Mid-infrared Continuous Wave Optical Parametric Oscillator

Coherent mid-infrared laser source operating in the spectral range of3-5μm has important applications in remote sensing, medical, spectroscopy,optical wireless communication and military fields. All-solid-state opticalparametric oscillator (OPO) which has compact struture, high stability, highefficiency, low threshold and wide tuning rangeisone of the most effectivetechniquetogeneratecoherent mid-infrared laser radiation.This dissertation is concentrated on the study of the continuous-wave (CW)OPO which utilizes a1064nm fiber laser as the pump source and a MgO-dopedperiodically poled LiNbO3(PPMgLN) as the nonlinear medium. Low threshold, highpower CW operation of singal singly resonant OPO(SRO) was built and the outputperformances are studied.The research status and development trend of mid infrared OPO areintroduced.The nonlinear crystal properties, resonant types and the methodsto obtain the signle frequency are summaried and compared.The idler wavelength tuning properties in3-5μm of the PPMgLN pumped bya1064nm laser are calculated theoretically, based onQuasi-phase matching(QPM) principle; and by usingthree-wave interaction coupled equations, thecalculations of the single-pass optical parametric gain, the oscillationthreshold, the output power and the conversion efficiency are made. In addidion,the influence of the phase mismatch is studied.Based on the calculation results in the second chapter a two-mirror linearcavity is designed. Considering the affect of astigmatism induced by the curvedcavity mirrors a bow-tie ring cavity is designed whichi is suitable for singlefrequency operation.Through the cavity optimization he threshold of linear cavity OPO is aslow as1.35W, and theidler output powerof3.2Wat3.2μ m is obtained with18W pumping. The wavelength tuning range of the output idler light is2.9-3.8μ mwhich is obtained by changing the operating temperature and poling periodof the nonlinear crystal. The pump threshold of the tow-tie cavity OPO is3W. The high threshold compared to the linear cavity is caused by the higherloss induced by four cavity mirrors. When the idler wavelength is3.4μ m the output idler power is2.6W. A narrower spectral linewidth of1.6nm is obtainedby the ring cavity OPO compared to that of the linear cavity OPO.The performance of the OPO can be further improved;a wider wavelengthtuning range could be obtained by the improvement of the coating design ofcavity mirrors, and single-frequency infrared output could be achieved by thefrequency selection of the resonant signal wave in the ring cavity.