Biological systems offer structural and functional solutions that often exceed those of engineered materials. Among them, diatoms — single-celled microalgae enclosed in highly ordered silica shells called frustules — have attracted particular attention as natural photonic crystals. Their nano- and microstructured architecture is known to support a range of light-management phenomena, including focusing, waveguiding, and spectral filtering, all of which potentially contribute to efficient photosynthesis. One of the predicted but experimentally elusive optical phenomena in diatom frustules is the Talbot effect: a near-field self-imaging of a periodic structure under coherent illumination. In natural frustules, the Talbot distance is on the order of a few micrometres, which makes direct visualisation of the longitudinal field evolution extremely challenging.
In a new paper published in Light: Advanced Manufacturing , a team of scientists led by Dr. Julijana Cvjetinovic from the Skolkovo Institute of Science and Technology (Skoltech), together with colleagues from the Kurchatov Complex of Crystallography and Photonics (NRC "Kurchatov Institute"), the Osipyan Institute of Solid State Physics RAS, and the Prokhorov General Physics Institute RAS, experimentally demonstrated the Talbot effect in a diatom-inspired three-dimensional structure in the terahertz (THz) regime. To overcome the resolution limits of current 3D printing technologies and the difficulty of probing the near field inside an intact biological frustule, the researchers applied geometric scaling: rather than trying to replicate the submicron features of the natural shell, they enlarged its architecture by a factor of approximately 2,000 while preserving its lateral periodicity, and probed it at proportionally longer wavelengths in the THz range. The scaled biomimetic models were fabricated using liquid crystal display (LCD) 3D printing and characterised at a wavelength of 911 µm, with hole sizes ranging from 100 µm to 1 mm. This approach extended the Talbot distance from micrometres to millimetres, making the longitudinal self-imaging process directly accessible to experiment. The experimental intensity distributions, recorded along and perpendicular to the propagation direction, agree well with numerical simulations performed using the Fourier modal method. At a distance of 4.6 mm behind the structure, the intensity at the focal points reached about half of that of the incident beam.
The fabricated structures replicate the native three-layer architecture of the diatom valve — the outer cribrum, the intermediate honeycomb-like areola walls, and the inner foramen plate — and reveal the distinct optical role of each layer. The cribrum, whose periodicity is much smaller than the working wavelength, behaves as an effective homogeneous medium, while the foramen layer and the areola network, with periodicities comparable to the wavelength, support pronounced near-field interference. The scientists summarise the rationale behind their approach:
"Natural diatom frustules predict Talbot self-imaging on a micrometre scale, which is hard to resolve experimentally inside a three-dimensional biological object. By scaling the geometry up by about 2,000 times and moving into the THz range, we kept the dimensionless ratio of wavelength to period unchanged and stretched the Talbot distance to the millimetre scale. This made it possible to directly map the longitudinal evolution of the field behind the structure and to separate the contributions of individual layers of the frustule architecture."
"The same scaling strategy gives an experimentally accessible platform for diatom-inspired photonics. The fabricated structures act as flat, three-dimensional diffractive elements: they redistribute the incident THz radiation into a regular array of localised 'hot spots' whose intensity reaches about half of that of the incoming beam. The calculated and measured Talbot periods agree to within experimental uncertainty," they added.
"Beyond confirming a classical optical phenomenon in a biomimetic, three-dimensional structure, this work provides a scalable route to fabricating bioinspired THz components. Such designs can serve as flat focusing optics, tunable resonant filters, and wavefront modulators, and they remain fully compatible with low-cost additive manufacturing. We see this as a step toward bringing nature-derived photonic architectures into modern THz systems, light-harvesting devices, and smart sensing technologies," the scientists conclude.
This research received funding from the Russian Science Foundation under grant No. 25-74-00119.
Light: Advanced Manufacturing
Talbot effect in diatom-inspired structures in the THz range