Microfocusing beamline for XUV-XUV pump-probe experiments using HH generation

The possibility to obtain micrometric focal spot in the extreme-ultraviolet (XUV) region opens the way to XUV-XUV experiments in high-order harmonics beamlines. A beamline designed for this purpose is here presented. The peculiarity of the optical design relies on the use of only toroidal mirrors in place of the more expensive Cartesian optics. The coma aberration, usually dominating the quality of the focal spot when toroidal mirrors are used with high levels of demagnification, is compensated using mirrors in a subtractive (Z-shape) configuration. In addition, the compensating output mirror decouples the length of the exit arm from the de-magnification factor, in this way the length of the exit arm can be increased to install even a large experimental chamber. Three mirrors with optical power are required, in order to assure an optimal focalization. In order to guarantee a day-to-day reproducible working condition, the mirrors are mounted on remotely adjustable optical stages, that are controlled via a genetic algorithm with the feedback on the quality of the focal spot. This solution helps the users to reach the best focalization conditions in a reliable way. The results obtained during the beamline commissioning phase are presented. Emphasis is placed in the characterization of the spot size and in the performances of the genetic algorithm.