Comparison of Optical Activity and Faraday Rotation in Crystalline Si02

Optical activity (OA) and Faraday rotation (FR) in SiO2 are compared from both a theoretical and an experimental points of view. A simultaneous derivation of the one‐oscillator formulas of FR and OA is presented. For OA this formula is extended to a semi‐classical expression, in analogy with earlier derivations of FR formulae. Starting from dispersion relations for crystals without inversion symmetry, it is possible to derive the OA formula, obtained earlier by Natori with the Kubo‐Greenwood formalism. Within the limits of accuracy and in the wavelength range 300 to 700 nm the experimental curves of OA and FR differ by a numerical factor only. Nevertheless the gap energies, obtained by fitting these curves with OA and FR formulas are different. The energy E = 9 eV is believed to correspond to the real direct band gap.