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.
KeywordsTransmission Line Switch Resistance Highly Orient Pyrolytic Graphite 2Los Alamos National Laboratory Picosecond Laser
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