Abstract

Four different forms of modulation spectroscopy were used to study water vapor absorption around 816 nm using GaAlAs semiconductor lasers. They are wavelength modulation at 1 kHz and 100 MHz, single-tone frequency modulation (FM) at 1 GHz, and two-tone FM at 1 GHz ± 10 MHz. Extrapolating from measurements on a 1.4% absorption we find that two-tone frequency modulation is sensitive to an absorption of 2.4 × 10⁻⁶. This is at least an order of magnitude more sensitive than single-tone FM and wavelength modulation.

© 1988 Optical Society of America

High-sensitivity frequency-modulation spectroscopy with a GaAlAs diode laser

Liang-Guo Wang, Duncan A. Tate, Haris Riris, and Thomas F. Gallagher
J. Opt. Soc. Am. B 6(5) 871-876 (1989)

Two-tone optical heterodyne spectroscopy using buried double heterostructure lead–salt diode lasers

Joel A. Silver and Alan C. Stanton
Appl. Opt. 27(21) 4438-4444 (1988)

Frequency modulation spectroscopy with lead–salt diode lasers: a comparison of single-tone and two-tone techniques

David E. Cooper and Russell E. Warren
Appl. Opt. 26(17) 3726-3732 (1987)

Frequency modulation and wavelength modulation spectroscopies: comparison of experimental methods using a lead-salt diode laser

David S. Bomse, Alan C. Stanton, and Joel A. Silver
Appl. Opt. 31(6) 718-731 (1992)

Frequency modulation spectroscopy at 1.3 μm using InGaAsP lasers: a prototype field instrument for atmospheric chemistry research

T. J. Johnson, F. G. Wienhold, J. P. Burrows, and G. W. Harris
Appl. Opt. 30(4) 407-413 (1991)