Abstract

Frequency modulation spectroscopy (FMS) in the wavelength range 700-1500 nm, is becoming increasingly important as an analytical technique for two reasons. One is the rapid development of diode lasers and the other is the improvement in detector technologies. Near-infrared diode lasers are inexpensive, reliable, and readily available. Line-locked wavelength modulation with second-harmonic (2f) detection using these diode lasers has been demonstrated to be a sensitive and accurate absorption technique.¹ This technique is ideal for small molecules such as H₂O, HCl, CO, and CO₂. By locking the wavelength to the molecular line of interest, the technique is well suited for continue and real-time monitoring applications as in gas chromatography (GC).

© 1994 Optical Society of America