Third-order nonlinear optical responses of nanoparticulate Co3O4 films

Abstract Third-order nonlinear optical responses of nanoparticulate Co3O4 films, prepared by sputtering and pyrolysis, were investigated. The sputtered Co3O4 film showed a large third-order nonlinear susceptibility (|χ(3)|) of 3.2×10−8 esu, determined by degenerate four-wave mixing (DFWM). This |χ(3)| is 7.1 times greater than that of the pyrolyzed Co3O4 film, attributable to the greater density and refractive index of the sputtered film. Time-resolved DFWM experiments show a slowly decaying component with a lifetime of approximately 100 ps existing for both films in addition to a fast decaying component. Nonlinear transmission experiments revealed both films exhibiting significant nonlinear absorption. The imaginary part of the susceptibility (Im[χ(3)]) found for each film was of the same order of magnitude as the |χ(3)| found by the DFWM method, showing that the major part of the fast decaying component of |χ(3)| comes from the nonlinear absorption.