Fig. 1. Energy level of the stimulated Raman scattering process受激拉曼散射过程能级示意图

Fig. 2. Raman-gain spectrum for fused silica at the pump wavelength of 1 μm当信号光与受激拉曼散射光同偏振时, 熔融石英在波长为1 μm附近的归一化拉曼增益曲线

Fig. 3. Diagram of fiber laser光纤激光器光路简图

Fig. 4. Diagram of high power continue wave fiber laser in experiment. PC, pump combiner; HR, high reflection fiber grating; OC, low reflection fiber grating; YDF, active fiber; GDF, passive fiber; CPS, cladding power stripper; QBH, quartz block head of a fiber optics cable; G, beam splitter; OSA, spectrum analyzer; PM1 and PM2, power meters.高功率连续光纤激光器实验光路图　PC, 抽运光合束器; HR, 高反光纤光栅; OC, 低反光纤光栅; YDF, 有源光纤; GDF, 无源光纤; CPS, 包层光滤除器; QBH, 输出准直头; G, 分光玻璃片; OSA, 光谱分析仪; PM1, PM2, 光功率计

Fig. 5. Spectra of the first group of fiber gratings: (a) Transmission spectrum of the high reflection grating; (b) reflection spectrum of the low reflection grating第一组光纤光栅光谱图　(a)为高反光栅透射谱; (b)为低反光栅反射谱

Fig. 6. Spectra of the second group of fiber gratings: (a) Transmission spectrum of the high reflection grating; (b) reflection spectrum of the low reflection grating第二组光纤光栅光谱图　(a)为高反光栅透射谱; (b)为低反光栅反射谱

Fig. 7. Output characteristics of the fiber laser with low reflection gratings of different bandwidth: (a) Output power curve; (b) backward leaked power curve不同光谱带宽低反光栅激光输出特性　(a)输出功率曲线; (b) 背向漏光曲线

Fig. 8. Spectra of output laser with low reflection gratings of different bandwidth: (a) 0.78 nm bandwidth; (b) 0.91 nm bandwidth; (c) 1.0 nm bandwidth; (d) 1.31 nm bandwidth不同光谱宽度的低反光栅输出光谱特性　(a)低反光栅光谱宽度为0.78 nm; (b) 低反光栅光谱宽度为0.91 nm; (c) 低反光栅光谱宽度为1.0 nm; (d) 低反光栅光谱宽度为1.31 nm

Fig. 9. Stimulated Raman scattering of low reflection gratings with different bandwidth at the output power of 840 W同等输出功率(840 W)下, 不同光谱宽度的低反光栅受激拉曼散射峰对比图

Fig. 10. Output characteristics of the fiber laser with low reflection gratings of different reflectivity: (a) Output power curve; (b) backward leaked power curve不同反射率低反光栅激光输出特性　(a)输出功率曲线; (b) 背向漏光曲线

Fig. 11. Spectrum of the leaked laser with OC of 10% reflectivity and 1.0 nm bandwidth背向漏光光谱图(OC: 10%, 1.0 nm)

Fig. 12. Spectra of output laser with low reflection gratings of different reflectivity: (a) 2.6%; (b) 5.2%; (c) 10.3%; (d) 11.6%不同反射率的低反光栅输出光谱特性　(a)反射率为2.6%; (b) 反射率为5.2%; (c) 反射率为10.3%; (d) 反射率为11.6%

Fig. 13. Stimulated Raman scattering of low reflection gratings with different reflectivity at the output power of 840 W同等输出功率水平下(840 W), 不同反射率的低反光栅受激拉曼散射效应对比图

Fig. 14. (a) Reflection spectrum of the OC of 2.5% reflectivity and 1.0 nm bandwidth; (b) spectrum of the output laser at the output power of 840 W(a)反射率为2.5%, 光谱带宽为1.0 nm的OC光谱图; (b)输出功率为840 W时的输出激光光谱图