A Compact 2.3 μm DFB-Laser CO Sensor Using MPC-LITES for Real-Time Monitoring of Cigarette Smoke

A compact and high-sensitivity carbon monoxide (CO) detection system based on multi-pass cell enhanced light-induced thermoelastic spectroscopy (MPC-LITES) was developed for real-time monitoring. A 2.3 μm distributed feedback (DFB) diode laser targeting the CO absorption line at 4300.699 cm^-1 was employed, offering strong line intensity and minimal interference from H₂O, CO₂, NO₂, and SO₂. The optimal modulation depth of 0.76 cm^-1 produced the maximum second harmonic (2<i>f</i>) signal. Experimental results demonstrated excellent linearity (R² = 0.998) and a minimum detection limit of 230 ppb at 1 s, further reduced to 47 ppb at 367 s by Allan deviation analysis. Application tests were carried out for real-time monitoring of cigarette smoke in a 20 m² indoor environment. Under closed conditions, the CO concentration rapidly increased to approximately 165 ppm, while in ventilated conditions, it peaked at 45 ppm and decayed quickly due to air exchange. The results confirm that the proposed MPC-LITES sensor enables accurate, real-time detection of transient CO variations, demonstrating strong potential for indoor air quality evaluation, environmental safety, and public health protection.