An intense light source, preferably of high monochromaticity, having its beam modulated at a frequency f.sub.o through a wavelength range including an absorption line of a species to be detected, energizes a chamber containing a sample of the species. The modulation frequency may also be a multiple or...http://www.google.fr/patents/US4051371?utm_source=gb-gplus-shareBrevet US4051371 - Opto-acoustic spectroscopy employing amplitude and wavelength modulation
Opto-acoustic spectroscopy employing amplitude and wavelength modulation
