UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2008 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
An experimental set-up for magneto-optical Kerr effect measurements for didactic purposes


Authors:
M. Ristici, I. Gruia, A. Patroi, B. Ionita, M. Rosu


Affiliation:
Faculty of Physics, University of Bucharest, Romania


E-mail
marin.ristici@4roptics.com


Keywords:
Kerr Effect,polarization,laser


Abstract:
The Magneto-Optic Kerr Effect (MOKE) consists in modifications of a beam when it is reflected by a material subjected to a magnetic field. The reflection can produce several effects, including: rotation of the direction of polarization of the light, introduction of ellipticity in the reflected beam and a change in the intensity of the reflected beam. MOKE is particularly important in the study of ferromagnetic and ferrimagnetic materials. For MOKE experiments, there are three “geometries”: POLAR, LONGITUDINAL and TRANSVERSE. These arise from the direction of the magnetic field with respect to the plane of incidence of the sample surface. The advantages of a laser beam to be used in MOKE experiments consist in: monochromaticity, small beam dimension and divergence, good polarization. Usually is used a gas laser (He-Ne, Ar+), semiconductor laser or a 532 nm YAG-Nd laser diode pumped. The laser beam is partially polarized, better or worse, depending on laser type, from 1:50 for 532 nm YAG:Nd to 1:500 for He-Ne. Sometimes it is necessary to improve the polarization of the incident beam by a polarizer. The set-up consists in a He-Ne laser, 1:500 polarized and 5 mW output power on the red line. A Wollaston prism was used to optimize the polarization of the laser beam. Alternatively, a polarization rotator can be used. A magnetic field of maximum 1 T can be generated. The polar geometry was preferred in our experiments (the magnetic field is parallel to the plane of incidence and normal to the sample surface). The analyzer is a Glan-Thompson prism. The optical signal is measured via an EMI 9558 QB photomultiplier and a photon counting electronics or, alternatively, an optical chopper and lock-in amplifier.