Fundamental scattering quantities for the determination of reflectance and transmittance.

The bidirectional reflectance distribution function (BRDF) and the bidirectional scattering - surface reflectance distribution function (BSSRDF), which relate radiance at the surface to irradiance and radiant flux, respectively, are regarded as the most fundamental scattering quantities used to determine the reflectance of objects. However, for materials where the optical radiation is transmitted under the surface, this radiance depends not only on irradiance and radiant flux, but also on the size of the irradiated area of the surface. This article provides insight into such dependence under the special condition in which the radiance is evaluated within the irradiated area and, consequently, is produced by both the insurface reflection and the subsurface scattering, in contrast to the situation in which the radiance is evaluated at non-irradiated areas and only subsurface scattering contributes. By explicitly considering both contributions, two other scattering quantities are defined: one that accounts exclusively for the insurface reflection and the other that accounts for subsurface scattering. In this regard, these quantities might be considered more fundamental than the BRDF and the BSSRDF, although they are coincident with these two functions apart from the above-mentioned special condition and for materials with negligible subsurface scattering. In this work, the relevance of the proposed scattering quantities is supported by experimental data, practical considerations are given for measuring them, and their relation to the bidirectional transmittance distribution function (BTDF) is discussed.

Multilayer four-flux matrix model accounting for directional-diffuse light transfers.

The four-flux model is a method to solve light radiative-transfer problems in planar, possibly multilayer structures. The light fluxes are modeled as two collimated and two diffuse beams propagating forward and backward perpendicularly to the layer stack. In the present contribution, we develop a four-flux model relying on a matrix formalism to determine the reflectance and transmittance factors of stacks of components by knowing those of each individual component. This model is also extended to generate the bidirectional scattering distribution function of the stack by considering an incoming collimated flux in any direction and by taking into account the directionality of the diffuse fluxes exiting from the material at the border components of the stack. The model is applied to opaque Lambertian backgrounds with flat or rough interfaces for which analytical expressions of the BSDF are obtained.

Tuning the surface plasmon resonance of silver nanoclusters by oxygen exposure and low-energy plasma annealing.

Real-time surface differential reflectance spectroscopy in the visible range is used to study the optical response of silver nanoclusters, prepared by magnetron sputtering deposition, during cyclic treatments in different oxygen atmospheres and low-energy bias argon plasma. Changes in the reflectance show that the exposure to non-ionized (or partially ionized) oxygen causes a red-shift and damping (or complete vanishing) of the resonance, while bias plasma annealing induces the opposite effects, due to oxygen desorption and structural reshaping of the nanoclusters. These results open up new opportunities for developing plasmon-based devices with high tunability of the surface plasmon resonance (energy, width and amplitude) due to an interplay between morphological and chemical modifications of the nanoclusters.

Comments on "Surface plasmon resonance of metal nanoparticles sandwiched between dielectric layers: theoretical modeling".

The Maxwell-Garnett's and Toudert's methods detailed in Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778, based on the Maxwell-Garnett and Yamaguchi effective medium models, respectively, have been used for calculating the absorbance alpha of a (BaF(2)/Ag)(5)/BaF(2) nanocomposite thin film identical to the one presented in Fig. 1 of Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778]. We propose that the discrepancies observed in this reference between the alpha spectra calculated by the two methods are due to a non rigorous use of both effective medium models by the author and show that adequate calculations lead to superposed spectra.

Quantitative modelling of the surface plasmon resonances of metal nanoclusters sandwiched between dielectric layers: the influence of nanocluster size, shape and organization.

The effects of size, shape and organization on the surface plasmon resonances of Ag nanoclusters sandwiched between Si(3)N(4) layers are studied by transmission electron microscopy and anisotropic spectroscopic ellipsometry. We present an easy-to-handle model that quantitatively links the nanostructure and optical response of the films, which are considered as dielectric/metal:dielectric/dielectric trilayers, with the central nanocomposite layer being an effective medium whose optical properties are described by an anisotropic dielectric tensor. The components of this tensor are calculated using a generalization of the Yamaguchi theory taking into account the real organization, size and shape distributions of ellipsoidal nanoclusters, whose electronic properties are assumed to reflect shape-dependent finite size effects. Using this model, it is shown that the optical response of the films in the visible range is dominated by the excitation of the surface plasmon resonance of the clusters along their in-plane long axis, while no surface plasmon resonance resulting from an excitation along their in-plane short axis can be observed due to damping effects. Moreover, the spectral position of this resonance appears to be mainly affected by the average shape of the clusters, and weakly by their size, their shape distribution and the electromagnetic interaction between them.

Sclerosing cholangitis in adults with cystic fibrosis: a magnetic resonance cholangiographic prospective study.

BACKGROUND/AIMS: Liver disease is a leading cause of morbidity in adult patients with cystic fibrosis. Diagnosis of limited liver involvement in asymptomatic patients is important since a safe and effective treatment with ursodeoxycholic acid can be used. We carried out a prospective open study to describe the intrahepatic biliary lesions using magnetic resonance cholangiography. METHODS: Twenty-seven adult patients with cystic fibrosis were prospectively enrolled, whatever their hepatobiliary status. All patients underwent liver function tests, ultrasonography and magnetic resonance cholangiography. Magnetic resonance cholangiograms were acquired on a Philips 1.5 Tesla unit using a 3D TSE MR sequence. Acquisition parameters (120 slices, 1.6 mm thickness, interslice overlap 0.8 mm) were followed by MIP reconstruction in two orthogonal planes. Magnetic resonance cholangiography images were assessed for the presence of stenosis, dilatations and rigidity corresponding to current criteria of cholangitis. Among the 27 cystic fibrosis patients, 18 (Group I) fulfilled none of the clinical, biological or ultrasonographic criteria of liver disease; the remaining nine (Group II) fulfilled the criteria for liver disease. In every patient, current causes of secondary sclerosing cholangitis had been excluded. RESULTS: All the Group II patients had abnormal magnetic resonance cholangiograms with features resembling those of primary sclerosing cholangitis in five, and simple biliary lesions in four. Nine Group I patients had abnormal magnetic resonance cholangiograms with primary sclerosing cholangitis-like lesions in five and simple biliary lesions in four. Magnetic resonance cholangiography anomalies were always dilatations, either isolated or associated with strictures and rigidity, both resembling those seen in cholangitis. They were seen in all the patients with known liver disease and in half the patients without evidence of liver disease. CONCLUSION: This study confirms the high frequency of intrahepatic biliary abnormalities in CF patients, which is probably underestimated by clinical, biological and ultrasonographic evaluation. The magnetic resonance cholangiography technique could be useful to detect early intrahepatic biliary tract involvement in cystic fibrosis patients.