Eur. Phys. J. D (2014) 68: 195
https://doi.org/10.1140/epjd/e2014-50086-6

Regular Article

High-order harmonic generation at high laser intensities beyond the tunnel regime^⋆

¹ Centro de Láseres Pulsados (CLPU), Parque Científico, 37185 Villamayor, Salamanca, Spain
² Department of Physics, Auburn University, Auburn, Alabama 36849, USA
³ ICFO-Institut de Ciències Fotòniques, Av. Carl Friedrich Gauss 3, 08860 Castelldefels (Barcelona), Spain
⁴ ICREA-Institució Catalana de Recerca i Estudis Avançats, Lluis Companys 23, 08010 Barcelona, Spain
⁵ Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, UK

^a e-mail: joseap@usal.es
^b Present address: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany

Received: 31 January 2014
Received in final form: 23 April 2014
Published online: 24 July 2014

Abstract

We present studies of high-order harmonic generation (HHG) at laser intensities well above saturation. We use driving laser pulses which present a particular electron dynamics in the turn-on stage. Our results predict an increasing on the harmonic yield, after an initial dropping, when the laser intensity is increased. This fact contradicts the general belief of a progressive degradation of the harmonic emission at ultrahigh intensities. We have identified a particular set of trajectories which emerges in the turn-on stage of these singular laser pulses, responsible of the unexpected growth on the harmonic efficiency at this high intensity regime. Our study combines two complementary approaches: classical analysis and full quantum mechanical calculations resulting from the numerical integration of the 3-dimensional time-dependent Schrödinger equation complemented with the time-frequency analysis.