Manipulation of Thermal Radiation Using Nano-photonic Devices
Details
Speaker:
Mr. Wah Tung Lau
PhD student
Department of Electrical Engineering at Stanford University
Date:
Thursday, 21 Aug 2008
Time:
4:00pm
Venue:
Rm 603,
Chow Yei Ching Building
Abstract:
With the advancement of nano-technology, manipulation of heat in nano-scale becomes very important. Most of the researches consider heat transfer as a diffusion process of phonons or electrons. In this talk, we will focus on heat in the form of electromagnetic waves, and see how nano-photonic devices can be used to engineer the (i) transport, and (ii) emission of heat based on various wave phenomena.
First, we will take a multi-layer photonic crystals structure as the heat-conducting medium. The crystal is composed of alternate layers of lossless dielectric slabs and vacuum such that heat is conducted only by photons. Two opposing mechanisms, evanescent tunneling of photons, and the effect of photonic band gaps, would alternatively enhance or suppress the thermal conductance of the medium. By merely tuning the thickness of the vacuum layers, we can control the relative dominance of these two mechanisms, and the medium can be switched from being thermally more conducting, to thermally more insulating, as compared to vacuum.
Next we will investigate the effect of evanescent and resonant waves on the emission of thermal fields to free space, by considering a planar lossy dielectric slab as the thermal source. At distances very closed to the slab surface, because of the evanescent waves, the energy spectral density is found to exceed the blackbody limit exponentially. Furthermore, due to guided wave resonance, alternate maxima and minima of the spectrum can be observed. We will see how these resonance fringes can be exploited to enhance or suppress radiative thermal transfer at nano-scale distances, and to realize thermal antennas where heat would be emitted directionally.
Biography of the speaker:
Wah Tung Lau is currently a PhD student in the Department of Electrical Engineering at Stanford University, under the supervision of Professor Shanhui Fan. His research focuses on theoretical and computational nanophotonics, with emphasis on the manipulation of thermal radiation using photonic crystals or other nanophotonic structures. He is an alumni of the Department of Electrical and Electronic Engineering at the University of Hong Kong, receiving his BENG degree before going to Stanford University, where he had also attained a MS degree in Electrical Engineering, and a PhD minor degree in Physics.
Enquiries:
clara@eee.hku.hk