When light is focused by a lens, faint rings appear around its bright central spot. These sidelobes can interfere with high-contrast imaging. In this project, I designed and fabricated a silicon nitride metasurface that changes how light passes into a lens, helping produce a cleaner focal spot. The filter was designed with broadband operation in mind, while the fabricated device was experimentally tested at 632.8 nm and showed reduced sidelobe intensity.

Optical bottle beams create small dark regions enclosed by brighter light, making them useful in optical trapping and particle manipulation. This collaborative project explored generating several such regions using a single silicon metasurface. The optical design was developed at Boston University. My contribution was fabricating the metasurface at IIT Madras, translating the provided design into precisely patterned nanoscale silicon structures.

Light-sheet microscopy illuminates a thin section of a sample so researchers can view biological structures with less background. Bessel beams are well suited to this because they stay narrow over extended distances, but their surrounding rings can wash out fine details. This research investigated combining Bessel beams in a way that preserves their useful propagation properties while reducing those unwanted rings. Experiments and imaging studies demonstrated how the resulting illumination can improve image contrast.

Related publication ↗

High-resolution light-sheet imaging over an extended depth remains a challenge. In this project, we investigated the use of specially shaped Bessel beams for excitation and fluorescence depletion. The beams were generated using dielectric metasurfaces and experimentally characterized. Their potential to produce a narrower illumination region was evaluated through numerical simulation. Improved STED resolution was not experimentally demonstrated. The associated manuscript was accepted by Applied Physics B.

A carefully designed metasurface is useful only if its nanoscale features can be reliably manufactured. This project focused on practical challenges in making beam-shaping meta-optics, particularly when using sensitive electron-beam lithography resist. By studying lithography, material behavior, etching, and pattern transfer, I investigated ways to produce more consistent nanoscale structures and improve the fabrication workflow.

Related publication ↗