Rotational excitation of molecules with long sequences of intense femtosecond pulses

TL;DR

This paper explores how long sequences of intense femtosecond laser pulses can create broad rotational wave packets in molecules, highlighting the role of centrifugal distortion and pulse timing optimization in achieving high rotational states.

Contribution

It demonstrates the use of long pulse sequences to generate rotational coherence and spectral broadening, addressing centrifugal distortion as a key obstacle.

Findings

Centrifugal distortion limits high rotational state access.

Optimized pulse timing partially mitigates centrifugal effects.

Long pulse sequences induce efficient spectral broadening.

Abstract

We investigate the prospects of creating broad rotational wave packets by means of molecular interaction with long sequences of intense femtosecond pulses. Using state-resolved rotational Raman spectroscopy of oxygen, subject to a sequence of more than 20 laser pulses with peak intensities exceeding $10^{13}$ W/cm$^{2}$ per pulse, we show that the centrifugal distortion is the main obstacle on the way to reaching high rotational states. We demonstrate that the timing of the pulses can be optimized to partially mitigate the centrifugal limit. The cumulative effect of a long pulse sequence results in high degree of rotational coherence, which is shown to cause an efficient spectral broadening of probe light via cascaded Raman transitions.