A newly developed ultra-sensitive Faraday optical rotation device

摘要

Faraday rotation is a magneto-optical phenomenon defined as the rotation of the polarizationplane of light passing through a transparent isotropic sample in the presence of an externallongitudinal magnetic field that causes an induced difference between the refractive indices forright and left circularly polarized light inside the sample. In this paper, we present the details of anewly developed ultra-sensitive Faraday rotation device consisting of a GaN-based light emittingdiode as the light source of wavelength range 400 – 480 nm. Two linear polarizers are used; thefirst polarizer is placed before the quartz sample cell to set a reference polarization angle whilethe other polarizer is connected to a stepper motor which is configured to change the polarizationangle of the light beam exiting the cell. A ring permanent magnet is coaxially fitted around thequartz cell and is employed to generate a strong external magnetic field of ～ 1 Tesla. Thedetection system consists of a sensitive and fast light detector coupled with an electronic circuitboard which is configured to record the finest Faraday rotation angle in the polarization directionof 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.