Diode pumped cw mode locked Nd:YVO 4 laser

Abstract

The efficient cw Mode Locking (cw-ML) regime was demonstrated in Nd:YVO₄ laser by means of saturable absorber mirror (SAM). The 0.3-at.% Nd³⁺ doped 10-mm-long YVO₄ crystal end pumped by 20 W diode module with beam shaper was applied as a gain medium located in the close vicinity to the rear flat mirror of first arm of Z-type resonator of 316 cm total length with two curved mirrors of 100-cm curvature radii. The SAM of 2%-saturable absorptance and saturation fluence of 0.050 μJ/cm² was mounted at the opposite end of resonator. The developed "dynamically stable" cavity design mitigates detrimental role of thermal aberration in gain medium, enforcing clean perfect mode locking even for highest pump densities. The cw-ML pulses with 47.5 MHz repetition rate and pulse durations in the range of 15-30 ps were observed for wide range of pump powers and output coupler losses. In the best case for 32% of output coupler transmission, up to 6.2 W of average power with near 35% slope efficiency were achieved. The thresholds for Q-switched ML, cw-ML regimes were 2.67 W and 6.13 W of pump power, respectively. For the maximum pump power of 20 W we obtained 133 nJ of pulse energy with 16-ps pulse duration, resulting in peak power higher than 8 kW. The threshold energy density at SAM giving the QML regime was estimated to be about 0.030 μJ/cm², threshold of cw-ML regime was 0.220 μJ/cm².