Dynamics of H₂⁺in intense laser fields

TLDR

Intense laser fields applied to small molecules reveal unexpected phenomena such as above‑threshold dissociation, bond softening, and vibrational trapping. The paper reviews these processes for the H₂⁺ ion and examines the experimental and theoretical tools used to study it. Experimental interpretation relies on electron and proton energy distributions, while theoretical modeling treats fragmentation as either a laser‑assisted half‑collision via Floquet theory or as a wavepacket evolving under a time‑dependent Schrödinger equation with a specified pulse shape. Short‑pulse experiments over a wide intensity range, analyzed with dressed potential curves, best align theory and experiment, and two‑colour phase‑locked radiation presents a promising avenue for coherent control of fragmentation dynamics.

Abstract

A number of unexpected features of small molecules subjected to intense laser fields, with wavelengths ranging from infrared to ultraviolet, have been observed or predicted in the past few years: above-threshold dissociation, molecular bond softening, vibrational population trapping. We review these processes for the case of the molecular ion H2+ and discuss the experimental and theoretical tools that are used to study this system. Both electron and proton energy distributions are used to interpret the experimental results. Theoretically, the fragmentation dynamics can be described equivalently as a laser-assisted half-collision process, using solutions of the time-independent Floquet theory, or as the evolution of a wavepacket subjected to a classical radiation held with a given pulse shape, using solutions of the time-dependent Schrodinger equation. A broad range of laser intensity and pulsewidth has been explored, with the short-pulse results (analysed in terms of 'dressed' potential curves) offering the best interface between theory and experiment. We finally report on a promising new avenue for coherent control of fragmentation dynamics, through the use of two-colour phase-locked radiation.