15min:

DAMIEN BIGOURD, ARNAUD CUISSET, SOPHIE MATTON, FRANCIS HINDLE, ERIC FERTEIN, ROBIN BOCQUET, WEIDONG CHEN, GAEL MOURET, Laboratoire de Physico-Chimie de l'Atmosphère, CNRS UMR-8101, Université du Littoral Côte d'Opale, 189A Ave. Maurice Schumann, 59140 Dunkerque, France.

A typical pump-probe pulsed THz set-up have been used for Time Domain Spectroscopy experiment in order to investigate free induction decay in carbonyle sulfide (COS). In the detected time domain signal, a transmitted pulse followed by commensurate transients pulses is observed. The molecules of COS respond to the terahertz excitation by reradiating a Free Induced Decay (FID) pulses : the molecules absorb the incident pulse and then a periodic rephasing and dephasing of the entire 60 excited equally spaced transitions occurs during the FID. Therefore the sample emits a series of terahertz pulse at the rate equal to the frequency separation between adjacent lines of 2 B, where B is the rotational constant,. The coherent transient pulse are so observe mainly in the case of linear or symmetric molecules. A model^b based on Maxwell-Bloch equation has been employed to estimate parameters such as the transition linewidth, the rotational and centrifugal distortion constant with the temporal form.