Using molecular alignment to track ultrafast collisional relaxation

Abstract

Field-free molecular alignment has been used in order to track the collisional relaxation occurring in a molecular gas. CO 2 molecules were initially irradiated by a short linearly polarized laser pulse resulting in the increase of their rotational energy. The evolution of the subsequent ultrafast relaxation process was optically probed after irradiating the sample with a second, weaker, short pulse leading to the alignment of the preheated molecules. Using classical molecular dynamic simulations, we were able to quantitatively reproduce the experimental shapes and amplitudes of the recorded revival transients for a time interval extending from 25 to 500 ps until thermalization of the gas sample is reached.

From Gyroscopic to Thermal Motion: A Crossover in the Dynamics of Molecular Superrotors

“…Transient molecular alignment has first been proposed [18] and later implemented as a powerful probe of collisional relaxation in a series of pioneering experiments [19][20][21]. The three relaxation steps, associated with (i) rotational decoherence, (ii) rotational reorientation, and (iii) rotation-translation (RT) thermalization, have been identified in the theoretical model [22], yet found to overlap in time too closely to enable an individual experimental study of each process separately [21].…”

Collisional dynamics in a gas of molecular super-rotors

“…The classical approach seems to be an appropriate tool for studying molecules at room temperature, excited to the quasi-classical rotational states with the angular momentum of tens to hundreds of ℏ. It has already been successfully used for analysis of the laser experiments on molecular alignment at dissipative conditions 20 21 22 . We studied the relaxation dynamics for several small linear molecules (such as N 2 , O 2 and CO 2 ) and found that they demonstrate a rather universal behaviour in the SR regime.…”

Control of molecular rotation with an optical centrifuge

“…Recent developments in controlling molecular rotation with nonresonant laser pulses [30,94] have stimulated active research on the exchange of energy between a rotating molecule and its environment. Transient molecular alignment has been first proposed [102] and later implemented as a powerful probe of collisional relaxation in a series of pioneering experiments [50,58,129]. The three relaxation steps, associated with (i) rotational decoherence, (ii) rotational reorientation and (iii) rotation-translation (RT) thermalization, have been identified in the theoretical model [42], yet found to overlap in time too closely to enable an individual experimental study of each process separately [58].…”