Ultrafast X-Ray Scattering of Xenon Nanoparticles: Imaging Transient States of Matter

Femtosecond x-ray laser flashes with power densities of up to ${10}^{14}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ at 13.7 nm wavelength were scattered by single xenon clusters in the gas phase. Similar to light scattering from atmospheric microparticles, the x-ray diffraction patterns carry information about the optical constants of the objects. However, the high flux of the x-ray laser induces severe transient changes of the electronic configuration, resulting in a tenfold increase of absorption in the developing nanoplasma. The modification in opaqueness can be correlated to strong atomic charging of the particle leading to excitation of ${\mathrm{Xe}}^{4+}$. It is shown that single-shot single-particle scattering on femtosecond time scales yields insight into ultrafast processes in highly excited systems where conventional spectroscopy techniques are inherently blind.