Extracting spectroscopic molecular parameters from short pulse photo-electron angular distributions

TL;DR

This paper uses quantum simulations to analyze how ultrashort laser pulses influence photoelectron angular distributions in Li₂, providing a method to extract molecular parameters from short pulse measurements.

Contribution

It introduces an analytical formula linking pulse duration effects to asymmetry parameters, enabling extraction of molecular parameters from ultrashort pulse data.

Findings

Angular distributions depend strongly on pulse duration.

Derived a simple analytical formula for asymmetry parameter variation.

Provided a method to extract asymptotic parameters from short pulse measurements.

Abstract

Using a quantum wave packet simulation including the nuclear and electronic degrees of freedom, we investigate the femtosecond and picosecond energy- and angle-resolved photoelectron spectra of the E($^1\Sigma_g^+$) electronic state of Li$_2$. We find that the angular distributions of the emitted photoelectrons depend strongly on the pulse duration in the regime of ultrashort laser pulses. This effect is illustrated by the extraction of a time-dependent asymmetry parameter whose variation with pulse duration can be explained by an incoherent average over different ion rotational quantum numbers. We then derive for the variation of the asymmetry parameter a simple analytical formula, which can be used to extract the asymptotic CW asymmetry parameters of individual transitions from measurements performed with ultra-short pulses.