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27. Aug. 2025
Cutting-edge science can be done even with ordinary potato starch. This is the conclusion reached by physicists from the Brno University of Technology and Palacký University in Olomouc, who studied the optical properties of potato starch grains. They discovered that, thanks to their unique structure, starch granules function as micro-lenses that can simultaneously focus an optical beam, change its polarization, and spin it into a vortex of light. From a physical point of view, starch performs spin-orbit conversion of light, which until now has only been possible with advanced nanotechnologies. The discovered mechanism expands the possibilities for controlling light and can be used for next-generation sensors, information transmission, and quantum computers.
"Our interest in starch was sparked by commonly available images from a polarizing microscope, in which the shapes of individual grains resemble the Maltese cross. It has long been known that these patterns are created by the special internal arrangement of starch grains. However, we focused on the full optical response of these grains and suspected that it might be related to the original way in which the polarization rotation of the electric field changes into the vortex motion of electromagnetic energy. In optical terminology, this interaction represents a change in the spin of light to its orbital angular momentum and is currently widely studied and used in classical and quantum physics," recalls Petr Bouchal, a physicist at BUT who initiated the research.
"The path to confirming our ideas was not easy. To fully understand the effects, it was necessary to perform an optical description of the internal structure of the starch grain. This consists of approximately spherical shells, similar to those found in onions, for example, but containing regularly arranged and radially oriented lamellae. The grain affects light in a special way. It changes the optical path of light in a similar way to a normal lens, but it also shapes it thanks to effects related to the change in the polarization state of light caused by lamellae pointing towards the center of the grain. It was extremely difficult to experimentally prove the interaction of both simultaneously occurring effects," adds Bouchal, who, together with Radim Chmelík, is behind the designs of special, previously patented microscopes used in the measurements.
"A good understanding of the interaction of light with starch grains and its reliable description proved the possibility of determining the polarization state of light incident on the grain directly from the focal trace captured by a conventional detector. We experimentally verified this simple yet reliable method of polarization measurement and even attempted to construct an original sensor that simultaneously measures the shape of the wavefront and the polarization state of light, which varies at different points on the wavefront. Although the shape heterogeneity of natural starch grains made it impossible to carry out the experiments to the originally intended extent, the functional principle of the sensor was clearly demonstrated," adds physicist Petr Viewegh, who participated in these experiments together with his colleague Petr Liška.
"The simultaneous measurement of wavefronts and spatially variable polarization of light is important for practical applications and presents a challenge for further research. Routine measurement would require the creation of an extensive matrix of grains with nearly identical parameters, which is not possible with natural starch. However, a viable approach is to create an artificial structure that more perfectly mimics the optical response of starch grains," believes Viewegh, who deals with the preparation of such materials.
Zdeněk Bouchal from Palacký University in Olomouc joined the research team of scientists from the Faculty of Mechanical Engineering and CEITEC at Brno University of Technology, consisting of Petr Bouchal, Petr Viewegh, Petr Liška, and Radim Chmelík. He created the theoretical framework for the experiments and performed the necessary calculations. The result of this collaboration is an article in the prestigious journal Advanced Optical Materials entitled Spin-Orbit Photonics with Potato Starch Lenses.
Research into natural starch grains shows how perfect the tools and structures available to nature are. "The ingenious optical effects revealed by our research are not limited to the starch under investigation, but are inherent in a wide range of structures known as spherulites. The spin-orbit effects, which we have explored theoretically and verified experimentally step by step, hold promise for the design of new optical components, sensors, and photonic chips, and open the way for applications in materials diagnostics and optical communications," concludes Bouchal.
Author: Iveta Hovorková
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