Tunable nonlinear optical properties in magnetic nanoparticles suspension under picosecond laser excitation

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In this paper, the intensity-dependent nonlinear optical absorption and nonlinear refraction behaviors of the Fe3O4 nanoparticles suspension exposed to the 1064 nm picosecond laser pulses (25 ps) were investigated by applying the Z-scan technique. A new type of saturation absorption curve of the magnetic fluids was obtained at lower excitation power levels. As the exciting energy increased, the nonlinear absorption changed from saturable absorption to reverse-saturable absorption, while the nonlinear refraction correspondingly reversed from self-defocusing to self-focusing. These interesting tunable nonlinear optical properties were attributed to the inter-valence charge transfer.