Research On Characteristics Of Pr³⁺:YLF All-solid-state Lasers In The Visible Band

Visible lasers are enthralling,due to its characteristic that can be directly perceived by the human eye.Visible lasers have been widely used in medical imaging,optical storage,laser projection and the like.It has been proved that many trivalent rare-earth ions(RE³⁺)could directly generate visible lasers with stimulated radiant energy.Trivalent praseodymium ion(Pr³⁺)is considered to be one of the most efficient rare-earth ions for the direct emission of visible laser.Pr:YLF crystal outperforms with its relatively large emission cross section and small phonon energy.In this thesis,a-cut 0.3at.%Pr:YLF crystals were adopted in the experiment.The crystals have dimensions of 3 mm×3 mm×10 mm and 3 mm×3 mm×6 mm.Based on the four-level system rate equation,the key parameters such as the light emission threshold,working efficiency,and output power in Pr:YLF lasers were theoretically derived.The conclusion is drawn that the laser threshold increases with the increase of the pump spot radius.Combined with the results of MATLAB numerical calculation and simulation,the F-P etalon made of 0.1mm thick fused silica was used for wavelength selection.With a self-made driving power source,a single-emitter blue laser diode（LD）with a center wavelength of 446.2nm was used as the pump source,and the maximum output power is5W.The size of the pump laser focal point after beam shaping was 59μm×55μm.The obtained maximum output powers at the deep red light 720.9nm and red light 698nm were720m W and 203m W,with the corresponding slope efficiencies being 30.85%and 9.87%,respectively.Both wavelengths of laser were linearly polarized,with the beam quality parameters M2 less than 1.8.Among all the solid-state lasers,fiber-coupled semiconductor lasers are widely used as pump sources due to their high power and convenience of practical use.In order to further explore the laser characteristics of Pr:YLF under high power conditions,a fiber-coupled blue LD module was used as the pump source.The pump source can provide maximum output power of 22.48W,and the center wavelength of the pump source was443.2nm.The tensile stress inside the crystal that was theoretically calculated at the maximum pump power.Combined with experimental tests,the following conclusions were reached:The tensile stress should not exceed 13.8MPa.The maximum incident power of the pump laser after collimation coupling was 20.55W,and the focus size of the pump beam was set to 320μm.In the 6mm-long crystal experiment,the output coupling mirror with1.8%transmittance showed a strong thermal lens effect with the absorption power exceeded 6.76W,and the output beam showed a high-order mode.In the 10mm-long crystal experiment,the highest output power obtained was 3.03W,and the corresponding slope efficiency was 30.04%.To the best of our knowledge,this experimental result is also the highest output power record of a Pr:YLF laser at 720.9nm.By inserting the F-P etalon into the cavity,the simultaneous output of 720.9nm and 698.0nm dual-wavelength lasers were achieved with the maximum output power was 1.03W.The resonant cavity was changed to a V-shaped resonant cavity composed of input mirrors with different curvatures.An LBO crystal was inserted into the cavity,and a maximum 116 m W ultraviolet laser output was obtained at 360.5 nm.