Zero loop-area Sagnac interferometer at oblique-incidence for detecting in-plane magneto-optic Kerr effect

We describe a zero loop-area Sagnac interferometer at oblique incidence fordetecting magneto-optic Kerr effect arising from in-plane magnetization in asample. By exploiting properties of polarization states under relevant crystal symmetrytransformation, we show that contributions from longitudinal and transverse Kerr effects can be separated.In addition we can select one optical arrangement out of four that detects thelongitudinal effect with the highest signal-to-noise ratio. Compared to finiteloop-area Sagnac interferometers operating at oblique incidence, the zero loop-areainterferometerinvolves significantly fewer optical elements and is thus more stable against drifts in the opticalsystem. For demonstration, we measured the in-plane magneto-optic Kerreffectfrom a 42-nm Nifilm