Guiding currents across specific paths in a controlled manner could allow protection against lightning strikes and high-voltage capacitor discharges, said Demetrios Christodoulides of the Center for Research and Education in Optics and Lasers (CREOL), part of 麻豆原创鈥檚 College of Optics & Photonics.

The team鈥檚 research was published today in 鈥淪cience Advances.鈥�

Using these judiciously shaped laser beams to produce electric discharges that unfold along a predefined course 鈥渃an even circumvent an object that completely occludes the line of sight,鈥� said Christodoulides, a Pegasus Professor of Optics and the Cobb Family Endowed Chair.

In some fields, electrical discharges are already used for things such as assisting the milling process, fuel ignition in combustible engines, and controlling hydrodynamics of high-speed gases, but developing ways to control and shape the path of an electrical spark has remained a challenge.

The recent introduction of 鈥渟elf-bending Airy beams,鈥� a non-diffracting waveform that gives the appearance of bending as it travels, opened up the opportunities of creating curved trajectories for the electrical discharges. By manipulating the shape of the laser, it is possible to control the trail of a spark.

Christodoulides was part of the 麻豆原创 team of researchers that created and observed an Airy beam for the first time in 2007. The new research published today is by Christodoulides and scientists from the Institut National de la Recherche Scientifique in Montreal, San Francisco State University, and four other institutions in Scotland, France and China.

The solution? Surround the beam with a second beam to act as an energy reservoir, sustaining the central beam to greater distances than previously possible. The secondary 鈥渄ress鈥� beam refuels and helps prevent the dissipation of the high-intensity primary beam, which on its own would break down quickly. A report on the project, 鈥淓xternally refueled optical filaments,鈥� was recently published in Nature Photonics.

Water condensation and lightning activity in clouds are linked to large amounts of static charged particles. Stimulating those particles with the right kind of laser holds the key to possibly one day summoning a shower when and where it is needed.

Lasers can already travel great distances but 鈥渨hen a laser beam becomes intense enough, it behaves differently than usual 鈥� it collapses inward on itself,鈥� said Matthew Mills, a graduate student in the Center for Research and Education in Optics and Lasers (CREOL). 鈥淭he collapse becomes so intense that electrons in the air鈥檚 oxygen and nitrogen are ripped off creating plasma 鈥� basically a soup of electrons.鈥�

At that point, the plasma immediately tries to spread the beam back out, causing a struggle between the spreading and collapsing of an ultra-short laser pulse. This struggle is called filamentation, and creates a filament or 鈥渓ight string鈥� that only propagates for a while until the properties of air make the beam disperse.

鈥淏ecause a filament creates excited electrons in its wake as it moves, it artificially聽seeds聽the conditions necessary for rain聽and lightning to occur,鈥� Mills said. Other researchers have caused 鈥渆lectrical events鈥� in clouds, but not lightning strikes.

But how do you get close enough to direct the beam into the cloud without being blasted to smithereens by lightning?

鈥淲hat would be nice is to have a sneaky way which allows us to produce an arbitrary long 鈥榝ilament extension cable.鈥� It turns out that if you wrap a large, low intensity, doughnut-like 鈥榙ress鈥� beam around the filament and slowly move it inward, you can provide this arbitrary extension,鈥� Mills said. 鈥淪ince we have control over the length of a filament with our method, one could聽seed the conditions needed for a rainstorm from afar. Ultimately, you could artificially聽control the rain and lightning over a large expanse with such ideas.鈥�

So far, Mills and fellow graduate student Ali Miri have been able to extend the pulse from 10 inches to about 7 feet. And they鈥檙e working to extend the filament even farther.

鈥淭his work could ultimately lead to ultra-long optically induced filaments or plasma channels that are otherwise impossible to establish under normal conditions,鈥� said professor Demetrios Christodoulides, who is working with the graduate students on the project.

鈥淚n principle such dressed filaments could propagate for more than 50 meters or so, thus enabling a number of applications. This family of optical filaments may one day be used to selectively guide microwave signals along very long plasma channels, perhaps for hundreds of meters.鈥�

Other possible uses of this technique could be used in long-distance sensors and spectrometers to identify chemical makeup. Development of the technology was supported by a $7.5 million grant from the Department of Defense.

鈥淭his counterintuitive process, which involves the concept of negative mass, mimics the behavior of a diametric drive,鈥� said Professor Demetrios Christodoulides of 麻豆原创鈥檚 College of Optics and Photonics. 鈥淓ven though ideas of this sort have been around for several years, they have never been successfully pursued because mass in nature is always a positive quantity.鈥� Diametric drive refers to the possibility of a self-contained, space-propulsion engine that operates without the need for any external fuel.

The study 鈥淥ptical diametric drive acceleration via action-reaction symmetry breaking鈥� recently published on the website of Nature Physics and was part of a project with other partner universities. Mohammad-Ali Miri, a 麻豆原创 graduate student in the Center for Research and Education in Optics and Lasers (CREOL), also participated in this work.

As everyone in introductory physics courses knows, Newton鈥檚 third law of motion states that the forces two bodies exert on each other are equal and opposite. As a result, two bodies of positive mass tend to accelerate toward each other when this pair of forces happens to be attractive.

However, if one of the two particles were to have a negative mass, this hypothetical arrangement would set up a system where the leading particle would constantly be 鈥渃hased鈥� by the trailing particle.

鈥淯nder these conditions, two interacting bodies will indefinitely accelerate in the same direction while keeping a constant distance between themselves,鈥� the study says. 鈥淥f course, given that in real life the mass of a particle is always positive, no such acceleration behavior that breaks the action-reaction symmetry has ever been reported.鈥�

In their experiment with the University of Erlangen-Nuernberg in Germany, the researchers used light pulses in a figure 8, fiber-optic platform to create the effect of attractive and repulsive forces.

鈥淚n the lab, one can create photon pulses with effective positive or negative masses,鈥� Ali Miri said. 鈥淭hey [pulses] could start chasing each other until reaching relativistic limits.鈥�

He said the concept of negative mass is not restricted to photons. Similar experiments can be performed in other settings, for example with electrons in crystalline solids.

鈥淲hile a realization of a Star Trek warp drive space-propulsion engine still remains a dream, the demonstrated optical diametric drive can provide new strategies in accelerating and steering optical pulses,鈥� Christodoulides said. 鈥淭his may have an impact on how one can control light in tomorrow鈥檚 optical networks.鈥�

The posted report can be seen by clicking .

Scientists led by Dr. Pavel Polynkin, associate research professor of optical sciences at the University of Arizona, and by professor Demetrios Christodoulides of the –College of Optics and Photonics at the 麻豆原创 in Orlando have created complex laser beam profiles to produce ultrafast self-bending laser beams.