Spatial light modulation for ultra-fast optics by wave-mixing in saturable amplifier

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Ultrafast lasers in pico-and femto-second regime have received intense attention in many fields : including extra-ultra-violet generation, laser machining, spectroscopy, and medical applications, etc. These applications require laser sources with high beam quality.An effective solution to correct an aberration in the laser system and generate high quality output is phase conjugation. Phase conjugation by four-wave mixing in a saturable gain medium has been an attractive subject because of its high phase conjugate reflectivity and fast temporal response. To date, efficient phase conjugation in the nano-second or CW regime has been, demonstrated.However, efficient phase conjugation in pico-and femto-second regime requires a broad emission band as well as a high small-signal gain, which makes ultrafast operation more difficult to achieve. A solid laser dye is a promising material for an efficient and tunable solid-state phase conjugate mirror because of its large stimulated emission cross-section and broad fluorescence band in the visible and near-infrared regions.We have demonstrated efficient phase conjugation for pico-second pulses with a solid dye. A phase conjugate reflectivity of 2.5 times was obtained. This value is the highest, to our knowledge, obtained by four-wave mixing in the pico-second regime.