Method and arrangement for determining and normalising the intensity of a measurement signal, in particular in the case of modulation laser absorption spectroscopy

摘要

The invention relates to a method and an arrangement, with the aid of which the intensity of a measurement signal can be determined and normalised, in particular in the case of modulation laser absorption spectroscopy or interferometry, only a single measuring detector being required, and an otherwise necessary reference channel no longer being required. With the aid of on-line normalisation when using a frequency-modulation method, a diode laser is modulated in such a way that at least one discrete frequency is imposed on it. The frequency-modulated laser radiation with an original intensity then undergoes in an absorption measuring cell an intensity reduction which is determined by means of phase-sensitive detection. According to the invention, a residual amplitude of the modulation signal is determined at the output of a single detector, this residual amplitude constituting a measure of the original intensity. This residual amplitude value can then be used for known intensity normalisation methods.