Ultrafast structural transformations in femtosecond laser-excited graphite

Summary form only given. We present here the results of a femtosecond time-resolved study of fast structural changes in laser-excited crystalline graphite exploiting the large optical anisotropy (birefringence) of this material. If a linearly polarized electromagnetic wave is reflected from the surface of an anisotropic medium, the polarization state changes, even at normal incidence. In uniaxial crystals, like graphite, this effect is strongest for reflection from surfaces containing the anisotropy axis, the situation realized in our experiments. Experimental results obtained by time resolved polarization microscopy on femtosecond excited graphite are presented where the temporal evolution of the normalized reflectivity for both s-and p-polarisation is presented.