Eur. Phys. J. D (2015) 69: 133
https://doi.org/10.1140/epjd/e2015-60104-x

Regular Article

High-order harmonic generation enhanced by coherent population return

¹ ICFO-Institut de Ciéncies Fotóniques, Mediterranean Technology Park, 08860 Castelldefels ( Barcelona), Spain
² Grupo de Investigación en ÓpticaExtrema, Universidad de Salamanca, 37008 Salamanca, Spain
³ Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany
⁴ Centro de Láseres Pulsados (CLPU), Parque Científico USAL, 37185 Villamayor, Salamanca, Spain

^a e-mail: alexis.chacon@icfo.es
^b e-mail: marcelo.ciappina@mpq.mpg.de

Received: 17 February 2015
Received in final form: 16 April 2015
Published online: 15 May 2015

Abstract

We present computations of high-order harmonic generation in atoms by using the coherent population return technique. This approach consists in two steps: firstly, the active medium is prepared in a coherent superposition of two bound states using a relatively long laser pulse which has a photon energy close to the energy gap between the states and then, the system is driven by an ultrashort infrared laser pulse. We demonstrate, by employing the numerical solution of the time-dependent Schrödinger equation in one and three dimensions, that using this scheme it is possible to enhance the harmonic conversion efficiency by several orders of magnitude. Our numerical results show that, on one hand the increase in ionization efficiency is responsible of an enhancement in the harmonic signal and on the other hand, the coherent preparation of the medium produces a much richer structure of the harmonic emission.