Ph.D Student | Dahan Nir |
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Subject | Geometrical Effects on Thermal Emission Induced by Surface Waves |

Department | Department of Mechanical Engineering |

Supervisor | Professor Erez Hasman |

Full Thesis text |

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material's surface texture is of substantial importance. Thermal emission from absorbing material is regarded as spontaneous emission and accordingly is considered to be incoherent and unpolarized. The surface properties of the absorbing material have a profound impact on the emission's optical properties, and can be established by studying the excitation of surface waves: surface phonon-polaritons (SPhPs) in polar crystal and surface plasmon polaritons in metals. In this dissertation, our goal is to manipulate thermal emission utilizing the coherence and the polarization properties of the surface waves. Specifically, we modify their dynamic properties by the geometric parameters of the structure in order to overcome the limitations introduced by the intrinsic properties of the mater. For that purpose, we investigate different coupling mechanisms of the surface waves to radiative waves. In the first case, a coupled resonant cavities structure is introduced. We show that it is possible to increase the spatial coherence length of the SPhPs by more than an order of magnitude compared with the coherence of the delocalized SPhPs. In the second case, a plasmonic bandgap structure upon gold produces a van-Hove singularity in the spectral density of states. As a consequence, the emission was enhanced along with a high spatial coherence length. Furthermore, we show that the radiative modes can be controlled according to the structure geometry. When a light source rotates with respect to an observer, its frequency is shifted in proportion to their relative angular velocity. This effect is known as the angular Doppler effect. We observed a spectral doublet in thermal emission from a spatially rotated structure. The interaction of surface waves with rotational structure is essentially geometric in nature and can be regarded as an energetic manifestation of the Berry’s phase. This effect is particularly interesting since its appearance is not constrained by a unique system but arises solely due to the structure's geometry. Theoretical calculations based on rigorous coupled-wave analysis and finite difference time domain methods are presented along with experimental results.