High Efficiency 355 Nm Laser By Employing A Flat-Flat Cavity With Improved Harmonic Beam Quality

A high efficiency 355 nm ultraviolet (UV) laser is obtained by intracavity frequency-tripling of a 1064 nm Nd:YVO4 laser in a flat-flat cavity. The 5.6 W UV maximum average output power is obtained at the incident pump power of 29 W at 808 nm and the repetition rate of 50 kHz, corresponding to the pump-UV conversion efficiency of 19.3%. The corresponding pulse width is 14.2 ns, with the energy of a single pulse and corresponding peak power estimated to be 112 mu J and 7.89 kW, respectively. The frequency doubling and tripling lasers are obtained by employing type-I phase-matching LiB3O5 (LBO) crystal with parallel surfaces and a type-II phase-matching LBO crystal with Brewster angle-cut uncoated surface, respectively. The beam quality of the 355 nm laser is measured to be M (x) (2) = 1.257 and M (y) (2) = 1.173, respectively. The reasons for improvement of harmonic beam quality are explained by simulating the laser field intensity distribution changes in two special directions during the nonlinear conversion process.