Applied Physics

Hitting the Spot in 3D

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Science  10 Dec 2010:
Vol. 330, Issue 6010, pp. 1457
DOI: 10.1126/science.330.6010.1457-a

High-density optical storage media, high-resolution spectroscopy, and surface imaging rely on the ability to focus a beam of light to as small a spot as possible. There are limitations, though, to how small a spot can be made. Certain tricks can be used, such as manipulating the phase of the incident light, so that interference effects can bring the size down close to and even beyond the diffraction limit. Because the light is incident from just one side, such tricks tend to concentrate on focusing the spot only in the two-dimensional (2D) plane and ignore the out-of-focus features along the optic axis. To provide focusing in a small volume, Mudry et al. address the asymmetry of light incidence by placing a mirror behind the focal plane. Their trick is to apply a time-reversal process, which just means that the illumination wavefront is shaped with a spatial light modulator so that the incident and reflected beams converge at the same point. Such a technique of focusing light to a small volume should be useful in 3D imaging applications.

Phys. Rev. Lett. 105, 203903 (2010).

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