Ultra-low threshold optically pumped random laser emission behavior of highly oriented pyrolytic graphite

Graphite is a semimetal and thus has no bandgap; photoluminescence is not expected from relaxed charge carriers. Here, however, an ultralow threshold optically pumped random lasing behavior in highly oriented pyrolytic graphite (HOPG) was observed under 488 nm Ar+ laser excitation at room temperature. In addition, this lasing behavior differs from the conventional random lasing process, i.e., the emission exhibits an ultra-low lasing threshold and a linear dependence on the laser excitation intensity in a low power range, and it saturates at high excitation densities. The theoretical model which accounts for the optically pumped random lasing behavior in HOPG has been proposed. (C) 2013 Elsevier B.V. All rights reserved.