High-efficiency OPO Laser Technology Based On Steep Front-edge Pump Light

The Optical Parametric Oscillator(OPO)is a parametric oscillator that oscillates in the optical frequency domain.It uses a second-order nonlinear effect to perform frequency conversion on the incident laser.Different wavelengths can be obtained by changing the parameters of the nonlinear crystal.With the continuous research of OPO by researchers,the theory and technology of OPO have made great progress.This article chooses the OPO output wavelength to be 800 nm,because the 800 nm laser has a wide range of applications in laser therapy,terahertz and other fields.The usual 800 nm laser acquisition technology is costly.However,it is difficult to increase the conversion efficiency of OPO using the general OPO technology route,and it is difficult to meet the needs of scientific research and engineering applications.In this paper,Nd:YAG passively Q-switched pulsed laser is used.The output pulse undergoes stimulated Brillouin scattering(SBS)and is shaped as a sharp forward trailing edge pulse.After doubling the frequency,the 532 nm pulse is generated as the pump pulse of OPO,and the final output of OPO is 800 nm laser pulse;the following is the main content of this study.1.The coupled-wave equations of the OPO process are deduced.Then based on the coupled-wave equation of OPO,the OPO oscillation threshold formula is deduced,and the factors affecting the OPO oscillation threshold are analyzed.Then the phase matching theory and the methods of phase matching are introduced.Finally the SBS theory and deduced the theoretical calculation model of the SBS process are introduced.2.The calculation of KTP crystal parameters needed to generate 800 nm laser was performed.The phase matching angle,the effective nonlinear coefficient and the corresponding crystal's departure angle of KTP crystal were calculated.Then the calculated parameters were used to simulate the OPO.The changes the light energy of the OPO output signal and the OPO energy conversion efficiency are studied by changing the pulse width of the pump pulse,the transmittance of the OPO output mirror,the length of the OPO cavity,and the length of the KTP crystal.Then using FC-770 as the SBS medium,the simulation of SBS pulse compression is carried out using the single-cell compression structure.The compression pulse width can be adjusted by the pump energy in the nanosecond range,and the energy conversion efficiency is also very considerable.3.The experimental study of OPO pumped respectively by the Gaussian pulse and the steep front-edge pulse obtained by SBS pulse compression.The OPO experiment pumped by steep front-edges pulse uses an OPO output mirror with a transmittance of 20% to obtain the maximum signal energy of 23.43 m J.The corresponding OPO energy conversion efficiency is 34.3%.Compared with the OPO experiment pumped by the Gaussian pulse,the OPO oscillation threshold is reduced,and the energy conversion efficiency is improved by about 10%.