Ammonia detection by use of quartz-enhanced photoacoustic spectroscopy with a near-IR telecommunication diode laser

A gas sensor based on quartz-enhanced photoacoustic detection and a fiber-coupled telecommunication distributed-feedback diode laser was designed and characterized for trace NH3 monitoring at a 1.53-microm wavelength (overtone absorption region). Signal and noise dependence on gas pressure were studied to optimize sensor performance. The ammonia concentration resulting in a noise-equivalent signal was found to be 0.65 parts per million by volume with 38-mW optical excitation power and a lock-in amplifier time constant of 1 s. This corresponds to a normalized absorption sensitivity of 7.2 x 10(-9) cm(-1) W/Hz1/2, comparable with detection sensitivity achieved in conventional photoacoustic spectroscopy. The sensor architecture can be the basis for a portable gas analyzer.