589nm And 820nm Lasers Based On Two-photon Excitation Of Sodium Atomic Return Flux

When ground-based optics telescope is used to observe the target in the space,wavefront phase distortion induced by atmospheric turbulence will greatly reduce the image resolution,that is,the “look clealy” problem for the telescope.In the high-energy laser system,the tip-tilt indetermination caused by atmospheric turbulence will make the laser shaking to reduce the energy concentration on the far field target,that is,the “look accurately” problem for the telescope.It can solve the “look clealy” problem with the use of adaptive optics based on monochromatic return flux.It can solve the “look accurately” problem with the use of adaptive optics based on bi-chromatic return flux or polychromatic return flux.Solving the above two problems can increase the sky coverage up to 100%.Sodium return flux is the most advanced return flux at present.Continuous-wave return flux and quasi-continuous-wave(QCW)return flux are two kinds of sodium return flux for their different operating mode.Compared with the sodium return flux laser operating at continuous wave mode,the sodium return flux laser with the QCW(microsecond pulse)operation can provide a time format,eliminating the interference of atmospheric Rayleigh scattering,so it can improve the image resolution.In this dissertation,we firstly propose a new approach based on the double resonant excitation of the 3S1/2-3P3/2 transition at 589 nm(D2 line)followed by the 3P3/2-3D5/2 transition at 820 nm for generating sodium return flux to correct wavefront distortion and tip-tilt error.Then,investigation and application of QCW 589 nm and 820 nm sodium return flux laser technology are studied to solve the above two problem.Theoretically,the common problem of the thermal effect of the gain medium,which affects the power,energy and beam quality of the sodium beacom laser,is analyzed.The design of the thermal near-unstable cavity and the thermally induced birefringence compensation technique,which can provide a guiding role for the design of 589 nm and 820 nm cavitys,are introduced.Then,the common technique of frequency conversion,which can produce a special wavelength for sodium return flux lasers,is introduced.Taking the sum-frequency generation(SFG)as an example,the relationship between the power density of the fundamental frequency and the size,which can provide the theoretical basis for the efficiency frequency conversion in the 589 nm and 820 nm laser designs,is obtained.In the aspect of experiment,high power side pump technique,thermal management and thermal effect compensation technique,relaxation oscillation suppression technique,lienwidth narrowing and wavelength controlling technique were used with theory analysis and numerical calculation of the thermal effect of the gain medium and the common technique of frequency conversion.As a result,high quality narrow linewidth tunable QCW microsecond pulse 1064 nm laser and 1319 nm laser were obtained through three mirror ring oscillation cavity scheme,double rod in series and the thermal near-unstable cavity.Based on the strcture of master oscillator power amplifier(MOPA),the 1064 nm laser with output power of 100 W and the 1319 nm laser with output power of 72 W were obtained using spatial pattern matching,time domain matching and two way amplification.Then 589 nm laser with output power of 35 W was obtained through efficiency SFG using LBO crystal for type I noncritical phase matching.The stepping motor and PZT were used for coarse and fine adjustment of the angle of the etalon inside 1064 nm seed laser.Based on the control program based on Labview language,a large wavelength scan range high presice tunable 589.159 nm sodium return flux laser was obtained with scan range from 589.002 nm to 589.182 nm(155GHz),linewidth of 0.3 GHz,wavelength drigf of ±0.2 GHz.Based on above result,a microsecond pulse sodium return flux laser practical prototype was successfully developed with maximum output power of 33 W,beam quality o f 1.4,linewidth of 0.3 GHz,wavelength drifr of ±0.2 GHz and it works stably more than 12 hours.Finally,the sodium laser guide star was successfully observed by the telescope of National Astronomical Observatories at Xinglong.The efficience of reture flux was more than 140 photons-m2/s/W/ion,which exceeded the requirements of TMT(Thirty Meters Telescope).We reach the program feasibility review by TMT and achieve an important breakthrough in this area.Similarly,with theory analysis and numerical calculation of the thermal effect of the gain medium and the common technique of frequency conversion,high energy microsecond pulse 1064 nm laser was obtained through the thermal near-unstable cavity and MOPA structure using the thermally induced birefringence compensation technique.Then high energy 532 nm laser was obtained through extra-cavity second harmonic generation(SHG)using LBO crystal for type I noncritical phase matching.Output energy of resonator with standing wave structure was calculated by rate equation in theoretically.By selecting the appropriate pumping region,output energy of 89 m J was obtained using the pattern matching and the prism tuning technique based on the large energy 532 nm laser.After increasing the size of the Ti:sapphire crystal,a high pulse energy and high beam quality 819.710 nm Ti:sapphire laser was developed using selecting frequency technique with birefringence filter and the linewidth narrow technique with etalon.The maximum output energy of 132.5 m J at 819.710 nm was achieved with a pulse width of 100 ?s.This is,to the best of our knowledge,the highest pulse energy at 819.710 nm with pulse width of hundred microseconds.