Near-IR telecommunication diode laser based double-pass QEPAS sensor for atmospheric CO₂ detection

A novel double pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for atmospheric CO₂ detection is developed by use of a 1.5 μm telecommunication diode laser. A low-cost high-reflection concave mirror is positioned behind a traditional QEPAS based acoustic detection module to enhance the absorption optical path and improve the detection sensitivity. The obtained minimum detection limit is 29 ppmV for 1 s averaging time which corresponds to a normalized noise equivalent absorption coefficient (NNEA, 1σ) of $2.\text{2}\times {10}^{-9}\text{c}{\text{m}}^{-1}\cdot \text{W}\cdot \text{H}{\text{z}}^{-\frac{1}{2}}$. With a 247 s averaging time, it demonstrates an ultimate detectable sensitivity of 1.74 ppmV. (paper)