A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

中文翻译：

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用于甲烷检测的窄线宽光纤激光泵浦中红外差频混合光源的性能特点

详细研究了在周期性极化铌酸锂 (PPLN) 晶体中具有光纤布拉格光栅 (FBG) 泵浦差频生成 (DFG) 的高功率、窄线宽 Yb 光纤激光器。在 3.3 微米处实现了大约 2.3 微瓦的中红外功率，斜率效率为 0.85 mW/W2。使用 0.1 米长的气室在 133 Pa 的压力下获得了 CH4 在 3038.497 cm-1（3.2911 微米）的多普勒展宽吸收光谱。 DFG 源的线宽被评估为小于 96 MHz观察到的光谱线宽。还演示了在光路长度为 10 m 的多通道池中实时监测环境空气中的 CH4（约 1.78 ppm）。