Self-Correction for Sensitive Resonant Photoacoustic Gas Analyzer

Photoacoustic spectroscopy (PAS) is a gas detection technology based on photoacoustic effect, offering advantages such as low gas consumption and high sensitivity. Resonant PAS, which utilizes the acoustic resonance amplification and high frequency modulation, further enhances sensitivity to a superior level. However, due to its background-free nature, PAS cannot perform self-correction using background signal like other spectroscopy technologies such as tunable diode laser absorption spectroscopy (TDLAS). As a result, PAS can suffer from a series of interference factors, including light power fluctuation, change in acoustic detector sensitivity, etc. To solve this, solid absorption can be introduced to generate the needed background signal, which is then used to normalize the measuring signal, thus self-correction is achieved [1]–[3]. The most used method is 2ft1f, where the first harmonic (background) of the detected signal is used to normalize the second harmonic (measuring signal). However, this method may not be optimal for the resonant PAS, which operates at the resonance frequency. In this case, either the two harmonics need to be separately obtained at different period with time-division modulation [2], or the sensitivity of one harmonic is sacrificed [3].