| Lasers emitting in the spectral region of 3 to 5 ?m have been widely applied in the fields of medical diagnosis,high-resolution molecular spectroscopy,remote sensing,nonlinear optics,Lidar,military countermeasures and many other scientific applications.As one of the most promising techniques for generation of mid-infrared laser,Optical Paramatric Oscillator based on Mg O:PPLN is widely used,because it has advantages such as high power,good beam quality and widely tunable wavelength.Dual-frequency lasers with beat note frequency at RF range have been proofed having better performance in situations of strong turbulences or scarttering.Therefore,dual-frequency laser at 3-5 ?m is an interesting topic with potential applications.This paper is concentrated on the study of the key technologies of CW-dualfrequency OPO which employed a 1064 nm DF fiber laser as the pump source and a 5% mol Mg O-doped periodically poled Li Nb O3(PPMg LN)as the nonlinear medium.A low threshold,broadly tunable,highly efficient operation of mid infrared dual-frequency laser was achieved.The single-pass optical parametric gain,the oscillation threshold,the output power and the conversion efficiency were calculated.A four-mirror ring cavity OPO was designed based on low threshold condition,and considering the optical resonator stable conditions,the mode matching between the pump and the signal wave,and the astigmation.Experimental research on dual frequency Mid IR OPO was carried out.The pump was a 30 W dual-frequency fiber laser MOPA with beat note frequency varying from 125 MHz to 175 MHz.The pump threshold of the ring cavity OPO was 2.88 W.An average dual-frequency idler output power of 1.88 W was obtained when the pump power was 9.31 W at 50 ?,corresponding to a converting efficiency of 20.2% from pump to mid IR.The idler wavelength was 3.4 ?m when the poling period was 30 ?m.The idler wavelength could be tuned from 3.05 ?m to 3.9 ?m by changing the temperature and the poling period. |
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