Study Of Frequency Conversion Of Solid State Laser

Laser has an irreplaceable position in industry,military,energy,medical treatment,communication and so on,because of its high monochrome,strong coherence and excellent directionality.It is called one of the greatest scientific achievements in the 20th century.However,limited by the energy level structure of laser gain medium,the laser output wavelength is too single to meet the needs of engineering and scientific research.The emergence of laser frequency conversion technology has successfully broken through this limitation,greatly broadened the window of laser output wavelength,become an effective means to obtain new laser sources,and opened a new era of laser technology.In the practical application process,the laser frequency conversion still faces some problems,for instance,poor beam quality or damage of optical components.In this paper,the frequency doubling and tripling process of solid-state laser are studied.The specific research contents are as follows.(1)In order to meet the requirement of high beam quality of laser source for water-soluble KDP crystal growth monitored by Michelson interferometry,a 532-nm CW green solid-state laser was designed to replace the He-Ne light source in order to compensate for the problems of low power,poor beam quality and relatively large water absorption of He-Ne light source.The output power of the laser is 300 mW,the beam quality factor is Mx2=1.03 My2=1.03,and the output power stability is 1%within 2 hours.(2)In order to meet the need of laser source for ultrasonic imaging,a switchable solid-state laser with output of 1064 and 532 nm was developed by using double resonator structure.By using polarization rotation and Brewster's law,the laser can work in different resonators and output different wavelengths by controlling the input and output of the rotatory crystal.The laser output repetition rate is 10 kHz.which reaches the upper level lifetime limit of Nd:YV04.The output power of 1064nm can reach 3.6W,with the pulse duration 11 ns,the beam quality factor Mx2=1.19,Mx2=1.18,respectively,and the output power of 532nm is 2.5 W,with the pulse width 10 ns.and the beam quality factor Mx2 = 1.2.Mx2=1.18,respectively(3)Aiming at the demand of 3C marking for short wavelength laser source,an ultraviolet laser was designed.In order to reduce the influence of thermal lens,the convex mirror is used as the front cavity mirror.In order to solve the problem of ultraviolet film damage,the Brewster angle cut LBO crystal is used as the frequency tripler,which can achieve three-wave separation and avoid inserting a spectroscope in the resonator.The repetition rate of the laser is adjustable.When the repetition frequency is 40 kHz,the output of 3.65W ultraviolet laser can be achieved.The pulse width is 17.5 ns.the beam quality factor is Mx2=1.13,Mx2=1.32,respectively.(4)In order to avoid the ultraviolet damage of fused quartz lens in inertial confinement fusion(ICF),the configuration scheme of convergent beam third-harmonic generation(THG)is studied theoretically and experimentally.The polarization,nonlinearity and phase matching of convergent beams are analyzed.The conversion efficiency of convergent beam is simulated,and the middle scale LBO three-tiled-crystals,is designed and tested.The convergent ultraviolet light of 110 mJ is obtained,and the THG conversion efficiency is 20%,which verifies the feasibility of the scheme.