An integrated near-infrared fiber-optic photoacoustic sensing demodulator was established for ultra-high sensitivity gas detection. The demodulator has capacities of interference spectrum acquisition and calculation, laser modulation control as well as digital lock-in amplification. FPGA was utilized to realize all the control and signal processing functions, which immensely improved the integration and stability of the system. The photoacoustic signal detection based on fiber-optic Fabry–Perot (F-P) acoustic sensor was realized by applying ultra-high resolution spectral demodulation technique. The detectable frequency of photoacoustic signal achieved 10 kHz. The system integrated lock-in amplification technology, which made the noise sound pressure and dynamic response range of sound pressure detection reached 3.7 μPa/√Hz @1 kHz and 142 dB, respectively. The trace CH gas was tested with a multi-pass resonant photoacoustic cell. Ultra-high sensitivity gas detection was accomplished, which was based on high acoustic detection sensitivity and the matching digital lock-in amplification. The system detection limit and normalized noise equivalent absorption (NNEA) coefficient were reached 3.5 ppb and 6.7 × 10 cmWHz, respectively. The devised demodulator can be applied for long-distance gas measurement, which depends on the fact that both the near-infrared photoacoustic excitation light and the probe light employ optical fiber as transmission medium.

中文翻译：

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用于超高灵敏度气体检测的集成近红外光纤光声传感解调器

建立了一种用于超高灵敏度气体检测的集成近红外光纤光声传感解调器。该解调器具有干涉谱采集与计算、激光调制控制以及数字锁相放大的能力。采用FPGA实现全部控制和信号处理功能，极大地提高了系统的集成度和稳定性。应用超高分辨率光谱解调技术，实现了基于光纤法布里-珀罗（FP）声传感器的光声信号检测。光声信号的可检测频率达到10 kHz。系统集成锁相放大技术，使得噪声声压和声压检测动态响应范围分别达到3.7 μPa/√Hz @1 kHz和142 dB。使用多通道谐振光声池测试痕量 CH 气体。基于高声学检测灵敏度和配套的数字锁相放大，实现了超高灵敏度气体检测。系统检测限和归一化噪声等效吸收 (NNEA) 系数分别达到 3.5 ppb 和 6.7 × 10 cmWHZ。所设计的解调器可以应用于远距离气体测量，这取决于近红外光声激发光和探测光均采用光纤作为传输介质。