Study On Key Techniques Of Compact High Efficiency End-pumped Solid-state Laser

The high efficiency Diode-pumped solid-state Laser?DPSSL?is the key device in lidar.In this thesis,we studied several core issues in end-pumped DPSSL with high repetition and compact structure.The thesis mainly includes four parts:the analysis of interaction between thermal effect and pump optical field distribution in high power DPSSL;thermal adaptive adjusting technique of laser beam quality;broadband absorption technique in end pumped Nd:YAG laser;the design of high efficiency of end-pumped DPSSL prototype.The analysis of interaction between thermal effect and pump optical field distribution in high power DPSSL.In high power laser diode?LD?end-pumped solid-state laser,due to the complicated interaction between pump optical field distribution and thermal effect,the method of analysis thermal effect used in low power could not be used,or would lead to large error.In the light of the above,the concept of iteration used in calculative method could fully consider the interaction between pump optical field distribution and thermal effect.So,the interaction in some typical LD end-pumped solid-state laser was analyzed,and the calculative error without considering the interaction was studied.At the meanwhile,by comparison abortion length of solid-state laser material with its effect focal length,a parameter K was put forward to measure intensity of the interaction,and it could be used to judge whether considering the interaction or not.Results showed when the parameter K was less than 0.1,the influence of the interaction could be ignored.Thermal adaptive adjusting technique of laser beam quality.Special distributions of pump beam and oscillating beam will be affected by thermal effect in solid state laser.The research showed that a specific pump power region was existed in end-pumped solid-state laser.In this interval,pump beam and ground-mode oscillating beam achieved large overlap in the gain medium under thermal effect,and resulted in high efficiency of pump source and better beam quality of laser.If out of the interval,the beam quality of laser would be deteriorated rapidly.Based on the characteristic,a end-pumped DPSSL was designed.Special distributions between pump beam and oscillating beam of the laser could achieve large overlap,and the M² factor was lower than 2.3 with pumping power ranging from 105W to 115W.Out of this range,the M² factor rapidly increased to more than 3.Broadband absorption technique in end pumped Nd:YAG laser.A scheme of Nd:YAG and Nd:YVO₄ crystal composite application was proposed to imrove the efficiency of DPSSL in high pump power.The Nd:YAG crystal with good thermal conductivity and optical properties was used as the front end of pump light absorption crystal,and placed a wider absorption spectrum Nd:YVO₄ crystal at its rear-end to absorb the pumping light energy composition,which was not absorbed by Nd:YAG crystal due to its narrow spectral width.Two kinds of crystals in the 1064 nm wavelength emission spectrum overlapped each other.The absorption of pump light energy could be converted to common oscillation laser wavelength,the efficiency of pumping light was improved.Meanwhile,the conventional Nd:YAG crystal can be influenced by LD wavelength shift easily due to its narrow absorption bandwidth,which will lead to fluctuating of output power.The proposed composite applications could effectively reduce the oscillating light power changing with pumping source working temperature fluctuations.The design of compact high effciency end-pumped DPSSL prototype.An compact high efficiency end-pumped DPSSL prototype was realized by module design.In the prototype,several key techniques had been used,such as:the local uniform pumping technique,the hard adjustment technique of output mirror,the doubly Q-switch technique and so on.And several methods of testing various parameters were introduced to measure the prototype.The test results met high repetition?10kHz?,narrow pulse width?3.6ns?,high peak power?1.1MW?,high beam quality?M²=3.9?,small size?80×90×180mm³?,high efficiency?wall-plug efficiency was up to 7.2%,optical conversion efficiency was up to38%?and stability?output power fluctuation was less than 1%?.The prototype could detect the target about 11.9 km far in the field experiment,and the results were excellent.Experiments showed that the prototype owned good engineering application prospects in interference,lidar and other fields.