Abstract

The reflectivity of the TM wave from magneto-optic nonlinear interfaces between magnetized films of media like nickel, iron, or YIG bounded by a nonmagnetic, nonlinear substrate or cladding, or mixed with nonmagnetic, nonlinear films is calculated for the widely used^1,2ATR configuration. The results mainly concern prism coupling but with the much less studied third-order nonlinear TM polarization³ being used. Progress toward extending the theory to include gratings is also discussed, however. Traditionally, magnetic-field orientations include transverse, polar, and longitudinal orientations, and these are the principal ones analyzed here. Longitudinal orientations involve some complex and novel nonlinear calculations because in such a case, even in the linear limit, TM and TE polarizations cannot be decoupled so that a linear Kerr rotation of the plane of polarization occurs. Questions concerning the optimum signal-to-noise ratio are addressed in order to try and arrange the highest value to coincide with the resonant angle positions. In this connection detailed comments on the trade-off between nonlinear and magneto-optic effects are given. Nonlinear ATR curves, the power flow along the surface, the first-order magneto-optical parameter, and the magnetic-field-induced rotation of the plane of polarization are all calculated for both plane waves and for finite beams with nonlocal nonlinearity. Again, because the latter is a difficult calculation to perform, the method alone is of great interest. The simpler transverse case can be cited as an example here. The ATR curves, as might be expected, break into branches at critical power levels, but this now feeds through into the relative change of the reflected intensity of light owing to the magnetization of the film. Any sharp decrease in this first-order magneto-optic quantity is now delayed by the nonlinearity, and a critical light intensity causes two or more branches to appear. For this same case we show that the forward field reflectivity actually switches to a second branch a little earlier than for the reverse field direction; hence, the resonance angles are not matched. Finally, comments on the exploitation of nonlinear magneto-optic effects in thin-film guided-wave geometries are included.

© 1990 Optical Society of America