A newly developed ultrasensitive Faraday optical rotation device

Abstract

Faraday rotation is a magneto-optical phenomenon defined as the rotation of the polarization plane of light passing through a transparent isotropic sample in the presence of an external longitudinal magnetic field that causes an induced difference between the refractive indices for right and left circularly polarized light inside the sample. In this paper, we present the details of a newly developed ultra-sensitive Faraday rotation device consisting of a GaN-based light emitting diode as the light source of wavelength range 400 – 480 nm. Two linear polarizers are used; the first polarizer is placed before the quartz sample cell to set a reference polarization angle while the other polarizer is connected to a stepper motor which is configured to change the polarization angle of the light beam exiting the cell. A ring permanent magnet is coaxially fitted around the quartz cell and is employed to generate a strong external magnetic field of ~ 1 Tesla. The detection system consists of a sensitive and fast light detector coupled with an electronic circuit board which is configured to record the finest Faraday rotation angle in the polarization direction of the transmitted light relative to the reference polarizer. In addition to the experimental details, the modes of operation and sensitivity of the device will be also presented.