Study On High-power Narrow Linewidth Fiber Lasers And Single-frequency Laser Seed Based On Yb-doped Fiber

High-power narrow linewidth linearly-polarized fiber lasers are widely used in coherent combination,spectral combination,nonlinear frequency conversion and the other fields.In this thesis,high-power short-wavelength(?1030 nm)narrow linewidth linearly-polarized Yb-doped fiber lasers are studied.In addition,the short-wavelength(1018 nm)Yb-doped lasers are used as the pump sources in the single-frequency laser system,and the influences of the tandem pumping technology on the single-frequency fiber laser system are studied.The main contents of this thesis are as follows:1.We theoretically and experimentally demonstrate a high-power linearly-polarized,narrow spectral linewidth laser amplifier at a central wavelength of 1018 nm.Theoretical model is established based on the rate equations of Yb-doped fiber laser,under the guidance of theoretical simulations,the parameters of laser system are optimized and the ASE is suppressed effectively.Finally the central wavelength of1018.3 nm,104 W output power with 3 d B and 20 d B spectral linewidth of?21 GHz and?72 GHz,respectively,a higher polarization extinction ratio>17.5 d B,high beam quality(M_x~2?1.62 andM_y~2?1.63)and the slope efficiency for the amplifier stage can reach 79%are achieved in the laser system.2.We theoretically and experimentally propose an all-fiber,kilowatts-level output power,linearly-polarized laser system with narrow spectral linewidth at a wavelength of 1030 nm in master oscillator power amplifier(MOPA)structure.The theoretical calculation shows that SBS can be effectively suppressed by increasing the linewidth of seed laser and the ASE can be effectively suppressed by reducing the length of gain fiber.In experiments the SBS effect is effectively suppressed by using the seed source with wide spectral linewidth.The maximum power of 925 W,the central wavelength of 1030.1 nm,a higher polarization extinction ratio of 15.2 d B,a narrow linewidth of?60 GHz,the near diffraction-limited beam quality(M~2<1.3)are achieved based on forward pumping method in our laser system.3.We theoretically and experimentally demonstrate two different cavity structures to realize single-frequency fiber laser at 1018 nm.We establish the numerical theoretical model to optimize the parameters of 1018 nm linear cavity single-frequency laser,the spectral transmission loss characteristics of single-mode-multimode-single-mode(SMS)device are analyzed to achieve 1018 nm laser in the ring cavity.The linear cavity laser can achieve the output power of 120 m W,the signal to noise ratio and the linewidth are 72 d B and 5 k Hz,respectively,besides the relatively intensity noise(RIN)is-134 d B/Hz.The ring cavity laser can reach the output power of 24.2 m W with the signal to noise ratio of 63 d B,the linewidth and RIN are 3.95 k Hz and-131 d B/Hz,respectively.4.A single-frequency 1064-nm Yb fiber laser tandem-pumped at 1018 nm is studied based on ring cavity.A maximum single longitudinal mode(SLM)output power of 231m W is obtained under the 1018-nm pump power of 1.4 W.The signal-to-noise ratio,spectral linewidth,and relative intensity noise are 72 d B,1.4 k Hz,and-141 d B/Hz,respectively.The spectral linewidth of 1064-nm single-frequency output under 1018-nm pumping is narrowed significantly in comparison with that under 976-nm pumping.Additionally,the laser performance under single-and multi-longitudinal-mode(MLM)1018-nm pump light is investigated.The result reveals that the SLM pump helps improve the behavior of noise.