Highly Sensitive Measurement of Oxygen Concentration Based on Reflector-Enhanced Photoacoustic Spectroscopy

Oxygen (O₂) is a colorless and odorless substance, and is the most important gas in human life and industrial production. In this invited paper, a highly sensitive O₂ sensor based on reflector-enhanced photoacoustic spectroscopy (PAS) is reported for the first time. A diode laser emitting at 760 nm was used as the excitation source. The diode laser beam was reflected by the adopted reflector to pass thorough the photoacoustic cell twice and further increase the optical absorption. With such enhanced absorption strategy, compared with the PAS system without the reflector, the reflector-enhanced O₂-PAS sensor system had 1.85 times the signal improvement. The minimum detection limit (MDL) of such a reflector-enhanced O₂-PAS sensor was experimentally determined to be 0.54%. The concentration response of this sensor was investigated when O₂ with a different concentration was used. The obtained results showed it has an excellent linear concentration response. The system stability was analyzed by using Allan variance, which indicated that the MDL for such a reflector-enhanced O₂-PAS sensor could be improved to 318 ppm when the integration time of this sensor system is 1560 s. Finally, the O₂ concentration on the outside was continuously monitored for 24 h, indicated that this reflector-enhanced O₂-PAS sensor system has an excellent measurement ability for actual applications in environmental monitoring, medical diagnostics, and other fields.