| All solid-state laser is widely used in laser radar,photoelectric countermeasure and other fields.Mode matching and thermal effect analysis compensation are always the research focus of all solid-state laser,which are of great significance to improve the output performance of laser.In this paper,through theoretical analysis and simulation calculation,the output characteristics of Nd:YAG laser under different mode matching and thermal effect compensation are simulated,which has certain theoretical guiding significance for the construction of laser.In this paper,the mode matching analysis is first carried out,and the overlapping efficiency factor is proposed to characterize the mode matching effect of LD end-pumped laser.Using a flat flat cavity,the length of the cavity is 73.1 mm,the front end face of the crystal is at the center of the optical length of the cavity,and the overlapping efficiency factor can reach 0.67 when the beam waist radius is 0.19 mm and the focus is 2.3 mm in the crystal.In the thermal effect analysis,the thermal effect is characterized by the temperature distribution of the gain medium,the thermal deformation of the front end surface and the temperature gradient.The simulation results show that increasing the pump power or decreasing the waist radius of the pump beam after focusing the pump light will lead to the thermal effect aggravation.When the pump power is 30 W and the waist radius of the pump beam after focusing the pump light is 0.19 mm,the maximum internal temperature of the gain medium is 103.4 ?,the maximum thermal deformation of the front end surface is 0.43 ?m and the extreme value of temperature gradient is 242.4;When the focus position of the pump light is not in the center of the cross section of the gain medium,the thermal deformation contour of the front end face will be deformed,which is not conducive to thermal compensation,and the maximum increase of the extreme value of temperature gradient is 11.7.The simulation results of the continuous output characteristics show that the threshold power increases with the increase of the waist radius of the pump beam after focusing the pump light and the transmittance of the output mirror;The oblique efficiency increases rapidly and then slowly with the increase of the transmittance of the output mirror,and the oblique efficiency is the highest under the optimum waist radius of the pump beam after focusing the pump light with the same transmittance of the output mirror,and 43.3% oblique efficiency is obtained;The continuous output power increases first and then decreases with the increase of the transmittance of the output mirror,which proves that there is an optimal transmittance of the output mirror,and the continuous output power is the largest under the optimal waist radius of the pump beam after focusing the pump light with the same transmittance of the output mirror.The rate equation of actively Q-switching is established.The simulation results show that the maximum single pulse energy can be obtained by choosing the appropriate effective beam area and output mirror transmissivity;The higher peak power can be obtained by reasonably increasing the pump power and output mirror transmissivity;The narrower pulse width can be obtained by reasonably increasing the pump power and output mirror transmissivity.In order to further increase the overlapping efficiency factor and obtain better thermal compensation effect,the overlapping efficiency factor of different cavity and different gain medium characteristics is analyzed.The pump power is 30 W,the overlapping efficiency factor increases by up to 0.2 when the flat-convex cavity is used;The overlapping efficiency factor of using Nd: YAG crystal with 16 mm length and 0.2% atom doping concentration is 0.03 at most higher than using that with 8 mm length and 0.4% atom doping concentration.The maximum internal temperature,the maximum thermal deformation and the extreme value of temperature gradient are decreased by 15.8 ?,0.07 ?m and 17.1 respectively.Under the simulation conditions of flat-convex lens curvature radius of-300 mm and Nd:YAG crystal length of 16 mm and doping concentration of 0.2% atom,the overlapping efficiency factor can reach 0.91 when the cavity length is 389.3 mm,the front end face of the crystal is in the center of the optical length of the cavity,the waist radius of the pump beam after focusing the pump light is 0.26 mm and the focusing position is 4.57 mm.Under the condition of the highest overlapping efficiency factor of 0.91,when the pump power is 30 W,the best output mirror transmittance is 34.2%,the threshold power is 10.2 W,the oblique efficiency is 40.6%,and the maximum continuous output power is 12.2 W;At the output of electro-optic Q-switching,the optimum transmittance of the output mirror is 45.5%,the threshold power is 13.4 W,the oblique efficiency is 30.4% and the maximum continuous output power is 10.1 W.When Q-switching frequency is 2 k Hz,4.5 m J single pulse energy,9.1 ns pulse width and 494.5 k W peak power can be obtained. |
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