FORMATION OF AMORPHOUS-CARBON ON MELTING OF MICROCRYSTALLINE GRAPHITEBY PICOSECOND LASER-PULSES

Observations of microcrystalline graphite subjected to picosecond lase r pulses reveal the formation of a liquid phase with a subsequent tran sition to a uniform amorphous state of a surface layer upon solidifica tion. This phenomenon is observed on a definite type of graphite and w ith the radiation incident on a plane parallel to the sixfold symmetry axis, and only for certain parameters of the laser pulse. A structura l analysis of the amorphous phase is performed by electron microscopy and Raman scattering spectroscopy. A periodic structure with a period of the order of the wavelength of the heating pulse is formed in the h eating region. The ''rulings'' of this periodic structure are oriented in the direction of polarization of the heating pulse. A study of the reflection kinetics of the probe laser pulse showed that the characte ristic existence time of the liquid phase and of the solidification pr ocess is similar to 10(-10) s. (C) 1997 American Institute of Physics.