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color="#000000"><b>Seminar on</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Modern Optics and Spectroscopy</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><i><b>Opaque lenses: Using disorder to bring
laser light to a focus</b></i></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Allard Mosk</b>,</font></div>
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color="#000000">University of Twente, The Netherlands</font></div>
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<div align="center"><font face="Times New Roman"
color="#000000">Tuesday, November 4, 2008</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">12:00
- 1:00 p.m.</font></div>
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<div><font face="Times New Roman" color="#000000">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.</font></div>
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<div><font face="Times New Roman" color="#000000">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.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">Grier
Room, MIT Bldg 34-401</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Refreshments served after the lecture</font></div>
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