Nonlinear change of refractive index of Co3O4 thin films induced by semiconductor laser (λ=405 nm) irradiation

Nonlinear change of the refractive index (n) and extinction coefficient (k) of Co3O4 thin films induced by a laser with lambda=405 nm (hnu=3.06 eV) irradiation was evaluated using equipment having an ellipsometric optical configuration. Nonlinear refractive index (n(2)) and extinction coefficient (k(2)) were +1.0x10(-10) m(2)/W (positive) and -2.6x10(-11) m(2)/W (negative), respectively. n(2) and k(2) at lambda=650 nm (hnu=1.91 eV) were -5.5x10(-11) m(2)/W and -8.7x10(-11) m(2)/W (both have negative signs). From these results and the fact that the Co3O4 thin film has the band-gap energy of 2.06 eV, the band filling effect can be seen as one of the most probable models describing the large nonlinear change of n and k of Co3O4 thin film. (C) 2002 American Institute of Physics.