Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources.

G Lambert,V Malka,S Sebban,A Dax,C P Hauri,J Perron,B Mahieu,B Vodungbo,J Gautier,M Fajardo,A Andreev,S Stremoukhov,A Sardinha,P Zeitoun,F Ardana-Lamas,J Luning

doi:10.1038/ncomms7167

Abstract

Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far. We here show how this limitation is overcome by using a cross-polarized two-colour laser field. With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics. To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M2,3 absorption edge around 67 eV. There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials.

Highlights

Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy
We show for the first time that one can achieve efficient generation of high harmonics at short wavelengths, with a high degree of elliptical polarization, and in a compact and extremely simple system, using an orthogonally polarized two-colour (o þ 2o) laser field
Due to dispersion effects inside the crystal (2o propagates faster than o), its thickness is restrained to a couple of micrometres to limit the temporal delay between the two pulse envelopes (Dt, Fig. 1a) and to preserve the high efficiency of the harmonic generation

Summary

Introduction

Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy. 1 LOA, UMR 7639, ENSTA-ParisTech, CNRS, Ecole Polytechnique, Chemin de la Huniere, F-91761 Palaiseau, France.

Results

Conclusion