Eur. Phys. J. D 55, 475-481 (2009)
https://doi.org/10.1140/epjd/e2009-00084-x

Controlling the divergence of high harmonics from solid targets: a route toward coherent harmonic focusing^*

¹ Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany
² Sektion Physik der Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany
³ Moscow Physics Engineering Institute, Kashirskoe Shosse 31, 115409 Moscow, Russia
⁴ Department of Physics and Astronomy, Queens University Belfast, BT7 1, NN Belfast, UK

Corresponding author: ^a rainer.hoerlein@mpq.mpg.de

Received: 13 November 2008
Revised: 5 February 2009
Published online: 13 March 2009

Abstract

Harmonic generation from relativistically oscillating plasma surfaces formed during the interaction of high contrast lasers with solid-density targets has been shown to be an efficient source of extreme ultraviolet (XUV) and X-ray radiation. Recent work has demonstrated that the exceptional coherence properties of the driving laser can be mirrored in the emitted radiation, permitting diffraction limited performance and attosecond phase locking of the harmonic radiation. These unique properties may allow the coherent harmonic focusing (CHF) of high harmonics generated from solid density targets to intensities on the order of the Schwinger limit of 10²⁹ W cm^-2 with laser systems available in the near future [Phys. Rev. Lett. 93, 115002 (2004)] and thus pave the way for unique experiments exploring the nonlinear properties of vacuum on ultra-fast timescales. In this paper we investigate experimentally as well as numerically the prospect of focusing high harmonics under realistic experimental conditions and demonstrate, using particle in cell (PIC) simulations, that precise control of the wavefronts and thus the focusability of the generated harmonics is possible with pre-shaped targets.