[MOS] November 4, 2008

[Zina Queen]

Seminar on

Modern Optics and Spectroscopy

Opaque lenses:  Using disorder to bring laser light to a focus

Allard Mosk,
University of Twente, The Netherlands

Tuesday, November 4, 2008

12:00 - 1:00 p.m.



Materials such as white paint, skin or bone are opaque because they 
have a microscopic disordered structure that scatters light. Light 
impinging on such a material becomes diffuse and only a fraction of 
it is transmitted. By controlling the shape of the incoming 
wavefront, using a two-dimensional spatial phase modulator, we can 
cause coherent light to interfere constructively at a target point 
behind the sample. We find that at the target point, the light forms 
a tight focus that is up to 1000 times brighter than the diffuse 
background.

Theorists have predicted that in any non-absorbing disordered sample 
there exist open eigenchannels: specific linear combinations of 
incoming waves which experience a transmittance of nearly one. Such 
eigenchannels have not been directly observed in condensed matter 
systems, however, they are the cause of phenomena such as universal 
conductance fluctuations. By carefully constructing a suitable 
wavefront we find we can selectively couple light to the open 
eigenchannels in a disordered optical material. As a result, the 
total diffuse transmittance increases. The magnitude of the increase 
is exactly as predicted by random matrix theory.



Grier Room, MIT Bldg 34-401
Refreshments served after the lecture
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