Molecular alignment echoes probing collision-induced rotational-speed changes

Abstract

We show that the decays with pressure of the alignment echoes induced in N 2 O-He gas mixtures by two laser pulses with various delays bring detailed information on collision-induced changes of the rotational speed. Measurements and classical calculations consistently demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the narrowing of the filaments with time. The variation of the echo decay thus reflects the ability of collisions to change the molecular rotation speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces. We also demonstrate that the collision-induced changes of the rotational speed within the filaments are the classical equivalents of the nonsecular exchanges among quantum coherences.

Echoes in a Single Quantum Kerr-nonlinear Oscillator

“…In contrast, classical echoes appear on the short time-scale and may still be measured. A similar situation was recently encountered in experiments [49][50][51][52] studying collisional rotational relaxation in dense molecular gases. Although the rotational revivals were essentially suppressed at high pressure, the classical alignment echoes were readily observable and successfully used to measure the relaxation rates.…”

Ultrafast collisional dissipation of symmetric-top molecules probed by rotational alignment echoes

“…the scanned range of delays between the two pulses) is studied. In any case, nonsecular effects, which are expected and likely present in the measurements, are included in the CMDS despite their classical nature, as demonstrated in [25]. Indeed, in the classical rotational phase space, they result from collisional transfers within the rotational speed filaments induced by the first pulse.…”

“…For the echoes, the same approach was used, except that the requantization procedure was not applied and purely Classical MDS (CMDS) were thus carried out. These choices were made in order to emphasize the fact that the revivals are of purely quantum nature while the echoes are a generic classical phenomenon, as demonstrated in the Supplementary Information of [25] (however note that, as for N2O [25], CMDS and rCMDS lead to very close results for the considered echoes in C2H6). As in our previous studies, the (r)CMDS enable to calculate the time evolution of the alignment factor under the conditions of the experiments (e.g.…”

Tracing the Coherent Manipulation of Rotational Dynamics by Shaped Femtosecond Pulse-Induced Two-Dimensional Rotational Coherent Spectrum

“…As the pulse becomes more complex, the structure of the revival signal will change relating to different rotational behaviors. For example, the rotational echo may occur in a two-pump pulse scheme, which has been discussed a lot recently. , Much information is hidden under the corresponding change of RCS with respect to these different revival signals, which has not been thoroughly studied yet.…”