Research On Passively Q-switched Vanadate Crystal Laser Based On Novel Transition Metal Dichalcogenides

Transition metal dichalcogenides,a new class of two-dimensional layered saturable absorbers,have received extensive attention in recent years.They have narrow band gap,excellent mechanical properties,electrical properties and optical properties,and have broad application prospects in the fields of nano-electronic devices and optoelectronic devices.Compared with other transition metal dichalcogenides,MoTe₂ has a smaller band gap,allowing electron transition from valence band to conduction band through 1.0μm photon absorption,which is suitable for 1.0μm passively Q-switched lasers.In order to broaden the application of transition metal sulfides in lasers at different wavelengths,ReS₂ materials were used for research.By changing the ratio of S and Reions,the band gap and modulation depth of ReS₂ can be flexibly adjusted,and the saturated absorption characteristics of ReS₂can be observed from visible to mid-infrared bands.In order to study the output characteristics of passively Q-switched laser with the transition metal dichalcogenides,a passively Q-switched laser was realized by using the semiconductor material GaAs,and the experimental data were compared horizontally.Yb³⁺-doped mixed vanadate crystals with La³⁺ion not only have excellent characteristics of Yb³⁺and vanadate crystals,but also have longer upper-level lifetime due to the inhomogeneous broadening effect of Yb³⁺emission spectrum.It has advantages in pulse energy storage,and is easy to obtain strong pulse energy.Here are the main research contents of this thesis.1.The energy level structure of the gain medium and the rate equation of the passively Q-switched laser are studied,the factors affecting the output characteristics of the continuous light are analyzed,and the relationship between the output characteristics of the continuous-wave laser and the transmittance of the output mirror as well as the output power and the pump power are numerically simulated.At the same time,the principle and rate equation of passive Q-switching are deeply studied,the factors affecting the output characteristics of the pulsed laser are analyzed,and the relationship between these characteristics and the transmittance of the output mirror is numerically simulated.This provides a theoretical basis for characterizing the saturable absorption properties of MoTe₂and ReS₂ and applying them to passively Q-switched lasers.2.The passive Q-switched mixed Yb:Lu_0.74Y_0.23La_0.01VO₄ crystal pulsed lasers based on MoTe₂,ReS₂ and GaAs were studied.In the experiment,the MoTe₂,ReS₂ film and GaAs wafer were used as a saturable absorber,and a 976 nm laser diode pumping method and a concave-plane resonator structure were used to achieve pulsed laser output respectively.In the Yb:Lu_0.74Y_0.23La_0.01VO₄/MoTe₂ laser,the narrowest pulse width was 500 ns,the highest repetition rate was 117 k Hz,the highest average output power was 0.33 W,the maximum single pulse energy was 2.8μJ,and the highest peak power was 5.6 W.In the Yb:Lu_0.74Y_0.23La_0.01VO₄/ReS₂ laser,the narrowest pulse width is 444 ns,the highest repetition rate is 123 k Hz,the highest average output power is 0.65 W,the maximum single pulse energy is 5.3μJ,and the highest peak power is 11.9 W.In the Yb:Lu_0.74Y_0.23La_0.01VO₄/GaAs laser,the minimum pulse width is 4 ns,the highest average output power is 0.50 W,the highest pulse repetition frequency is 30 k Hz,the maximum single pulse energy is 16.7μJ,and the highest peak power is 4.2 k W.Through horizontal comparison,MoTe₂ and ReS₂ can increase the pulse repetition frequency,and ReS₂ has the characteristics of pulse energy enhancement.GaAs can reduce the pulse repetition frequency and shorten the pulse width,so it can further enhance the pulse energy and peak power.It is also proved that the mixed Yb:Lu_0.74Y_0.23La_0.01VO₄ crystal can be used as the gain medium of high energy pulse laser.