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1.
J Biomed Opt ; 18(8): 87003, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23922125

RESUMO

A first accurate measurement of the complex refractive index in an intralipid emulsion is demonstrated, and thereby the average scatterer particle size using standard Mie scattering calculations is extracted. Our method is based on measurement and modeling of the reflectance of a divergent laser beam from the sample surface. In the absence of any definitive reference data for the complex refractive index or particle size in highly turbid intralipid emulsions, we base our claim of accuracy on the fact that our work offers several critically important advantages over previously reported attempts. First, our measurements are in situ in the sense that they do not require any sample dilution, thus eliminating dilution errors. Second, our theoretical model does not employ any fitting parameters other than the two quantities we seek to determine, i.e., the real and imaginary parts of the refractive index, thus eliminating ambiguities arising from multiple extraneous fitting parameters. Third, we fit the entire reflectance-versus-incident-angle data curve instead of focusing on only the critical angle region, which is just a small subset of the data. Finally, despite our use of highly scattering opaque samples, our experiment uniquely satisfies a key assumption behind the Mie scattering formalism, namely, no multiple scattering occurs. Further proof of our method's validity is given by the fact that our measured particle size finds good agreement with the value obtained by dynamic light scattering.


Assuntos
Algoritmos , Materiais Biomiméticos/química , Emulsões/química , Lipídeos/química , Nefelometria e Turbidimetria/métodos , Refratometria/métodos , Materiais Biomiméticos/análise , Emulsões/análise , Lipídeos/análise , Teste de Materiais/métodos , Tamanho da Partícula , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
2.
Appl Opt ; 45(25): 6477-86, 2006 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-16912786

RESUMO

We present a refractometer based on the principle of total internal reflection that can sensitively record, in real time, the refractive index of fluids over a wide range of refractive indices. The device uses a divergent laser beam and a linear diode array, and has no mechanical or optical moving parts, enabling us to achieve the measurement of a refractive index at a sensitivity level of 10(-6). Our refractometer does not rely on interferometry, thus enabling the device to be compact, portable, and inexpensive. To the best of our knowledge, this is the first time a noninterferometric device that performs real-time differential refractometry with a sensitivity of better than 10(-5) has been demonstrated in the literature. We show that our experimental results agree very well with Fresnel theory. We establish a theoretical limit on the sensitivity of this class of refractometers.

3.
Opt Lett ; 29(23): 2713-5, 2004 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-15605481

RESUMO

We present experimental evidence that the intensity correlations of light scattered from a cold-atom cloud are sensitive to the presence of small amounts of radiation trapping in an atomic sample of density 6 x 10(8)/cm3, with an optical depth (for a resonant light beam) of 0.4. This density and optical depth are approximately an order of magnitude less than the density and on-resonance optical depth at which effects of multiple scattering in cold-atom clouds have been previously observed [Phys. Rev. Lett. 64, 408 (1990)].

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