Peering inside 3D chaotic microcavities with X-ray vision

In the world of optics, tiny structures called microcavities—often no wider than a human hair—play a crucial role in technologies ranging from lasers to sensors. These microscopic resonators trap light, allowing it to circulate millions of times within their boundaries. When perfectly shaped, light inside them moves in smooth, circular paths. But when their symmetry is slightly disturbed, the light begins to behave unpredictably, following chaotic routes that can lead to surprising effects like one-way laser emission or stronger light–matter interactions.

Until now, most research on this chaotic behavior has focused on flat, two-dimensional microcavities. These are easier to study because their shape can be seen and measured under a microscope. But truly three-dimensional (3D) microcavities—where deformation occurs in all directions—have remained largely unexplored. Their internal geometry is difficult to capture without cutting or damaging the sample, making it hard to understand how light behaves inside them.

A new study published in Advance Photonics Nexus changes that. An international team of researchers has developed a way to image and analyze 3D chaotic microcavities without harming them. They used X-ray microcomputed tomography (µCT), a technique commonly found in medical and materials science labs, to scan a slightly deformed silica microsphere. This allowed them to reconstruct its full 3D shape with submicron precision.

With this detailed model, the team could calculate how light travels through the deformed cavity. They found that when the shape is distorted in multiple directions, light doesn’t just bounce around randomly—it spreads throughout the entire cavity in a process known as Arnold diffusion. This confirms a long-standing theoretical prediction about 3D chaotic light dynamics.

According to Professor Síle Nic Chormaic, corresponding author on the report and director of the Light-Matter Interactions for Quantum Technologies Unit at Okinawa Institute of Science and Technology Graduate University, “This work opens a new window for exploring 3D wave chaos, nonlinear optics, and quantum photonics. Beyond fundamental studies, the approach could inspire new designs for high-sensitivity sensors, broadband microlasers, and complex optical networks that harness chaotic dynamics for enhanced performance.”

The ability to measure and predict light behavior in these complex structures opens new possibilities for both fundamental science and practical applications.

For details, see the original Gold Open Access article by K. Tian et al., “X-ray microcomputed tomography of 3D chaotic microcavities," Adv. Photon. Nexus 4(6), 06606 (2025), doi : 10.1117/1.APN.4.6.066006.