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A comparison between the absolute gonioreflectometric scales at the Helsinki University of Technology (TKK) and the Physikalisch-Technische Bundesanstalt (PTB) has been accomplished. Six different reflection standards were measured for their 0:45 spectral radiance factor between 250 and 1650 nm in 10 nm intervals. Also, the 0:d reflectance factor between 400 and 1600 nm in 100 nm intervals was determined from goniometric reflectance measurements over polar angles with subsequent integration within the hemisphere above the sample. Goniometric comparisons covering such an extensive wavelength range and also several different sample materials are rarely implemented. For all but one sample, the difference between the results obtained at the TKK and the PTB was, with the exception of a couple of measurement points, within the expanded uncertainty (k = 2) of the comparison at least up to a wavelength of 1400 nm. All differences between the measurement results can be understood, except for one translucent sample in the visible wavelength range. The effect of sample translucency was found to be significant in the NIR wavelength region. Also, a general tendency of an increase of the TKK values relative to the PTB values in the UV region was observed. Possible causes for this phenomenon are discussed.

Interlaboratory comparisons, referred to as key comparisons, are completed for many metrological units within the framework of the mutual recognition arrangement of the Bureau International des Poids et Mesures. These comparisons are the responsibility of consultative committees of the different metrological areas. In the case of the Consultative Committee for Photometry and Radiometry, there are currently about 20 key comparisons for various measurands. While interest in the field of bidirectional reflectance has been growing in recent years among users in industry and research and development, there is currently no dedicated key comparison to demonstrate scale conformity. This is the basis of the comparison of the bidirectional reflectance scales between the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). Measurements of two distinct sets of white diffuse reflectance standards, two sintered polytetrafluoroethylene samples and two matte ceramic samples, were performed using the common and widely used 0∶45 geometry. The wavelength range of the comparison spans the ultraviolet (λ≥330 nm) to the near infrared (λ≤1150 nm), a technically important region. In total, five different facilities participated in this bilateral investigation. The results of the comparison show good agreement within the combined uncertainties.

We used a flow cytometer together with an intensified CCD camera to record spatially resolved light scattering from micrometer-sized single particles and single oriented particle agglomerates. Experimental differential cross sections of an oriented dumbbell made from two identical polystyrene spheres were compared with theoretical values calculated within the discrete dipole approximation, and good agreement was achieved. Furthermore, characteristic two-dimensional patterns of the scattered-light intensity were recorded for single blood cells, yielding information on the cells' shape and volume. Besides flow cytometry, we observed and analyzed differential light scatter of particle clusters of known size, shape, and orientation located within an optical trap.

Homogeneity measurements in a gold-coated integrating sphere at eight wavelengths in the range from 400 to 2000 nm are presented and discussed. The inner sphere wall was scanned with a mirror-based internal sphere scanner at 288 different positions. The spatially resolved measurements show the transition from poor reflectivity, associated with large inhomogeneities at 400 nm, to high reflectivity in the infrared region at 2000 nm, associated with only small deviations. From the measurements the spectrally dependent relative uncertainty of the radiance of the inner sphere wall was deduced. A spectrally dependent sphere homogeneity correction factor F(lambda) relative to a specific point within the sphere wall was also derived.