present invention, 1 Watt (W) of 244 nm radiation is delivered by a prior-art, intracavity frequency-doubled argon-ion laser. Fundamental radiation having a wavelength of about 976 nm is generated in an external-cavity surface-emitting semiconductor laser-resonator (OPS laser-resonator). The 244 nm radiation is mixed in a cesium lithium borate (CLBO) optically-nonlinear crystal with about 500 W of 976 nm radiation circulating in the OPS laser-resonator to provide about 100 milliwatts (mW) of radiation having a wavelength of about 195 nm.
Dispersion characteristics of CLBO allow that the 244 nm radiation can be directed into the CLBO optically-nonlinear crystal without passing through any optical components of the second resonator, thereby avoiding potential absorption losses in those components. Similarly, the 195 nm radiation generated by the sum-frequency mixing, and residual 244 nm radiation, leave the second resonator without passing through any optical components thereof.
In another embodiment of the inventive laser system, the optically-nonlinear crystal in the active, second laser-resonator is commonly located in a passive, travelling-wave ring-resonator ring-resonator arranged to recirculate and build up the 244 nm radiation passing through the CLBO crystal, thereby increasing the output power of 195 nm radiation to about 800 mW.


REFERENCES:
patent: 4914658 (1990-04-01), Stankov et al.
patent: 5050179 (1991-09-01), Mooradian
patent: 5131002 (1992-07-01), Mooradian
patent: 5289485 (1994-02-01), Mooradian
patent: 5408481 (1995-04-01), SAcheps
patent: 5412674 (1995-05-01), Scheps
patent: 5461637 (1995-10-01), Mooradian et al.
patent: 5627853 (1997-05-01), Mooradian et al.
patent: 5651019 (1997-07-01), Goldberg et al.
patent: 5809048 (1998-09-01), Shichijyo et al.
patent: 5912910 (1999-06-01), Sanders et al.
patent: 5991318 (1999-11-01), Caprara et al.
patent: 6198756 (2001-03-01), Caprara et al.
patent: 6301273 (2001-10-01), Sandeers et al.
patent: 6304585 (2001-10-01), Sanders et al.
patent: 0 608 866 (1994-08-01), None
patent: WO 00/64017 (2000-10-01), None
A.H. Paxton et al., “Design of external cavities for vertical-cavity semiconductor lasers,”Proceedings of the SPIE—The International Society for Optical Engineering, 1993, vol. 1868, pp. 235-243.
J.V. Sandusky et al., “A CW External-Cavity Surface-Emitting Laser,”IEEE Photonics Technology Letters, vol. 8, No. 3, Mar. 1996, pp. 313-315.
M. Kuznetsov et al., “High-Power (>0.50-W CW) Diode-Pumped Vertical-External-Cavity Surface-Emitting Semiconductor Lasers with Circular TEM00Beams,”IEEE Photonics Technology Letters, vol. 9, No. 8, Aug. 1997, pp. 1063-1065.
A. Rosiewicz et al., “Optical pumping improves VCSEL performance,”Laser Focus World, Jun. 1997, pp. 133-136.
W.J. Alford et al., “Intracavity frequency doubling of an optically-pumped, external-cavity surface-emitting semiconductor laser,”Advanced Solid State Laser Conference, Sandia National Laboratories, SAND-98-2108C, CONF-990105, Dec. 31, 1998, 5 pages in length.
G.C. Bhar et al., “Widely tunable deep ultraviolet generation in CLBO,”Optics Communications, vol. 176, Mar. 15, 2000, pp. 199-205.
W.P. Risk et al., “Diode laser pumped blue-light source based on intracavity sum frequency generation,”Applied Physics Letters, vol. 54, No. 9, Feb. 27, 1989, pp. 789-791.
P.N. Kean et al., “Generation of 20 mW of blue laser radiation from a diode-pumped sum-frequency laser,”Appl. Phys. Lett., vol. 63, No. 3, Jul. 19, 1993, pp. 302-304.
K. Koch et al., “Raman Oscillation with Intracavity Sum-Frequency Generation,”IEEE Journal of Quantum Electronics, vol. 35, No. 1, Jan. 1999, pp. 72-78.
Y.K. Yap et al., “High-power fourth- and fifth-harmonic generation of a Nd:YAG laser by means of a CsLiB6O10,”Optics Letters, vol. 21, No. 17, Sep. 1, 1996, pp. 1348-1350.

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

CW far-UV laser system with two active resonators does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with CW far-UV laser system with two active resonators, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CW far-UV laser system with two active resonators will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3024410

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.