Relativistic interaction of ultra short laser pulses with nanostructured solids Generation of hot and dense plasmas under relativistic interaction of ultra intense high contrast femtosecond laser pulses with solid targets is among the most exciting research topics in high energy density physics. Such plasmas would be also extremely beneficial for the area of astrophysics and nuclear physics for the development of the efficient sources of hard X ray radiation. Nanophotonics opens a new chapter in this research. It was recently argued that nanowire arrays used as targets allow a larger penetration depth of the laser energy to a μm scale leading to the volumetric plasma heating. As a result of the very efficient laser energy absorption electron densities of 1023 1024 cm 3 with multi keV temperatures can be reached. However this relatively new field research is still poorly understood while no thorough comparative studies of the interaction with flat and nanostructured solids have been conducted. This thesis investigates the influence of the target morphology on the plasma parameters and produced hard X ray emission in different regimes of interaction. The potential of the nanowires has been studied in a number of experiments with a focus on X ray spectroscopy techniques. Besides the commonly used approach utilizing short wavelength laser pulses (UV visible or near IR spectral range) for the production of laser induced plasmas a novel regime of interaction with long wavelength pulses (mid IR) has been investigated. The performed analysis of the measured X ray spectra together with the Particle In Cell code and FLYCHK (collisional radiative code) simulations have shown that the plasma dynamics in the case of the nanowire and flat targets are strikingly different. This results in the effective heating of the plasma volume. It has been demonstrated that the nanowire morphology provides a possibility to generate a larger volume of hot dense plasmas at the given laser pulse parameters.