Polarization Dependence of the Cr3+ R-Line Fluorescence from Sapphire and Its Application to Crystal Orientation and Piezospectroscopic Measurement

TLDR: In this paper, the room temperature polarization characteristics of the ruby R lines have been studied by monitoring the fluorescence intensity as a function of excitation direction relative to the crystallographic axes of a ruby crystal, and the findings provide the basis for a high-spatial-resolution spectrophotometric method to determine the optical c-axis of chromium-doped Al2O3 crystals using the angular dependence of the intensity ratio of the R2 line to the R1 line.

Abstract: The room-temperature polarization characteristics of the ruby R lines have been studied by monitoring the fluorescence intensity as a function of excitation direction relative to the crystallographic axes of the ruby crystal. The R lines are strongly polarized in the basal plane but have no preferred vibration direction within the basal plane. However, the degree of polarization, P, of the R1 and R2 lines is not the same, being PR1=87% and PR2=62%. The phenomenon is explained in terms of the absorption anisotropy and the probability of spontaneous emission. The findings provide the basis for a high-spatial-resolution spectrophotometric method to determine the optical c-axis of chromium-doped Al2O3 crystals using the angular dependence of the intensity ratio of the R2 line to the R1 line. The application to the orientation determination of sapphire fibers embedded in composites and the corresponding residual stress components are discussed together with the possibility of measuring the texture in the Al2O3 polycrystalline thin films such as oxidation scales. Furthermore, the consequences of polarization orientation on piezospectroscopic measurements are discussed.