Optically Active Materials: Physicists Solve Problem that is More than One Hundred Years Old

Optically Active Materials: Physicists Solve Problem that is More than One Hundred Years Old

The orientation of the electric field associated with the light is commonly referred to as polarization. Although one cannot perceive it with the naked eye, it is applicable in many ways in everyday life. It is used, for example, to perceive 3D effects in the cinema or to avoid reflections. Whereas in glass and many transparent plastics the polarization is maintained after the passage of the light beam, in materials with a so-called chiral structure in which the right-left symmetry is broken, the polarization direction is rotated. These materials are called optically active. Physicists at Leipzig University have achieved a breakthrough in describing the properties of these materials. Their research results have now been published in the renowned journal "Optics Letters".

With this new ellipsometer the polarization-sensitive measurements were carried out. Photo: Chris Sturm/Leipzig University

The description of the properties of optically active materials and their interaction with light is performed with so-called material equations. Well-known physicists developed different models for these equations at the beginning of the last century. An experimental verification of the applicability and validity of these different equations was previously not possible with the usual transmission experiments.

Researchers of the Felix Bloch Institute at Leipzig Univwersity around Prof. Dr. Marius Grundmann recently were able to check the validity of the different models for the material equations based on experimental results. They determined the optical activity with polarization-sensitive reflection measurements. They studied potassium titanyl phosphate, which is used among others in green laser pointers, and evaluated the measured polarization change of the reflected light with different models. They succeeded in determining the optical activity of the potassium titanyl phosphate in the experiment. "This experiment is one of the few available experiments of this kind," says Grundmann. The researchers at Leipzig University were also able to prove experimentally for the first time that only material equations which are symmetric with respect to electric and magnetic fields bijectively and correctly describe the optical properties and thus also the optical activity and the interaction of the light with the material.

A typical representative of an optically active material found in almost every household is sugar. Fructose or glucose, for example, can be distinguished by the direction of their polarization rotation. Among other things, the optical activity has practical significance in determining the purity of materials, for example in medicaments, which can achieve very different effects in left- or right-handed execution

The work of the physicists of the Felix Bloch Institute was supported by the German Research Foundation. The experimental work was carried out by the scientists using a major research instrument approved by the Sächsischen Aufbaubank (SAB) in the project "COSIMA" within the framework of the program "Verbesserungen der Forschungsinfrastruktur und Forschungsvorhaben mit jeweils anwendungsnaher Ausrichtung" by the Saxon State Ministry of Science and the Arts.

Reference:
C. Sturm, V. Zviagin, M. Grundmann
Applicability of the Constitutive Equations for the Determination of the Material Properties of Optically Active Materials
Optics Letters 44, 1351 (2019)

Source:
Translated from the Press Release of Leipzig University

Further Information:
Prof. Dr. Marius Grundmann
Felix Bloch Institute for Solid State Physics
Tel.: +49 (0) 341 97-32 650
Email | Website

last modified: 15.05.2019

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