Hyper-Rayleigh scattering measurements of magnetite nanoparticles: Determination of the first order hyperpolarizability anisotropy

Autor(es)

Goncalves, E. S. ; Fonseca, R. D. ; De Boni, L. ; Figueiredo Neto, A. M. ; Chien, LC ; Broer, DJ ; Musevic, I ; Lee, B

• Tipo de documento: Artigo Científico
• Fonte: EMERGING LIQUID CRYSTAL TECHNOLOGIES XIV; v. 10941, p. 13-pg., 2019-01-01.

Resumo

The hyper-Rayleigh scattering technique was used to determine the first order hyperpolarizability beta of magnetic nanoparticles dispersed on colloidal solutions. Pulse trains of mode-locked pulses of 100 ps on an a Q-switcher envelope of 150 ns emitted by a Nd:YAG laser, centered on 1064 nm, were used since this method allows measurements as a function of the incident beam intensity without the need of external elements. In order to determine the procedure to measure second-order optical nonlinearities on magnetic nanoparticles and avoid cumulative effects during the measurements, that lasts between to consecutive pulse trains, the results were studied for different values of the Q-switcher repetition rate, from 5 Hz to 800 Hz. Since cumulative effects were verified for higher values of repetition rates, all measurements were performed at the rate of 30 Hz. Therefore, the first-order hyperpolarizability beta was measured in the presence and absence of external magnetic field of magnitude H = 800 G. The linear attenuation spectrum was determined and didn't change with the appliance of magnetic field since large aggregates of nanoparticles were not formed. Nonlinear scattering measurements were performed in the case were the laser light polarization was parallel and perpendicular to the external field lines, employing a half-wave plate to change the light polarization state. In the absence of magnetic field, beta(H=0) = 8.5(1) x 10(-28) cm(5)/esu, while in their presence of magnetic field, beta(parallel to) = 9.8(2) x 10(-28) cm(5)/esu and beta(perpendicular to) = 8.1(1) x 10(-28) cm(5)/esu, showing an anisotropy beta(parallel to) - beta(perpendicular to)/beta(parallel to) of about 17%. (AU)

• Processo FAPESP: 15/20555-2 - Geração de segundo harmônico por partículas centrossimétricas de colóides magnéticos
• Beneficiário: Eduardo Sell Gonçalves
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 08/57685-7 - Instituto Nacional de Ciência e Tecnologia de Fluídos Complexos
• Beneficiário: Antonio Martins Figueiredo Neto
• Modalidade de apoio: Auxílio à Pesquisa - Temático
• Processo FAPESP: 16/20886-1 - Modernização da linha de Espectroscopia Óptica Não Linear ultrarrápida: Absorção transiente e chave kerr óptica com controle da polarização.
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• Processo FAPESP: 11/13616-4 - Propriedades ópticas e estruturais de elastômeros e fluidos complexos de interesse biológico
• Beneficiário: Antonio Martins Figueiredo Neto
• Modalidade de apoio: Auxílio à Pesquisa - Temático