Study On 2.79?m Pumped BaGa₄Se₇ Optical Parametric Oscillation Technique

Mid-infrared lasers with wavelengths in the range of 3-12 ?m are particularly attractive for many important applications in atmospheric detection,bio-medicine,scientific research and military.Optical parametric oscillators have the advantage of compactness,narrow linewidth,and broad tunability,and hence become one of the major development directions for 3-12?tunable coherent infrared lasers.However,OPO has two main problems at present,First,the lack of high-quality optical crystals with high transmission range,high damage threshold and high nonlinear coefficient at the same time limits the wavelength tuning range and pulse energy output of mid-infrared laser with optical parametric oscillation;the second is the long-wave pump source lacking high beam quality and high peak power.The existing mature pump sources are mainly 1?m and 2?m near-infrared lasers.When converted by OPO to mid-infrared laser,especially the wavelength of laser was above 5?m,near-infrared?pump?laser ×1 has a large quantum loss??=?₁/?₂?due to the distance from the parametric laser ×2,which reduces the infrared laser conversion efficiency,output energy and beam quality of the optical parametric oscillation.In view of the above problems,based on the new infrared crystal BaGa₄Se₇?BGSe?,the development of high peak power nanosecond 2.79?m laser was carried out,and the efficient BGSe-OPO system with 2.79?m pumping was studied.The specific research content of the paper is as follows:1.The energy transfer mechanism between Cr,Er:YSGG,Er:YSGG,Er:YAP and other 2.79?m laser crystal materials under different pumping modes is analyzed theoretically.The thermal effect in the side pump 2.79?m laser system is studied,and the compensation methods of thermal lens effect and thermal depolarization effect are deeply studied.In the semiconductor side pump Er:YSGG electro-optic Q-switched laser,the double-cavity structure is designed to effectively solve the problem of energy drop caused by the thermal depolarization effect,and the thermal lens of the crystal is compensated by the end face grinding method at 20 Hz.In the case,a 2.79?m laser output with a pulse energy of 71 mJ and a pulse width of 58 ns was obtained.In the flash-pumped Cr,Er:YSGG laser,a plano-convex cavity type with thermal compensation was used,and an ultra-high peak power density of 80 MW/cm²@10Hz,high beam quality M² =1.6 was obtained.The problem of high peak power nanosecond laser output at high repetition rates at this band was solved.2.The coupling equations of three-wave interaction are studied theoretically and the optical parametric oscillation process is deeply analyzed.According to the BaGa₄Se₇ refractive index equation,the wavelength-angle tuning curve of angle-tuned class I phase matching is calculated by MATLAB programming,based on this,a high-precision wide tuning range and high conversion efficiency BaGa₄Se₇-OPO experimental equipment is designed..In terms of experiments,the high-quality 2.79?m Cr,Er:YSGG laser and self-grown high-quality BGSe crystal,combined with high-precision angle tuning device and high conversion efficiency BGSe-OPO system,obtained the maximum pulse energy of 3.5mJ@10Hz,pulse width 21ns,wide tunable range 3.94-9.55?m,high beam quality factor M²x=5.0,M²y-4.6 laser output,the corresponding light-to-light conversion efficiency is 18.9%,and the oblique efficiency is as high as 31.6%.The slope efficiency is 59%higher than the highest slope efficiency reported previously.By comparing the theoretical data with the experimental experiment tuning curve,the BGSe-OPO tuning curve with higher precision is reported,which provides a reference for the researchers related to BaGa₄Se₇.