Mid-infrared Gas Raman Laser Source Based On Hollow-core Anti-resonant Fiber

Mid infrared lasers are widely used in industry,military and medical fields,turning into a research hot spot in recent years.High-power mid-infrared laser can be achieved by gas Raman scattering based on hollow-core fiber(HCF),providing an effective way for mid-infrared laser emission.Hollow-core anti-resonant fiber(HC-ARF)has the advantages of wide transmission band,low loss,high damage threshold and single-mode transmission,which has been widely applied in research area of gas Raman lasers.In this paper,by designing the structure of HC-ARF,low-loss optical waveguides with different wavelength bands are realized.The methane gas in HC-ARF pumped by a nanosecond laser enables the generation of multi-order Stokes and anti-Stokes light.High-peak-power laser was used to pump methane in mid-infrared HC-ARF,achieving high-peak-power mid-infrared Raman laser.The relationship among mid-infrared Raman laser output power,pressure and pump power was also studied.The main research contents are divided into the following parts:1.Firstly,the basic concepts related to Raman scattering are introduced,and the principle of Raman scattering is summarized.Secondly,the spontaneous and stimulated Raman scattering(SRS)are compared and analyzed.The transient and steady-state SRS is analyzed by the coupled-wave equation of SRS.The vibrational and rotational SRS are introduced.Finally,the Raman threshold in HCF is studied.2.The three types of principles including anti-resonance reflection,leakage mode theory and multi-layer model theory used to explain the mechanism of HC-ARF for guiding light are studied.The simulation method,characteristics of guiding light and drawing process of HC-ARF are described.3.The molecular structure and Raman properties of methane gas are studied.In order to achieve the Raman scattering light of methane gas,a nodeless HC-ARF with a core diameter of 44 ?m and a cladding hole diameter of 24 ?m is designed and fabricated.The efficiency of light-gas interactions in free-space,capillary,and air-core antiresonant fibers is compared.Multi-order Raman scattering light are generated by1064 nm nanosecond laser pumping methane.The calculated threshold of steady-state SRS in the HC-ARF is about 4.5 ?J,and the experimental results of Raman scatteringgenerated by methane are analyzed.4.In order to obtain a mid-infrared Raman laser source,a mid-infrared HC-ARF with a core diameter of 68 ?m and a cladding hole diameter of 34 ?m is designed and manufactured.The simulation loss of the fiber at 1.064 ?m and 1.544 ?m are <0.03dB/m and 0.015 dB/m respectively,and the measured loss of 2.812 ?m is 0.41 dB/m.The repetition rate of the 1064 nm solid picosecond laser is 1 kHz.The pulse width is12 ps.The peak power can reach 91 MW.When the coupled pump power is 766 mW,the output peak power of 1.544 ?m Raman laser is 5.9 MW,and the corresponding quantum conversion efficiency is 14%.High-peak-power mid-infrared 2.812 ?m Raman laser source is obtained.The maximum average power of 2.812 ?m Raman laser is 113 mW.The peak power can reach 9.5 MW.The corresponding quantum conversion efficiency is 40%.High-peak-power mid-infrared 2.812 ?m Raman laser sources is obtained by the high-peak-power laser pumping methane in the mid-infrared HC-ARF.This provides an effective way for the generation of high-peak-power mid-infrared lasers.