Sun protection and hydration of stratum corneum: a study by 2-D differential method.

OBJECTIVE: The stratum corneum is the outermost layer of the skin. Its components and its morphology (such as the size of its cells) play a role in sun protection, and it has been noted that the stratum corneum hydration can change these properties. Sunscreens, applied on the skin, can be more or less effective depending on the stratum corneum characteristics. We therefore propose to simulate the quality of the sun protection and the effect of the stratum corneum hydration on the sun protection. METHODS: We first determined the sunscreen distribution on a plastic substrate using an optical coherence tomography device. We were then able to calculate, by 2-D differential method, the extinction of several sunscreens. We modelled the hydration of the stratum corneum, by changing the substrate with corneocytes of different thicknesses. RESULTS: Our results showed that hydrated stratum corneum protects more against the UV. The benefit from changing the substrate varies depending on the sunscreen applied. CONCLUSION: We modelled sunscreens on different substrates using electromagnetic simulations. To compare these results with measurements, we have to carefully hydrate or dehydrate the SC: the simulations did not take into account modifications of the surface (water on the surface for example) or any change in the characteristics of the stratum corneum other than the modification of the corneocytes thickness.

An enhanced contrast to detect bulk objects under arbitrary rough surfaces.

We study a selective light scattering elimination procedure in the case of highly scattering rough surfaces. Contrary to the case of low scattering levels, the elimination parameters are shown to depend on the sample microstructure and to present rapid variations with the scattering angle. On the other hand, when the slope of the surface is moderated, we show that this parameters present smoother variations and little dependence to the microstructure, even when the roughness is high. These results allow an important selective reduction of the scattered light, with a basic experimental mounting and an analytical determination of the elimination parameters. Such selective scattering reduction is demonstrated by simulations and experiments and applied to the imaging of an object situated under a highly rough surface.

An alternative scattering method to characterize surface roughness from transparent substrates.

An alternative scattering method is developed to characterize surface roughness from the two faces of transparent substrates. Specific weights are attributed to each surface in the scattering process, due to the large substrate thickness. The resulting roughness spectra are shown to quasi-overlap those of near field microscopy.

Optical properties calculated for multidielectric quarter-wave coatings on microspheres.

Optical properties of overcoated microspheres are calculated and compared to those of planar multilayers, in regard to the sphere diameter. The classical criteria for in-situ optical monitoring is analyzed to control the growth of films on the spheres. Most coatings are multi-dielectric quarterwave stacks used in the thin film community.

International round-robin experiment to test the International Organization for Standardization total-scattering draft standard.

An international round-robin experiment has been conducted among laboratories in different countries to test the measurement and the data-analysis procedures in the International Organization for Standardization draft standard ISO/DIS 13696 for measuring total scattering from low-scatter laser optics. Ten laboratories measured total backscattering from high-reflectance mirrors, 50% beam splitters, and antireflection-coated windows. Results were sent to the Laser Zentrum Hannover, which acted as coordinator and analyzed all the backscattering data. The results showed that the procedure in the draft standard was useful for measuring and reporting backscattering for low-scatter optics. Problems encountered in the round-robin experiment included the accumulation of particles on the surfaces, particularly on the high-reflectance mirrors.

Angle-resolved polarimetric phase measurement for the characterization of gratings.

A goniometric ellipsometer is used to recover the optogeometrical parameters of metallic gratings. The phase difference between TE and TM polarizations in all the diffracted orders is measured as a function of the incidence angle. The groove depth, together with the refractive indices of all the media of the diffracting structure, is determined for a holographic sinusoidal aluminum grating. It is shown that a thin layer of alumina on top of the grating must be considered.

Multiscale roughness in optical multilayers: atomic force microscopy and light scattering.

We have previously shown that macroscopic roughness spectra measured with light scattering at visible wavelengths were perfectly extrapolated at high spatial frequencies by microscopic roughness spectra measured with atomic force microscopy [Europhys. Lett. 22, 717 (1993); Proc. SPIE 2253, 614 (1994)]. These results have been confirmed by numerous experiments [Proc. SPIE 2253, 614 (1994)] and allow us today to characterize thin films microstructure from a macroscopic to a microscopic scale. In the first step the comparison of light scattering and atomic force microscopy is completed by optical measurements at UV wavelengths that allow us to superimpose (and no longer extrapolate) the spectra measured by the two techniques. In the second step we extract multiscale parameters that describe the action of thin-film coatings on substrate roughness in all bandwidths. The results obviously depend on materials and substrates and deposition techniques. Electron-beam evaporation, ion-assisted deposition, and ion plating are compared, and the conclusions are discussed in regard to the deposition parameters. Finally, special attention is given to the limits and performances of the two characterization techniques (light scattering and atomic force microscopy) that may be sensitive to different phenomena.

Ellipsometry of light scattering from multilayer coatings.

A scatterometer is extended and allows us to perform ellipsometric measurements on scattered light in each direction of space. Experimental data are given for single thin-film layers and optical coatings and reveal unexpected results. The phenomena are investigated by means of the electromagnetic theories of surface and bulk scattering that emphasize the role of partial correlation and localized defects.