Edge and vertical surface emitting lasers around 2.0-2.5 μm and their applications

One of the main concerns in environmental issues is the accumulation of pollutant gases in the atmosphere. This gives rise to a need for convenient ways of detecting these gases. In this paper we review some fundamentals of a technique called 'tunable diode laser absorption spectroscopy', which is suitable for making a portable gas analyser. We focus on the 2.2-2.4 mum range which corresponds both to a transparency window in the atmosphere and to high absorption bands of the main pollutant gases. We present two GaInAsSb/AlGaAsSb laser diodes which meet well the requirements for a portable gas analyser: a laser diode emitting at 2.38 mum exhibiting a monomode emission (side-mode suppression ratio 30 dB) and a laser diode emitting at 2.30 mum able to operate continuous wave up to 140 degreesC. Thanks to these diodes we designed a set-up for gas detection using the tunable diode laser absorption spectroscopy technique. We have reached a sensitivity as good as 1 ppm for CH4 at atmospheric pressure. Finally, we present a promising technique called 'intra cavity laser absorption spectroscopy' making use of a new device, the 'vertical external cavity surface emitting laser', which may allow us to increase sensitivity by a factor of 10(5).