Design of a fully automated bidirectional laser reflectometer; application to emissivity measurement
Abstract
paper describes a fully automated bidirectional reflectometer and some of its applications. The main features of the apparatus include bidirectional reflectance distribution function (BRDF), and bidirectional transmission distribution function (BTDF) measurements for both cases of polarization (s and p). In our system, three angular parameters are controlled through the sample holder while the fourth is the angular position of the detector which can rotate in a horizontal plane. The linearly polarized light source is a gas discharge laser using CO (5 gm) or CO2 (10.6 μm). In order to control the incident polarization, we use two tilted ZnSe windows mounted on a rotation stepping motor in the laser cavity. It enables us to maintain a fixed state of incident polarization during the sample rotation. As a consequence of the design of the sample holder, the relative position of the sample and incident beam remains perfectly constant while the detector explores the whole space. Data acquisition, motor displacements and further data treatments including graphical display are performed by a microcomputer. Data for some diffusers are presented. Determination of the emissivity of an opaque solid using bidirectional reflectance data is considered.