| 摘要 |
In a wavelength modulation spectroscopy method and system the light of a tunable light source is modulated with a frequency f<SUB>0</SUB>, while the wavelength is swept over an interaction feature of a sample to be measured. The light of the light source is passed to a sample for interacting and thereafter detected and demodulated at a higher harmonic Nf<SUB>0</SUB>. To suppress effects of fluctuations of the optical transmission of the system on the measurement, originating from varying dust loads, high temperature, gas turbulence etc. in the measurement path ( 3 ), a burst signal in form of an envelope modulated pilot tone is added to the modulation of the light ( 1 ) of the light source ( 2 ) synchronously with the wavelength sweeps at a wavelength outside the interaction feature of the sample. The injected burst signal is at the detection frequency Nf<SUB>0</SUB>, where N>= 2 , and is detected together with the measured spectrum from the sample and act as absorption normal, which the spectrum can be calibrated against.
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