Research On Narrow-linewidth High-power Fiber Amplifier And Its Pump Frequency Conversion In External Cavity

Tunable visible light sources with narrow-linewidth and high-power have been used in a wide range of applications,such as laser spectroscopy,laser display,ocean exploration.How to achieve the high performance visible light source is a research hotspot in the field of laser technology.Due to the thermal management convenience and the limitation to the laser mode of the high power fiber MOPA system,it is an effective way to realize narrow linewidth,high power and tunable light sources by using fiber MOPA system.Therefore,based on fiber MOPA system and external cavity frequency conversion technology,this paper develops a study to achieve narrow linewidth,high power,tunable visible light source.The specific contents are as follows:1.The narrow-linewidth high-power fiber MOPA system has been built.Starting from the theoretical principle of fiber amplifier,the rate equation of fiber amplifier with continuous signal and pulsed signal has been analyzed separately.The amplification process of continuous signal in MOPA structure is numerically simulated.A narrowlinewidth high-power continuous fiber amplifier is realized,the average power is amplified to 30 W while maintaining the excellent beam quality and narrow linewidth of the solid laser seed.The nonlinear effects such as SBS and SRS which are common in narrow linewidth pulsed fiber amplifiers are studied,and the method of increasing the threshold of corresponding nonlinear effects is given.A narrow linewidth(~0.1 nm)pulsed fiber amplifier is realized with a single pulse energy of ~1 mJ,whoes repetition rate is 10 kHz.The peak power of the pulsed fiber amplifier is 20 kW.2.A variety of cavity structures of visible light sources based on fiber MOPA and frequency conversion technology have been designed.Considering the conditions of external cavity mode matching and phase matching,the tunable wavelength-range of OPO with PPLN as the QPM nonlinear crystal is analyzed.It is about 1380~1600 nm by changying the polarization period and temperature of the PPLN.The phase matching angle for the frequency doubling of the visible light band by using KTP crystal is calculated.According to Gaussian beam propagation theory and ABCD matrix,the MATLAB is used to simulate the beam variation of Gaussian beams in different external cavity(V-type and butterfly-type).Based on the above theoretical calculations,a variety of external cavity structures based on fiber amplifier pump for visible light sources are designed.3.By using the self-built 1 mJ narrow linewidth(0.1 nm)pulsed fiber MOPA,the experimental study of the OPO/SHG in external cavity to achieve visible light source has been carried out.Based on the pulsed fiber amplifier,the two-mirror OPO cavity has achieved a wide range of tunable wavelength output from 1380 nm to 1600 nm through periodic tuning and temperature tuning.In the V-type OPO/SHG folding cavity,red light output in watt level has been achieved at 10.05 W pump power,the maximum output power is about 1.25 W(center wavelength is 710.2 nm).The conversion efficiency from pump light to red light is 12.5%.The linewidth of the output light is 0.3 nm.