Study On The Continuous Wave And Acousto-Optic Q-Switched Pulse Laser Characteristics Of Yb:KLuW Crysta

For many years,the monoclinic Yb-doped potassium lutetium double tungstate crystal,Yb:KLuW（Yb:KLu（WO₄）₂）,has attracted much attention due to its promising continuous-wave（CW）,mode-locking,and passive Q-switching laser performance.Additionally,Yb:KLuW proves also to be one of the few self-Raman Yb-ion laser crystals that are of practical importance at present.However,studies on active Q-switching of this crystal have not yet been carried out;whereas for the previous laser investigations,the excitation of the crystal was achieved by use of its main absorption peak around 981 nm.In this dissertation,an extensive research for the Yb:KLuW crystal is conduced into its CW laser properties exhibited in the case of excitation utilizing the weak short-wavelength absorption band,acousto-optic Q-switching laser performance,and self-Raman frequency conversion.The research results achieved and the conclusion reached are summarized as follows.For the excitation using the weak short-wavelength absorption band,the unsaturated absorption fraction of the crystal for the 935-nm broad-band pump beam turns out to be almost the same as for the 976-nm narrow-band one;but a weaker absorption saturation effect is found for the 935-nm pumping,which would be beneficial to increasing the excitation efficiencies under high-power pumping conditions,for crystal samples of limited lengths.High-efficiency CW laser operation is realized with an N_p-cut Yb:KLuW crystal under the excitation of 935-nm broad-band pump beam in a plano-concave resonator.An output power of 5.71 W is generated under the optimum output coupling of T=5%,with an optical-to-optical efficiency of 42%,while the slope efficiency being53%.Even under a high output coupling of T=50%,the output power produced could still reach 3.22 W,and the slope efficiency is 43%.With a plano-concave resonator and 976-nm narrow-band pumping,stable acousto-optic Q-switching laser operation of an N_p-cut Yb:KLuW crystal is demonstrated over a repetition frequency range of 3-60 k Hz.A pulsed output power of 5.03 W is produced at 60 k Hz of repletion rate,with optical-to-optical and slope efficiencies being respectively 50.2%and 63%;while the shortest laser pulses of 3.3ns in duration are generated at low repetition rates less than 5 k Hz.The pulse energy,duration,and peak power,which could be obtained at an intermediate repetition rate of 20 k Hz,are 140.0μJ,4.7 ns,and 30.2 k W,respectively.With acousto-optic Q-switching at repetition rates in the range of 3-50 k Hz,stimulated Raman scattering of the Yb:KLuW crystal and the resulting self-Raman frequency conversion are realized,enabling the fundamental oscillating laser radiation at 1031.9 nm to be converted in part into Raman laser radiation at 1138.2 nm.The maximum Raman output power produced was measured to be 0.25 W,and the Raman conversion efficiency was determined as 6.0%;the corresponding pulse energy,duration,and peak power being,respectively,12.5μJ,2.1 ns,and 6.0 k W.