In this paper we report the results of a laboratory study for detecting the important atmospheric molecule HCl using a tunable diode laser coupled to a multipass White cell. In contrast to many such prototype studies, the calibration in this work was carried out near the concentration range of interest and verified using three different techniques. Employing a 40-m path length, we have demonstrated a detection limit (SNR = 1) in the 150–230 parts-per-trillion range at pressures around 9 Torr.
Alan Fried, Robert Sams, and Walter W. Berg, "Application of tunable diode laser absorption for trace stratospheric measurements of HCI: laboratory results," Appl. Opt. 23, 1867-1880 (1984)