Investigation On KTiOAsO₄ Crystal With Cascaded Optical Parametric Oscillator

Optical parametric oscillator?OPO?is a research hotspot and important direction of non-linear frequency conversion for its many advantages,such as wide tuning range,high conversion efficiency and compact structure.The OPO cascading process further broadened the laser output spectrum and provide a new method for generating mid-infrared source.High quality non-linear optical crystal can greatly improve the conversion efficiency of the cascade OPO.KTiOAsO₄?KTA?crystal is a potential non-linear optical crystal for cascade OPO,owing to its many excellent characteristics such as high damage threshold,nonlinear coefficient and stable physico-chemical properties.In addition,KTA-OPO based on non-critical phase matching?NCPM?is no walf-off angle.In this dissertation,different Nd³⁺lasers pumped self-cascaded KTA-OPO were compared and their output characteristics were analyzed.The main contents are listed as follows.1.The self-cascaded KTA-OPO emitting at 2.59?m was driven by a laser diode end-pumped Q-switched Nd:YVO₄ laser at 1064 nm.A Nd:YVO₄ crystal was used as the fundamental crystal for its large emission cross-section which is benefits to the conversion efficiency.An average output power of 445 mW of second order signal wave at 2.59?m was obtained with the pulse repetition frequency of 60 kHz,and the incident pump power of 8.7 W.2.The self-cascaded KTA-OPO emitting at 2.50?m was driven by a laser diode end-pumped Q-switched Nd:YLF laser at 1047 nm.The negative thermal lens effect of Nd:YLF crystal is good for improving the mode-mismatch resulted from the thermal effect.And its long fluorescence lifetime contributes high single pulse energy at low pulse repetition frequency.Under a pump power of 9.7 W and the pulse repetition frequency of 15 kHz,the maximum average output power of605 mW of second order signal wave at 2.50?m was obtained,corresponding the single pulse energy up to 40?J.3.The self-cascaded KTA-OPO emitting at 2.67?m was driven by a laser diode end-pumped Q-switched Nd:YAP laser at 1080 nm.Nd:YAP crystal has outstanding thermal conductivity and mechanical property which allows the OPO normal operation at high pump power.Under a pump power of 12.4 W and the pulse repetition frequency of 20 kHz,the average output power of 330 mW at 2.67?m was obtained.