Solid Infrared Laser Theory And Experimental Research

Laser diode pumped high power solid state lasers have many applications in the manufactures,scientific researchs and military technologies,owing to the advantages of high efficiency,high beam quality,compact structure and being last.Solid state lasers doped Nd³⁺ operating at near-infrared 1.06μm have been designed into kinds of geometry including rod, disc and fiber.The laser rods adaptive to various pumping structure,with good overlap between resonator mode and pumping mode,compaction and convenience,are most extensively applied.Infrared 2μm laser has the advantages including eyes -safety,the strong absorption in water and low absorption in atmosphere,adaptive to fiber transmission,which are fit for the coherent laser radar,remote sensing and the precise surgery.Xenon Flashlamp-pumped Cr:Tm:Ho:YAG laser operating at 2.1μm is applicable in the osteotomy, the lithotripsy,the ablation of soft tissue and so on.Nowadays one of the most important problems in research of high power solid state lasers is the thermal management which consists of the three aspects:firstly,improving the radiation efficiency of the pump source and the enengy conversion efficiency of laser to depress the total heat dissipation in laser material. Secondly,actualizing the effective cooling to dispel the heat dissipation.Thirdly, compensating or lowering the thermal effects.This dissertation expatiated on the theoretical and experimental studies on the thermal management of high power solid state lasers.Theoretical studies:The theoretical model for the heat generation coefficient of continuous pumped actively Q- switched Nd:YAG laser was developed.The functional relation between the heat generation coefficient and quantum efficiency,Stokes efficiency, radiation efficiency,overlap efficiency and energy storage efficiency was founded.The model took into account the effects on the heat generation coefficient from repetition rate of Q-switch and pumping rate.It was found that the actively Q- switched operating solid satet laser has more heat dissipation than the free operating laser does.The model for calculating the stability of the resonator containing a laser rod with curvature ends was developed,which was based on the transfer matrix theory of Gauss beam. The results from the numerical simulations on some typical resonators indicate that the laser rod with curvature ends can expand the stable region of plano-plano,plano-concave and plano-convex cavity notability;despite the laser rod with curvature ends can improve the stability of above mentioned cavities,it costs the effective mode volume.Experimental studies:An experimental study on LD side pumped high power Nd:YAG laser was detailed,which employed a laser rod with curvature ends and was pumped by seven LD arrays around the rod.A output laser power of 1414W was achieved at the maximum pump electrical power of 6820W,realizing the electrical-optical conversion efficiency of 21%. The experimental results confirmed that employing the laser rod with curvature ends to compensating thermal lens effect is available.An experimental method measuring the thermal focal length of solid state laser was designed basing on the analysis of the dynamic thermal stable resonator.By measuring the pump energy where a stable resonator becomes unstable,taking into account the resonator stability conditions,the thermal lens coefficient of the laser rod can be calculated.The thermal focal lengths of flashlamp-pumped Cr:Tm:Ho:YAG laser in various pumping conditions was calculated and the effects of the pumping pulse width and the cooling water temperature was analyzed.The measured thermal lens coefficient is 5.59dpt/kW,4.84 dpt/kW,4.38 dpt/kW at the pumped pulse width of 400μs,600μs,800μs,respectively.The measured thermal lens coefficient is 5.76 dpt/kW,5.59 dpt/kW,5.36dpt/kW at the cooling water temperature of 25℃,20℃,15℃,respectively.Utilizing the above results,the temperature distribution in laser rod cross section was estimated.A Xenon Flashlamp-pumped Cr:Tm:Ho:YAG laser operating at 2.1μm operating at both single pulse and repetiotion-rate pump has been demonstrated.The resonator length,output couple transition,cooling water temperature,pumped pulse width and pumped repetition-rate dependents of laser output energy was investigated experimentally.It was founded that laser output energy decline with the resonator length increasing.The quasi-three level nature of Ho laser at room temperature and high order term of thermal lens effect take responsibility for the phenomenon which laser output energy increase with cooling water temperature reduced.The laser energy varies with pumped pulse width and pumped repetition-rate,which is by reason of some factors,such as effective storage energy and thermal lens effect.The maximum laser average power of 25.8W at 10Hz repetition frequency with slope efficiency of 4.3%and the maximum laser pulse energy of 3.3J with a maximum slope efficiency of 4.9%at single pulse pump are obtained.