Single-frequency Ring Laser Oscillation and Power Amplification System

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 1 064 nm single-frequency 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 1 064 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.