Tunable picosecond infrared pulses generated by optical parametric generation/amplification from a LiNbO ₃ crystal

The optical parametric generation and the amplification characteristics of a LiNbO ₃ crystal pumped by the fundamental output of a picosecond Nd:YAG laser were studied. The wavelength change of the signal output (from 1.4 μm to 2.1 μm) due to angle tuning of the crystal agreed with the phase-matching curve obtained from the known dispersion relation. With an initial pump energy of 20 mJ and an intensity of 1.8 GW/cm ₂ passing twice through the same LiNbO ₃ crystal by use of a retroreflecting gold mirror, the maximum parametric output energy of the combined signal and idler beams was 1.8 mJ at the degenerate point and decreased monotonically to less than 100 μJ at a signal wavelength of around 1.4 μm. The linewidth of the signal wavelength near 1.5 μm was estimated from the absorption spectrum of the output in an acetylene ( ¹³C ₂H ₂) gas cell.