Design and Simulation of High-Q Photonic Crystal Cavities for Nanostructured Particle Accelerators
Author
Jensen, Christian Terp
Term
4. term (FYS10)
Education
Publication year
2026
Submitted on
2026-05-29
Abstract
This project investigates two-dimensional photonic crystal cavities as candidate geometries for future nanostructured particle accelerators. A photonic crystal is a material with a periodic pattern that can control how light propagates. The work focuses on finite line-defect cavities, which were analyzed using eigenfrequency simulations in COMSOL. The aim was to identify resonance modes (oscillations of the electromagnetic field) with a high Q-factor, strong field confinement, and a longitudinal electric field component aligned with the intended particle trajectory. The cavity geometries were optimized by modifying the waveguide width, applying a cosine-shaped lattice stretch, and varying the radii of the holes in the crystal. Using these methods, an optimized 2D cavity with a Q-factor of 78120 was found. A more compact, “minimum viable” geometry was also identified, which preserved the qualitative cavity-mode profile while achieving a Q-factor of 24941. To make the geometry more directly relevant for particle acceleration, an air-defect cavity was also studied. In this design, a narrow air channel surrounded by dielectric material forms the defect. This structure supported a strongly localized mode with a very high Q-factor of 3.83 × 10^6 and an acceleration score of Sacc = 0.5256, which quantifies how effectively the longitudinal electric field can accelerate particles along the channel. The results indicate that the proposed design strategy can produce promising 2D cavity candidates for nanostructured particle accelerator applications. However, full 3D simulations are required to evaluate vertical radiation losses and the realistic performance of slab-based devices.
Dette projekt undersøger todimensionale fotoniske krystalresonatorer som mulige grundgeometrier til fremtidige, nanostrukturerede partikelacceleratorer. En fotonisk krystal er et materiale med et periodisk mønster, der kan styre lysets udbredelse. I arbejdet blev såkaldte line-defekt-resonatorer analyseret ved hjælp af egenfrekvenssimulationer i programmet COMSOL. Målet var at finde resonansmodi (svingninger af det elektromagnetiske felt) med høj Q-faktor, stærk feltindeslutning og en elektrisk feltkomponent langs den retning, som de ladede partikler skal bevæge sig i. Resonatorernes geometri blev optimeret ved at ændre bølgelederbredden, strække gitteret med en cosinus-formet overgang og variere hulradierne i krystallen. På den måde blev der fundet en optimeret 2D-resonator med en Q-faktor på 78120. Derudover blev en mere kompakt, “mindst mulige” geometri identificeret, som stadig bevarede den samme type feltmønster, men med en Q-faktor på 24941. For at gøre designet mere direkte anvendeligt til acceleration af partikler blev der også undersøgt en luft-defekt-resonator, dvs. en resonator hvor en smal luftkanal omkranset af dielektrisk materiale udgør defekten. Denne struktur understøttede en stærkt lokaliseret mode med en meget høj Q-faktor på 3,83 × 10^6 og en accelerationsscore på Sacc = 0,5256, som måler, hvor effektivt den elektriske feltkomponent kan accelerere partikler langs kanalen. Resultaterne peger på, at den anvendte designstrategi kan levere lovende 2D-resonatorer til brug i nanostrukturerede partikelacceleratorer. For at vurdere energitab i den lodrette retning og den faktiske ydeevne i realistiske, tredimensionelle strukturer kræves der dog fulde 3D-simulationer.
[This abstract has been rewritten with the help of AI based on the project's original abstract]
Keywords