Abstract

Ellipsometry yields information on the phase difference, Δ, between the s- and p- waves after reflection and the ratio of the Fresnel coefficients, tanα = r_s/r_p. From these the permittivity can be determined. The experimental technique is greatly improved by using phase modulated incident light (Jasperson 1969). If the film contains a magneto optic layer the reflectivity matrix is a 2x2 complex matrix (Sprokel 1984) and the phase shift caused by the Kerr effect becomes mixed with the phase shift caused by reflection. One way to differentiate between the two is to reconfigure the ellipsometer for normal incidence. Then the reflectivity matrix is skew-symmetric and the phase shift caused by reflection is cancelled. However, exact normal incidence cannot be achieved leaving some residual error and reassembling the instrument is at best time consuming. Careful analysis of the reflectivity matrix shows that the two effects, the phase shift due to reflection and the phase shift caused by the Kerr effect, can be separated by selecting the angle of the analyzer - a Wollaston prism - at any angle of incidence. The mathematical details will be described, here we summarize the results and provide one example for a simple FeTb/SiO₂ film. The optics is shown schematically in Figure 1. The modulator is a commercial unit operating at 50 kHz. The intensities I₁ and I₂ of the two beams exiting from the Wollaston are measured using matched photo detectors. The difference ΔI = I₁ - I₂ and the sum ΣI = I₁ + I₂ are obtained electronically. The information is contained in the modulation of ΔI and ΣI and is most conveniently obtained using a Fourier Transform technique.

© 1985 Optical Society of America