Research On 1.5?m Hollow-core Fiber Gas Raman Laser

The eye-safe 1.5 ?m laser sources with the wavelength located in the atmospheric window have great applications in the field of laser communication,laser radar,remote sensing and so on.Due to the thermal effect and varieties of nonlinear effects existed in high power operation,the traditional 1.5 ?m Er-doped fiber lasers meet grreat challenges in power scaling with narrow linewidth output.Stimulated Raman scattering in gas-filled hollow-core fiber provides a novel method to overcome these difficulties and to obtain 1.5 ?m laser output with high power and narrow linewidth.In this thesis,the 1.5 ?m hollow-coer fiber gas laser based on stimulated Raman scattering is studied experimently and theorectically.The main contents of this thesis are listed as follows:1.The light guidance mechanism in hollow-core fiber is introduced,including the mode theory for leaky hollow-core fiber,the Marcatili-Schmeltzer's formula,the cladding leaky mode coupling model and the anti-resonance reflectiong optical waveguide model,and the applications and limitations of each theory are also discussed.The numerical model of the ice-cream shaped hollow core fiber is built,and the mode characteristics and the transmission losses of the fundemental mode in the hollow-coer fiber are analysized using the finite element method.The transmission losses of the ice-cream shaped hollow-coer fiber is also measured by the cut-off mothed,the experimental results agrees well with the simulation and the ARROW mode's prediction.2.The process of gas stimulated Raman scattering in hollw-coer fiber is analysed in electromagnetic field theory,the Raman gain coefficient in steady-state stimulated scattering process and the gain reduction ratio in the transient state stimulated Raman scattering processes are also discussed.Considering the ice-cream shaped hollow core fiber used in our experiment and the characteristics of stimulated Raman scattering in alkene gases,the coupled wave equations to described the process of stimulated Raman scattering in alkane gases filled hollow core fiber are built up in the laser rate equation form.3.The high peak power,narrow linewidth,single-pass 1.5 ?m emission generation in ethane-filled hollow-core fiber based on stimulated Raman scattering is carried out for the first time.The spectrum,linewidth,pulse shape and the near-field pattern of the Stokes transition are measured detailedly in the experiment.The maximum peak power of about 400 kW is achieved at 1553.7 nm in the 6 meter long hollow-core fiber with 2 bar ethane gas filled.And the Raman conversion efficiency is about 38%,with a corresponding slope efficiency of about 61.5% and the Stokes linewidth of about 6.3 GHz.4.An ultra-efficient fiber gas Raman laser amplifier in methane-filled hollow-core fiber operating at 1.5 ?m is carried out for the first time.A CW tunable 1.5 ?m single frequency seed laser is coupled into the hollow-core fiber together with a 1064 nm pulsed pump laser using a shortpass dichromic mirror,and then amplified by stimulated Raman scattering of the methane gas.The influence of the seed laser on the output features of the amplifier is analysed in the experiments.With the introduction of the seed laser,the Raman threshold has been reduced and the Stokes linewidth has been narrowed.At the same time,the residual pump power is promoted to convert into the Stokes power under the influence of the seed laser,resulting an improvement of the Raman conversion efficiency.A maximum optical-to-optical conversion efficiency of 66.4% has been obtained,resulting in a record near quantum-limit efficiency of 96.3% in a 2 m long hollow-core fiber filled with only 2 bar methane gas.