| The 2μm pulsed laser had a wide range of applications due to its safe range for the human eye and atmospheric transmission window.This type of laser had weak attenuation during atmospheric transmission and can cover resonance absorption peaks of various gas molecules and atoms.Fields such as laser lidar,laser medicine,and optoelectronic countermeasures can benefit from the technology of 2μm all-solid-state pulsed lasers.Consequently,exploring 2μm all-solid-state pulsed lasers had significant research value.In recent years,with the development of 2μm pulsed lasers,2μm all-solid-state pulsed lasers using two-dimentional materials as saturable absorbers have received widespread attention due to high quantum efficiency.Among them,Sn S2 two-dimentional material has become a representative Q-switched material in the near-infrared and mid-infrared regions due to its low cost,sensitivity to thickness and wide operating bandwidth.Up to now,Sn S2 as a saturable absorber for 2μm all-solid-state pulsed laser has not been reported.In view of this,this paper investigated the output characteristics of Tm3+doped pulsed solid-state lasers using Sn S2 as a saturable absorber to contribute to related fields.The present paper commenced with a detailed account of the preparation of Sn S2 saturable absorbers using the ultrasonic liquid-phase exfoliation method,followed by a comprehensive characterization of their thickness,characteristic vibration peaks,and modulation depth.The structure,physicochemical properties,and nonlinear optical properties of the saturable absorber were also described in detail.Additionally,the working principle of the saturable absorber in passively Q-switched lasers was thoroughly examined,along with a meticulous analysis of the effects of various characteristic parameters,such as saturable fluence,modulation depth,unsaturable loss,and recovery time,on its modulation ability.The energy level structure of Tm3+transition and spectral characteristics were introduced,the rate equation of quasi-three-level laser system under the steady state were derived.In the subsequent phase,the paper used the theory of resonant cavity and calculated the effects of changing the length of the resonant cavity and the curvature of the input mirror on the g parameters and laser radius of the plane-plane cavity and plane-concave cavity under different thermal focal lengths.The paper designed a plane-plane cavity and a plane-concave cavity within the stable range of the simulated resonant cavity.Finally,based on the designed resonant cavities,a plane-plane cavity Tm:YAP laser and a plane-concave Tm:YAP laser were constructed,and the continuous-wave performance was discussed.Then,experimental research was conducted on plane-plane cavity Q-switched laser and plane-concave cavity Q-switched laser using the prepared Sn S2 saturable absorber.The plane-concave cavity resonant structure showed the best Q-switched laser output performance,with an average output power of 464 m W,a pulse width of 2.373μs,a repetition frequency of81.15 k Hz,and single pulse energy and peak power of 5.72μJ and 2.37 W,respectively.In order to enhance the output performance of the Q-switched lasers,this study performed corresponding improvement experiments,which involved the re-design of the resonant cavity and the use of a long cavity with different output couplings.The experimental results showed that the Q-switched laser achieved the maximum average power,shortest pulse width,and highest repetition frequency when the output coupling transmittance was set to 5%,corresponding to values of 621 m W,3.061μs,and 70.42 k Hz,respectively.Furthermore,the highest single pulse energy and peak power were obtained at 2.5%output coupling,with values of 12.41μJ and 2.90 W,respectively. |
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