Time and place
Wednesday, 29 April 2026, at 13:00, Building 421, Auditorium 072
Principal supervisor
Professor Rafael Taboryski, DTU
Co-supervisors
Professor Henri Jansen, DTU Nanolab
Dines Erschens, Ibsen Photonics
Kristian Buchwald, Ibsen Photonics
Examiners
Chair Senior Researcher Radu Malureanu, DTU
Professor Samuli Antero Franssila, Alto University
Head of Commercial at Quantum cph, Anil Slipsager Thilsted
Moderator at defence
Director Jörg Hübner, DTU
Abstract
Diffractive optics are nanoscopic, carefully patterned surfaces that can bend and shape light in ways ordinary lenses and mirrors cannot. They are key ingredients in technologies we rely on every day and increasingly in those just arriving: high-performance spectrometers, fiber-optic communication, laser defense systems, and the compact displays used in augmented and virtual reality.
Ibsen Photonics is a Danish company specializing in diffraction gratings. Diffraction gratings are able to split and steer light into different directions based on the light’s wavelength, and they are the building blocks of Ibsen’s product portfolio. These are made by etching periodic line patterns into fused silica (SiO2) using plasma, and while this approach works well, future optical designs increasingly require materials with a much higher refractive index to achieve better performance. One promising candidate is tantalum pentoxide (Ta2O5), a material that can manipulate light more strongly but is also much harder to pattern accurately at the nanoscale.
The work presented here develops new plasma-based etching methods to fabricate these demanding nanostructures. Instead of relying on fragile photoresist layers, the study shifts toward more robust techniques and carefully optimized plasma chemistries that allow deep, precise, and uniform etching over large areas.
Several key advances are demonstrated. Complex gas mixtures in plasma are shown to etch tantalum pentoxide efficiently, with fine control over the shape of the resulting structures. A novel reactor concept is proposed that could reduce the use of environmentally harmful gases while simplifying industrial equipment. The behavior of sulfur hexafluoride plasmas is analyzed in depth, revealing ways to make fused silica etching faster, cleaner, and more repeatable. Finally, the work shows that even complex tantalum-based nanostructures can be etched cleanly using a single gas and with good control of the process temperature.
Together, these results point toward more scalable, environmentally conscious, and industrially robust manufacturing routes for next-generation diffractive optics, helping turn cutting-edge optical designs into real-world products that shape how we see, measure, and interact with light.
