Picatinny engineers set phasers to ‘fry’

PICATINNY ARSENAL, N.J. — Sci­en­tists and engi­neers at Picatin­ny Arse­nal are busy devel­op­ing a device that will shoot light­ning bolts down laser beams to destroy its tar­get. Sol­diers and sci­ence fic­tion fans, you’re wel­come.

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A guid­ed light­ning bolt trav­els hor­i­zon­tal­ly, then hits a car when it finds the low­er resis­tance path to ground. The light­ning is guid­ed in a laser-induced plas­ma chan­nel, then it devi­ates from the chan­nel when it gets close to the tar­get and has a low­er-resis­tance path to ground. Though more work needs to be done, Picatin­ny Arse­nal engi­neers believe the tech­nol­o­gy holds great promise.
Click to enlarge

“We nev­er got tired of the light­ning bolts zap­ping our sim­u­lat­ed (tar­gets),” said George Fis­ch­er, lead sci­en­tist on the project.

The Laser-Induced Plas­ma Chan­nel, or LIPC, is designed to take out tar­gets that con­duct elec­tric­i­ty bet­ter than the air or ground that sur­rounds them. How did the sci­en­tists har­ness the seem­ing­ly ran­dom path made by light­ning bolts and how does a laser help? To under­stand how the tech­nol­o­gy, it helps to get a brief back­ground on physics.

“Light trav­els more slow­ly in gas­es and solids than it does in a vac­u­um,” explained Fis­ch­er. “We typ­i­cal­ly think of the speed of light in each mate­r­i­al as con­stant. There is, how­ev­er, a very small addi­tion­al inten­si­ty-depen­dent fac­tor to its speed. In air, this fac­tor is pos­i­tive, so light slows down by a tiny frac­tion when the light is more intense.”

“If a laser puts out a pulse with mod­est ener­gy, but the time is incred­i­bly tiny, the pow­er can be huge,” Fis­ch­er con­tin­ued. “Dur­ing the dura­tion of the laser pulse, it can be putting out more pow­er than a large city needs, but the pulse only lasts for two-tril­lionths of a sec­ond.”

Why is this impor­tant?

“For very pow­er­ful and high inten­si­ty laser puls­es, the air can act like a lens, keep­ing the light in a small-diam­e­ter fil­a­ment,” said Fis­ch­er. “We use an ultra-short-pulse laser of mod­est ener­gy to make a laser beam so intense that it focus­es on itself in air and stays focused in a fil­a­ment.”

To put the ener­gy out­put in per­spec­tive, a big fil­a­ment light bulb uses 100 watts. The opti­cal ampli­fi­er out­put is 50 bil­lion watts of opti­cal pow­er, Fis­ch­er said.

“If a laser beam is intense enough, its elec­tro-mag­net­ic field is strong enough to rip elec­trons off of air mol­e­cules, cre­at­ing plas­ma,” said Fis­ch­er. “This plas­ma is locat­ed along the path of the laser beam, so we can direct it wher­ev­er we want by mov­ing a mir­ror.”

“Air is com­posed of neu­tral mol­e­cules and is an insu­la­tor,” Fis­ch­er said. When light­ning from a thun­der­storm leaps from cloud to ground, it behaves just as any oth­er sources of elec­tri­cal ener­gy and fol­lows the path of least resis­tance.

“The plas­ma chan­nel con­ducts elec­tric­i­ty way bet­ter than un-ion­ized air, so if we set up the laser so that the fil­a­ment comes near a high volt­age source, the elec­tri­cal ener­gy will trav­el down the fil­a­ment,” Fis­ch­er elab­o­rat­ed.

A tar­get, an ene­my vehi­cle or even some types of unex­plod­ed ord­nance, would be a bet­ter con­duc­tor than the ground it sits on. Since the volt­age drop across the tar­get would be the same as the volt­age drop across the same dis­tance of ground, cur­rent flows through the tar­get. In the case of unex­plod­ed ord­nance, it would det­o­nate, explained Fis­ch­er.

Even though the physics behind the project is sound, the tech­ni­cal chal­lenges were many, Fis­ch­er recalled.

“If the light focus­es in air, there is cer­tain­ly the dan­ger that it will focus in a glass lens, or in oth­er parts of the laser ampli­fi­er sys­tem, destroy­ing it,” Fis­ch­er said. “We need­ed to low­er the inten­si­ty in the opti­cal ampli­fi­er and keep it low until we want­ed the light to self-focus in air.

Oth­er chal­lenges includ­ed syn­chro­niz­ing the laser with the high volt­age, ruggedi­z­ing the device to sur­vive under the extreme envi­ron­men­tal con­di­tions of an oper­a­tional envi­ron­ment, and pow­er­ing the sys­tem for extend­ed peri­ods of time.

“There are a num­ber of high-tech com­po­nents that need to run con­tin­u­ous­ly,” said Fis­ch­er.

But despite the chal­lenges, the project has made notable progress in recent months.

“Def­i­nite­ly our last week of test­ing in Jan­u­ary 2012 was a high­light,” said Tom Shadis, project offi­cer on the pro­gram. “We had a well thought-out test plan and our ARDEC and con­trac­tor team worked togeth­er tire­less­ly and effi­cient­ly over long hours to work through the entire plan.

“The excel­lent results cer­tain­ly added to the excite­ment and cama­raderie,” added Fis­ch­er.

As devel­op­ment con­tin­ues, Shadis said that those involved with the project nev­er lose sight of the impor­tance of their work.

“We were all proud to be serv­ing our warfight­ers and can pic­ture the LIPC sys­tem sav­ing U.S. lives,” Fis­ch­er said.

Press release
U.S. Army

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