Effects of gamma-irradiation on the characteristics of a ruby laser

An increase in the absorption cross section responsible for optical pumping of a ruby laser occurs as a result of γ-irradiation. As single crystal ruby is irradiated with Co
⁶⁰
γ-rays, the usual absorption bands which exist between 200 and 550 mμ change from four distinct bands to one continuous absorption band. Similar work on sapphire, the host crystal for ruby, indicates that the majority of this increased absorption is experienced by the Cr
⁺⁺⁺
ion in ruby. Thermoluminescence data are presented showing that electron traps with activation energies of about 0.64 and 0.78 eV are formed in ruby as a result of γ-irradiation. These traps remain in the crystal until it is annealed at about 800°C. It is found that the threshold energy for laser action increases in relation to the amount of irradiation. This effect is also manifested as a decrease in the luminescence of the R
1
line after γ-irradiation. A model has been devised to explain the changes in Cr
⁺⁺⁺
ions due to γ-irradiation and to show how this affects laser action. Theoretical curves are presented indicating how the energy output vs. energy input varies with the amount of γ-irradiation. These data show a definite increase in threshold energy, and at higher pump energies they suggest the possibility of higher efficiencies than possible before irradiation. These theoretical results are supported by experimental data.