Study On 2.1?m Laser Based On Nd:MgO:PPLN Crystal

2.1?m laser has strong penetration ability in the air and is in the band of strong water absorption.It has very important application prospects in many fields such as laser radar,laser ranging and laser medical.However,the structure of the 2.1?m laser is complex and bulky.In order to simplify the physical structure of the existing 2.1?m laser,the Nd-doped MgO:PPLN crystal is used as the self-conversion medium in this paper,the gain process and QPM-OPO(Quasi-Phase Matching Optical Parametric Oscillator)process are unified to realize self-optical parametric oscillation in single Nd:MgO:PPLN crystal.The 2.1?m self-optical parametric oscillation laser based on Nd³⁺doped MgO:PPLN crystal was studied.In theory,the absorption and emission characteristics of Nd:MgO:LN crystals and the refractive index variation of crystals at different temperatures were analyzed.The thermal effect model of the crystal is established,and the temperature distribution of the crystal under different pump spot radius and power is simulated.Based on the temperature tuning curve,the influence of the thermal expansion of the crystal temperature rise on the degenerate wavelength of 2.1?m is analyzed,and the crystal polarization period is determined to be 32.55?m.Based on ABCD matrix theory,the distribution changes of fundamental light spot and parametric light spot are simulated,and the matching mode of fundamental light spot and parametric light spot is optimized.Secondly,the ultra-threshold multiple is simulated and analyzed.By optimizing the selection of relatively high 2.1?m degenerate light to reduce the parametric light threshold.Finally,the theoretical model of active Q-switched rate equation is established.The simulation results show that the narrowest pulse widths are 40.76 ns and 5.39 ns for the fundamental and parametric light at60 k Hz repetition rate.In the aspect of experiment,the self-OPO-based frequency-optic experiment of short cavity and composite cavity was carried out.In the composite cavity,when the pump power is 27.58 W,a single 1 084 nm fundamental-frequency continuous output of 9.12 W is obtained.When the repetition rate is 60 k Hz,the maximum output power of the fundamental light is 8.68 W,and the pulse width is 55.45 ns.On this basis,the 2.1?m self-OPO experiment was further carried out.When the temperature is set to 70°C and the repetition rate is 60 k Hz,a 2.1?m laser output with a central wavelength of 2168 nm,a linewidth of 86.4 nm and a maximum of 1.13 W is obtained.The pulse width is 8.41 ns and the fundamental-frequency optical-parametric optical conversion efficiency is 13.03%.The experimental results are basically consistent with the theoretical analysis,which verifies the feasibility of self-optical parametric oscillation output of 2.1?m degenerate laser based on Nd:MgO:PPLN crystal,and realizes the miniaturization of 2.1?m laser.