环形腔单频激光振荡及功率放大系统研究

Single-frequency Ring Laser Oscillation and Power Amplification System

设计研制了波长为1064 nm的半导体激光器泵浦单频Nd∶YAG激光振荡及功率放大系统。仿真分析了激光晶体的端面温度分布,采用低掺杂浓度激光晶体和端面键合方式有效改善了晶体棒的端面热效应。激光振荡级采用环形腔内插入法拉第旋光器、偏振片、半波片和声光Q开关的方式,在重复频率25 Hz下获得了能量2.18 mJ、脉冲宽度63.2 ns的单向单频脉冲激光输出。经过一级放大后,最终获得了能量15.85 mJ、脉冲宽度62.7 ns的单频脉冲激光输出。

All-solid-state single-frequency pulse lasers have been widely used in coherent laser detection,laser remote sensing,laser ranging,and other fields due to their advantages of narrow line width,long coherent length,high stability,and compact structure.In recent years,in the field of coherent laser detection,the demands for wind field measurement,aerosol detection,and coherent imaging are increasing,and single-frequency lasers are the key devices of lidar.Among them,the 1064 nm singlefrequency pulsed laser based on Nd∶YAG crystal can not only be directly used as the light source of lidar for wind field and aerosol detection,but also can generate single-frequency laser output of other wavelengths through nonlinear frequency conversions such as frequency doubling,sum frequency,and optical parametric oscillation.In this paper,an LD-pumped single-frequency Nd∶YAG master oscillator and power amplifier system with a wavelength of 1064 nm has been developed.Nd∶YAG crystal has a high absorption at 808 nm.The crystal absorbs a large amount of the pump light,which will induce the thermal lensing effect and decrease the quality and stability of the beam.The thermal effect is more serious when the crystal is pumped continuously.Therefore,it is very important to decrease the thermal effect.In this paper,the steady-state heat transfer model of the Nd∶YAG rod is studied,and three Nd∶YAG rod models with different parameters are built for comparative analysis.It is shown from the simulated results that the temperature of the Nd∶YAG rod can be decreased by low doping concentration and end-face bonding.In the experiment,a six-mirror ring cavity is used as the oscillator.A Faraday polarizer,a polarizer,and a half-wave plate are inserted into the cavity to eliminate the spatial hole-burning effect and obtain a unidirectional single-frequency laser output.The laser pulse is obtained by an acousto-optic Q-switch.A pulse output with an energy of 2.18 mJ and a pulse width of 63.2 ns is obtained at the repetition rate of 25 Hz,and its single-frequency characteristic is validated by monitoring the waveform of the output pulse.In order to achieve a higher energy output,a power amplification system is established after the oscillator.The pulsed laser with an energy of 1.85 mJ incidents in the amplifier after being shaped by a lens.An LD side-pumped Nd∶YAG module is used in the power amplification system.After the amplification,a laser output of 15.85 mJ with a pulse width of 62.7 ns is obtained with the gain of about 8.6 times.The single-frequency ring laser oscillation and power amplification system has potential applications in lidar and optical parametric oscillators.