Study On LD Pumped Nd:GdVO₄ MOPA Laser

Lasers with high repetition rates, high power and good beam quality are widely used in space-based lidar, nonlinear frequency conversion and industrial processing. Traditional diode-pumped solid-state lasers have advantages of high efficiency and compactness. However it is often very difficult to realize the high power and good beam quality at the same time. Diode-pumped solid-state lasers based on a master oscillator power amplifier (MOPA) configuration can meet the requirements simultaneously. Aimed at the acquisition of lasers with high repetition rates, high power and good beam quality, we analyzed the 1.06μm lasers with MOPA configuration theoretically and experimentally by using 879nm LD as the pumping source and new composite Nd:GdVO₄ as laser material.Based on the theory of rate equation we deduced the pump threshold, output power, pulse energy and pulse width in CW operation and Q-switching operation while the Nd:GdVO₄ laser is end-pumped by a laser diode. The stored energy, extraction efficiency and the relation between the output fluence and input fluence are deduced when the power amplifier is work at steady-state amplification and pulse amplification. We also calculated the extraction efficiency and the relation between the output fluence and input fluence taking the issue of 879nm LD end-pumped Nd:GdVO₄ laser.The 879nm LD end-pumped composite Nd:GdVO₄ laser oscillator was experimentally researched. By using single-end-pumped structure a 12.2W output was achieved corresponding to the total optical-optical efficiency of 42.2% in CW operation and a 4.9kW peak power output was achieved with the pulse duration of 17.5ns in 100kHz Q-switching operation. By using dual-end-pumped structure a 24.5W output was achieved corresponding to the total optical-optical efficiency of 43.2% in CW operation and a 17.7kW peak power output was achieved with the pulse duration of 13.1ns in 100kHz Q-switching operation. A method to obtain laser with single polarization direction was suggested by using a 879nm wave plate to rotate the polarization direction of the pump source.Based on the structure of master oscillator followed by two power amplifiers we analyzed the factors that influence the performance of the power amplifier. When the polarization direction of the signal laser parallels to the c-axis of the laser crystal and the ratio between signal size and pump size is 0.8 we obtained the optimum performance. In CW operation 30.6W TEM₀₀ mode output was achieved corresponding to the PA extraction efficiency of 35.1% and total optical-optical efficiency of 40.3%. In Q-switching operation 27.9W average power output was achieved at the 100kHz repetition rates with the pulse duration of 19.3ns, the peak power of 14.5kW corresponding to the PA extraction efficiency of 37.1% and total optical-optical efficiency of 35.0%. The enhancement of the beam quality and the pulse-sharp distortions during the amplifying process were also observed and analyzed.