Eur. Phys. J. D (2012) 66: 169
https://doi.org/10.1140/epjd/e2012-20750-0

Regular Article

Breakdown of dipole approximation and its effect on high harmonic generation

Department of Chemistry, Indian Institute of Technology, Guwahati, 781039 Assam, India

^a e-mail: gupta@iitg.ernet.in

Received: 22 December 2011
Received in final form: 9 February 2012
Published online: 29 June 2012

Abstract

Here, we present a study of high-harmonic-generation using the model system of polyacetylene when irradiated with intense laser-field. The system is prepared in a time-periodic Floquet-state. Only odd-order harmonics are obtained within dipole approximation due to the dynamical-symmetry of the Floquet-state. However, odd as well as even-order harmonics are obtained in case of beyond-dipole approximation. Dipole approximation is expected to be valid when the electron during oscillation is confined to a very small region compared to the wavelength of light. However, it is found that the dipole approximation breaks down even if the electron remains delocalised over a region less than 1 nm.