Divided into four sections, this work presents the proceedings of an international symposium on monitoring of gaseous pollutants by tunable diode lasers. Focusing on atmospheric trace gas detection, the presentations 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 mu-m 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 an expert discussion of a vital research area.

In 1986, an International Symposium on Monitoring of Gaseous Pollut- ants by Tunable Diode Lasers was organized by the Fraunhofer-Institut fuer Physikalische Messtechnik in Freiburg, FRG, and held at this institution on November 13-14, 1986. The papers presented at that occasion extensively covered the applications of tunable diode laser spectroscopy (TDLS) to the analysis of trace and exhaust gases together with the latest improvements brought to the tech- niques used. It was generally consented by the participants that meetings of this kind are of major importance and should take place on a regular basis. The organizers were thus encouraged to plan a Second International Sympo- sium on Monitoring of Gaseous Pollutants by Tunable Diode Lasers which was held two years later on October 17-18, 1988, again in Freiburg. In addi- tion to the main subjects treated in the first Symposium, the Scientific Programme this time presented a session on the development of lead chalco- genide lasers. Once more, only a limited attention was given to applica- tions in high resolution molecular spectroscopy. In order to complete the update, sessions on components and techniques were included in the Pro- gramme. As for the previous Symposium, some space was also given to alter- native optical techniques. This time, in particular contributions on laser photoacoustic detection were included.

The 3rd International Symposium on Monitoring of Gaseous Pollutants by Tunable Diode th Lasers, held at the Fraunhofer Institute in Freiburg on October 17th and 18 , continued a tradition, established by the two preceeding meetings held at the same location, in 1986 and 1988. The steadily increasing number of participants and contributions emphasizes the need for such a meeting, which is unique in Europe and appreciated abroad. This third symposium in particular, was specially marked by the presence of the former Eastern Block Countries, with a number of scientists, and contributions, from the USSR (stilI existing at the time of the meeting) and from East Berlin. The large number of contributions proposed, originally, as oral presentations, could not be fitted in the schedule of the two-day limit which the participants to the previous meetings had recommended. To take account of these contributions, poster sessions were held, combined with extended discussion time. This intensified personal interaction was much appreciated by the participants.