by Chiba University
edited by Stephanie Baum, reviewed by Robert Egan

Concept and experimental demonstration of terahertz circular dichroism imaging. Circularly polarized terahertz radiation (left: blue, right: red) interacts with a moir¨¦ metasurface, producing distinct spectral responses and spatially resolved circular dichroism distributions (top). The chirality-dependent response reverses for mirror-imaged structures, demonstrating the ability to visualize the spatial distributions of chirality. Credit: Professor Katsuhiko Miyamoto / Chiba University, Japan

In nature, there exist structures that are mirror images of each other but cannot be perfectly superimposed. These are known as chiral objects, derived from the Greek word for "hand," since left and right hands share the same relationship. Although similar in structure, chiral molecules exhibit different behaviors, and chirality is central to life itself. DNA has a twisted chiral structure, and living organisms prefer one handedness over the other. This distinction is equally important in drug design, materials science, and nanotechnology.

Probing chirality with terahertz light

One way to distinguish chiral molecules is by measuring their response to circularly polarized light in the terahertz (THz) region. THz waves lie between microwaves and infrared light and are especially sensitive to subtle collective motions and twisting structures in materials. However, conventional THz measurements average the signal across an entire sample, making it impossible to determine how chirality varies across different locations.

Now, researchers from Chiba University, Japan, and Tohoku University, Japan, have shown that this limitation can be overcome, allowing chirality to be visualized as two-dimensional images, much like creating a map of chirality across a material. The work appears in ACS Photonics.

The team and their motivation

The research team was led by Professor Katsuhiko Miyamoto from the Graduate School of Engineering, Chiba University, together with first author Ms. Uina Chiba, also from the same institute. The team also included Dr. Seigo Ohno from the Department of Physics, Tohoku University, and Dr. Takeo Minari from the Research Center for Functional Materials, National Institute for Materials Science, Japan.

"This work was inspired by a simple question. Conventional measurements only reveal averaged chirality, but what does the actual spatial distribution look like? We wondered whether directly visualizing chirality as an image could provide deeper insights, which motivated us to pursue this research," says Prof. Miyamoto.

Building a moir¨¦-type chiral metasurface

To generate regions with different chirality in the same material, the researchers built a moir¨¦-type metasurface by stacking microscopic silver disk patterns with a slight offset or rotation. These structures were fabricated at a micrometer scale so that they could strongly interact with THz light. By carefully designing the overlapping patterns, the researchers created an artificial surface containing both right-handed and left-handed twisting regions, allowing them to create and control different chiral configurations in a designed system.

When circularly polarized THz waves were directed onto the metasurface, different regions responded differently depending on their local chirality. One area showed a right-handed response, while another displayed a left-handed response. In this way, the researchers could directly visualize how chirality varied across the structure.

Unprecedented resolution and applications

The new approach could spatially resolve chirality distributions with a resolution of approximately 100 ¦Ìm, roughly the thickness of a human hair. Such alternating arrangements of right-handed and left-handed chirality within a single sheet had never been directly observed using conventional measurement techniques, which average signals across an entire sample.

"We succeeded in visualizing the coexistence of different chiralities for the first time in the world. These findings are expected to find applications in the quality evaluation of next-generation materials, the analysis of biomolecular structures, and the development of new THz devices," says Prof. Miyamoto.

Future directions for THz chirality imaging

As advances in nanofabrication make increasingly sophisticated chiral materials possible, the proposed method could provide a reliable way to examine whether these structures function as intended without damaging the material.

Looking ahead, the researchers expect to expand the technology to a broader frequency range from 2 to 15 THz, enabling more detailed structural analyses. The approach could eventually support new diagnostic techniques for visualizing abnormal protein aggregates linked to disease, help inspect advanced signal-control devices for next-generation communication systems such as Beyond 5G and 6G, and detect subtle distortions inside quantum and soft materials.

Publication details
Multiscale chirality in moir¨¦ metasurfaces revealed by terahertz circular dichroism spectroscopic imaging, ACS Photonics (2026). DOI: 10.1021/acsphotonics.6c00372

Journal information: ACS Photonics