Molecules probed with a slow chirped-pulse excitation: Analytical model of the free-induction-decay signal

Daniele Fontanari (1) , Cédric Bray (1) , Guillaume Dhont (1) , Gaël Mouret (1) , A. Cuisset (1) , Francis Hindle (1) , Robin Bocquet (1) , Kevin Hickson (2)

1 LPCA - Laboratoire de Physico-Chimie de l'Atmosphère
2 ISM - Institut des Sciences Moléculaires

Most of chirped pulse experiments refer to a theoretical study from [J. C. McGurk, T. G. Schmalz, and W. H. Flygare, J. Chem. Phys. 60, 4181 (1974)] which is well tailored to interpret the signals obtained with very fast chirped pulses, but is not sufficient to account for the signals in the case of slower chirped pulses used in spectroscopy to increase the signal to noise ratio. A theoretical study of the polarization of molecules in a cell, uniform supersonic jet or molecular beam and subjected to a chirped pulse is presented. Three degrees of approximation for the polarization are introduced and are compared with the numerical solution of the optical Bloch equations. These expressions enter the analytic expression of the free induction decay signal which is validated against experimental data on the rotational emission spectra of OCS molecules. A relation between the pulse duration, the line position in the chirped pulse and the signal amplitude is proposed in the thermalized case. It assists in the optimization of the chirped pulse parameters and in the estimation of the error associated with the line intensity.

Domaines: Physique [physics]

Daniele Fontanari, Cédric Bray, Guillaume Dhont, Gaël Mouret, A. Cuisset, et al.. Molecules probed with a slow chirped-pulse excitation: Analytical model of the free-induction-decay signal. Physical Review A, 2019, 100 (4), pp.043407. ⟨10.1103/PhysRevA.100.043407⟩. ⟨hal-02322177⟩