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We investigate size-dependent nonlinear polarization due to Wannier excitons confined in CuCl quantum dots (QD's) with a radius R of 15--80 embedded in glass. The third-order optical susceptibility ^ (3) measured at 80 K increases as a function of radius and subsequently decreases after reaching a maximum value of 210^-6 esu at R50. 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 ^ (3) originates from the size-dependent oscillator strength of coherently generated excitons in the QD. The oscillator strength varies as R^2. 2 for 19R40 and is enhanced by a factor of 940 at maximum compared to that of bulk exciton.
Tokizaki et al. (1993) studied this question.