Optical pair interactions in the four-wave mixing spectrum of Nd3+ -doped β’’-Na-alumina

Abstract

We report the first observation of the nearly degenerate four-wave--mixing spectrum of ${\mathrm{Nd}}^{3+}$-doped \ensuremath{\beta}''-Na-alumina. In a new application of continuous-wave high-resolution nearly degenerate four-wave mixing, a linewidth analysis of \ensuremath{\sim}1-kHz-wide optical resonances in heavily doped samples has been used to explain concentration-dependent, nonradiative decay of Nd ions which is obscured in conventional fluorescence-decay studies. Quantitative four-wave--mixing saturation studies also reveal a transition between a ``closed'' and an ``open'' quantum system due to pair interactions at a Nd density of \ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.