Detection and quantification of multiple molecular species in mainstream cigarette smoke by continuous-wave terahertz spectroscopy

Continuous-wave terahertz spectroscopy by photomixing is applied to the analysis of mainstream cigarette smoke. Using the wide tunability of the source, spectral signatures of hydrogen cyanide $\left(\mathrm{HCN}\right)$, carbon monoxide $\left(\mathrm{CO}\right)$, formaldehyde $\left({\mathrm{H}}_2\mathrm{CO}\right)$, and water $\left({\mathrm{H}}_2\mathrm{O}\right)$ have been observed from 500 to $2400\mathrm{GHz}$. The fine spectral purity allows direct concentration measurement from the pure rotational transitions of $\mathrm{HCN}$ and $\mathrm{CO}$. The quantification of the measurement was validated by the means of a calibration gas containing $\mathrm{CO}$. The potential of this technique for trace gas detection is demonstrated with an estimated detection limit of $\mathrm{HCN}$ equal to 9 parts in ${10}^6$.