Enhanced Goos-Hanchen Shift in a Ferromagnetic Sample in Polar Moke Orientation

Sruthi, N. (2019) Enhanced Goos-Hanchen Shift in a Ferromagnetic Sample in Polar Moke Orientation. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Magneto-Optic effects arise from the interaction between electromagnetic radiation and magnetically polarized materials involving their electronic structure. One of them is the Magneto-Optic Kerr effect(MOKE) in which the polarization of a linearly polarized light becomes elliptical after reflection from a magnetized medium and this polarization rotation is proportional to the magnetization of the medium. This effect originates from the anisotropy incorporated in the system due to magnetization in a particular axis, which in our case is perpendicular to the sample. This break in symmetry appears as off-diagonal terms in the dielectric tensor of the medium which are proportional to its magnetization. Optical beam shifts are basically manifestations of the deviation from geometrical optics predictions. It was observed that the centroid of an optical beam can shift both tranverse or longitudinally either after reflection or transmission depending on the nature of the origin of the shift. The resulting k-vector gradient of an incident planewave results in a geometric Berry phase in the k-space which manifests as a transverse shift of the beam centroid known as Imbert-federov(IF) shift. Similarly the dispersion of the Fresnel Reflection coefficients results in a longitudinal shift known as Goos- Hanchen(GH) shift. Here, we observe how the latter varies with magnetic field, in case of a partially reflected beam from two Ferromagnetic samples - Permalloy and Cobalt. Ferromagnetic samples are chosen to exploit their enhanced magnetization which is also characterized using standard polarization modulated MOKE measurements. The shifts can be both spatial(real) and angular(imaginary). We observe the angular shift which varies with the distance from the sample to the point of detection. The aim is to formulate the theory of an ENHANCED longitudinal Goos-Hanchen shift that was observed in both the samples in a typical Polar MOKE setup without any amplification tools such as Weak measurement. Goos-Hanchen shift has been identified in a lot of Nanophotonics applications such as for example, in optical heterodyne sensors, GH shift is used to measure beam angle, refractive index, displacement, temperature, and film thickness. GH shift has also been used to characterize the permittivity and permeability of different materials in optical microscopy and lithography, in detection of biomolecules etc.

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