Study On Output Characteristics And Thermal Effects Of End-pumped Nd:YAG Pulsed Lasers

In recent years,with the development of Diode Pumped Solid State Laser（DPSSL）,DPSSL is widely used in military,scientific research,mechanical processing and other fields due to its high efficiency,small size,light weight and high stability,such as laser ignition,laser ranging,laser radar,laser cutting,medical laser,and the like.In this paper,the output characteristics and thermal effects of LD end-pumped Nd:YAG lasers are studied.It is hoped that the LD end-pumped DPSSL will contribute to the work.Firstly,the characteristics of the Nd:YAG laser crystal were studied.The advantages of the crystal as a gain medium were analyzed.The energy level structure of the crystal was theoretically analyzed,which explained the reason why the 808nm band was selected as the pump light.Combined with the absorption of pump light,the temperature field distribution in the crystal and the thermal lens effect of the crystal due to uneven temperature distribution were explored.Secondly,based on the four-level rate equation model describing the Nd³⁺-doped laser system.The influence of the output characteristics of the laser with output mirror transmittance,pump spot size and coupling ratio was calculated.The coupling system suitable for LD single-tube free space pumping was designed and combined with the thermal lens effect to design the optimal resonant cavity.Finally,the above research results were verified by experiments.Using a crystal of 0.4at.%at a pump power of 9.03W,a laser output with a maximum output of 4.97W was obtained,a slope efficiency of 73.5%,and a light-to-light conversion efficiency of 55%were obtained.Thirdly,laser diode arrays（LDAs）were used as the pumping source,two coupling systems suitable for LDAs were designed,and the output characteristics of the pulse pump laser were obtained through experiments.The light guiding cone was used as coupling system,a single-pulse output of 121mJ was obtained at a pump pulse single pulse energy of280mJ,and the oblique efficiency was 48.6%.Finally,in order to obtain a larger peak power,an electro-optic Q-switch was inserted into the laser to realize active Q-switching.The four-level system actively Q-rate equations were solved numerically and the factors affecting single-pulse energy,pulse width and peak power were analyzed.A reasonable laser was designed based on the rate equation.When the pumping source selected 30Hz,300μs,50Hz,200μs two output modes,30mJ and 25mJ single pulse output were obtained respectively,the pulse width was 18ns and 16ns respectively,and the oblique efficiency was 11.63%and 14.71%.The housing suitable for the laser was designed,the housing dimensions were 220mm（length）×110mm（width）×68mm（height）and the total weight was 2.2kg.Thermal of the housing of a loaded laser under adiabatic conditions were simulated.The results show that the laser housing can guarantee the normal operation of the laser.