Fiber-amplifier-enhanced resonant photoacoustic sensor for sub-ppb level acetylene detection

A near-infrared fiber-amplifier-enhanced resonant photoacoustic spectroscopy (PAS) sensor is developed for sub-ppb level acetylene (C2H2) detection. The photoacoustic excitation source is composed of a telecommunication distributed feedback (DFB) laser and an erbium-doped fiber amplifier (EDFA). The weak photoacoustic second-harmonic signal is demodulated by a field-programmable gate array (FPGA) based lock-in amplifier. For sensitivity improvement, wavelength modulation spectrum and wavelet denoising methods are employed. The PAS sensor is optimized in terms of resonant frequency and current modulation depth for C2H2 detection at the wavelength of 1532.83 nm. The linearity of the sensor response to the laser power and C2H2 concentration confirms that saturation does not occur with the excitation power less than 1 W. With 1 W excitation power and 60 s averaging time, the detection limit (1δ) is achieved to be 0.37 ppb, which is the best value compared with other photoacoustic C2H2 sensors ever reported so far.