Abstract

We report an investigation of a nonlinear optical absorption phenomenon observed in LaCl₃ crystals doped with Pr. When these crystals are illuminated with a laser beam of 529 nm wavelength and intensity in excess of a certain critical value, the light is strongly absorbed. The laser radiation is resonant with a Pr³⁺ transition from the first excited state (³H₅) to a high optical state (³P₁), and absorption is accompanied by strong fluorescence output from 3p₁ and 3p₀ to several lower-lying levels. Since the resonant transition does not include the ground state, it is not expected a priori that any absorption should occur (see Fig. 1). This is an example of the so-called photon avalanche phenomenon¹.

© 1988 Optical Society of America