Third-order nonlinear susceptibility and hyperpolarizability of cdse nanocrystals with femtosecond excitation

Single beam femtosecond Z-scan spectroscopy at 775 nm revealed that the effective third-order nonlinear susceptibility and hyperpolarizability of CdSe colloidal nanocrystals near the Bohr radius were similar to 0.7 - 1.0 x 10(-22) m(2)/V-2 and similar to 0.18 - 2.0 x 10(-44) m(5)/V-2, respectively. The non-resonant nonlinearity increase for CdSe colloidal quantum dots withbigger than average diameters is attributed to their absorption cross-section being larger and their bandgap energy being narrower than those of the quantum dots with smaller sizes.