Lights off, spot on!
Researchers of the University of Twente and the FOM Foundation have managed to focus light through turbid media, by selectively blocking parts of the incident wavefront. They literally turn off the lights in order to obtain a bright spot. In the future, this can lead to methods to focus light inside biological tissue. A possible application is light therapy. The results are published in the leading American journal Optics Express on 15 February 2011.
Suppose a laser beam is sent through a piece of paper. At the back side of the paper, you see a weak speckled intensity pattern. This disordered pattern is due to interference of fields: the light waves intensify each other at some locations and weaken each other at other locations. By selectively removing parts of the wavefront, the researchers obtain a clear bright spot at a controlled location.
The new method is called 'binary amplitude modulation'. The researchers used two different modulators to focus light through the samples. One is a conventional liquid crystal-based modulator and the other a microelectromechanical system (MEMS)-based modulator. The MEMS modulator contains a million tiny mirrors that can adjust their position very fast. Using MEMS modulators, the method is relatively cheap and can work 1000 times faster than the current method (wavefront phase shaping). The fast performance is essential to focus light through dynamic media, such as biological tissue. Hence applications in medicine are brought much closer.
Referentie
Title: Focusing Light Through Random Photonic Media by Binary Amplitude Modulation
Authors: Duygu Akbulut, Thomas J. Huisman, Elbert G. van Putten, Willem L. Vos and Allard P. Mosk
Contact
Duygu Akbulut +31 (0) 53 489 5476
Complex Photonic Systems (COPS)
Faculty of Science and Technology and MESA+ Institute for Nanotechnology
University of Twente
PO Box 217
7500 AE Enschede
The Netherlands
Group website: http://cops.tnw.utwente.nl/