The interaction of excited atoms and few-cycle laser pulses

J E Calvert,A S Kheifets,D E Laban,Han Xu,X M Tong,R D Glover,I V Litvinyuk,A J Palmer,K Bartschat,R T Sang,D Kielpinski

doi:10.1038/srep34101

Abstract

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown.

Highlights

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse
Inelastic recollision can result in secondary electron promotions within the parent ion, either causing a direct secondary ionisation known as non-sequential double ionisation (NSDI)[4] or exciting another valence electron to a higher energy state
In order to examine the response of spin-averaged Ne* to ionisation intensity a number of data runs were performed at different laser intensities with Keldysh parameters ranging from γ = 0.37 to 2.32

Summary

Introduction

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. The precise control of the carrier envelope phase (CEP) of a few-cycle laser pulse in strong laser-matter interactions opens many possibilities[5,6,7] All these effects share a common starting point, namely, the strong-field ionisation of an atom. Inelastic recollision can result in secondary electron promotions within the parent ion, either causing a direct secondary ionisation known as non-sequential double ionisation (NSDI)[4] or exciting another valence electron to a higher energy state This excitation lowers the effective second ionisation potential of the atom, thereby providing the opportunity for ionisation in the remainder of the laser pulse in a process known as recollision-enhanced secondary ionisation (RESI)[11]. Another possible interaction is the recombination of the wavepacket with the www.nature.com/scientificreports/

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