Micro-focusing of broadband high-order harmonic radiation by a double toroidal mirror

Summary, in English

We present an optical system based on two toroidal mirrors in aWolter configuration to focus broadband extreme ultraviolet (XUV) radiation. Optimization of the focusing optics alignment is carried out with the aid of an XUV wavefront sensor. Back-propagation of the optimized wavefront to the focus yields a focal spot of 3.6 × 4.0 μm² full width at half maximum, which is consistent with ray-tracing simulations that predict a minimum size of 3.0 × 3.2 μm². This work is important for optimizing the intensity of focused high-order harmonics in order to reach the nonlinear interaction regime.