Efficient injection-seeded kHz picosecond LBO optical parametric generator

We report a highly efficient optical parametric generator (OPG) in lithium triborate (LBO). A frequency-doubled passively mode-locked diode-pumped Nd:YVO₄ oscillator amplifier (MOPA) system is used as the pump radiation source. Focussing according to the theory of Boyd and Kleinman leads to a pump power density of 50 GW/cm², which is well below the damage threshold of LBO of 80 GW/cm². The overall conversion efficiency reaches a value of 72% measured at degeneracy. The tuning range of the OPG ranges from 760 nm (signal) to 1770 nm (idler) when referring to an overall conversion efficiency of 50%. The beam quality is excellent for conversion efficiencies below 40% (M ²<1.3). The typically 10 nm (RMS) broad spectrum can be narrowed by injection seeding the OPG. Injection seeding is demonstrated for a signal wavelength of 922.54 nm. A seed cw power of 30 nW is sufficient to reduce the spectral width to 0.1 nm (RMS). The measured injection-seeded OPG pulse duration is 9 ps (FWHM). This results in a time–bandwidth product of 1.30, which is 4.1 times the theoretical limit of 0.315 for sech²-shaped pulses.