“Laser-based infrared spectroscopy for sensitive chemical sensing”
Frans J.M. HARREN - Life Science Trace Gas Facility, Department of Molecular and Laser Physics, Radboud University, Nijmegen, the Netherlands
Thu, Nov. 16th 2006, 11:00
NIMBE Bât 522, p 138, CEA-Saclay
Recently, continuously tunable, quantum cascade lasers and Optical Parametric Oscillators (OPOs) have been developed for the mid-infrared wavelength region. They provide continuous wave (cw) laser output at relatively high power (several hundreds of milliWatts up to Watts) and emit any desired wavelength within the infrared wavelength range from 2.5 to 5 m. Accurate detection of specific gases becomes into reach thanks to the infrared fingerprint absorption spectrum of molecular gases in this wavelength region, the high laser powers and the exact tuning capabilities of lasers. When the lasers are combined with sensitive spectroscopic techniques, such as photoacoustic spectroscopy and cavity ring down spectroscopy, gases can be determined extremely sensitively under atmospheric conditions.
Research is focused on the detection of small molecules such as NO, H2O, CO2, C2H6, CH4. Detection methods, detection limits, absorption strengths, linearity in response from ppmv to sub ppbv (part per billion volume, 1:109) mixing ratio, accuracy and interference with other gasses will be discussed.
The laser based gas sensors typically reach detection limits around 1 part per billion (volume mixing) for small molecules and possess a time resolution of only a few seconds. This has made lasers applicable for a wide variety of applications in biological and medical research. An example will be demonstrated of its usefulness in Life Science by recording (at 4.32 µm) the exhaled CO2 patterns in real-time from a single ant (Lasius Niger) and fruit fly (Drosophila melanogaster).