An intensity-stabilized diode-laser spectrometer for sensitive detection of NH3

In this paper, we report on a compact analyzer for ammonia monitoring in the air based on near-infrared wavelength-modulation diode-laser absorption spectroscopy. Particular attention is devoted to the problem of residual amplitude modulation (RAM), which is responsible for the occurrence of the line profiles' distortions. The RAM effects are eliminated by means of an intensity-control feedback loop based on an acoustooptic modulator. This offers the advantage of simplifying enormously the spectral-analysis procedure, which, otherwise, would require a considerable amount of calculation if the RAM distortions were considered.