Performance investigation of high-efficiency widely tunable subnanosecond optical parametric generator and amplifier...

We report on experimental and theoretical studies of widely tunable high-efficiency subnanosecond optical parametric generator (OPG) and amplifier (OPA) based on a 2 cm long multigrating MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal pumped by a passively Q-switched Nd:YAG micro-laser. Our OPG can be continuously tuned from 1442 nm to 4040 nm with signal wave energies ranging from 33 μJ to 265 μJ and total OPG conversion efficiency up to 46 % that depended on the pump focusing conditions. Characterization of spatial properties of the OPG determine Lorentzian spatial profile of the signal beam with M ²≈2 that was also dependent on the pump focusing conditions. High OPG gain and subsequent pump depletion led to the adjustment of the output signal pulse duration in the range of 242 - 405 ps by varying the incident pump power. By using a distributed feedback (DFB) continuous-wave (CW) 1550 nm wavelength seed laser for the OPA operation we reduced the generation threshold up to 1.6 times, increased maximum conversion efficiency by 4 - 20%, and achieved nearly transform-limited output signal pulses. Experimentally measured characteristics were supplemented by numerical simulations based on the quantum mechanical model for the OPG, and classical three-wave interaction model for the OPA operation.