Optical Sensor of Magnetic Dynamics: A Balanced-Detection MOKE Magnetometer

Team Members

LI Junxiang E1127462@u.nus.edu

Patricia Breanne Tan Sy pb.sy82@u.nus.edu

Idea

We will use a laser-based magneto-optical Kerr effect setup featuring a high-sensitivity differential photodiode array to measure the Kerr rotation angle induced by surface magnetism. This system serves as a versatile optical platform to investigate how external perturbations such as magnetic fields or radiation source alter the magnetic ordering of materials, allowing for the quantitative extraction of the magneto-optical coupling coefficients of various thin films.

Experimental Setup

MOKE Experimental Setup

We utilize a 658 nm HL6501 red Continuous Wave (CW) laser. The beam passes through an ND filter to attenuate its intensity. To achieve continuous intensity control while maintaining a pure linear polarization (S or P), a combination of a fixed Polarizer, a rotating Half-Wave Plate (HWP), and a second Polarizer is used. The beam is then directed via a Non-Polarizing Beam Splitter (NPBS) and focused onto the sample by an objective lens. The reflected light, carrying the Kerr rotation signal, is collected and directed into a Wollaston prism. The prism splits the beam into two orthogonal components (($I_1$ and $I_2$), which are then captured by a Balanced Detector. The micro-Kerr rotation (${\theta }_K$), induced by the material's magnetic properties, is extracted from the normalized difference of the two intensities, effectively cancelling out laser intensity noise

Reference

1. McCord, J. Progress in magnetic domain observation by advanced magneto-optical microscopy. J. Phys. D: Appl. Phys. 48, 333001 (2015).