Tiny, hollow wires can produce doughnut-shaped laser light that could be used to levitate small objects or transmit information.
Conventional lasers typically make beams that appear as a single, small point of light when they hit a surface. But for some novel communication technologies that use light to transfer information, it can be better to use lasers that produce hollow beams like a drinking straw, which appear as a ring of light when they hit a surface.
Such hollow laser beams could be used to manipulate and levitate small objects in the lab 鈥� and they could even act as an optical fibre down which other information-carrying light signals can be sent. at NTT Basic Research Laboratories in Japan and his colleagues have worked out how to make such lasers in miniature.
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They began with a small slab of sapphire, and developed a method of depositing gallium nitride 鈥� a hard, crystalline material 鈥� on its surface. They then shaped the gallium nitride into a tiny forest of hollow nanowires, each with an outer radius of a few hundred nanometres 鈥� smaller than the width of a human hair. These nanowires are the lasers.
To test their abilities, the researchers injected energy into the nanowires by illuminating them with ultraviolet light. When they used a detector to capture the light emitted by the nanowires, they noticed that the wires鈥� hollow structures 鈥� which made the light bounce around inside them before escaping 鈥� caused them to emit tubular light beams with a cross-section shaped like a doughnut. Through repeated experiments, Takiguchi and his colleagues found nanowires with a 200-nanometre outer radius made for the most efficient lasers.
at the University of Manchester, UK, says this is the first time anyone has reported building hollow nanowire lasers, which is a highly technical challenge. But it may take many adjustments before they are ready to use in a practical way. For instance, powering them with UV light is too energetically costly for most applications, and they currently produce laser light at wavelengths that are not compatible with standard communication devices, he says. 鈥淭his is an exciting proof of principle, although challenging to use in applications,鈥� says Parkinson.
ACS Photonics
