2.8 ps pulses from a mode-locked diode pumped Nd:YVO4 laser using quadratic polarization switching

An experimental and theoretical study on a new passive mode-locking technique based on a second order non-linear crystal cut for type II SHG is presented. The method exploits the cascading of sum and difference frequency generation to realize an intensity-dependent polarization rotation. A numerical model was developed to predict and optimize in terms of pulse duration, the performance of a laser passively mode-locked by quadratic polarization switching. The influence of the cavity design, the influence of the nonlinear crystal GVD and the benefit of GVD compensation were considered. Predictions are compared with experimental data measured with a diode-pumped Nd:YVO4 laser. Transform-limited pulses as short as 2.8 ps were obtained at 1064 nm with an average power of 670 mW.