Abstract

Although divalent Sm in CaF₂ was the first rare earth (RE) system to exhibit laser action, trivalent RE compounds have dominated solid-state laser development up to the present. Divalent RE ions are of interest because the d levels are generally much lower in energy than in RE³⁺ ions. As a result, the broad 4f - 5d absorption bands are often centered in the visible region. The dipole allowed 5d - 4f transitions are expected to possess high emission crosssections and broadly tunable emission Unfortunately, except for Sm²⁺:CaF₂, laser emission in RE²⁺ crystals is often due to f-f transitions characterized by long lifetimes and low cross-sections.

© 1987 Optical Society of America