Critical slowing down and dispersion of avalanche upconversion dynamics

Abstract

The temporal response time on an avalanche upconversion transition is shown to undergo critical slowing down near the avalanche threshold. Also, the nonlinear refractive index is predominantly real, despite the resonant nature of the avalanche phenomenon. These findings are in excellent agreement with density-matrix analyses showing that cross relaxation dramatically alters the effective excited-state lifetime and that off-resonance absorption curiously dominates the wavelength dependence of the nonlinear refractive index. © 1997 The American Physical Society.