APPLICATION OF PERMITTIVITY TENSOR FOR ACCURATE INTERPRETATION OF MAGNETOOPTICAL SPECTRA

The inaccuracies of widely used approximations to the theory of the off-diagonal elements epsilon1 = epsilon1' + iepsilon1'' of the permittivity tensor are examined. Errors occurring in the ''diamagnetic'' case can become important when curve fitting is employed to extract parameter values from Bi-substituted magnetic garnets. A discrepancy between the exact and approximate forms of the epsilon1' relation (which is responsible for Faraday rotation and Kerr ellipticity at lower energies) as a function of transition energy is found in the low-energy (wavelength lambda approximately 1 mum) tails of the lines and originates from the dropping of a nonresonant term from the complete theory. Errors also occur in the line shapes near resonance where the ratio of the excited-state splitting to the Lorentzian linewidth approaches unity (DELTA/GAMMA --> 1 ). A family of curves with DELTA/GAMMA as a parameter is presented, and an exact expression relating DELTA/GAMMA to the resonance value of epsilon1'/epsilon0'' (where epsilon0'' is the imaginary part of the diagonal element epsilon0) is derived.