Generation of subpicosecond continuously frequency-tunable infrared pulses

An investigation was made of a cavity optical parametric oscillator (COPO) utilizing a KDP crystal pumped synchronously with the second harmonic of a picosecond neodymium phosphate glass laser with passive mode locking. A strong discrimination of the time profile of the signal under conditions of gain saturation and group velocity mismatch resulted in generation of subpicosecond pulses (~0.5 psec) in the COPO when the duration of the pump pulses was 3–5 psec. The COPO was tunable in the range 0.82–1.3 μ, the energy efficiency of the conversion process was 2%, and the average energy of a single subpicosecond pulse was 20 μ J. A numerical analysis was made of the transient parametric amplification in the COPO and the subpicosecond COPO was optimized so as to reduce the pulse duration and increase their contrast.