Measuring the Faraday effect in olive oil using permanent magnets and Malus’ law

Abstract

We present a simple permanent magnet set-up that can be used to measure the Faraday effect in gases, liquids and solids. By fitting the transmission curve as a function of polarizer angle (Malus' law) we average over fluctuations in the laser intensity and can extract phase shifts as small as ± 50 µrads. We have focused on measuring the Faraday effect in olive oil and find a Verdet coefficient of V = 192 ± 1 deg T −1 m −1 at approximately 20 • C for a wavelength of 659.2 nm. We show that the Verdet coefficient can be fit with a Drude-like dispersion law A/(λ 2 − λ 2 0 ) with coefficients A = 7.9 ± 0.2 × 10 7 deg T −1 m −1 nm 2 and λ 0 = 142 ± 13 nm.

Komponenten der Messunsicherheit eines Faraday-Magnetometers

“…Hierbei wird die anregende Flussdichte als bekannt vorausgesetzt und die Drehung Δϕ als Funktion der Empfindlichkeit betrachtet. Die Anwendung betrifft Materialien mit hohen Verdet-Konstanten, wie beispielsweise Pflanzenöle [25]. Olivenöle lassen sich hierüber unter anderem hinsichtlich ihrer Reinheit oder chemischen Degradation aufgrund von schlechten Lagerungsbedingungen untersuchen [12].…”

White-light versus discrete wavelength measurements of Faraday dispersion and the Verdet constant

“…Measurements of the Faraday effect and Faraday dispersion have become a staple of the undergraduate optics laboratory [27][28][29][30][31][32][33][34][35][36][37][38]. The standard technique is to use a linear polarizer after the Faraday medium to measure the rotation.…”

“…To characterise Faraday dispersion, we can either measure the rotation at discrete wavelengths [35,37] (vertical lines in figure 1) or at all wavelengths simultaneously using white light [22] (horizontal lines in figure 1). The white-light technique has also been used to measure optical rotation in other circularly birefringent media such as sugar solutions [39].…”

Optical rotation of white light

“…An experimental investigation of ORD of a chiral liquid yields insight into the decomposition of linearly polarized light in a circular basis and light-matter interactions; consequently, it is a wellstudied undergraduate laboratory activity, providing an attractive complement to studies of the Faraday effect. 3 An overview of the typical experimental apparatus and technique used can be found, for example, in Refs. 4 and 5 or 6.…”