Research On 2μm Pulsed Solid-state Laser Based On Tantalum Aluminum Carbide Material

The 2μm pulsed solid-state laser is mechanically and optically compact,furthermore,it is reliable and easy to operate.Its output laser wavelength is in the absorption band of various components in the atmosphere,which brings a number of application scenarios,such as the use of remote sensing principles have been put into use to measure the concentration of specific components in the atmosphere using2μm laser,or 2μm lidar to measure the wind field around the landing of spacecraft,or even 2μm satellite-based lidar to observe the Earth’s atmospheric wind speed profile image.In addition,2μm lasers,with their easy absorption by water,have great value and potential in areas such as human tissue removal surgery and the provision of high quality eye-safe power lasers（100m J/cm²）.Among them,yttrium aluminum garnet（YAG）monodoped Tm³⁺Tm:YAG crystal is the most reliable gain medium for 2μm pulsed lasers because of its high quantum efficiency and excellent absorption and emission bands.Based on the theory of passively Q-switched/mode-locked（PQS/PML）of laser and resonator theory,this paper prepared a new type of MAX-phase ceramic material Ta₄AlC₃ as a saturable absorber（SA）,carried out passively Q-switched and mode-locked experiments on Tm:YAG laser with linear cavity and Z-shaped cavity structure,and focused on the comprehensive exploration and research of two Tm:YAG laser properties.First,the physical properties of Ta₄AlC₃ materials were investigated,and Ta₄AlC₃ crystal sheet dispersions were prepared by ultrasonic exfoliation,followed by spin coating to make Ta₄AlC₃ saturable absorbers（Ta₄AlC₃-SA）,which were characterized by scanning electron microscopy,projection electron microscopy,X-ray diffraction,and Raman spectroscopy.After that,a nonlinear performance test laser device was designed and built to study the nonlinear absorption performance of Ta₄AlC₃-SA at 2μm laser,and the modulation depth of Ta₄AlC₃-SA was known to be8.0%.Then,the energy level jump and absorption spectra of Tm:YAG crystal were analyzed,and its absorption peak at nearly 800 nm was tested,and the rate equation theory of Tm:YAG laser operating in continuous wave mode and passively Q-switched mode was explored.The Tm:YAG continuous and passively Q-switched lasers were designed and built with the narrowest pulse widths of 933ns and 997ns in the stable passively Q-switched range for both transmittance at T=1.5%/2.5%,corresponding to pulse repetition frequencies of 135.1kHz and 148.2kHz,respectively,and the single pulse energy at 933ns was calculated to be 6.20μJ with a peak power of 6.65W.The center wavelengths in continuous wave mode and passively Q-switched are 2015.43nm and 2011.86nm,respectively,and the beam quality factor in the x and y axes areM_x²=1.04 andM_y²=1.08,respectively.Finally,based on the theory of passively mode-locked,a Ta₄AlC₃-SA-based passively mode-locked Tm:YAG laser was designed and built,and the output laser characteristics of the passively mode-locked laser were investigated.The Tm:YAG laser resonant cavity is 89 cm long,the output mirror T_OC=1.5%,and the laser output power in continuous wave mode reaches 1.74 W at the LD input power of 22.9 W.The laser slope efficiency is 7.6%.When the passively mode-locked mode is stabilized,the average laser output power drops to 0.56W,and its slope efficiency is 2.5%.At an input pump power of 14.1W,the Tm:YAG laser appears Q-switched-mode-locked,and at an input pump power of 20.1W,the Tm:YAG laser appears continuously mode-locked.The shortest pulse width of the passively mode-locked laser was 541 ps,the peak pulse power was 6.16 W,and the energy of the single pulse was 3.33 n J.The spectrum meter showed that the shortest pulse of541 ps was obtained at a repetition frequency of 168.18 MHz,and the center wavelengths of the Tm:YAG laser were 2014.8 nm and 2012.4 nm in the continuous and passively mode-locked modes,respectively.The diffraction limitsM_x²=1.14 and M_y²=1.09 in the x/y axis were tested.