I want to talk about light

What a poetic opening to your talk! This is what Sir John Pendry did when he gave a talk at the IIN Symposium few months back. He then went to describe light as the dance between electricity and magnetism, where the rhythm of the dance is the frequency of the light (I can’t remember his exact wording, but it was something similar). In order to reinforce the importance of the subject he is talking about - light, he also make the analogy that, “… in English, we use I see to mean I understand …”. Whoa, such connection has never come across my mind! Well, I guess it is partially due to that English is not my native language.

The topic Pendry was actually talking about is metamaterial. From my standpoint, it has become a very popular topics, spearheaded by Pendry himself. To educate myself, I found the wikipedia entry (where else!) quite informative. Also, both David Smith and Douglas Natelson have written very good pieces about it. Back to Pendry’s talk, he stated that he wants to bend light, but not to just simply bend it like a lens will do, but to have the light conformally go around a subject, hence hiding the object. Here is where the metamaterial come into play: its job is to guide the light around the object. (see figure taken from Pendry’s paper)

Materials in nature can not do that, since they’re made from mostly identical constituents, hence they have homogenous optical properties. But nanotechnolgy provides a viable solution since now we can design and make structures that with dimension smaller than the (visible) light’s wavelength. That defines metamaterial, and one just needs to design the constituent structure cleverly according to how one wants to manipulate the light.

Other than cloaking, what else can metamaterials do? One thing is to enable negative index of refraction (e.g. Veselago lens), to bend the light in the “wrong” direction. Then some exotic, or total unexpected behavior can happen. Pendry gave a very vivid example: if the index of refraction of water is made negative, then a fish swimming in the water will appear to be floating above the water in the air.

What else we can do with this? Instead of hiding a massive object (cloaking), one can then instead magnify a tiny particle, whose dimension might be much smaller than the visible light’s wavelength. The method is to “coat” the tiny particle with a metamaterial-made cloth, which direct the incident light away, to make a large shadow.

I walked away from Pendry’s talk with the false sense that I have totally understood metamaterials. But isn’t that what I am looking for from a talk like this, that I remember the big message clearly, even few months later? One of such experiences is a talk given by Paul McEuen few years back in the APS March meeting (my first March meeting), about their work on spin-orbit coupling in Carbon Nanotube (paper here). More to come please!