Research On 2?m Laser Source Based On SRS In Hydrogen Filled Hollow Core Fiber

Laser emissions around 2?m,which can also be named“eye safe”and contain atmospheric transmission bands,have great advantages in the applications of medical surgery,material processing,environment monitoring,space optical communication,nonlinear frequency conversion and so on,and have attracted intensive attentions.All-fiber configuration 2?m laser source is especially popular due to its compactness,stability and good beam quality.Now,2?m Tm³⁺doped,Ho³⁺doped and Tm³⁺/Ho³⁺co-doped fiber lasers have reached a level of maturity,but they still suffer various nonlinear effects,which blocks the way to obtaining high peak-power together with narrow linewidth,which is useful for optical parametric nonlinear frequency conversion.Stimulated Raman scattering?SRS?in hydrogen-filled hollow-core fiber is an effective new access to obtaining high peak-power narrow linewidth 2?m pulse lasers.So,this paper carried out abundent theoretical and experimental research on 2?m laser source based on SRS in hydrogen-filled anti-resonant hollow-core fiber.The primary contents and results are listed as follows:1.The research background of 2?m laser emission is disscussed.The development of hollow-core fiber and its applications especially in gas SRS are introduced.2.The optical guiding mechanism especially anti-resonant reflecting waveguide?ARROW?model of anti-resonant hollow-core fiber is introduced.An Ice-cream anti-resonant hollow-core fiber model is constructed by COMSOL.The transmission band based on this model is computed and agrees well with the transmission curve of the experimental result.3.The theories of hydrogen SRS in hollow-core fiber are carried out,stressing on Raman gain coefficiency of hydrogen and the Raman process of transient and steady states.A steady-state SRS model reference to rate equation theory that describes the coupling among the pump,the vibrational Stokes and rotational Stokes is given.Then single-pass hydrogen SRS experiments are preliminarily carried out.The impact of fiber length,hydrogen pressure,pump power and polarization on the output of vibrational Stokes is studied.4.High peak-power,narrow linewidth 2?m fiber gas Raman laser experiments are carried out for the first time.By optimizing the pump scheme,hydrogen pressure as well as fiber length,a 150kW peak-power with 2 GHz linewidth sub-nanosecond pulsed laser of 1908nm vibrational Stokes wave is achieved.The optical conversion efficiency is³0%,conresponding to a⁵4%quantum conversion efficiency.5.Hydrogen-filled hollow-core fiber 2?m Raman amplifier is achieved for the first time.By the means of introducing a 1908nm narrow linewidth fiber laser as a seed to the single configuration,the Raman threshold is reduced and the rotational Stokes is depressed significantly.A promoted power conversion efficiency to vibrational Stokes wave of⁴1%is obtained,corresponding to a⁷3.5%quantum conversion efficiency and a 160kW peak-power with linewidth of 2⁴GHz.