Infrared Linewidth and Line Position Measurements Using Diode Lasers with Internal Calibration

Abstract

Measurements in the infrared region using semiconductor lasers, particularly as applied to atmospheric pollution monitoring, depend critically on the availability of reliable line positions and linewidth information. We demonstrate a unique internal calibration technique such that spectral locations can be determined accurately, to the order of the monochromaticity of the laser. This is based on low-pressure absorption measurements and subsequent fitting of a Voigt profile and determining the Doppler component. With this technique, we are able to determine the self- and the N₂-broadening parameters of the NH₃ line at 852.7 cm⁻¹ to be 26.2 ± 0.4 MHz Torr⁻¹ and 5.2 ± 0.1 MHz Torr⁻¹, respectively. Also, the spectral locations for several SO₂ lines in the 1180.1 cm⁻¹ region were determined accurately.