Sathwik Bharadwaj

Accurate analysis of the electromagnetic fields inside waveguides and cavities with re-entrant boundaries is crucial for many multi-scale device applications. In earlier approaches, the singularities that exist in electromagnetic field gradients inside such waveguides and cavities significantly reduce the accuracy of the calculations. In our scheme, these singular behaviors are treated using Hermite finite elements combined with analytical regularization of the action integral. We show that this approach provides considerably higher accuracy as compared with other methods employed in the literature. Specific calculations are presented for three typical regions: (a) an L-shaped waveguide, (b) an L-cavity, and (c) a cubic cavity with an octant removed to form a triple-junction corner. The method can be adapted to evaluate very high electromagnetic fields in any complex structures displaying “hot points.”

Spinning thermal radiation is a unique phenomenon observed in condensed astronomical objects, including the Wolf-Rayet star EZ-CMa and the red degenerate star G99-47, due to the existence of strong magnetic fields. Here, by designing symmetry-broken metasurfaces, we demonstrate that spinning thermal radiation with a nonvanishing optical helicity can be realized even without applying a magnetic field. We design nonvanishing optical helicity by engineering a dispersionless band that emits omnidirectional spinning thermal radiation, where our design reaches 39% of the fundamental limit. Our results firmly suggest that metasurfaces can impart spin coherence in the incoherent radiation excited by thermal fluctuations. The symmetry-based design strategy also provides a general pathway for controlling thermal radiation in its temporal and spin coherence.