Two-component intra-cavity photoacoustic spectroscopy sensor using Y-shaped photoacoustic cell with two resonant cavities

Abstract

In this paper, an intra-cavity photoacoustic spectroscopy (PAS) gas sensing system based on a 3D printed Y-shaped PAS cell with two longitudinal resonant cavities is designed for two-component detection. The sensor embeds the Y-shaped photoacoustic cell in the resonator of fiber ring laser for the intra-cavity gas detection, improving the laser power in the gas detection. The two resonant cavities of the Y-type PAS cell are formed into C-band and the L-band lasers, guaranteeing the laser stable output of C-band and the L-band. Comparing with the conventional dual-wavelength laser, the dual-wavelength laser scheme proposed in the paper eliminates the model competition and possesses much higher laser stability. A dedicated wavelength modulator is used to control the fiber bragger grating (FBG) to generate the stress change, and then scan the absorption peaks of the corresponding gases. The second harmonic (2f) PAS signal is used to calculate the gas concentration. The acetylene (C2H2) and carbon dioxide (CO2) were detected based on the frequency division multiplexing (FDM) technique using two resonant cavities. A microphone is used to simultaneously detect the photoacoustic signals of two resonance cavities. A demodulation frequency with a frequency intervals of 100 Hz ensures there is no cross-interference in demodulation of signals from each resonant cavity. The trace detection of C2H2 and CO2 was realized at normal temperature and pressure. The PAS signal intensity was further improved by optimizing the modulation amplitude and incident laser power. The minimum detection limits (MDLs) and the linear fit R-squared values (R2) of C2H2 and CO2 were 529 ppbv, 0.99971, 282 ppmv and 0.99991, respectively. It indicates that the two-component gas sensing system in this paper has good linearity and high sensitivity. It provides a valuable trace gas detection device for multi-component gas detection.