Direct Time-Domain Observation of l-Doubling via Centrifugal-Distortion Pre-compensation

TL;DR

This paper presents a method to directly observe l-doubling in molecular rotational dynamics by using shaped femtosecond laser pulses to pre-compensate centrifugal distortion, revealing fine rotational features in the time domain.

Contribution

The authors demonstrate a novel spectral phase shaping technique that pre-compensates centrifugal distortion, enabling clear time-domain observation of l-doubling contributions in molecules.

Findings

Cubic spectral phase compresses revivals into near single-cycle events.

Distortion-free revivals reveal temporally separated l-doubling contributions.

Method is robust against experimental imperfections.

Abstract

We demonstrate direct time-domain observation of l-doubling contributions in molecular rotational dynamics using shaped femtosecond laser pulses. By imposing a tailored spectral phase on the excitation pulse, we pre-compensate centrifugal distortion, which otherwise leads to temporally broadened, multi-cycle revival structures that obscure fine rotational features. A cubic spectral phase [Phys. Rev. A 107, 053108 (2023)] compresses selected revivals into near single-cycle events, in agreement with an analytic expression derived from molecular rotational constants, enabling predictive pulse design beyond numerical optimization. The resulting distortion-free revivals reveal temporally separated l-doubling contributions that remain unresolved in conventional impulsive alignment experiments. The method proves robust against experimental imperfections, including spatial light modulator discretization. While selective control of individual l-doubling components becomes feasible, here we focus on their direct observation in the time domain.