Research On The Growth And Laser Properties Of Yb:LaCOB Crystal

Yb-doped rare-earth calcium oxyborate crystals are an important class of Yb-ion laser materials.In such crystals the Yb ion is of a large Stark splitting in its ground state,long fluorescence lifetime,and small stimulated emission cross-section,making it quite feasible to realize low-threshold,high-power highly efficient continuous-wave?cw?laser operation,or to achieve high-energy pulsed laser output by use of Q-switching.The crystal of Yb:LaCa₄O?BO₃?₃?Yb:LaCOB?is a relatively new member of the Yb-doped oxyborates.Currently the cw laser power produced by Yb:LaCOB crystal is limited to 2-3W level;while its pulsed laser properties still remain unknown.In this work for thesis,we conducted an intensive experimental investigation into the growth and laser properties of Yb:LaCOB crystal,having grown by Czochralski method large-size crystals of high optical quality,achieving high-power highly efficient cw laser output under conditions of diode laser pumping,and realizing passively Q-switched pulsed laser operation with Cr⁴⁺:YAG,2D MoTe₂,2D MoS₂,or 2D Bi₂Te₃ topological insulator serving as saturable absorber.The cw laser properties and their anisotropy of Yb:LaCOB crystal are studied by using samples cut along the X,Y,and Z principal optic axes.The laser performance is found to be similar for X-and Z-cut crystals,with the output power reaching about 7-W level and laser slope efficiencies of54%-58%.The highest output power attainable with Y-cut crystal can reach 11.0W,with optical-to-optical and slope efficiencies being respectively 62%and 67%.More importantly,the laser operation of Y-cut crystal exhibits complex polarization state varying behavior.Under certain resonator output coupling,dual-polarization-state laser operation could be realized over the entire pumping range,with the maximum output power exceeding 10W.Stable passively Q-switched laser operation of Yb:LaCOB crystal is realized in a plane-parallel resonator,with a Cr⁴⁺:YAG plate of initial transmission of 99.3%acting as saturable absorber,generating a pulsed output power of 3.8W at a repetition rate of 71kHz,the slope efficiency being 49%.Passively Q-switched laser operation of Yb:La COB crystal,induced by a 2D MoTe₂ saturable absorber,is achieved in a plane-parallel resonator over an output coupling range of 10%-95%.A pulsed output power of 2.11W is produced at a repetition rate of 357kHz,with a slope efficiency of 32%;the highest attainable pulse energy,minimum pulse duration,and highest peak power are,respectively,6.6?J,103ns,and 52.4W.The pulsed output power produced by 2D MoS₂ passive Q-switching amounts to 1.61W,with the corresponding pulse energy,duration,and peak power being4.1?J,220ns,and 18.6W,respectively.Passively Q-switched laser operation induced by 2D Bi₂Te₃ is realized in the 1.07-1.08mm long-wavelength sideband of the Yb:LaCOB crystal,by suppressing the high-gain laser oscillation in its main emission band through the use of a cavity mirror having special coatings.A pulsed output power of 1.76W is generated at a low repetition rate of 140kHz with a slope efficiency of 38%,the corresponding pulse energy,duration,and peak power being 12.6?J,288ns,and 43.8W,respectively.