NONINTRUSIVE, FAST AND SENSITIVE AMMONIA DETECTION BY LASER PHOTOTHERMAL DEFLECTION

A recently developed non-intrusive photothermal deflection (PTD) instr ument allows sensitive, rapid and quantitative detection of local ammo nia concentrations in the air. Ammonia is vibrationally excited by an infrared CO2 laser in an intracavity configuration. A HeNe beam passin g over the CO2 laser beam (multipass arrangement) is deflected by the induced refractive index gradient. The detection limit for ammonia in ambient air is 0.5 ppbv with a spatial resolution of a few mm3. The ti me resolution is 0.1 s (single line) or 15 s (multi line). The system is fully automated and suited for non-stop measuring periods of at lea st one week. Results were compared to those obtained with a continuous -flow denuder (CFD).