LED light unlocks 3D optical fingerprints inside materials without lasers
The study is published in Nature Photonics, and the research team was led by Professor YongKeun Park of the Department of Physics, in collaboration with Professor Seung-Mo Hong's team at Asan Medical Center and Professor Seokwoo Jeon's team at Korea University.
Some materials possess an inherent property called optical anisotropy, in which the refractive index changes depending on the direction in which light passes through. This is a decisive optical fingerprint that reveals the internal structure and molecular arrangement of the material.
There are two types of optical anisotropy. Uniaxial anisotropy refers to the case where only one direction is special, like a pencil, while biaxial anisotropy is a more general and complex case where all three directions differ, like a brick.
From DTT to LED-based iDTT
Professor YongKeun Park's research team previously developed dielectric tensor tomography (DTT), a technology capable of measuring this optical fingerprint in three dimensions, opening a path for 3D dielectric tensor measurement that had not previously existed.
However, conventional DTT required a precise laser interferometer, which caused noise in images, reduced accuracy, and made the system highly sensitive to external vibrations. In particular, there were technical limitations in expanding it to large-area samples such as biological tissues.
The iDTT developed by the research team performs a total of 48 independent measurements by precisely controlling the polarization and angle of light used in hospitals. Through this, it reconstructs in three dimensions the dielectric tensor, a 3×3 matrix that represents how a material responds to light, including refraction and absorption, in all directions. It mathematically describes the characteristics of materials whose optical properties vary depending on direction.
The core of iDTT lies in the introduction of an LED light source. By using LED illumination as an incoherent light source, iDTT fundamentally resolves these noise issues and greatly improves measurement stability and practicality.
In fact, in a direct comparison using a sample with micrometer-scale periodic molecular alignment structures, the research team confirmed that iDTT clearly reconstructed fine structures that were almost invisible due to noise in conventional laser-based DTT.
The iDTT technology is expected to be applicable across materials science, semiconductors, pharmaceuticals, biomedicine, and displays.
The research team succeeded in making visible in three dimensions how molecules are arranged inside liquid crystal particles. They also precisely observed fibrosis, a phenomenon in which tissue hardens in colon tissue after radiation therapy without any additional staining.
In addition, even when different crystalline materials such as quartz and calcium chloride were mixed together, the system automatically distinguished each material based solely on differences in their response to light (anisotropy), without chemical analysis.
Furthermore, in materials composed of multiple crystals, the technology nondestructively analyzed the orientation of each small crystal and whether the crystals were well aligned with each other (coherence) or misaligned (incoherence). Through this, the team confirmed that iDTT is a new analytical method capable of connecting microscopic internal structures with physical properties such as material strength.
Professor YongKeun Park stated, "This study suggests the possibility of replacing material anisotropy measurements that previously relied on large-scale facilities or destructive analysis with compact optical microscopy," adding, "As stable dielectric tensor measurements are now possible using LEDs, this technology will become a new standard for nondestructive precision analysis used across various industrial fields."
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