Optical boomerangs, ultralight fractal materials, and more

(Press-News.org) Optical Boomerangs P. Aleahmad et al. Physical Review Letters (forthcoming)

P. Zheng et al. Physical Review Letters, 109, 193901 (2012)

Bending light around corners is usually done with mirrors, but now scientists have realized self-bending light beams that propagate along curved paths.

Two independent groups have reported experiments on special light waves that can skid around curves. The researchers demonstrated that modified laser beams can be made to move along parabolic and elliptical paths. Furthermore, if obstacles are in their path, these beams can self-heal, regrouping and continuing on their way. The research shows that such self-bending behavior can be achieved in both two and three dimensions. These sort of "optical boomerangs" could be used to move particles around with laser tweezers, or to manipulate optical data on an optoelectronic chip.

Ultralight Fractal Materials Daniel Rayneau-Kirkhope, Yong Mao (contact author), Robert Farr Physical Review Letters (forthcoming)

Researchers have studied theoretically how ultralight materials can be built based on a fractal design: a geometry whose patterns look the same when observed at different scales.

Their design strategy is based on a hierarchical approach: elementary units are first assembled that can be used as building blocks for the next level of assembly. The resulting structures, reminiscent of the metal frame of the Eiffel Tower, are to a large extent hollow, yet they are predicted to retain the same mechanical properties of standard materials. The scheme is particularly suited to design large structures with limited load, such as solar sails that propel spacecrafts, whose weight may be reduced by a factor of 100 or more.

Meson Decay Shows the Arrow of Time Jean-Pierre Lees et al. Physical Review Letters (forthcoming)

By measuring the decay of certain subatomic particles called B- mesons, scientists have found the first evidence that, even at the microscopic level, time flows in a preferred direction.

While most things in the macroscopic world only get older, many of the fundamental laws of physics are perfectly time-symmetric: according to the standard model most physical process can be "rewound" to go exactly back to where they started. According to theory, an exception is the electroweak interaction, the force responsible for the radioactive decay of nuclear subatomic particles. The BaBar collaboration at the SLAC National Acceleration Laboratory at Stanford has now proven this experimentally. BaBar compared the decay of B-mesons, running the process in both the forward and backward direction. The result showed that the decay is different in the two cases, providing the first direct experimental evidence for the violation of time reversal symmetry.

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