2-PHOTON ABSORPTION IN SEMICONDUCTOR NANOCRYSTALS

Measurements of the two-photon absorption coefficient in semiconductor -doped glasses were performed. The imaginary part of the third-order o ptical susceptibility in the semiconductor particles is derived by com bining nonlinear-optical-transmission data with small-angle neutron-sc attering (SANS) results, which give the volume fraction of the nanocry stals. We find that the absorptive nonlinearity of the nanocrystals (w ith radii, also measured by SANS, in the range 2-11 nm) is close to th at of the bulk semiconductor, in contrast to recent predictions and da ta.