Optical rotation of white light

Abstract

Plane-polarized monochromatic light is rotated in an optically active medium. The extent of the rotation is wavelength dependent, following an optical rotatory dispersion (ORD) curve. Typically, this phenomenon is studied by using a few discrete wavelengths. Here, we demonstrate optical rotation of white light. Corn syrup is used as the medium as large angles of optical rotation can be generated in compact containers. The Drude expression for ORD and Malus' law are used to predict the spectrum of the light transmitted as a function of the angle between polarizers located on either side of the sample. Despite the transmission spectrum of corn syrup in the absence of polarizers being unremarkable, optical rotation leads to a dramatic change in color because a “notch” is generated in the spectrum of the transmitted light. The extinction region can be translated across the spectrum by rotating the analyzer. The experimentally measured location of the region of maximum extinction and the color of the transmitted light are in excellent qualitative agreement with the predicted values. The experiment is ideal both as a lecture demonstration and for quantitative investigation in an undergraduate laboratory of the spectral distribution of light transmitted by a chiral medium.