Tunable, high-power, narrow-band picosecond IR radiation by optical parametric amplification in KTP

We report on an optical parametric amplifier (OPA) based on two potassium titanyl phosphate (KTP) crystals in a walk-off compensating geometry. An Nd:YLF regenerative amplifier at a 1-kHz repetition rate serves as the pump source. The seed beam is delivered by a synchronously pumped frequency-stabilized optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN). At pump intensities of about 7 GW/cm(2) large amplification factors of more than 10(4) were achieved, resulting in pulse energies of more than 450 muJ and 350 muJ for the signal and idler pulses, respectively, at a 1-kHz repetition rate. In the saturation regime the time-bandwidth product increases from two to three times the Fourier limit, with a pulse duration of 105 ps and a bandwidth of 12.7 GHz at the highest intensities employed.