Narrow Pulse Width And High Energy Nd:YAG/Cr⁴⁺:YAG Passively Q-switched Laser

Passively Q-switched lasers with narrow pulse width and high energy are widely used in many fields,such as laser ranging,laser spectroscopy,medical beauty,and military.In order to obtain larger single pulse energy and narrower pulse width,this paper makes in-depth theoretical and experimental research on Cr4+:YAG crystal with initial transmittance less than 20%.The main research contents of this paper are as follows(1)Using the theory of rate equations,a brief theoretical analysis and calculation of the passively Q-switched laser is carried out,and then the calculation expressions of parameters such as peak power,pulse width and single pulse energy are derived.The simulation model was established by using MATLAB software.In the simulation research,the output characteristics of the Nd:YAG/Cr4+:YAG passively Q-switched laser were compared when the initial transmittance of Cr4+:YAG crystal was less than 20%.The effects of pump pulse width,pump power and output coupling mirror reflectivity,cavity length and non-uniform pumping on the output characteristics of the laser are investigated The simulation found that the pump pulse width and pump power mainly affect the repetition frequency of the pulse,the first pulse setup time and pulse period at different initial transmittances are also obtained.The optimal output coupling mirror reflection exists,in which the maximum single pulse energy and the minimum pulse width can be obtained respectively at different initial transmittances.The cavity length mainly affects the peak power and pulse width of the laser output,and the increase of cavity length will significantly increase the pulse width.The smaller the initial transmittance of Cr4+:YAG crystal,the larger the single pulse energy,the more the pulse width narrow,the smaller the repetition frequency,the smaller the Q-switching efficiency.Simulation studies of non-uniform pumps have found that they have a major influence on the interval of the output pulses and the pulse setup time(2)The characteristics of the output pulse energy and pulse waveform of the laser in Q-switching mode are studied experimentally.The results of the Q-switching experiment show that the influence of the pump energy,the initial transmittance of the Cr4+:YAG crystal,and the cavity length and other parameters on the output pulse 1s basically consistent with the results of the simulation analysis.In the cavity length experiment,it is also found that Q-switching and mode-locking occurs in some cases.The narrowest pulse width of 6.7ns and the largest single pulse energy of 138.lmJ is obtained when the experiment is in the Cr4+:YAG crystal with initial transmittance of 6.21%.