Abstract
The production of gas phase atomic and ionic line spectra accompanying the high laser fluence
irradiation of solid surfaces is well known and is most often due to the production and interaction
of high densities of atoms, ions, and electrons generated from laser-induced breakdown. The
resulting plasma expands and moves rapidly away from the irradiated spot and is accompanied by
intense emission of light. This type of “plume” is well studied and is frequently exploited in the
technique of chemical analysis known as laser induced breakdown spectroscopy. Here, we describe
a similar but weaker emission of light generated in vacuum by the laser irradiation of single crystal
ZnO at fluences well below breakdown; this emission consists entirely of optical line emission
from excited atomic Zn. We compare the properties of the resulting laser-generated gas-phase light
emission (above and below breakdown) and describe a mechanism for the production of the
low-fluence optical emission resulting from a fortuitous choice of material and laser wavelength.