Study On The Characteristics Of The Active And Passive Dual-Loss Modulated Intracavity OPO Based On WS₂ Two-Dimensional Material

Nonlinear frequency conversion technology can make a laser with fixed radiation wavelength produce coherent light of different wavebands.Since 1961,Franken et al.Have successfully realized the frequency-doubled of SiO₂ Ruby UV laser output.The technology of frequency-doubled conversion has been recognized for the first time.In 1962,the theory of optical parametric oscillator?OPO?was proposed by Kroll for the first time.OPO is technical,which generate coherent light of mid-infrared and near-infrared band,has attracted more and more attention.1.5-1.6?m near-infrared human eye-safe band is in an atmospheric transmission window.In recent years,the near-infrared laser with high peak power,narrow pulse width and high stability has important research significance and application value in the fields of lidar,remote sensing,environmental monitoring,medical treatment,wind speed detection,driverless vehicle,robust light optics.The research of high peak power and the sub-nanosecond optical parametric oscillator is also hot.The all-solid-state active and passive dual-loss modulated laser pumped by LD significantly improves the peak power,optimizes the pulse stability and compresses the pulse width.The intracavity optical parametric oscillator?IOPO?with high peak power,narrow pulse width and high stability can be achieved by using the technology of active and passive dual-loss modulation.Active and passive dual-loss modulation is a technology which combines active modulation device and passive saturated absorber in the laser cavity to improve the pulse stability,narrow the pulse width,and significantly improve the peak power and single pulse energy.Tungsten disulfide?WS₂?two-dimensional nanomaterial has been used as passive saturable absorber in this paper.Because of their unique photoelectric properties,photoluminescence effect,super capacitance conversion,and good nonlinear absorption effect.The main contents of this paper are summarized as follows:?1?A 2.5 nm-thickness 3-layer tungsten disulfide?WS₂?saturable absorber?SA?was successfully fabricated by the electron beam evaporation?EBE?combined with post vulcanization.In this paper,the optical micrograph,scanning electron micrograph,Raman spectrum and atomic force micrograph of the sample material was analyzed in detail.And the nonlinear transmission of WS₂-SA was measured by the two power meter method.?2?The physical properties and laser characteristics of Nd³⁺:YVO₄ and Nd³⁺:GdVO₄crystals were studied.The output characteristics of the WS₂ passively Q-switched laser were experimentally investigated.The output parameters of AOM actively Q-switched laser and AOM+WS₂ dual-loss Q-switched laser were compared.Under the same condition,the pulse width of the latter was narrow,the peak power was high,and the single pulse energy was more significant.Besides,this device was more conducive to nonlinear frequency conversion.?3?The phase-matching theory of KTP crystal was introduced in this paper.Besides,the thermal effect of the nonlinear crystal and the distribution of the refractive index inside the KTP were also analyzed.The gradient distribution of refractive index will affect the increase of walk-off effect and the decrease of nonlinear coefficient in the process of OPO conversion,thus affecting the conversion efficiency of OPO.?4?The experiments of AOM Q-switched IOPO and AOM+WS₂ active and passive dual-loss Q-switched IOPO were compared.It was observed that the insertion loss and the saturable absorption mechanism of WS₂ could make part of the heat concentrated in the material.This way alleviate the thermal effect in the nonlinear crystal and made the average output power,single pulse energy and peak power all of that were optimized.?5?AOM+WS₂ dual-loss Q-switched and mode-locking?QML?IOPO has successfully realized high peak power sub-nanosecond signal light output.The experimental device model was optimized by using the synchronous pump theory.With the increase of incident pump power,a single pulse mode-locked optical parametric oscillator was realized...