Theoretical And Experimental Study Of Narrow Spectral Width Mid-Infra Red Optical Parametric System

Narrow spectral width,high-power lasers operating in 2-5 μm wavelength regions have been of worthy for various applications,including terahertz field generating,medical diagnosis,environmental monitoring,optical communications,military countermeasures,scientific,civilian and defense.This type of laser is usually obtained by inserting the etalons,gratings and other components into the OPO.However,loss will be imported,and thus the output threshold of lasers will increase and the conversion efficiency and the output power will decrease.A scheme for obtaining mid-infrared laser with narrow spectral width and high power is designed,in which the spectral width compression components are not used.First,the quasi-phase matching and OPO theories have been systematically studied,and the specific calculation models are given.On the basis of theoretical analysis,the key issues in the design of OPO system are analyzed and discussed.Secondly,a pump source with the output power of 72.8 W and the spectral width of about 0.05 nm is built with 1064 nm Nd:YAG main oscillation power amplifier(MOPA)structure.By adjusting the power and the diameter of pump light spot in PPMgLN crystal of the OPO,we can control the gain intensity in the crystal and the spectral width of mid-infrared laser.In the OPO,when the pump power is about three times of the threshold,0.7 W,2.907 μm seed laser with spectral width less than 1.12 nm is obtained.Finally,the PPMgLN crystal based on OPA technology is analyzed theoretically and experimentally.The seed light was first entered the pre-OPA,when the pump power was 10 W,the output power of the seed light was amplified to 2.26 W and the optical-optical conversion efficiency was 15.6%.In the second OPA,the pump light spot diameter was adjusted from 0.7 mm to 0.84 mm,and when the pump power was increased to 26 W,the 2.907 μm idler output power was amplified to 6.35 W and the optical-optical conversion efficiency was 15.7%.In the two-stage OPA process,the spectral width of the parametric light remains unchanged.