Research On End And Side Pumped Tm:YLF Slab Crystal Laser

1.9μm-laser is in the range of human eye safety,and in the atmospheric window,which has high transmittance to the atmosphere,and has important applications in laser remote sensing,medical and health,military fields.Single-doped Tm all-solid-state laser is one of the main technical means to achieve 1.9μm laser at present.In this paper,an end-to-side hybrid pumping structure is proposed to solve the thermal imbalance problem caused by the conventional end-pumped structure.The high power Tm:YLF 1.9μm laser output is realized.The specific research work is carried out from both theoretical and experimental aspects:In theory,the physical and chemical properties of Tm:YLF laser gain medium,such as thermal conductivity,thermal expansion coefficient and refractive index,are studied and analyzed.The operation model of Tm:YLF rate equation based on quasi-three-level structure is established.The influence of pump spot,crystal size,doping concentration and output mirror transmittance on the output characteristics of Tm laser system is deeply analyzed.Further,based on the end-side hybrid pump structure,the heat source function inside the crystal was determined,and the thermal stress distribution model of Tm:YLF laser crystal under different pump structures was established.The influence of different pump spot sizes,pump power and end-face-side power matching conditions on the thermal stress analysis of the crystal under end-face pump and hybrid pump structures was analyzed.Finally,optimized parameters of laser system with pump spot of 5×1mm~2,end-side power matching of equal proportion and output mirror transmittance of T=40%.In the experiment,the focusing coupling optimization design of the array pump is first carried out to achieve the optimal adjustment of the spot size of the fast and slow axis of the pump light.At the same time,the structure of Tm:YLF laser resonator is optimized based on optical transfer matrix.The experimental study of high power Tm:YLF laser is carried out.Under the end-pumped structure,the size of the pump spot is 5×1mm~2,the absorption pump power is 232.1 W,and the laser output is 53.1 W.On this basis,the side-pumped structure is added.When the side-pumped spot size is 10×1mm~2,the end-pumped power is212.2 W,and the side-pumped power is 62.1 W,the laser output is 55.7 W,and the corresponding slope efficiency is 16.3%.In the meantime,the volume grating is added to the end-side pumping structure to control the laser output wavelength,and the 1880 nm band output is finally suppressed.The 1907.3 nm band laser output with a linewidth of 0.32nm is obtained.Finally,the beam quality of the end-side hybrid-pumped Tm:YLF slab laser is measured.The beam quality M_y~2 and M_x of the fast axis and the slow axis are 1.45 and53.67,respectively.