Efficient self-pumped phase conjugation with a loop geometry in a Rhodamine-6G solid dye laser amplifier Hirofumi Watanabe, Takashige Omatsu, and Mitsuhiro Tateda Department of Information and Image Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
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Abstract: We present what to our knowledge is the first demonstration of self-pumped phase conjugation in a laser-pumped solid-state Rhodamine-6G dye saturable amplifier. Phase-conjugate energy reflectivity of as much as 2100% at 557 nm has been obtained. 2003 Optical Society of America OCIS codes: (190.5040) Phase conjugation, (190.4380) Nonlinear optics, Four-wave mixing, (140.3280) Laser amplifiers, (140.2050) Dye laser
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Self-pumped phase conjugation (SPPC) of an external input beam by use of a laser amplifier in self-intersecting loop geometry is particularly attractive because of its simplicity and efficiency [1-5]. Until now, SPPC has been demonstrated for several laser amplifiers, such as a flash-lamp-pumped Nd:YAG, a diode-pumped Nd:YVO4, and a laser-pumped Ti:sapphire. Solid dye lasers [6-10], in which dye-doped polymer is used as a gain material, have received much attention, because they can offer compact, inexpensive, and tunable lasers in the visible region. However, their poor thermal properties including extremely low thermal
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(C) 2003 OSA
Received November 21, 2002; Revised January 22, 2003
27 January 2003 / Vol. 11, No. 2 / OPTICS EXPRESS 176
conduction prevent power scaling and high-repetition operation. One solution for correcting the thermal effects is application of self-pumped phase-conjugate mirrors to the solid dye laser. In addition, the upper-level lifetime of dyes is much shorter (approximately nanoseconds) than that of Nd:YAG (~200 µs). The very short upper-level lifetime of dyes makes solid dye SPPC difficult to achieve. In our previous reports [11,12] we demonstrated efficient phase conjugation by degenerate four-wave mixing in an injection-seeded solid dye laser. This system exhibits extraction of phase-conjugate energy of as much as ~140 times the total energy injected externally; however, it requires good spatial overlap between the injected beam and counterpropagating pump beams already existing in the cavity. Here we present what we believe to be the first demonstration of a self-pumped phase-conjugate mirror with loop geometry in a solid dye laser amplifier. We obtained experimental phase-conjugate reflectivity of as much as 2100% at 557 nm. The solid dye consisted of a matrix of poly(methyl methacrylate) with less than 0.1-wt.% Rhodamine-6G dye doping. It measured φ 50 mm × 8 mm. Population inversion was obtained by longitudinal laser pumping from both sides of the solid dye by use of a frequency-doubled Q-switched Nd:YAG laser with a pulse duration of 10 ns at 2.5 Hz. A commercial narrowband (
