WASHINGTON, March 15In the latest twist on optical knots, New York University (NYU) physicists have discovered a new method to create extended and knotted optical traps in three dimensions. This method, which the NYU scientists describe in the Optical Society's (OSA) open-access journal Optics Express, produces "bright" knots, where the maximum of the light intensity traces out a knotted trajectory in space, for the first time allowing microscopic objects to be trapped along the path of the knot. The method may even, one day, help enable fusion energy as a practical power source, according to the NYU team.
Optical traps can be used to confine and manipulate small objectsranging in size from a few nanometers to several hundred micrometersin 3-D. They work because variations in the intensity of the light produce forces that push small objects toward bright regions. The trapping of small objects is widely used for a broad range of research applications in biophysics, condensed matter physics and medical diagnostics.
Ordinary optical traps use Gaussian laser beams that focus to a spot. The beams being used to create extended optical traps focus instead to curves, much like the bright patterns on the bottom of swimming pools. And these bright curves can be tied in knots.
Knotted traps are made by imprinting a computer-generated hologram on the wavefronts of an otherwise ordinary beam of light. NYU undergraduate student Elisabeth Shanblatt and NYU physicist David Grier, the authors of the Optics Express paper, use a "liquid-crystal spatial light modulator" to project their holograms. This is essentially the first cousin of a conventional LCD television screen. The spatial light modulator imprints a calculated pattern of phase shifts onto the light. When the modified beam is brought to a focus with a high-power lens, the region of maximum intensity takes the form of a 3-D curve. This curve can cross over and through it
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Optical Society of America