Efficient, high peak power, Q-switched, tunable diode pumped Tm:YLF laser

Abstract

The Tm:YLF laser end-pumped by a fiber coupled laser diode bar, actively Q-switched with tunability option was worked out and examined for low duty factor and true cw pumping regimes. The numerical model of such a laser including thermo-optic effects was developed to examine properties of Q-switching regimes. Above 7-W and near 30% slope efficiency was demonstrated in free-running mode for low duty factor pumping for the best case. Above 2-W output power was obtained in cw pumping regime for 220-mm long cavity and 15% transmission of output mirror. The cw output power was limited here by reabsorption losses and thermal lensing. The Lyot's filter tuning in 1845-1935 nm range with 3-nm linewidth was achieved for free-running regime. The divergence angle was about 4.3 mrad and estimated parameter M2 < 1.3. For Q-switching regime, the acousto-optic modulator made of fused silica was deployed. In the best case of low duty factor pumping (10-ms pump duration, 10-Hz repetition rate) pulse energy was 10.5 mJ, pulse duration was about 20 ns corresponding to near 0.5 MW of peak power. In case of cw pumping for maximum incident pump power of 19 W we have demonstrated 10-mJ pulses of 220 kW peak power for 133 Hz of repetition rate. The output energy and peak power was limited here by damages of applied laser elements. The peak power of 12 kW and 1.7 W of average output power were achieved for the highest rep. rate of 1 kHz.