We have observed and studied a nonlinear response of dispersive dielectric multilayer mirrors (DM). It was found that the structure of the mirror itself causes strong enhancement of the electric field inside the multilayer stack consequently triggering strong two-photon absorption (2PA). We have developed a mathematical model, that allows estimation of the coefficient of the 2PA, β, subsequent prediction and to some extent tuning of the strength of the nonlinear response of any multilayer coating.
Extreme Ultraviolet (XUV) sources based on femtosecond laser - high order harmonic generation (HHG) in atomic gases are presently in a period of rapid development. The HHG sources offer the additional advantage of delivering much shorter pulses compared to those of plasma generation or synchrotron sources. Furthermore, because they are coherent sources with high photon energy, they support attosecond pulse (10-18 s) generation, pushing the frontiers in both science and technology. These pulses open up research on unprecedented time scales, characteristic of bound electron motion. Issues related to the production and characterization of such pulses are presented.