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Published in

IOP Publishing, Journal of Physics B: Atomic, Molecular and Optical Physics, 12(53), p. 124002, 2020

DOI: 10.1088/1361-6455/ab7c3f

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Attosecond transient absorption of a continuum threshold

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Abstract The laser-field-modified dipole response of the first ionization threshold of helium is studied by means of attosecond transient absorption spectroscopy. We resolve light-induced time-dependent structures in the photoabsorption spectrum both below and above the ionization threshold. By comparing the measured results to a quantum-dynamical model, we isolate the contributions of the unbound electron to these structures. They originate from light-induced couplings of near-threshold bound and continuum states and light-induced energy shifts of the free electron. The ponderomotive energy, at low laser intensities, is identified as a good approximation for the perturbed continuum response.