Spectroscopic determination of soot in the environment

摘要

A metal fiber Raman filter and a diode, preferably a wide-band, multimode, i.e. a pump diode, laser are used. Pulsed emission is used to prevent heating of the sample. The wavelength of the laser is to be about 800 nm to limit fluorescence. Normally this kind of laser can be cooled by a Peltier cooler and can be battery driven so that a portable unit can be constructed. In order to prevent the return of stray radiation onto the sample, holographic -, tinted lens -, or interference filters or interference grids are used. Signal quality is improved by amplitude modulation of the laser in combination with lock-in amplification. A CCD array could be used to transform the spectroscopically differentiated radiation into electrical signals. Optical amplifiers could also be used.