Probing Asymmetric Molecules with High Harmonic Generation. [Original manuscript as prepared on 22/05/2011]

TL;DR

This paper demonstrates how high harmonic generation can be used as a sensitive probe of electronic asymmetry in molecules, revealing detailed phase and amplitude differences in electron recollision processes.

Contribution

It introduces a novel method to measure and analyze electronic asymmetry in molecules using high harmonic generation and attosecond science.

Findings

First measurement of high harmonics from oriented gas samples

Determined phase asymmetry of attosecond XUV pulses from CO molecules

Identified asymmetries in electron recollision phase and amplitude

Abstract

Asymmetric molecules look different when viewed from one side or the other. This difference influences the electronic structure of the valence electrons, thereby giving stereo sensitivity to chemistry and biology. We show that attosecond and re-collision science provides a detailed and sensitive probe of electronic asymmetry. On each 1/2 cycle of an intense light pulse, laser-induced tunnelling extracts an electron wave packet from the molecule. When the electron wave packet recombines, alternately from one side of the molecule or the other, its amplitude and phase asymmetry determines the even and odd harmonics radiation that it generates. This harmonic spectrum encodes three manifestations of asymmetry; an amplitude and phase asymmetry in electron tunneling; an asymmetry in the phase that the electron wave packet accumulates relative to the ion between the moment of ionization and recombination; and an asymmetry in the amplitude and phase of the transition moment. We report the first measurement of high harmonics from oriented gas samples. We determine the phase asymmetry of the attosecond XUV pulses emitted when an electron recollides from opposite sides of the CO molecule, and the phase asymmetry of the recollision electron just before recombination. We discuss how the various contributions to asymmetry can be isolated in future experiments.