Graphite as a Picosecond Laser Activated Opening Switch
In a recent experiment, HUANG et al. [l] 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 a well-defined threshold of 140 mJ/cm2 at 566 nm. They have found that the imaginary part of the refractive index reaches lower than 0.5 at 566 nm. 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 . The time-resolved experiments [l] also show that the phase transformation is completed in time scales as short as ~ 10 ps and that the new phase lasts for approximately 3 ns. In the work presented here, we directly assess the change of resistivity of a HOPG sample used as a laser-activated switch. We confirm the results reported in [l] by observing a large increase in the sample’s resistivity under intense picosecond laser illumination. This unique property could allow one to use graphite as an opening switch since its conductivity in the c-plane, in the dark state (σ ≅ 105 (Ohm.Cm)-1) is almost as good as that of pure copper. It could then be compared with semiconductor optoelectronic switches, noting that its operation is exactly inverse: it is conductive in the dark and its resistance increases when illuminated above the threshold.
KeywordsMicrowave Graphite Sapphire
Unable to display preview. Download preview PDF.
- 2.S. Fahy, S.G. Louie and M.L. Cohen: preprint.Google Scholar
- 3.K.H.. Schoenback, M. Kristiansen and G. Shoefer: Proc. IEEE 72, 8 (1984).Google Scholar
- 5.E.A. Chauchard, C.C. Kung, M.J. Rhee, Chi H. Lee and V. Diadiuk: Proc. of the Conference On Lasers and Electrooptics, ( San Francisco, CA 1986 ).Google Scholar