Abstract

In a recent experiment, Malvezzi et al. have observed a large decrease in the reflectivity of a semimetallic sample of highly oriented pyrolytic graphite (HOPG) as it is illuminated by an intense picosecond laser pulse when the fluence is above the melting threshold. They have found that the imaginary part of the refactive index reaches lower than =0.5 at 566 nm [1]. This unexpected result indicates that a phase transformation occurs and that the high temperature phase, which they believe to be liquid, is non-metallic. This experimental observation is consistent with the result of the recent pseudo-potential calculation that there is an energy gap in "isotropic" carbon [2]. The time resolved experiments [1] also show that the phase transformation is completed in time scales as short as ~10 ps.

© 1987 Optical Society of America