Carrier-Envelope-Phase Dependent Dissociation of Hydrogen

TL;DR

This paper investigates how the carrier-envelope phase (CEP) of few-cycle laser pulses influences hydrogen molecule dissociation, revealing CEP-dependent asymmetries, interference effects, and the impact of pulse chirp on dissociation efficiency.

Contribution

First experimental observation of CEP dependence in hydrogen dissociation yield and asymmetry, with detailed analysis of interference pathways and pulse chirp effects.

Findings

CEP affects dissociation asymmetry and yield.

Interference between multi-photon pathways explains CEP effects.

Chirped pulses can enhance dissociation probability.

Abstract

We studied dependence of dissociative ionization in H2 on carrier-envelope phase (CEP) of few-cycle (6fs) near-infrared (NIR) laser pulses. For low-energy channels, we present the first experimental observation of CEP dependence for total dissociation yield and the highest dwgree of asymmetry reported to date (40%). The observed modulations in both asymmetry and total yield could be understood in terms of interference between different n-photon dissociation pathways - n and (n+1) photon channels for asymmetry, n and (n+2) photon channels for yield - as suggested by the general theory of CEP effects (Roudnev and Esry, Phys. Rev. Lett. 99, 220406 (2007), [1]). The yield modulation is found to be Pi-periodic in CEP, with its phase strongly dependent on fragment kinetic energy (and reversing its sign within the studied energy range), indicating that the dissociation does not simply follow the CEP dependence of maximum electric field, as a naive intuition might suggest. We also find that a positively chirped pulse can lead to a higher dissociation probability than a transform limited pulse.