Research On Multi-pass Gain 2μm Tm:YLF Slab Laser

The 2μm laser is in the atmospheric window,has strong penetration into the atmosphere,and is in the safe range of the human eye.It is widely used in laser medicine,laser remote sensing,photoelectric countermeasure and other fields.Therefore,the study of high beam quality Tm³⁺laser system has important application value.In this paper,the multi-pass gain Tm:YLF slab laser is studied.The multi-pass gain technology is used to improve the crystal gain performance while ensuring the simple and compact structure of the laser.Finally,the high beam quality laser output of the multi-pass gain Tm:YLF slab laser is realized.The main research contents are as follows:In theory,the energy level structure of Tm³⁺system and the physical characteristics of Tm:YLF are analyzed.Based on the characteristics of LD array multimode pump beam,a plane wave theoretical model suitable for Tm:YLF slab laser is established.The single-pass gain,double-pass gain and multi-pass gain Tm:YLF slab laser are simulated.The effects of different crystal lengths,output mirror reflectivity and pump spot sizes on the output characteristics of the laser are discussed respectively.Based on the thermal model of LD array single-ended pumped Tm:YLF slab crystal,the thermal effects of crystal under different pump spot sizes and different pump powers are analyzed,and the thermal focal length of Tm:YLF slab crystal is calculated.A simple and compact multi-pass gain Tm:YLF slab laser is further designed to optimize the parameters of the resonant cavity.In the experiment,a multi-pass gain Tm:YLF slab laser experimental platform was built.The LD array single-end pumped Tm:YLF slab crystal was used,and the crystal size was 2×12×20mm³.The effects of different output mirror curvature radius,transmittance and cavity length on the output characteristics of the laser are studied respectively.Finally,a stable laser output of 2.45W with a slope efficiency of 8.8%was obtained at a pump power of 62.7W.At the same time,the beam quality is measured.The M²factor in the x-axis direction is 2.81,and the M²factor in the y-axis direction is 1.79.