English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The refractive and absorptive nonlinear optical properties of ferrofluids, made with magnetite nanoparticles in water or oil, and of thin films made from the ferrofluids, are investigated by z-scan technique. A Gaussian pulsed laser beam, with pulse width of ∼ 200 femtoseconds and wavelength of 800 nm is used in the nonlinear refractive index n2 and two-photon absorption coefficient β measurements. The beam characterization is detailed, as well as the samples optical and structural characterization. The nanoparticles mean diameters, especially, are achieved by X-ray diffractometry, small angle X-ray scattering and transmission electron microscopy. An electro-optical modulator and an electromechanical shutter are applied in the setup to avoid the thermal nonlinear optical effects, that could be present due to the sample heating by the beam. n2 and β are measured as a function of the mean nanoparticles diameters, and as a result, β values decrease when the diameters decrease. Besides, the β values comparison for samples with different concentrations allows the determination of the magnetite two-photon absorption cross section σ2PA. The nonlinear absorption and refraction are also studied as a function of an external magnetic field applied in the thin films and ferrofluids. For the last, β values increase with the field when its direction is parallel to the light polarization, and decrease with field when its direction is perpendicular to the polarization. The possible reasons are discussed, and some elements of the third-order optical susceptibility are obtained from these results. keywords: magnetite nanoparticles, z-scan, nonlinear refraction, two-photon absorption.

Estudo das propriedades ópticas não lineares de ferrofluidos e filmes finos de magnetita na escala de tempo de femtosegundos