Morphology dependent nanosecond and ultrafast optical power limiting of CdO nanomorphotypes

Abstract

A versatile approach to the fabrication of cadmium oxide (CdO) nanospheres, nanoflakes and nanoparallelepiped shapes through chemical precipitation and hydrothermal methods is studied. The growth mechanism of nanostructures is elucidated on the basis of capping agent and reaction time. The crystalline nature and various geometrical shapes of nanostructures are examined by X-ray diffraction and high resolution transmission electron microscopic analysis. Nonlinear optical absorption and optical power limiting studies of nanostructures are carried out using the open aperture z-scan technique in the nanosecond (ns) and femtosecond (fs) excitation time scales. Optical nonlinearity is found to arise from effective two- photon absorption involving excited state absorption. The magnitude of the effective two-photon absorption coefficient is calculated and found to be in the range of 10⁻¹⁰ m W⁻¹ for ns and 10⁻¹⁵ m W⁻¹ for fs. The nonlinear optical study discloses that the nonlinear optical absorption and optical limiting threshold values are strongly related to nanomaterial morphology. The Brunauer–Emmett–Teller (BET) surface area analysis also confirms our claim that the optical nonlinearity is strongly dependent on the morphology as well as surface area of the nanomaterial. Thus the present nanomorphotypes have potential applications in devices for optical limiting, optical switching, pulse shaping, pulse compression and optical diode action.