Vandana Sharma | Transient Negative Polarizability & Laser Induced Fragmentation | Physics 2019
Channel: BMBSC Archive Talks
Date: 2020-06-26

Polarizability is a fundamental molecular property governing inter-molecular and light-molecule interactions. Molecules, seeking to minimize their energy in the presence of a short-lived but intense laser field, undergo rotation and alignment mediated through the static polarizability. Here, we demonstrate
an anomalous suspension of this alignment, as observed through the velocity imaging of the fragmentation following the strong-field ionization of O2 molecule by ultrashort (35 fs, 400 nm) laser pulses. Alternately, in concomitant experiments with 800 nm laser pulses (25 fs), the expected alignment is indeed observable. We analyze these results in conjunction with a semi-classical model of the induced rotation in the molecular ion involving polarizabilities of the participating excited states. It emerges that transient negative polarizability on the time scales of several femtoseconds frustrates the alignment of the molecular ion. This singular molecular behavior, visualized here for the first time in fragmentation, is not only of fundamental interest but can potentially be applied for terahertz photonics.