Study On The Technology Of 2 μm All-fiber,Chirped Pulse Amplification

Fiber lasers in the 2μm band have important applications in many fields,like gas molecular detection,bio-medicine,industrial processing,remote sensing and imaging,and military confrontation.At the same time,the wavelength of 2μm is situated in the anomalous dispersion region of common mid-infrared fluoride fibers,so the 2μm pulsed laser can work as a pump source for the generation of the supercontinuum in fluoride fiber.The technology of chirped pulse amplification is one of the important approaches to achieve high peak power pulse output in the pump source.When the all-fiber structure is adopted for the chirped pulse amplifying system,the output beam quality,the stability and compactness of the overall system structure can be improved while higher power output,and better thermal management performance can also be achieved.Therefore,the research on 2μm all-fiber chirped pulse amplification technology is of great significance to promote the development and practical application of mid-infrared supercontinuum source generated in fluoride fiber.In this paper,the 2μm chirped pulse amplification system with all-fiber structure is taken as the research object,and the theoretical analysis,parameter design and comparative experiment are studied separately.The main contents are as follows:The soliton pulse output from 2μm mode-locked laser is taken as the research object theoretically.Combined with the nonlinear Schr?dinger equation,the transmission model of hyperbolic secant soliton pulse in positive dispersion fiber is established.The simulation shows the pulse evolution of width and chirp volume in the transmission process.By comparing the numerical calculation with the experimental results,the range of the length of the dispersion fiber suitable for the group velocity dispersion and the self-phase modulation effect in the transmission process is clarified.A self-made 2μm pulsed laser based on nonlinear polarization rotation effect mode-locking was built as a seed stage.A new 2μm all-fiber CPA technology solution based on dispersion management is proposed,which uses Chirped Fiber Bragg Grating as the dispersion compensation device for the broadening and narrowing stages.Through the experimental exploration on the parameters of the device in various stages,the precise control of the dispersion and nonlinear effects at each level can be realized,so that the spectrum and pulse width of the operational output of each stage can be effectively regulated.The ultimate power output of 10 W is achieved in a 2μm all-fiber CPA system based on dispersion management.The estimated output pulse width is below 10 ps and the peak power can reach up to 30 k W level.Based on the experience of various parameters and structure design of CPA system,a 2μm all-fiber CPA system was built.The output of the CPA system has an average power output of 3.72 W,with the repetition frequency of 31.6 MHz.Its output pulse width is narrowed to～10 ps and the corresponding output peak power is about 11.7 k W.Then the 2μm all-fiber CPA system was firstly applied to pump a piece of In F₃ fiber.A mid-infrared supercontinuum source based on In F₃ fiber was obtained.The output power was 2.536 W with the conversion efficiency of 80%.The output spectrum has a20-d B spectral width from 1855 to 3250 nm with the long wavelength edge up to 3650nm.