Research On The Characteristics Of High Repetition Rate Passively Q-switched Laser Of Yb:KLu(WO₄)₂ Crystal

In comparison with most of the known Yb-ion laser crystals,the monoclinic Yb:KLu（WO4）2 possesses large stimulated emission cross-section and short fluorescence lifetime,making it particularly suitable in generating high-repetition-rate pulsed laser operation through passive Q-switching.In this work for the thesis,we carried out,under the conditions of longitudinal pumping by a fiber-coupled high-brightness 975-nm diode laser,a comprehensive and intensive experimental investigation into the 2D MoS₂,WS₂or MoTe₂ passive Q-switching and Cr^4（10）:YAG passive Q-switching of the Yb:KLu（WO₄）₂crystal in a near-microchip cavity,realizing highly efficient,high-power and high-repetition-rate pulsed laser operation.Stable 2D MoS₂,WS₂ or MoTe₂ passive Q-switching laser action is achieved with resonator output couplings of T≧70%.Depending upon the 2D saturable absorber utilized,the highest pulsed output power produced ranges from 1.87 to 2.45 W;slope efficiency from 56%to 71%;minimum pulse duration from 36 to 43 ns;while the maximum pulse repetition rate reached falls in a range of 2.18-2.52 MHz.Compared to the 2D MoS₂ passive Q-switching of the Yb:KLu（WO₄）₂ crystal laser that was reported previously,the pulsed output power achieved in this work proves to be increased by one order of magnitude;laser efficiency improved by 8-10 times;pulse duration shortened by5-6 times;while the pulse repetition rate obtained represents the highest value for solid-state lasers passively Q-switched with 2D saturable absorbers.Stable passive Q-switching,induced by a Cr⁴⁺:YAG plate having an initial transmission of T₀（28）99.3%,is achieved under output couplings of T≧80%,with the same resonator and pumping conditions.A maximum pulsed output power of 1.83 W is generated with a slope efficiency of 60%,the pulse duration being 39 ns;while the corresponding pulse repetition rate reaches 0.97 MHz.The repetition rate attained here turns out to be far beyond the upper limit imposed by the recovery time of Cr⁴⁺:YAG,implying an anomalous passive Q-switching.