Monitoring of Gaseous Pollutants by Tunable Diode Lasers

By now it has been nearly twenty years since the pioneering studies at the MIT-Lincoln Laboratories, Lexington, USA, demonstrated the unique capabilities of lead salt tunable diode lasers (TDL) for infrared absorption spectroscopy. The progress in the use of TDL instrumentation for a wide variety of scientific applications was described by a great number of papers since, however, comparatively few meetings were specifically devoted to this subject. In 1980 the conference on "High Resolution Infrared Spectroscopy Applications and Developments" at the National Bureau of Standards in Gaithersburg, USA, reviewed the state of the art of tunable diode lasers together with Fourier Transform Spectroscopy and other laser spectroscopic techniques. Three years later in 1983 the SPIE Conference in San Diego, USA, dedicated one meeting to "Tunable Diode Laser Development and Spectroscopy" Applications. It appeared appropriate after a further interval of three years to organize another meeting about this quickly advancing field. In November of 1986 an International Symposium on "Monitoring of Gaseous Pollutants by Tunable Diode Lasers" was organized by and held at the Fraunhofer-Insti tut fuer Physikalische Messtechnik in Freiburg, FRG. The main emphasis of this conference was put on the applications of TDL techniques to the solution of problems of environmental relevance : The measurement of atmospheric trace gases and the monitoring of exhaust gases from automobile and power plant stack emitters. The state of diode laser development and application of TDL instruments to scientific molecular spectroscopy were not directly subjects of the meeting.

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Monitoring of Gaseous Pollutants by Tunable Diode Lasers is divided into four sections: I -- Atmospheric Trace Gas Detection; II -- Diode Lasers and Their Properties, including Progress in IV-VI Physics and Optoelectronic Devices; III -- Techniques, Systems, Components; IV - Special Applications. Atmospheric trace gas detection was of central interest, and the presentations clearly demonstrate the impressive capabilities of the diode laser technique. Reports on IV-VI mid-infrared diode lasers stress those properties -- radiation noise and emission linewidth -- which are essential for application to ultra-high sensitivity pollution monitoring. Two reports on III-V systems emitting at wavelengths shorter than 3 mum show that the less severe cooling requirements can lead to more compact equipment which can be used to detect pollutants via overtone absorption bands. The presentations on IV-VI physics and devices stress the physical and technological aspects of mid-infrared diode lasers. Laterally structured diode lasers are discussed in detail. There is also extensive material which compares traditional AM and the more recent FM techniques. The reports on special applications point to new directions for research, thus rounding off a complete, expert discussion of a vital research area.

Contenu
Atmospheric Trace Gas Detection.- Measurement of atmospheric gases by tunable diode laser absorption spectrometry.- Measurements of hydrogen chloride in the marine atmosphere with a tunable diode laser.- A transportable laser system for remote sensing of road traffic emissions.- Derivative monitoring: cross calibration techniques via atmospheric gases with stable concentration.- Air pollution monitoring with a mobile CO2 laser photoacoustic system.- Post detection data handling techniques for application in derivative monitoring.- Application of intracavity laser spectroscopy for pollution detection.- High frequency modulation spectroscopy with a lead salt diode laser.- Aircraft-based sensor for fast response measurements of atmospheric trace gases.- Automated diode laser spectrometer for monitoring five atmospheric trace gases.- High altitude aircraft measurements of carbon monoxide using tunable diode lasers.- Measurements of formaldehyde in the troposphere.- Portable diode laser spectrometer for trace gas analysis.- Spectral gas analysis of polyatomic molecules by tunable diode lasers.- Exhaust Gas Monitoring.- Multicomponent automobile exhaust measurements.- HNO2, NO2 and NO measurements in automobile engine exhaust by optical absorption.- NH3-measurements in power plants with DENOX installations.- Stack gas control by diode laser spectrometers in power plants.- Special Applications.- Application of high resolution infrared techniques to semiconductor processes.- Development of a diode laser photometer for hydrogen fluoride (HF) emission monitoring.- A hydrogen fluoride analyzer using pulsed integrative spectroscopy.- Plasma diagnostics and high resolution spectroscopy of molecular ions using tunable diode lasers.- Minutes of a Post-Symposium Round TableDiscussion on Atmospheric Trace Gas Analysis by Tunable Diode Laser Spectroscopy.- List of Participants.- Index of Authors.