[en] The authors have investigated the optical properties of highly oriented pyrolytic graphite by picosecond pump-probe techniques. Their results at 1.9 and 1.06 μm have shown that a new phase occurs as soon as a critical fluence F/sup th/ = 140 mJ/cm/sup 2/ is exceeded. Above this value the reflectivity drops considerably from the original value. To understand the nature of this new phase, which we identify as the liquid phase, they have performed new measurements at 532 nm. The reflectivity data at 100 ps after the irradiation are summarized for the three wavelengths investigated. Data points are shown for two different values of the input laser fluence F, i.e., F = 0 and F = 500 mJ/cm/sup 2/. Contrary to the behavior of silicon and other semiconductors, which exhibit metallic reflectivities after surface melting, the new phase in graphite is characterized by lower reflectivities in a wide wavelength range. This indicates a decrease in both the real and imaginary parts of the index of refraction. More light can, therefore, penetrate the material, thus heating further layers. This process can provide a considerable depth of transformed material much thicker than the initial absorption depth. Moreover, the thermal diffusion, which is intrinsically lower than in the metallic case, is slowed by the lower gradients so that surface evaporation will be a major cooling channel at later times