Manifestations of the Dicke Narrowing at Fast Recording of High-Resolution Absorption Spectra Using Frequency-Tunable Lasers

The possibility of performing quantitative absorption measurements of particle concentrations using frequency-tunable lasers is investigated. At fast frequency scanning, when the recording time of spectrum is shorter or comparable with its formation time, well-known time-dependent interference interactions between the radiation incident on an absorbing medium and the radiation induced in it are observed. Under these conditions steady-state absorption spectra are distorted, and the classical relations lying in the basis of absorption measurements are violated. The character of the distortions depends on the type and density of particles, their absorption state, the mechanisms of spectra formation, and the laser beam power and geometry. In this paper, we report the results of studying the manifestations of Doppler profile narrowing caused by the Dicke effect in time-dependent spectra and their influence on the results of measuring the concentrations of absorbing particles. It is shown that the static spectrum can be reconstructed and quantitative measurements by integrated absorption spectroscopy can be performed under these conditions.