'Optical Fiber' Made Out of Thin Air
Lasers were used to create a column of low-density air surrounding a core of higher-density air that acted like a conduit to channel light.
Lasers may bring to mind military-grade weaponry or the pew-pew sounds of science fiction blasters, but powerful laser tech can be used for less destructive purposes. Scientists and engineers are now aiming lasers at persistent problems like air turbulence, inoperable tumors and drug addiction. Here's a look at the ways zapping something with a beam of light can actually help rather than hurt.
J.P. Wolf / University of Geneva
Scientists -- and super villains -- have long wanted to control the weather with technology. What once seemed like a wild dream has become possible in theory. In late 2013, the World Meteorological Organization conference in Geneva held a Laser, Weather and Climate conference where participants discussed controlling lightning and condensation with laser assists.
More recently researchers at the University of Florida and the University of Arizona surrounded one laser beam with another, a technique they think could help a high-energy beam go greater distances.
In 2010, neurosurgeons from Washington University were among the first in the United States to use a laser probe on brain tumors thought to be inoperable. The team, led by chief of neurosurgery Ralph G. Dacey Jr., employed the new MRI-guided probe from Monteris Medical to kill cancer cells deep in a patient’s brain, leaving the surrounding tissue intact. Last year the laser probe, called the NeuroBlate Thermal Therapy System, was cleared by the Food and Drug Administration.
Laser beams could be the key to getting hearts beating correctly, an alternative to current electrode-based pacemakers that can do damage to heart muscle over the long-term. In 2010, scientists from Case Western University and Vanderbilt University successfully paced a live quail embryo heart with light from an infrared laser.
While we don’t quite have human optical pacemakers yet, a team from the University College London recently made headway with a separate laser-based technique. They’re hoping to create an “optical pacemaker” for the diaphragm that could help patients with motor neuron diseases like ALS breathe independently.
Apira Science Inc.
Apira Science Inc.’s iGrow helmet to combat baldness may not look serious at first, but the company says this low-level laser therapy has been proven effective at stimulating cell activity around weak hair follicles. The helmet interior has red laser and LED light diodes that go to work in multiple weekly sessions over several months.
Apria points to an article in the journal Lasers in Surgery and Medicine that concluded low level laser therapy improved hair counts for men with alopecia compared to a placebo light-up helmet.
B. Chen / NIDA
Could controlling addiction be as easy as flipping a switch? In 2013, scientists from the National Institutes of Health and the University of California were able to turn off compulsive behavior in rats through a combination of genetic engineering and laser light delivered through fiber optic cables. When they turned on a laser light in the brain region responsible for decision-making and impulse control, the compulsive cocaine seeking was gone, according to researcher Antonello Bonci.
While lasers were used for the study, techniques like noninvasive transcranial magnetic stimulation would probably be used for human trials.
Craik Sustainable Living Project, Flickr Creative Commons
A team from Leibniz University Hanover led by biosystems engineering professor Thomas Rath has been working on a way to eradicate pesky weeds with lasers. In 2012 he and his colleagues investigated mid-infrared range lasers as an alternative to herbicides.
A year later Leibniz University engineers shifted their focus and began studying the effects of near-infrared lasers on pests like aphids and whiteflies. They hope the right lase blast will safely kill the pests while leaving the host plants unaffected.
Last summer frequent fliers got a glimmer of hope for smoother travel. Researchers at the German Aerospace Center DLR’s Institute of Atmospheric Physics began testing technology that can detect turbulence, particularly the clear air kind that’s nearly impossible to predict. The device goes onboard a plane and emits short-wave ultraviolet laser radiation along the direction of flight, according to DLR. This reveals fluctuations in air density that indicate turbulence ahead. DRL has been testing the tech on flights in Europe with the goal of extending the detection distance to 20 miles.
lloydabell34, Flickr Creative Commons
Stanford University bioengineering, psychiatry and behavioral science professor Karl Deisseroth is a pioneer in using a technique called optogenetics, which involves genetically modifying neurons so they make a light-sensitive protein. Those cells can then be turned on or off with laser-based light.
Recently a group from University College London led by neurobiologist Linda Greensmith used optogenetics on paralyzed mice. Her group grafted genetically engineered motor neurons onto severed nerves in mice legs. Shining blue light on them restored nerve connectivity, reversing the paralysis.
Scientists say they have turned thin air into an 'optical fiber' that can transmit and amplify light signals without the need for any cables.
In a proof-of-principle experiment they created an "air waveguide" that could one day be used as an instantaneous optical fiber to any point on earth, or even into space.
The findings, reported in the journal Optica, have applications in long range laser communications, high-resolution topographic mapping, air pollution and climate change research, and could also be used by the military to make laser weapons.
"People have been thinking about making air waveguides for a while, but this is the first time it's been realized," says Professor Howard Milchberg of the University of Maryland, who led the research, which was funded by the US military and National Science Foundation.
Lasers lose intensity and focus with increasing distance as photons naturally spread apart and interact with atoms and molecules in the air. Fiber optics solves this problem by beaming the light through glass cores with a high refractive index, which is good for transmitting light.
The core is surrounded by material with a lower refractive index that reflects light back in to the core, preventing the beam from losing focus or intensity. Fiber optics, however, are limited in the amount of power they can carry and the need for a physical structure to support them.
Milchberg and colleagues made the equivalent of an optical fiber out of thin air by generating a laser with its light split into a ring of multiple beams forming a pipe. They used very short and powerful pulses from the laser to heat the air molecules along the beam extremely quickly.
Such rapid heating produced sound waves that took about a microsecond to converge to the centre of the pipe, creating a high-density area surrounded by a low-density area left behind in the wake of the laser beams.
"A microsecond is a long time compared to how far light propagates, so the light is gone and a microsecond later those sound waves collide in the center, enhancing the air density there," says Milchberg.
The lower density region of air surrounding the centre of the air waveguide had a lower refractive index, keeping the light focused.
"Any structure [even air] which has a higher density will have a higher index of refraction and thereby act like an optical fiber," says Milchberg.
Once Milchberg and colleagues created their air waveguide, they used a second laser to spark the air at one end of the waveguide turning it into plasma. An optical signal from the spark was transmitted along the air waveguide, over a distance of a meter to a detector at the other end.
The signal collected by the detector was strong enough to allow Milchberg and colleagues to analyze the chemical composition of the air that produced the spark. The researchers found the signal was 50 per cent stronger than a signal obtained without an air waveguide. The findings show the air waveguide can be used as a "remote collection optic," says Milchberg.
"This is an optical fiber cable that you can reel out at the speed of light and place next to that you want to measure remotely, and have the signal come all the way back to where you are."
Australian expert Professor Ben Eggleton of the University of Sydney says this is potentially an important advance for the field of optics.
"It's sort of like you have an optical fiber that you can shine into the sky, connecting your laser to the top of the atmosphere," says Eggleton. "You don't need big lenses and optics, it's already guided along this channel in the atmosphere."
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