Abstract
The wavelength dependence of the Faraday effect may be measured either sequentially at particular wavelengths using narrow band sources, or simultaneously at many wavelengths using a white-light or broadband source. We apply both methods to measure the wavelength dependence of the Verdet constant of a terbium gallium garnet crystal. We show that although the white-light measurement offers the advantage of requiring only one source, it is more prone to systematic errors than using multiple laser sources.
Highlights
In 1845 Michael Faraday made a key step in the unification of optics and electromagnetism with the discovery that a magnetic field changes the polarization of light propagating in a medium [1]
The Faraday effect is important in laser physics where it is used to realise an optical diode—a device that transmits light in only one direction [2,3,4], and in Faraday filtering, where Faraday dispersion allows the realisation of narrowband filters [5,6,7,8,9,10,11,12,13,14], which are important for atmospheric and solar monitoring [15,16,17,18,19,20]
This effect is known as Faraday dispersion and can be understood by considering linearly polarised light to be an equal superposition of right and left circular polarisations
Summary
In 1845 Michael Faraday made a key step in the unification of optics and electromagnetism with the discovery that a magnetic field changes the polarization of light propagating in a medium [1]. Note that the magnetically induced rotation θB(λ) is a function of the wavelength λ, i.e. the Verdet constant depends on λ. This effect is known as Faraday dispersion and can be understood by considering linearly polarised light to be an equal superposition of right and left circular polarisations. The standard technique is to use a linear polarizer after the Faraday medium to measure the rotation. We compare measurements of the Verdet constant of terbium gallium garnet (TGG) using white-light and discrete laser wavelengths. The discrete-wavelength technique necessitates the use of many lasers to measure the Faraday dispersion, with a concomitant larger overhead. The close to ideal nature of laser sources, including a well-defined centre wavelength, small beam divergence and low intensity fluctuations makes the laser method less prone to systematic errors
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