Spectro-temporal studies of Xe-Cl excimer laser-induced arterial wall fluorescence.

We report on spectro-temporal fluorescence studies of cadaver femoral arterial walls at different stages in the progression of atherosclerosis. After excitation with a Xe-Cl excimer pulse, the time course of the fluorescence spectrum was recorded over time, and time-resolved multispectral analysis was performed. Then, under the assumption of linearity, we derived a linear spectro-temporal kernel (a weighting function) which describes the temporal behavior of the fluorescence process independently of the pulse width of the photoexcitation. The data analysis revealed both static and dynamic fluorescence characteristics which exhibited a good correlation with histological findings.

Surface bidirectional reflection distribution function and the texture of bricks and tiles.

We study and analyze properties underlying the visual appearance of materials such as the surface bidirectional reflection distribution function and texture. The spatial distribution of scattered light in relation to the incident light determines the surface appearance and can be partly specified by the bidirectional reflection distribution function, which is defined as the directionally dependent ratio of radiance to irradiance. We perform gonioradiometric measurements on samples of bricks and tiles. To describe the reflection mechanisms in the surfaces under study, we combine models of specular and diffuse reflectance from rough surfaces and fit them to the experimental data. We also collect images and determine the textural differences in the surface appearance, resulting from the variation in the illumination direction and the viewing directions.

Diffuse and specular reflectance from rough surfaces.

We present a reflection model for isotropic rough surfaces that have both specular and diffuse components. The surface is assumed to have a normal distribution of heights. Parameters of the model are the surface roughness given by the rms slope, the albedo, and the balance between diffuse and specular reflection. The effect of roughness on diffuse reflection is taken into account, instead of our modeling this component as a constant Lambertian term. The model includes geometrical effects such as masking and shadowing. The model is compared with experimental data obtained from goniophotometric measurements on samples of tiles and bricks. The model fits well to samples with very different reflection properties. Measurements of the sample profiles performed with a laser profilometer to determine the rms slope show that the assumed surface model is realistic. The model could therefore be used in machine vision and computer graphics to approximate reflection characteristics of surfaces. It could also be used to predict the texture of surfaces as a function of illumination and viewing angles.