Research On Passive Q-switching Caused By Two-dimensional Bi₂Te₃ Topological Insulators In Yb Ion Lasers

Two dimensional?2D?topological insulators such as Bi₂Te₃,are a new class of 2D saturable absorbers that appeared in recent years.Because of their extremely short recovery or relaxation time,this class of 2D topological insulators can be utilized as high-speed passive Q-switch to induce passive Q-switching in solid-state lasers,generating high-repetition-rate pulsed laser radiation.However,due to the limit imposed by thermal effects inside the 2D material film arising from unsaturated absorption of laser radiation,the pulsed output power,which was attainable from Yb-or Nd-ion lasers passively Q-switched by these 2D topological insulators,has remained for a long term at1-W level,whereas the shortest pulse duration obtained was about 400 ns.In this work for the thesis,by use of a plane-parallel cavity of high output coupling to reduce the intracavity circulating laser power and hence to mitigate the thermal effects inside the 2D saturable absorber,we have realized stable 2D Bi₂Te₃ passive Q-switching in Yb:LuPO₄,Yb:YCOB,and Yb:GdCOB crystal lasers,making the pulsed output power increase to 4-5 W level,the minimum pulse duration being reduced to less than 40 ns.Employing a 4-mm near-microchip cavity that was pumped by a 975-nm diode laser,passively Q-switched laser operation of an Yb:LuPO₄ laser was realized,with the output coupling in a range of T=10%-90%.Under the optimal output coupling of T=50%,high-repetition-rate pulsed laser action was achieved at 1014.5 nm,producing a maximum output power of 5.02 W at a repetition rate of 1.67 MHz with a slope efficiency of 54%;the pulse duration was 55 ns.With the output coupling increased to T=80%,dual-wavelength pulsed laser operation could be obtained at 1004.9 and 1012.7 nm,generating an output power of 3.94 W at 1.38 MHz,with pulse duration measured to be34 ns;the maximum pulse energy and highest peak power achieved were 3.0?J and 85.3W.Under the same pumping conditions,stable passive Q-switching was realized in Yb:YCOB and Yb:GdCOB lasers under high output couplings,by use of similar plane-parallel resonators.For the optimal output coupling of T=70%,the highest pulsed output power of 3.85 W was produced from the Yb:YCOB laser at a repetition rate of 400kHz,the resulting pulse energy,duration,and peak power were respectively 9.63?J,96ns,and 100.3 W.The optimal output coupling of Yb:GdCOB laser proved to be T=50%,under which the pulsed output power reached 2.38 W at 325 kHz;the corresponding pulse energy,duration,and peak power were 7.32?J,104 ns,and 70.4 W,respectively.