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

Abstract

We describe a zero loop-area Sagnac interferometer at oblique incidence for detecting magneto-optic Kerr effect arising from in-plane magnetization in a sample. By exploiting properties of polarization states under relevant crystal symmetry transformation, 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 the longitudinal effect with the highest signal-to-noise ratio. Compared to finite loop-area Sagnac interferometers operating at oblique incidence, the zero loop-area interferometer involves significantly fewer optical elements and is thus more stable against drifts in the optical system. For demonstration, we measured the in-plane magneto-optic Kerr effect from a 42-nm Ni film.

Improving the sensitivity of DC magneto-optical Kerr effect measurement to 10−7rad/Hz

“…Although it can be well adapted to the measurement of polar magnetization, a high-sensitivity probe of in-plane magnetization, i.e., longitudinal-and transverse-MOKE, remains challenging. By inserting reflection optics to fold the obliquely-incident beam path backward, the modified Sagnac interferometer can be applied to measure the in-plane magnetization with a sensitivity of 10 −6 rad= Hz p [19,20] . Another widely used approach is based on high-frequency modulation of the sample magnetization, which may reach the lowest noise floor of several 10 −9 rad with sensitivity of ∼10 −7 rad= Hz p [7,21,22] .…”