Studies On Bar-stack LD Pumped Tm：YLF Slab Lasers

Ho³⁺laser pumped by Tm³⁺laser is an efficient2μm laser source which is widelyused in medicine, remote sensing, military and mechanical processing and other fields.Bar stack LD pumped single-crystal Tm³⁺laser can reduce the volume and facilitate thestructure, so the research of high power1.9μm Tm³⁺doped single crystal laser systemhas important application value and practical significance. On the Basis of obtaininghigh-power output laser by using1.9μm Bar stack LD pumped Tm:YLF laser, studieson theory and experiment would be carried out in this thesis.Based on the energy level structure of Tm³⁺system, its radiative transitionmechanism has been analyzed in detail. According to Tm:YLF crystal’s absorption andemission spectrum, the effective gain cross section calculation expression was given.The output wavelength under different polarizations of the crystal has been analyzed.The output laser of σ polarization has a great emission cross section aroud1.908μm. Avolume Bragg grating and F-P etalon was used to restrict the laser wavelength avoidingthe water vapor absorption peaks near1908μm. According to the spatial distribution forthe pump is not well difined, the pump beam can be approximated as simple plane wave.A laser model based on plane wave analysis was established, and the relevant physicalexpressions under steady-state operation were given. The simulations and calculationsprovide the basis for the experiment. The thermal effect of crystal is an important factorconstraining the power scaling of the Tm:YLF solid-state laser, so the causes which arethe upconversion and quantum effects have been discussed intensively. A thermalmodel of the slab crystal was established, and the temperature distribution and stressdistribution of the slab were simulated. The thermal effects of the crystal under differentspot size of the pump were analyzed as well. The simulation analysis results were inagreement with that the Bar stack LD pumped slab structure is more conducive to easethe thermal effect. The simulations results provide a basis for follow-up trial design.The pump beam intensity of the fast axis can be approximately equivalent to aGaussian beam under the collimation and focus. According to the principle of beamrenovating and exchanging, a beam shaping system of Bar stack LD was designed. Withthe method of fasx axis matching, the pump-laser spot ratio was setted to be1.5and aplano-concave cavity designed accordingly. Single-ended one-way, single-ended two-way and double-end-pumped three forms were designed, and optimized the resonatorparameters. Under the pump size of⁵×1mm², with the pump power of449W,115W1.908μm stable output of narrow linewidth laser was obtained for1.5×6×12mm³Tm（2.5at.%）:YLF laser, corresponding to the slope efficiency of30.5%, and the crystalwas well when pump power was449W. The M2factors of the fast axis and slow axis at the output power of100W were calculated to be1.62and58.42respectively. The beamquality of the slow axis has been significantly improved due to the role of the etalon.The output laser beam section is elliptical, and the beam is different Gaussian typealong each axis. Additionally, a preliminary discussion of1.908μm beam transformationhas been taken base on the principle of Gaussian beam transformation, and a method ofbeam shaping by using cylindrical lens for both directions was presented.