Highly sensitive ¹³C¹⁶O₂-laser photoacoustic detection of ammonia, phosphine and arsine in air

A photoacoustic ¹³C¹⁶O₂-laser-based gas analyser that permits low concentration measurements of pollutants in ambient air is described. The use of an isotopic ¹³C¹⁶O₂ laser makes it possible to overcome the background absorption caused by atmospheric carbon dioxide. The resonant photoacoustic cell is placed inside the cavity of the laser. The minimum detectable absorption of 3 * 10^-9 cm^-1 (concentration detection limit 0.3 ppbv for ammonia, 3 ppbv for arsine and 4 ppbv for phosphine) is reached at a time resolution of 30 s. The results of absorption measurements on individual lines of the 00 degrees 1-10 degrees 0 band of the ¹³C¹⁶O₂-laser for ammonia, arsine and phosphine in flowing nitrogen are reported. The concentration measurements for these substances in atmospheric air flows with different dilution ratios are carried out.