Role of Excited States In High-order Harmonic Generation

S. Beaulieu, S. Camp, D. Descamps, A. Comby, V. Wanie, S. Petit, F. Légaré, K. J. Schafer, M. B. Gaarde, F. Catoire, and Y. Mairesse

Phys. Rev. Lett. 117, 203001 – Published 8 November 2016

Abstract

We investigate the role of excited states in high-order harmonic generation by studying the spectral, spatial, and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct extreme ultraviolet emission through free induction decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift.

Received 25 March 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.203001

Physics Subject Headings (PhySH)

Multiphoton or tunneling ionization & excitation Photoemission Spontaneous emission Stark effect

Atomic, Molecular & Optical

Authors & Affiliations

S. Beaulieu^1,2, S. Camp³, D. Descamps¹, A. Comby¹, V. Wanie^1,2, S. Petit¹, F. Légaré², K. J. Schafer³, M. B. Gaarde³, F. Catoire¹, and Y. Mairesse¹

¹Université de Bordeaux—CNRS—CEA, CELIA, UMR5107, F33405 Talence, France
²Institut National de la Recherche Scientifique, Centre EMT, J3X1S2 Varennes, Quebec, Canada
³Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001, USA