Nonlinear optical properties of ionic magnetic colloids in the femto- and millisecond time scales: change from convergent-to-divergent lens-type behaviors

Abstract

The Z-scan technique is used to measure the nonlinear refractive index n 2 and the nonlinear absorption coefficient ␤ of ionic magnetic colloids as a function of the nanoparticles' diameter ͑D rx ͒ in the femto-and millisecond time-scale regimes. A change from a convergent-lens type (at a femtosecond time scale) to a divergent-lens type behavior (at a millisecond time scale) is observed. From the values of n 2 and ␤ measured in the femtosecond time-scale regime, the third-order susceptibility ͑3͒ is calculated and is shown to depend on D rx : the smaller the D rx , the bigger the ͑3͒ . A possible origin of the high values of ͑3͒ found may be confining effects related to the physical nanoscale of the magnetic particles.

Characterization of the Biocompatible Magnetic Colloid on the Basis of Fe<SUB>3</SUB>O<SUB>4</SUB> Nanoparticles Coated with Dextran, Used as Contrast Agent in Magnetic Resonance Imaging

“…The Z-scan (ZS) technique 16 in the femtosecond (fs) and millisecond (ms) time-scales was applied to investigate the nonlinear optical properties of the magnetic colloid associated to electronic and thermal mechanisms, 15 respectively. The details of both experimental setups are available in Soga et al 20 In the fs time-scale regime, a mode-locked Ti:sapphire laser ( = 790 nm) was used in ZS experiments. The pulse width was 508.5 fs.…”

Investigation of the optical absorption of a magnetic colloid from the thermal to the electronic time-scale regime: measurement of the free-carrier absorption cross-section

“…They are magnetic colloids composed of iron oxide nanoparticles, coated with surfactant agents, dispersed in a liquid carrier [9]. This confining effect was previously reported in Fe 2 O 3 [8] and CoFe 2 O 4 [4] nanoparticles by measuring the third-order nonlinear refractive index and absorption. The third-order susceptibility χ 3 was shown to be dependent on the nanoparticle size in the case of the Cobalt particles and, besides the existence of the TPA, evidence of the FCA was observed in the experiments with maghemite particles.…”

“…Each particular process, related to the material properties, is characterized by a time-scale [1,2]. For example, thermal [3,4], molecular reorientation [5], and electronic transitions [2] processes have typical time-scales of milliseconds, picoseconds, and femtoseconds, respectively.…”

“…In the second case, the entire transmitted beam is detected by the photodetector and is named open-aperture configuration. The ZS technique has been extensively used to investigate nonlinear properties of different materials [3][4][5][12][13][14][15][16][17]. The Sheik-Bahae formalism (SBF) assumes a local interaction between the sample and the radiation field, disregarding thermal (nonlocal) phenomena, which are considered in the thermal-lens model (TLM) proposed in the 1960s [18][19][20].…”

Cluster formation in ferrofluids induced by holographic optical tweezers

“…Ferrofluids consist of magnetic nanoparticles (diameter ∼10 nm), which are dispersed in a liquid often with the use of surfactants [1]. Thus the ferrofluids are colloidal suspensions and have both liquid and magnetic properties, which are useful for various applications [1][2][3][4]. The ferrofluids are stable, which means there is no particle aggregation or phase separation even in strong external magnetic fields.…”