A gas volume concentration is determined. An electromagnetic radiation is emitted (state 1) through the gas volume. The radiation is filtered by temporally modulating the spectral transmission of said filter so as to obtain a temporal modulation of the energy of the radiation transmitted by the gas volume...http://www.google.com/patents/US6133573?utm_source=gb-gplus-sharePatent US6133573 - Method and device for determining a gas volume concentration
