Dual Beam MOKE Detection to Suppress the Effect Of Modulated Interference Effects In PEM

The Magneto-Optical measurement method is often used to measure the magnetic hysteresis of thin films and multilayers. The method is more sensitive than vibrating sample magnetometry and allows for remote measurements. A Photo elastic modulator (PEM) is used to enhance the S/N ratio. The sample's magnetic moment is proportional to the 2f intensity signal. Strong coherent noise at the modulator oscillation's frequency and its harmonics arises due to interference between the primary laser beam and beams that undergo multiple reflections in the PEM's optic head. In dual beam MOKE detection, the beam transmitted through the sample is split in two high quality linearly polarized beams by a Wollaston Prism. The intensity of the beams is measured by two Si detectors employing lock-in amplifiers. Optics and detectors are mounted in an optical rotation stage allowing for them to be rotated together around the setup's optical axis. A PC running Labview was used to control the PEM angle, the magnetic field, and the Polarizer and Analyzer angles. Above-mentioned coherent noise can be largely reduced by subtracting the 2f components of both transmitted beams [1]. [1] Md. Abdul Ahad Talukder, Wilhelmus J. Geerts, AIP Advances 7, 085320 (2017).