BRDF measurements of graphite used in high-temperature fixed point blackbody radiators: a multi-angle study at 405 nm and 658 nm

Abstract

We have measured the polarization-resolved bidirectional reflectance distribution function (BRDF) for two types of graphite used in the fabrication of high-temperature fixed point blackbody cavities in and out of the plane of incidence. Measurements were made at room temperature using 405 nm and 658 nm laser sources, and the samples were illuminated at angles of incidence varying from normal incidence to 70 •. All of the samples exhibited non-Lambertian behaviour, including enhanced forward scatter at high incident angles, especially for s-polarized incident light. The directional-hemispherical reflectance for unpolarized incident light, obtained by integrating the BRDF measured at individual points in a hemisphere over the sample, ranged from 0.083 to 0.101, depending upon sample and incident angle. The potential impact of these measurements on emissivity models for graphite blackbody radiators and radiance temperature scale dissemination is discussed.

Polarized optical scattering by inhomogeneities and surface roughness in an anisotropic thin film

“…The total diffuse transmittance, which is π 〈 f r 〉 when the data are sampled uniformly in projected-cosine space [30], is approximately 0.0093. The BTDF (11-element of the Mueller matrix) shows a distinctive arc of scattering passing through the normally transmitted direction, as observed in the past [31].…”

Optical reflectance of pyrheliometer absorption cavities: progress toward SI-traceable measurements of solar irradiance

“…1. The uncertainty in ARS( θ r,j ) at each viewing angle follows previous uncertainty estimates for GOSI;[8] note that a standard uncertainty u(y) in a general measurand y means that the value with its standard uncertainty (coverage factor k = 1) is y ± u(y) . [19] We also often use the relative standard uncertainty u(y)/y .…”

“…The relative uncertainty contributions from the geometrical factors D and A r are each less than 0.1%. [8] Detector linearity uncertainty arises from the electronics used to measure P r /P i ; there are many orders of magnitude of signal level between incident power and reflected power, and we must also transfer the calibration from a photodiode (used for measuring P i ) to a PMT (used for measuring P r ). The uncertainty in P r is dominated by laser speckle produced by the interaction of the focused, coherent laser source with the surface roughness.…”

“…This method for measuring diffuse reflectance has been performed in the past on high- and low-reflectance uniform samples. [8-11] In this work, we extend the goniometric technique to cavity reflectance. We used a 532 nm laser source and a gonioreflectometer,[12] which allows both spatial scanning of the cavity and angle-resolved measurement of reflectance, to measure the cavity reflectance as a function of viewing angle and illumination position on the cavity.…”

Full four-dimensional and reciprocal Mueller matrix bidirectional reflectance distribution function of sintered polytetrafluoroethylene

“…Mueller matrix properties in the plane of incidence are reported in [11–15]. A small number of measurements are reported out of the plane of incidence [16, 17], while [1–4, 11] considered the wavelength dependence of the optical properties. These works leave gaps in the availability of information, especially for out-of-plane geometries and for its polarization properties.…”