New visible laser transitions in the mercury halides

Recently a new class of visible lasers, the mercury halides, has been discovered. Because the ionization energy of mercury is lower than that of the rare gases, the mercury halides radiate at longer wavelengths than the rare-gas halides. The paper summarizes the characteristics of the new high-power visible lasers operating on the B2Sigma(+)1/2-to-X2Sigma(+)1/2 transition of HgCl at 5576 A and the same molecular electronic transitions of HgBr at 5018 A and 4984 A. In both cases, the upper laser state is ionic in nature and is formed directly by chemical reactions in an electron-beam-excited mixture of high-pressure Ar/Xe and small amounts of Hg, and CCl4 or HBr. The lower laser level is the molecular electronic ground state which is covalent in nature and bound by the order 1 eV. The ionic character of the upper laser level provides the opportunity to utilize the highly efficient formation processes important in lasers such as KrF. The lasing and spontaneous emission experiments are carried out in an aluminum laser cell. Lasing on the excited HgCl and HgBr band transitions introduces new high-power laser sources at visible wavelengths.