Description of DFM

DFM has during the past 17 years been active in the development of laser spectroscopic methods for monitoring purposes and more recently as a primary reference method. To this end fundamental ro-vibrational bands have been monitored by the laser difference frequency technique, which generate radiation in the mid-infrared region, as well as by tuneable telecom lasers. These two techniques will be applied in the described project together with multipath absorption cells. DFM will use a range of tuneable diode lasers that cover the 1,3 μm - 1,6 μm region, which coincide with many overtone and combination bands of the molecules of interest. These bands are considerably weaker than the fundamental bands of the molecules. However, the attraction is that the monitoring systems can be made very compact and portable using optical fibres and are therefore likely to be the method of choice in future measurements schemes. DFM will use a tunable laser around 3.3µm for monitoring fundamental bands. In addition a recently developed heterodyne cavity ring down spectrometer is available for sensitive monitoring.

Within the JRP DFM will perform high-resolution laser absorption spectroscopy of selected molecules of major interest for environmental monitoring. Line strength, line shapes and absorption wavelength will be measured for the selected molecular species. DFM has during the past 4-5 years investigated the possibility for using hollow-core photonic band gap fibres for spectroscopy with considerable success. This approach can be useful for very weak lines and will be applied if relevant. DFM has recently made considerable impact on line shape modelling and will make use of this know how in the JRP.

These absorption measurements will be compared with those obtained by the other JRP-Partners using other techniques to increase the level of confidence and to demonstrate equivalence. The effect of possible interference will be investigated. For example, DFM has recently investigated the ammonia molecule, which have been shown to adsorb to walls and therefore have the potential for giving wrong results when performing quantitative measurements. Finally, DFM has experience in spectroscopic quantum number assignments and have the experimental techniques to assist in this.