Nanophotonics: Discovering the Magic of Light in Nanostructures

author: Evelyn Hu, Harvard School of Engineering and Applied Sciences, Harvard University
published: Jan. 6, 2014,   recorded: March 2008,   views: 3262
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Description

Evelyn Hu meticulously describes designing and building a new generation of optical materials from nano-sized elements. She hopes to harness “the magic of light in nanostructures.”

Hu walks through her research of exploring and exploiting the properties of different optical materials. She first cites the most important aspects of an optical material, such as its color (emission and absorption wavelength); its ability to convert energy efficiently; how long it remains excited when stimulated; and whether we “get more output than we put in.”

Hu looks for optical material in nature, then superimposes another pattern on it, substantially transforming it at the atomic level. In one case, she uses gallium arsenide of a wavelength or so thickness, and pokes such tiny holes in it that photons of light behave differently when they encounter the structure. As Hu says, “I’m sculpting out a particular environment for photons.” Her gallium arsenide nanostructures contain a tiny cavity or “sweet spot” that creates a high intensity electromagnetic field that interacts in a specific way with photons and atoms. Each structure has a unique optical signature. Hu makes an analogy to an organ pipe, an acoustic resonator, which due to its unique geometry, produces a different pitch as air moves through it.

Hu goes on to describe how a nanostructure works with simple low energy, high energy electron states, and how the cavity exerts influence on atoms to create a relationship between electronic and photonic states, what she calls “weak coupling.” Hu has also been mixing matter and light to create new quantum states. She describes placing an atom precisely in the sweet spot, exciting it to release a photon, changing the photon’s state and stimulating an atom again: “If I do this procedure exactly right… we can transfer energy between the environment and the atom almost forever.”

To achieve the optimal effect, atoms and photons must behave predictably and do as they’re directed. To accomplish this, Hu and colleagues have fashioned semiconductor quantum dots 50 angstroms wide as tunable optical emitters, and fabricated photonic crystal membranes with patterns etched out by electron beams. Hu’s found she can control and manipulate the release of photons more and more precisely within her nano environments, creating new quantum mechanical states, and exerting a “much more powerful influence on the nature of light.” This work, concludes Hu, has “profound implications for processing information.”

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