Design And Study On High-repetition-rate Optical Parametric Oscillator At 1.73 ?m

As an unique optical source,laser plays an indispensable role in modern society.Infrared lasers have a wide range of potential applications in various fields,such as in spectroscopy,remote sensing,optical communications,biomedicine,military and so on.The recent research shows that laser emitting at 1.73 ?m wave band can be applied to photoacoustic imaging technology(PAT).Optical Parametric Oscillator(OPO)transfers energy of an intense electromagnetic wave called pump wave to two other tunable waves of different frequency,these are called the signal wave and idler wave.This effect opens up new spectral regimes for coherent radiation where it is difficult to provide suitable lasers.In this thesis,the threshold of OPO is firstly studied on the basis of theoretical analysis,then an OPO pump source was realized by a two-stage mechanical laser diode(LD)end-pumped oscillator-amplifier system.Two LDs emitting at 808 nm with maximum output power of 47 W,and were imaged into the Nd:YAG and Nd:YVO4 laser crystals by two groups of 2:5 coupling lenses,respectively.There is an electro-optically Q-switched module.A 1064 nm pulsed laser with pulse repetition frequency(PRF)of 2 KHz and pulse duration of 10 nsec magnitude was realized.The laser beam quality was high and the out power is stable which can meet the requirements of OPO.For OPO system,potassium titanyl phosphate(KTP)was chosen as nonlinear crystal for its good optical and mechanical property,big effective nonlinear coefficient and high damage threshold coefficient.Two KTP crystals were cut in a special way to realize type II critical phase matching(CPM),and were placed with adverse orientation in order to reduce the walk-off effect and maximize the effective nonlinear coefficient as much as possible.By optimizing the parameters of OPO cavity,a maxim um output power of 2.2 W at the signal wavelength 1.73 ?m was obtained with high repetition rate of 2 KHz,and the maxim um optical-optical and slope efficiencies were22.8% and 61.1%.This work provides an excellent candidate laser source for bond selective imaging of deep tissue,and also provides a reliable theoretical as well as experimental basis for the industrialization of new solid state laser.