Multiwatt KTiOPO4 optical parametric oscillators pumped within randomly and linearly polarized Nd:YAG laser cavities

We present 2 experiments on intracavity pumping of a KTiOPO4 (KTP) optical parametric oscillator (OPO) within a high power 1064nm Nd:YAG laser cavity producing multiwatt level 2-micron outputs. In such high power regime, the Nd:YAG rod laser suffers significant thermally-induced birefringence loss when it is linearly polarized. Hence in the first experiment, we present our intracavity KTP OPO pumped within the simple cavity of an unpolarized Nd:YAG laser. This simple configuration, with I-micron high reflectors forming the Nd:YAG laser cavity and R=75% and 100% 2-micron mirrors forming the short (2.5cm) flat-flat OPO cavity, delivered 6.5W of 2-micron output power at 3kHz Q-switched operation. Next we pumped our intracavity OPO within a more complex polarized Nd:YAG laser cavity. In this second experiment, we compensated for the thermally-induced birefringence loss in the Nd:YAG laser by using a re-entrant laser cavity with a Faraday rotator, and the OPO was pumped within one arm of this set-up. In this case, we also obtained similar to 6.5W of 2-micron output. Finally, studies of the temporal profiles of the 1 and 2-micron laser beams also revealed interesting multiple pulse features in such intracavity OPO output.