| 摘要 |
According to the invention, a first laser beam 1 coming from a laser generator 101 tuned to an absorption line of the species to be measured is made to propagate in the reactive medium 3 along a predetermined direction X' X and in a first sense, and a second laser beam 2 coming from the same tuned laser generator 101, but having a small predetermined delay, is made to propagate along the said predetermined direction, and in a sense opposite to the said first sense, a portion of the light energy which has been absorbed along the excitation beams 1, 2 and has caused the emission of fluorescence is collected along the said predetermined direction at two separate points A and B of the reactive medium 3 which are very close together, the fluorescence emitted by the two separate points A, B is measured in order to determine, for each of these two points A, B, a pair of fluorescence signals which are shifted in time, and the absolute concentration of the absorbent chemical species present in the reactive medium 3 is deduced from the measurements of the two pairs of fluorescence signals. <IMAGE>
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