Abstract

Hydrogen chloride gas is measured by absorption in the second overtone band near 1.2 μm using an InGaAsP diode laser. The strength and air-broadening coefficient of the H35Cl P(3) line are measured. The line strength is ~18% higher than the previous grating spectrometer measurement and suggests that the commonly used experimental value for the 3 ← 0 HCl vibrational moment may be low. High-frequency two-tone FM detection is also used in this study to measure trace concentrations of HCl. Using a multimode laser, the sensitivity limit is 3-parts per million HCl in air at 50 Torr, corresponding to a minimum detectable fractional absorption (multimode) of 4 × 10−6. Optimization of the detection method should permit real-time measurement of concentrations below 0.1 ppm. The low cost and convenient operating characteristics of InGaAsP diode lasers make them attractive for many applications in high-resolution near-IR spectroscopy and trace species detection.

© 1988 Optical Society of America

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