Multispectral Imaging via a Single Metasurface Structure: A Robust Platform for Optical Security

Multispectral imaging is a sophisticated technique used in various fields like remote sensing, astronomy, art conservation, agriculture, and medicine. It involves capturing image data at specific wavelengths across the electromagnetic spectrum, beyond the visible range. Unlike traditional photography that captures images in the visible spectrum (red, green, blue), multispectral imaging extends to other wavelengths, including infrared, ultraviolet, and sometimes even X-rays. These images which are captured in multiple bands where each band records a different portion of the spectrum, providing unique information not visible in regular light. For example, in remote sensing, different bands can highlight vegetation health, water bodies, or geological features. The industrial applications of multispectral imaging are significant for example in it is used in satellites and aerial surveys to study Earth’s surface, monitor environmental changes, assess agricultural lands, and map geological features. It can be used for diagnostic purposes, like identifying different tissues and their conditions. Moreover, it helps in monitoring crop health, soil conditions, and managing resources.

In a new study published in the ACS Applied Materials & Interfaces by Dongkyun Kang, Yeongseon Kim, and led by Professor Myeongkyu Lee from the Department of Materials Science and Engineering at Yonsei University, the researchers discussed the development of a multispectral imaging technique using a planar cavity-type metasurface, aimed at enhancing optical security applications such as identification, authentication, and anti-counterfeiting. The researchers created a multilayered structure that records both visible and infrared images independently on solid surfaces. This innovative approach demonstrates a significant advancement in optical security technology by enabling the simultaneous recording of distinct color and thermal images in a single structure, which is both flexible and robust against bending.

The authors developed a multispectral imaging technique using a planar cavity-type metasurface. This technique is designed to simultaneously record visible and infrared (IR) images on solid surfaces. The team designed a planar cavity structure consisting of a Color Control Unit (CCU) and an Emission Control Unit (ECU). The CCU’s role was to control the visible color by varying its thickness, while the ECU was responsible for spatially tuning the IR emission through a laser-induced phase change in a Ge2Sb2Te5 (GST) layer. The structure was fabricated on various substrates, including silicon, plastic, and paper. The key to its functionality was in how the visible and IR images were independently recorded due to the unique properties of the CCU and ECU. A pivotal part of the process involved the laser-induced phase change in the GST layer within the ECU. This allowed for the selective crystallization of the GST film, which played a crucial role in controlling the IR emission pattern. The researchers manipulated the thickness of the CCU and the phase change in the ECU, which resulted in simultaneously imprint distinct color and thermal images onto the same structure. This dual-recording capability is what makes their approach innovative in the realm of optical security.

The most notable achievement for the authors in the new study was the ability to imprint both color (visible) and thermal (IR) images on the same structure without interference between the two. This dual capability offers a new level of security in applications like anti-counterfeiting and authentication. The metasurface proved to be both flexible and durable, with the capacity to be fabricated on different substrates and remain stable against bending. This broadens its potential applications in various fields. The researchers demonstrated that both the color and emission intensity of the images could be spatially modulated within the structure. This adds an extra layer of security, as it makes the reverse engineering of the captured images more challenging. The study’s findings suggest a promising new direction for optical security technologies. The unique properties of the multispectral imaging technique can be leveraged for advanced identification, authentication, and anti-counterfeiting measures.

In conclusion, Professor Myeongkyu Lee and colleagues presented a pioneering approach in multispectral imaging, offering a robust and versatile platform for optical security. By integrating innovative materials and laser technologies, this research unlocks new horizons in creating secure and tamper-proof visual markers. The findings not only contribute significantly to the field of optical security but also set a precedent for future explorations in multispectral imaging and its applications.