Observation of rotational revivals for iodine molecules in helium droplets using a near-adiabatic laser pulse

Abstract

Listen

Translate article

A 160-ps near-Gaussian, linearly polarized laser pulse is used to align iodine (${\mathrm{I}}_{2}$) molecules embedded in helium nanodroplets. The rise time of the laser pulse is sufficiently long and smooth that the alignment, characterized by $\ensuremath{\langle}{cos}^{2}{\ensuremath{\theta}}_{2\mathrm{D}}\ensuremath{\rangle}$, behaves adiabatically during the pulse turnon. However, after the laser pulse has turned off $\ensuremath{\langle}{cos}^{2}{\ensuremath{\theta}}_{2\mathrm{D}}\ensuremath{\rangle}$ stays above 0.50 and a recurrence structure occurs \ensuremath{\sim}650 ps later. Measurements on isolated (${\mathrm{I}}_{2}$) molecules with identical laser pulses are used to identify, through analysis of the observed half- and full-rotational revivals, that the nonadiabatic postpulse alignment dynamics results from a mild truncation of the trailing edge of the laser pulse. This truncation establishes a well-defined starting time for coherent rotation, which leads to the revival structures observed both for isolated molecules and molecules in He droplets. In the latter case the time-dependent $\ensuremath{\langle}{cos}^{2}{\ensuremath{\theta}}_{2\mathrm{D}}\ensuremath{\rangle}$ trace recorded here is compared to that obtained previously for a 450-fs alignment pulse. It is found that the observed revivals are very similar.