Manipulating thermal radiation using nano-photonic structures
By: Gaurang Ravindra Bhatt
Publisher: [publisher not identified]
Published: 2022
Place of publication: [New York, N.Y.?]
Language: eng
Description: Emission of electromagnetic radiation due to the temperature of a body is an inherent property in nature. Electromagnetic radiation sources relying on thermal emission are critical in application of energy harvesting, lighting, spectroscopy and sensing. However, many of these sources, typically made of several hundreds of microns thick bulk objects, are inefficient and radiate much less power than an ideal blackbody. In the first part of this work, we demonstrate an efficient thermal emitter based on material films that are nanometers thin. Nano-film based thermal sources are generally poor emitters, but have received much interest lately since they require significantly lower heating power compared to their bulk counterparts. We show a novel approach for realizing thin-film based blackbody emitters by placing them inside an external optical cavity, engineered to provide enhancement of thermal emission while maintaining a constant temperature. Our approach is independent of the emitter material and can be tuned to operate at any temperature since the optical elements and the emitter are physically disconnected.

The work opens new avenues for realizing blackbody-type thermal sources consuming significantly lower heating power than the current state-of-art, thus suggesting direct applications in lighting, spectroscopy and energy harvesting. Furthermore, we utilize the nano-film broadband emitters for demonstrating heat transfer that beats conventional blackbody limit at deep-subwavelength distances. We demonstrate the first of its kind, fully integrated and re-configurable thermo-photovoltaic on silicon platform. We report over an order of magnitude increase in generated electrical power by electro-statically tuning the distance between a suspended hot emitter TE ~ 880 K) and an underlying detector (maintained at TD ~ 300 K) from ~500 nm to ~100 nm. We believe this demonstration will be influential for the fields of active energy harvesting as well as in realizing integrated thermal control systems. In the third part of this work, we shift our focus away from broadband emitters, towards spectrally narrow band thermal emitters and propose a novel technique for long-distance transport of thermal radiation.

In order to do so, we rely on enhanced near-field heat transfer over blackbody limits aided by surface plasmon polaritions (SPP). We then show that a dispersion engineered sub-wavelength waveguide can allow required states for SPP aided electromagnetic emission to propagate. We show computational analysis of the a composite structure using the open-source electromagnetic solvers SCUFF-EM that captures the effects of surface current distribution induced electromagnetic field effects inside and outside the emitter. We furthermore show a prototype structure of the proposed thermal-waveguide with doped silicon emitters that support SPP. We discuss the measurement technique and present preliminary results of thermal transport over a waveguide that is ~34 μm long. We believe that our proposed approach shown here could advance the field towards development of novel devices for thermal control.
Notes: Department: Electrical Engineering.

Thesis advisor: Michal Lipson.

Thesis (Ph.D.)--Columbia University, 2022.