Multi-wavelength LDAs Pulse Pumped Nd:YAG Laser

DPSSL(diode pump solid state laser)are widely used in spaceborne altitude measurement,laser lidar,nonlinear conversion and many other fields,benefit from their high energy and good beam quality.In this thesis,high temperature LDAs side-pumped Nd:YAG lasers are studied.Utilizing the advantages of low heat dissipation pressure of the high-temperature LDAs pump source,we effectively decreased the volume of the refrigeration system and obtained a stable Q-switched laser output with good beam quality.The multi-wavelength LD side-pumped Nd:YAG laser was also studied.The Multi wavelength LDAs side-pumped Nd:YAG laser was studied in this paper.By taking advantage of the spectral linewidth of the Multi wavelength LDAs pump source,the temperature control system was avoided,making the laser more miniaturized and low energy consumption.Firstly,by comparing other laser crystals doped with neodymium ions and analyzing the physical and optical properties of Nd:YAG crystals,we selected the Nd:YAG crystals as the laser gain medium.The rate equation of the four-level system of Nd:YAG crystal was deduced.According to the active Q-switched theory,the Q-switched rate equations were established,and the output energy and pulse width were solved.According to the basic formula of heat conduction,the heat effect of Nd:YAG crystal was calculated,and the heat distribution of side-pumped Nd:YAG crystal was simulated by Ansys.Then,the output characteristics of high temperature LDAs side pulse pumped Nd:YAG lasers were studied.By analyzing the energy level particle distribution of Nd:YAG crystal under high temperature operation,it was found that the higher crystal working temperature was beneficial to increase the laser gain.The high thermal conductivity of the tungsten copper heat sink was used to dissipate the pump source,and the TEC temperature control made the pump source work stably at 60±3°C.Under the conditions of a pump current of 150 A,a pump pulse width of 250?s,and a repetition frequency of 20 Hz and 1Hz,the maximum single pulse energy of 230 m J and 246 m J were achieved corresponding to the pulse durations of 8.4ns and 7.8ns.The results show that the use of high temperature LDAs pump source could effectively reduce the refrigeration pressure of the temperature control system,and reduce the volume of the refrigeration system to make the laser more compact.It was a feasible solution to realize a laser of large energy and miniaturization.Finally,in order to extend the laser operation temperature,a multi-wavelength LDAs side-pumped Nd:YAG crystal was used.A 4-laser diode was used as the pump source to test the emission wavelength of the pump source at 25,35,45,55°C,respectively.And the absorption efficiency of the Nd:YAG crystal with temperature was analyzed.Under the conditions of a pump pulse width of 250?s,a pump current of 150 A,an output mirror transmittance of 70%,and a repetition frequency of 20 Hz and 1Hz,the maximum single pulse energy of 191 m J and 198 m J were achieved corresponding to the pulse durations of13.4ns and 12.8ns.The laser output energy increased at first and then decreased within25?55°C,and the minimum output pulse energy was 179 m J.The results show that the use of a multi-wavelength LDA pump source could realize the laser working in temperature-free operation,which was an effective method to reduce the volume,weight,and power consumption of the laser.It also broadened the applicability of the laser working temperature.