Valentin C, Douillet D, Kazamias S, Lefrou Th, Grillon G, Augé F, Mullot G, Balcou Ph, Mercère P, Zeitoun Ph
Laboratoire d'Optique Appliquée, Ecole Nationale Supérieure des Techniques Avancées--Ecole Polytechnique, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7639, Chemin de la Hunière, F-91761 Palaiseau, France.
Opt Lett. 2003 Jun 15;28(12):1049-51. doi: 10.1364/ol.28.001049.
We present a direct method of studying the focusability of an intense, short-pulse extreme-ultraviolet (XUV) beam obtained by high-harmonic generation. We perform near-field imaging of the focal spot of five high-harmonic orders strongly focused by a broadband toroidal mirror. To visualize the focal spot directly, we image the fluorescence induced by an XUV beam on a cerium-doped YAG crystal on a visible CCD camera. We can thus measure the harmonic spot size on a single image, together with the Strehl ratio, to evaluate the quality of focusing. Such techniques should become instrumental in optimizing the focusing conditions and reaching intensities required for exploring attosecond nonlinear optics in the XUV range.
