Diode laser-based spectroscopic detection of trace species in atmospheric, combustion and environmental monitoring

Diode lasers are utilized widely in fiberoptic communications, scanning and laser printing. An often overlooked but growing application of diode lasers is the spectroscopic monitoring of molecular species. The lead-salt mid-infrared diode lasers that operates at cryogenic temperatures have been used as laboratory spectroscopic tools for quite some time, and have been used in field measurements of trace species. Rapid growth in fiberoptic communication has yielded single mode, room temperature operated, near-infrared diode lasers that are small, rugged, and fiberoptic compatible. Due to generally weak transition strengths found in near-infrared overtone and combination bands, high sensitivity detection techniques are often utilized to improve the detection sensitivity. Also growing in application are high power diode lasers that can pump solid-state laser gain elements or are amenable themselves to the nonlinear conversion in wavelengths. The author describes examples drawn from his experiences of diode laser-based spectroscopic detection in atmospheric, combustion, and environmental monitoring. The characteristics of diode lasers suited for spectroscopic detection are described, followed by an overview of the high sensitivity detection techniques used. Selected examples of different applications highlight the unique advantages of diode laser-based trace species monitoring.