Sensitive carbon monoxide detection based on light induced thermoelastic spectroscopy with a hollow waveguide and 2.3 m diode laser

In this paper, a sensitive carbon monoxide (CO) detection system based on light induced thermoelastic spectroscopy (LITES) using a hollow waveguide (HWG) and 2.3 mu m diode laser is reported. The HWG has an inner diameter of 4 mm, in which light and CO gas can fully react. Its large inner diameter makes optical coupling easier compared to hollow-core anti-resonant fiber (HC-ARF). In addition, it has the advantages of wide transmission band range, simple structure and low loss. An absorption line of CO located at 4288.26 cm-1 was chosen, therefore a diode laser with an emission wavelength of 2.3 mu m was selected as the excitation source. In the experiment, the current modulation depth of the CO-HWG-LITES sensor was optimized to 34.6 mA. The results demonstrated a very nice linear relationship between the CO concentration and the corresponding 2f signal peak value, indicating that the CO-HWG-LITES sensor had a superior linear response to the gas concentration. The minimum detection limit (MDL) for CO in this system was determined to be 31.6 ppm. Finally, the Allan deviation analysis was performed and results indicated that the MDL can reach 4.7 ppm when the integration time was 100 s.