Research On Anti-Resonance Hollow-Core Fiber Gas Raman Light Source

At present,doped fiber is the traditional way to achieve fiber lasers.However,due to the low damage threshold of the solid-core fiber and the existence of various competitive nonlinear effects,it is difficult to obtain high power and narrow linewidth output at the same time,therefore,doped fiber laser is limited in applications.Gas stimulated Raman scattering has been proved to be a new and effective means to achieve nonlinear frequency conversion,which can simultaneously produce high peak power and narrow linewidth laser output,however,gas Raman scattering in a gas chamber is usually limited by the interaction intensity of the laser with the gas.The advent of hollow-core fiber has greatly improved the interaction strength between the pump laser and gases,providing hollow-core fiber gas Raman laser great advantages in achieving high-efficiency frequency conversion.In view of this,this paper mainly conducts theoretical and experimental research on hollow-core fiber gas Raman laser,and the contents are as follows:1.The light guiding mechanism of anti-resonance hollow-core fiber is studied,and the difficulties in using traditional mode theory to explain hollow-core fiber are discussed.At the same time,we have introduced some related models such as the anti-resonant optical waveguide(ARROW)model.We have also studied gas Raman scattering theoretically,including Raman gain coefficient,transient and steady-state Raman processes and so on.The laser rate equation model is used to establish the coupled wave equations of pump laser and Stokes light.2.A high average power 1.5 ?m fiber methane Raman laser experiment was carried out.By optimizing the experimental optical path structure,hollow core fiber length and methane pressure,the effective conversion from 1064 nm pump light to 1544 nm vibration Stokes light was achieved.The average output power is 0.83 W,the light-to-light conversion efficiency is about 45%,corresponding to a quantum efficiency of 65%,and the stimulated Raman threshold is only about 5 ?J.The high-power 1.5 ?m laser output obtained from the experiment can be used as the pump source of the next-stage Raman effect to achieve the cascade Raman structure and realize the mid-infrared laser output.3.The experimental study of high average power 2 ?m fiber hydrogen Raman laser was carried out,and the effective conversion from 1064 nm pump light to 1909 nm vibration Stokes light was realized.The maximum output average power was 570 mW,corresponding to a quantum efficiency of 51%.The high-power 1.9 ?m laser output obtained from the experiment can also be used as the pump source of the next-stage Raman effect to achieve the cascade Raman structure and realize the mid-infrared laser output.4.The cascaded Raman experiment was carried out and the frequency conversion from 1 ?m pump light to 3 ?m Stokes light was realized,providing an effective method to realize the mid-infrared laser output.The methane-methane cascade Raman experiment can be divided into two stages.In the first stage,we use a high peak power 1064.6 nm laser as the pump source to obtain a 1543.9 nm 1st Stokes light output with the quantum conversion efficiency of 87%.In the second stage,we used the 1543.9 nm Stokes light obtained in the first stage as the pump source,and coupled it into another hollow-core fiber filled with methane,achieving 2.8 ?m 2nd Stokes light output with the quantum conversion efficiency of 75%.The total quantum conversion efficiency from the 1064 nm pump source to the 2809 nm 2nd Stokes light was 65%.By changing the gas in the first-stage hollow fiber in the methane-methane cascade Raman experiment from methane to helium,we obtained the helium-methane cascade Raman experimental system.At 4 bar helium gas pressure the first-order quantum conversion efficiency was 44%,and the second-stage quantum conversion efficiency was 77%.In the experiment,the total efficiency from the 1064 nm pump source to the 2866 nm 2nd Stokes light is 34%.