Optical: systems and elements – Optical frequency converter – Parametric oscillator
Reexamination Certificate
2002-01-15
2004-12-21
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
Parametric oscillator
C359S326000
Reexamination Certificate
active
06833945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solid state lasers and frequency shifting of laser output. More specifically, the present invention relates to frequency shifted solid state laser output operative in the 8-12 micron range.
2. Description of the Related Art
Lasers are currently widely used for communication, research and development, manufacturing, directed energy and numerous other applications. For many applications, the energy efficiency, power and light weight of solid state lasers make these devices particularly useful. Because only a few crystals lase and each crystal lases at a unique fundamental frequency, the wavelengths which can be generated by a laser are limited.
Solid state lasers currently lase in the range of one to three microns. For certain applications, there is a need to reach longer laser operating wavelengths. In particular, there is interest in the 8-12 micron (&mgr;m) region. A system which can generate pulsed, tunable radiation at these wavelengths is particularly useful for the remote detection of chemical agents and other chemical species. Unfortunately, the 8-12 &mgr;m region is a very difficult wavelength region to access. No current solid-state laser source is capable of emitting pulsed, tunable laser output in this region.
Wavelength conversion of commonly available 1 micron lasers to the 8-12 micron region using optical parametric oscillators (OPOs) and difference frequency generation (DFG) has been demonstrated, but the overall energy conversion efficiencies were low. See for example: 1) S. Chandra, T. H. Allik, G. Catella, R. Utano, J. A. Hutchinson, “Continuously tunable 6-14 &mgr;m silver gallium selenide optical parametric oscillator pumped at 1.57 &mgr;m,” Appl. Phys. Lett. 71, 584-586 (1997); and 2) R. Utano and M. J. Ferry, “8-12 &mgr;m generation using difference frequency generation in AgGaSe
2
of a Nd:YAG pumped KTP OPO,” in
Advanced Solid State Lasers, OSA Trends in Optics and Photonics
(Optical Society of America, Washington, D.C., 1997), Vol. 10, pp. 267-269.
One approach involved the use of a 1 micron laser to pump a potassium titanyl phosphate (KTP) OPO, whose signal wave output at 1.57 microns was then used to pump a silver gallium selenide (AgGaSe
2
) OPO to produce 6-14 micron output. Optical parametric oscillators (OPOs) have been widely used to shift the fundamental output of a laser from one wavelength to another through the use of a nonlinear crystal. Unfortunately, the use of OPOs limits the efficiency of the system. This is due to the fact that the energy in the input laser beam is split between plural output beams. In the described system, the KTP OPO output is a less than optimal pump source for the AgGaSe
2
OPO.
Hence, a need remains in the art for an efficient, tunable system or method for converting the output of a typical 1 &mgr;m laser to the 8-12 &mgr;m range.
SUMMARY OF THE INVENTION
The need in the art is addressed by the present invention, a novel system and method for efficiently generating tunable pulsed laser output at 8-12 microns by converting the output of a standard 1 micron laser using a serial optical parametric oscillator (OPO) conversion scheme which uses the non-linear crystals rubidium titanyl arsenate (RTA) and silver gallium selenide (AgGaSe
2
). This system can generate tunable 8-12 micron output in a more efficient manner than that which has been previously demonstrated. A key aspect of this approach is the use of the RTA OPO to produce a secondary signal output at 3.01 microns with greater than 25% overall 1 micron to 3.01 micron conversion efficiency.
The system includes a laser, a first optical parametric oscillator of unique design, and a second optical parametric oscillator. The first oscillator is constructed with an energy shifting crystal and first and second reflective elements disposed on either side thereof. Energy from the laser at a first wavelength is shifted by the crystal and output at a second wavelength. The second wavelength results from a secondary process induced by a primary emission of energy at a third wavelength, the third wavelength resulting from a primary process generated from the first wavelength in the crystal. Mirror coatings are applied on the reflective elements for containing the primary emission and enhancing the secondary process. The second optical parametric oscillator then shifts the energy output by the first OPO at the second wavelength to the desired fourth wavelength. In the illustrative embodiment, the first optical parametric oscillator includes an x-cut rubidium titanyl arsenate crystal and the second optical parametric oscillator includes a silver gallium selenide crystal. The first wavelength is approximately 1.06 microns, the second wavelength is approximately 3.01 microns, the third wavelength is approximately 1.61 microns, and the fourth wavelength is in the range of 8-12 microns.
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Moore et al, “The Tandem Optical Parametric Oscillator”, IEEE Journal of Quantum Electronics, vol. 32, no. 12, Dec. 1996, pp. 2085-2094.*
Chandra, S. et al.: “Continuously Tunable, 6-14 Mum Silver-Gallium Selenide Optical Parametric Oscillator Pumped at 1.57 Mum”, Applied Physics Letters, American Institute of Physics, NY, US, vol. 71, no. 5, Aug. 4, 1997, pp. 584-586, XP000699619.
Moore, G. T. et al.: “A Simultaneously Phase-Matched Tandem Optical Parametric Oscillator” IEEE Journal of Quantum Electronics, IEEE, vol. 34, No. 5, May 1, 1998, pp. 803-810, XP000751982.
Alkov Leonard A.
Gunther John E.
Lee John D.
Raytheon Company
Schubert William C.
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