"Long before it's in the papers"
January 28, 2015


Step toward man-made lightning reported

April 14, 2008
Courtesy Optical Society of America
and World Science staff

In what they call a first step to­ward con­ven­iently trig­ger­ing ar­ti­fi­cial light­ning, sci­en­tists say they have touched off elec­tric dis­charges in thun­der­clouds by shoot­ing pow­er­ful la­sers at them.

Lightning near Tuc­son, Ariz. (Im­age cour­tesy NOAA)

“We gen­er­at­ed light­ing pre­cur­sors,” said Jérôme Kas­par­ian of the Uni­ver­s­ity of Ly­on in France, one of the re­search­ers. 

Cre­at­ing light­ning is an im­por­tant tool for stu­dy­ing the mech­a­nisms of light­ning and test­ing the light­ning re­sist­ance of air­planes and in­fra­struc­ture, added Kas­par­ian and col­leagues.

Sci­en­tists have been able to trig­ger light­ning strikes since the 1970s by shoot­ing small rock­ets, spool­ing long wires be­hind them, in­to thun­der­clouds. But only about half these at­tempts work, said Kas­par­ian and col­leagues. La­ser tech­nol­o­gy, they added, could make the pro­cess ea­sier, cheaper and could open up new ap­plica­t­ions.

Light­ning still is­n’t fully un­der­stood, though it been stud­ied since the times of Ben­ja­min Frank­lin, who fa­mously tied a key to the end of a kite string and flew the kite in a thun­der­storm. When sparks leapt from the key, he cor­rectly con­clud­ed light­ning is an elec­tri­cal cur­rent.

Kas­par­ian and col­leagues, atop New Mex­i­co’s South Baldy Peak dur­ing two storms, said they used la­ser pulses to cre­ate fil­a­ments of charged gas that con­duct elec­tricity akin to Frank­lin’s kite string. No air-to-ground light­ning was trig­gered be­cause the fil­a­ments were too short-lived, the re­search­ers said. But fur­ther im­prove­ments, they added, could come by re­pro­gram­ming their la­sers with more soph­is­t­icated pulse se­quences.

Pulsed la­sers may be a pow­er­ful way to trig­ger light­ning be­cause they can form many so-called plas­ma fil­a­ments, the in­ves­ti­ga­tors said. These are chan­nels of ion­ized, or charged, air mo­le­cules that act like con­ducting wires ex­tend­ing in­to the cloud.

The idea of us­ing la­sers to trig­ger light­ning was first sug­gested more than 30 years ago, but could­n’t be put in prac­tice be­fore be­cause pre­vi­ous la­sers weren’t pow­er­ful enough, the sci­en­tists said. 

Kas­par­ian and col­leagues in­volved in the Ter­amo­bile proj­ect, an in­terna­t­ional pro­gram in­i­ti­at­ed by Na­tional Cen­ter for Sci­en­tif­ic Re­search in France and the Ger­man Re­search Founda­t­ion, built a pow­er­ful mo­bile la­ser capa­ble of gen­er­at­ing long plas­ma chan­nels by fir­ing ul­tra­short la­ser pulses. 

They tested their device at the Lang­muir Lab­o­r­a­to­ry in New Mex­i­co, which is equipped to meas­ure at­mos­pher­ic elec­tri­cal dis­charges. The lab, atop 10,500-foot South Baldy Peak, is in an ide­al place be­cause its al­ti­tude places it close to the thun­der­clouds, the group ex­alained. The re­search­ers said they meas­ured the elec­tri­cal ac­ti­vity in the clouds af­ter dis­charg­ing la­ser pulses, and that sta­tis­ti­cal anal­y­sis showed the pulses in­deed en­hanced the elec­tri­cal ac­ti­vity there. The find­ings ap­pear in the latest is­sue of the re­search jour­nal Op­tics Ex­press.

* * *

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In what they call a first step toward conveniently triggering artificial lightning, scientists say they have touched off electrical discharges in thunderclouds by shooting powerful lasers at them. “We generated lighting precursors,” said Jérôme Kasparian of the University of Lyon in France, one of the researchers. Creating lightning is an important tool for studying the mechanisms of lightning and testing the lightning resistance of airplanes and infrastructure, added Kasparian and colleagues. Scientists have been able to trigger lightning strikes since the 1970s by shooting small rockets, spooling long wires behind them, into thunderclouds. But only about half these attempts work, said Kasparian and colleagues. Laser technology, they added, would make the process quicker, cheaper and could open up new applications. Lightning still isn’t fully understood, though it been studied since the times of Benjamin Franklin, who famously tied a key to the end of a kite string and flew the kite in a thunderstorm. When sparks leapt from the key, he correctly concluded lightning was an electrical current. Kasparian and colleagues, atop New Mexico’s South Baldy Peak during two storms, said they used laser pulses to create filaments of charged gas that conduct electricity akin to Franklin’s kite string. No air-to-ground lightning was triggered because the filaments were too short-lived, the researchers said. But further improvements, they added, could come by reprogramming their lasers with more sophisticated pulse sequences. Pulsed lasers may be a powerful way to trigger lightning because they can form many so-called plasma filaments, the investigators said. These are channels of ionized, or charged, air molecules that act like conducting wires extending into the cloud. The idea of using lasers to trigger lightning was first suggested more than 30 years ago, but couldn’t be put in practice before because previous lasers weren’t powerful enough, the scientists said. Kasparian and colleagues involved in the Teramobile project, an international program initiated by National Center for Scientific Research in France and the German Research Foundation, built a powerful mobile laser capable of generating long plasma channels by firing ultrashort laser pulses. They tested their laser at the Langmuir Laboratory in New Mexico, which is equipped to measure atmospheric electrical discharges. The lab, atop 10,500-foot South Baldy Peak, is in an ideal place because its altitude places it close to the thunderclouds, the group exalained. The researchers said they measured the electrical activity in the clouds after discharging laser pulses, and that statistical analysis showed the pulses indeed enhanced the electrical activity there.