Mesoscopic enhancement of optical nonlinearity in CuCl quantum dots: Giant-oscillator-strength effect on confined excitons.

We investigate size-dependent nonlinear polarization due to Wannier excitons confined in CuCl quantum dots (QD's) with a radius R of 15-80 A embedded in glass. The third-order optical susceptibility χ (3) measured at 80 K increnses ns a function of radius and subsequently decreases after reaching a maximum value of 2×10 -6 esu at R∼50 A. Homogeneous widths and longitudinal relaxation times were also measured and the results were analyzed taking into account a two-level atomic model. We obtain evidence that the size-dependent χ (3) originates from the size-dependent oscillator strength of coherently generated excitons in the QD