An anisotropy of some electrical and optical properties of p-rhombohedra1 boron has been investigated by Dietz et al. (1) and by Kierzek-Pecold et al. (2). In the first of these papers the authors have measured an anisotropy in the resistivity and in the absorption coefficient. In the second, the anisotropy of the reflectivity has been investigated for photon energies between 1 and 6 eV. It was shown that the direction parallel to the rod axis (Rd is some selected optical direction.The purpose of the present measurements was to investigate the optical activity of p -rhombohedral boron by measuring some polarization effects in the wavelength range between 0.7 and 1.57 eV. The measurements were carried out using the typical optical system with monochromator, polarizer, analyzer, and detector.The light incident on the sample was linearly polarized, while the light transmitted through the sample was elliptically polariged. Moreover, the long axis of the ellipse was rotated by some angle with respect to the plane of polarization of the incident radiation. These two effects, i. e. ellipticity and rotation of plane of polarization, are associated with the intrinsic optical activity of p -rhombohedra1 boron.The boron samples used in the experiment are the same as those used for reflectivity measurements (2). In all cases the rod axis was parallel to the surface of the sample, i. e. perpendicular to the propagation of light. The measurements were carried out for two polarizations of the incident radiation. In the first case, the electric vector was parallel to the rod axis (E It R ) and in the second perpendicular (EIRa). It can be .seen on Figs. 1 and 2 that the rotation of the long axis of the ellipse does not depend on the direction of the linear polarization of the incident radiation. In the case of ellipticity there is some difference for both polarizations. This differerne is maximum for photon energy I. 5 eV. Also, extremal values of ellipticity are observed for this photon energy. This is probably due to interband transitions, since the energy of about 1.5eV corresponds to the energygap. a
