Theoretical Simulation And Experimental Study Of High Power Mid-infrared Optical Parametric Oscillator

This dissertation is composed of three parts:the design and realization of high power pump laser source; the simulation of nano-second singly resonant OPO; the design and realization of high power mid-infrared OPO.As pump laser source with good quality is necessary to obtain high power, high efficiency mid-infrared OPO, side-pumped and end-pumped laser sources with good beam quality and high power are developed respectively. Two main thermal effects in side-pumped laser are introduced:thermal birefringence and thermal lens effect. The depolarization and thermal bifocal lens and thermal lens aberration effects in solid state laser and their influences on output power of TEMoo-mode are analyzed. Using the4f imaging system and silicon rotator for point-to-point compensation of laser rod cross section, depolarization effects have been compensated and mitigated.62W TEMoo laser was obtained at the repetition rate of10kHz. The influence of spherical aberration in end-pumped laser is analyzed, and with a optimized plane-plane asymmetrical resonator,50W TEMoo laser was obtained.As the wide wavelength tunability, simple construction and the ability to output high power, narrow spectrum width laser, OPO pumped by solid state laser is one of the most important sources to obtain mid-infrared laser. How to achieve high conversion efficiency, good beam quality and stability in OPO is the research focus in recent years. In this dissertation, some simulation and calculation is carried out based on the coupled-wave equation in nonlinear crystal with step-by-step integration method. The influences of pump laser power density, reflectivity of the cavity mirror, loss in cavity and resonant wavelength are analyzed. The back conversion tends to be serious as the drop of the pump laser energy and the rise of signal and idler laser energy in the nonlinear crystal, which will reduce the conversion efficiency seriously. We find that the back conversion can be mitigated through optimization of the reflectivity of the cavity mirror in SRO. Based on the realization of the high power pump laser sources and simulation of the parametric oscillation, we optimized the cavity parameter and obtained9.4W,8W and9.2W3.8μm laser respectively with homemade side-pumped, end-pumped laser and high power slab laser as the pump source. In addition,we obtained8.5W2.7μm laser with the homemade end-pumped laser as pump source. Comparing the output characters of OPO with different parameters, we verified the accuracy of our simulation.