| 2.1μm laser has been widely used in laser medicine,laser radar and optoelectronic countermeasure.Narrow width and high Power which is needed for application are important developing direction with broad prospects for development.Optical parametric oscillator with quasi phase matching technique based on MgO:PPLN is the effective way to obtain 2.1μm laser.However,this way was influenced by Frequency degenerate point,line width of pumped light and high gain of strong pumping,which cause line width of 2.1μm laser broadening.For this problem,relative theory and experiments were researched in this paper.In theory,tunable characteristics of MgO:PPLN crystal was studied.Based on gain,threshold and conversion efficiency of 2.1μm single tuning optical parametric oscillator of MgO:PPLN,1.064μm high repetition pumping source and elements parameters of optical parametric oscillator were designed with optimum.The reasons of center wavelength shifting and line width broadening of 2.1μm laser were analyzed and broadening value of 2.1μm laser line width was calculated in theory.According to these basis,by studying the parameters of grating thickness,d,spatial frequency of the grating,f,and modulation amplitude of the refractive index,δn,the influence of line width narrowing was analyzed on the premise of spectral selectivity.In experiments,2.1μm degenerate laser output power of 5.51 W was obtained in free operation with folding type external cavity pump structure,which the power of 1064 nm laser was 12.9 W and the temperature of MgO:PPLN crystal was fixed at 50.5°C.The line width of laser was 109 nm.2.904 W of 2.1μm laser output of narrow line width was achieved with optical conversion efficiency of 22.5% for injecting VBG grating elements,which laser line width was effectively narrowed to 0.17 nm. |
