Study On Nanosecond Optical Parametric Oscillator And Its Applications

Optical parametric oscillators (OPOs) have been recognized as versatile sources of coherent light for spectral regions where lasers perform poorly or are unavailable. They are capable of providing tunable radiation across extended spectral regions. Among all the different operating conditions for OPOs (continuous wave, nanosecond, picosecond and femtosecond regime), the nanosecond regime has seen the most important development. The main reason the availability of very energetic pump pulses of short duration leading to high pump peak powers. This leads to high gain and conversion efficiency from pump to signal and/or idler wave in the nonlinear crystal. The robustness and compactness of nanosecond OPOs make them and their applications extremely attractive in research. How to obtain lower the OPO threshold, higher the parametric conversion efficiency and output power, wider spectrum tuning range, and, at the same time, improve the running of its reliability and stability have always been the hot topics in OPO techniques. Some special designs of nanosecond OPOs have been analyzed theoretically in detail in the thesis. The dynamic processes of intracavity optical parametric oscillators (IOPOs) pumped by lasers actively Q-switched as well as passively Q-switched have been studied both theoretically and experimentally.Firstly, the principle of OPO operation and its physical basis, and key factors affecting the OPOs dynamic process are analyzed systematically in theory. The phase-matching conditions for nonlinear crystals both KTiOPO₄ (KTP) and LiNbO₃ (LN) in OPOs are calculated. In calculating the threshold and conversion efficiency of OPOs, walk-off effect in collinear pumping, length of nonlinear crystal and OPO cavity, coupling ratio of OPO output couplers, power density and pulse width of pump pulses, spatial mode coupling coefficients between pump and parametric beams and nonlinear crystal absorption are all considered as well as how the multimode pump beam affect the gauss mode spot sizes of signal and/or idler and the processes of OPOs.Secondly, the pump sources employed in our OPOs are analyzed in details. The dynamic processes of lasing and nonlinear actions of the Nd³⁺:YAG (or (Ce,Nd):YAG) laser Q-switched both actively and passively, and, with IOPOs into its cavity are...