Study On High-performance High-power KHz Linewidth Single-frequency Fiber Laser And Its Application In Frequency Doubling

High-power narrow-linewidth single-frequency fiber laser(HPSFL) is an important field of fiber lasers, which has some important applications in fiber sensing, range finding, high precision spectroscopy, nonlinear frequency conversion and coherent beam combining. The master-oscillator power-amplifier(MOPA) configuration is often used to generate SF laser output with high power and narrow linewidth. Furthermore, the frequency doubling with quasi-phase matching is an effective way to obtain the SF green laser. In this paper, based on the homemade narrow-linewidth SF seed oscillators, the MOPA structure and external cavity frequency doubling, a series of high-performance high-power k Hz linewidth SF laser are demonstrated. The specific research contents and research results are as follows:(1) The DBR centimeter-length phosphate fiber SF laser oscillator is designed and built. Through the optimization of phosphate fiber length and ASE suppression management, the 1.0 μm and 1.5 μm linearly-polarized(LP) SF lasers generated several hundreds of milliwatt output directly from the laser cavity with the signal-to-noise ratio(SNR) of > 70 d B, the polarization extinction ratio(PER) of > 30 d B and laser linewidth of several kilohertz. Output characteristics of the seed oscillator are analyzed and discussed.(2) Based on the rate equations and propagation equations, the theory model of Er3+/Yb3+ co-doped and Yb3+-doped fiber amplifier are established. Using the theoretical model, output performances of the SF MOPA lasers on the signal power, signal wavelength, pump power and pump wavelength are simulated and analyzed.(3) By using a 1535 nm SF seed oscillator and short Er3+/Yb3+ co-doped phosphate fiber, the core pumped ultra-compact MOPA laser is constructed. It is found that the SNR and relative intensity noise(RIN) of the MOPA laser is slightly degradated, but the laser linewidth is not broaden. An output power of 611 m W, the laser linewidth of < 2 k Hz and the output power per unit length of up to 150 m W/cm are obtained experimentally. Then, using a 1560 nm LP SF seed oscillator and Er3+/Yb3+ co-doped polarization-maintaining(PM) fiber, the cladding pumped one-stage MOPA laser is demonstrated. By effectively suppressing stimulated brillouin scattering(SBS) and managing unnecessary coupling light, the SBS threshold, stability and reliability of laser system can be improved. An output power of 10.9 W, the laser linewidth of < 3.5 k Hz, the PER of > 24 d B and the SNR of > 70 d B are achieved experimentally.(4) By using a 1014 nm SF seed oscillator and Yb3+-doped phosphate fiber, the core pumped high-efficiency and high-SNR MOPA laser is investigated theoretically and experimentally. It is found that the conversion efficiency and SNR of the 4.0 cm MOPA laser is optimal. An output power of 1059 m W, the optical-to-optical conversion efficiency of 81.4% and the SNR of > 62 d B are obtained experimentally. Then, using a 1083 nm LP SF seed oscillator and Yb3+-doped single-cladding PM fiber, the core pumped high-SNR PM MOPA laser is investigated. By increasing the input power and stripping ASE directly, the SNR of laser system can be improved obviously. An output power of 1.03 W, the SNR of > 70 d B and the PER of >25 d B are achieved experimentally. Moreover, using a 1064 nm LP SF seed oscillator and two-stage Yb3+-doped double-cladding PM fiber amplifiers, the high-power LP MOPA laser is carried on. By managing ASE and suppressing SBS effectively, the SNR and SBS threshold of laser system also can be improved. A stable output power of 41 W, the laser linewidth of < 6 k Hz, the RIN of <-140 d B/Hz and the PER of > 22 d B are obtained experimentally.(5) Based on homemade 1064 nm continuous wave high-power SF fiber laser and external cavity single-pass frequency doubling, the different crystals are tested, its SH output power and conversion efficiency are compared and analyzed. It is found that the conversion efficiency of the single grating lithium tantalate(LT) crystal is more higher, to further increase the fundamental power and effective management of thermal effect, which can improve the SH output power continuously. The SH 532 nm green power of 6.4 W, the conversion efficiency of 29.8% and the RIN of <-140 d B/Hz are obtained experimentally. The double LT crystals frequency doubling is conducted. Studies show that the double crystals cascading can improve the SH output power and conversion efficiency obviously, the experiment achieved the SH conversion efficiency is about 34.4%. Using the single grating LT crystal and pulsed SF laser to carry on frequency doubling. By increasing the fundamental peak power, the conversion efficiency can be improved further. With the repetition frequency of 10 k Hz and pulse width of 80 ns, the SH conversion efficiency of approximately 42.1% is obtained.