Lightning storm over city in purple light
π Science and technology
Lasers: promising applications for research and beyond

The Lightning Rod project: a laser beam to control lightning

Aurélien Houard, Researcher at LOA* at ENSTA Paris (IP Paris)
On March 15th, 2023 |
5 min reading time
Aurélien Houard
Aurélien Houard
Researcher at LOA* at ENSTA Paris (IP Paris)
Key takeaways
  • Lightning strikes cause between 6,000 and 24,000 victims each year worldwide.
  • Lightning rods are used to protect against lightning strikes, but they have several shortcomings: limited coverage, electromagnetic interference, or power surges.
  • The Laser Lightning Rod (LLR) project aims to use lasers to deflect lightning strikes.
  • The LLR uses laser technology capable of producing ultrashort, intense laser pulses at a rate of 1,000 shots per second.
  • While a laser beam can deflect lightning, the protection provided needs to be as optimal as possible.

Aurélien Houard is coor­di­nat­ing an EU-fund­ed con­sor­tium that includes three Swiss insti­tu­tions – the Uni­ver­si­ty of Gene­va, the Uni­ver­si­ty of Applied Sci­ences and Arts, and the École Poly­tech­nique Fédérale de Lau­sanne (EPFL) – as well as TRUMPF Sci­en­tif­ic Lasers in Ger­many, André Mysy­row­icz Con­sul­tants and Ari­ane­Group. The team has devel­oped a laser fil­a­men­ta­tion tech­nol­o­gy capa­ble of deflect­ing the path of a light­ning strike, work that could lead to bet­ter light­ning pro­tec­tion for crit­i­cal infra­struc­ture such as airports.

Light­ning is a major nat­ur­al haz­ard and is esti­mat­ed to cause between 6,000 and 24,000 deaths per year world­wide. Light­ning also caus­es pow­er out­ages, for­est fires and dam­age to elec­tron­ic equip­ment cost­ing bil­lions of euros each year.

A light­ning bolt forms when the tur­bu­lent air of a thun­der­cloud vio­lent­ly dis­rupts the ice crys­tals and water droplets it con­tains, tear­ing elec­trons from their atoms to cre­ate a plas­ma (an ionised gas). This process cre­ates areas of oppo­site elec­tri­cal charge that can con­nect dis­charg­ing elec­tric­i­ty as they do so.

Today, the most com­mon method of light­ning pro­tec­tion is still pro­vid­ed by a 300-year-old con­cept invent­ed by Ben­jamin Franklin: the light­ning rod. This con­duc­tive met­al anten­na pro­vides a pref­er­en­tial point of impact for light­ning dis­charges and guides the gen­er­at­ed cur­rent safe­ly to the ground. How­ev­er, this type of light­ning con­duc­tor offers only lim­it­ed cov­er­age – over a radius rough­ly equiv­a­lent to its height. Fur­ther­more, these struc­tures only pro­tect against the direct effect of light­ning and, by attract­ing light­ning strikes, they can even increase indi­rect effects such as elec­tro­mag­net­ic inter­fer­ence and pow­er surges on elec­tron­ic equipment.

A “mobile” lightning rod on the Säntis mountain

Sci­en­tists have been think­ing about using intense laser beams as alter­na­tive types of “mobile” light­ning con­duc­tors as ear­ly as the 1970s, when the first long-pulse lasers able to guide mega­volt dis­charges a few metres in the lab­o­ra­to­ry were devel­oped. But it was the devel­op­ment of intense fem­tosec­ond pulse lasers, enabling the gen­er­a­tion of long plas­ma fil­a­ments, that rev­o­lu­tionised the field in the 1990s. The idea: these laser beams are fired towards a cloud. Very intense fil­a­ments of light are then formed in the beams and ionise the nitro­gen and oxy­gen mol­e­cules in the air, there­by cre­at­ing free elec­trons. Since the long fil­a­ments of ionised air are more con­duc­tive than the sur­round­ing areas, these chan­nels cre­ate a path along which the elec­tri­cal dis­charges of the light­ning flash can travel.

Aurélien Houard and col­leagues suc­cess­ful­ly test­ed their idea in the sum­mer of 2021 in the Swiss Alps – on the Sän­tis moun­tain in North-East­ern Switzer­land, to be exact. The 2,500-metre-high moun­tain is a hot spot for light­ning, with more than 100 strikes record­ed each year on the 124-metre-high com­mu­ni­ca­tions tow­er at its sum­mit. The researchers set up their laser near the com­mu­ni­ca­tions tow­er, which took four years of devel­op­ment and lab­o­ra­to­ry test­ing and emits picosec­ond laser puls­es with an ener­gy of more than 500 mJ at a rate of 1000 pulses/second.

Thanks to the laser, the pro­tec­tion radius was increased from 120 m to 180 m around the tower.

Dur­ing their exper­i­ments, which last­ed three months, the tow­er was struck by at least 16 light­ning strikes, four of which occurred when the laser was switched on. The researchers were able to divert these four light­ning strikes using the laser. They were also able to record the tra­jec­to­ry of one of the strikes using two high-speed cam­eras. The record­ings revealed that the light­ning trac­er ini­tial­ly fol­lowed the laser path for about 60 m before reach­ing the tow­er, which means that the pro­tec­tive radius increased from 120 m to 180 m around the tower.

The imme­di­ate appli­ca­tions of this tech­nol­o­gy would be to pro­tect crit­i­cal infra­struc­ture such as air­ports, launch pads, nuclear pow­er plants, sky­scrap­ers and forests from light­ning. The laser light­ning con­duc­tor would be switched on when need­ed dur­ing thun­der­storms and when a thun­der­cloud was detected

“The LLR laser light­ning rod project was ini­ti­at­ed by my team and that of my Swiss coun­ter­part, Jean-Pierre Wolf at the Uni­ver­si­ty of Gene­va,” says Aurélien Houard. “We have been work­ing on the sub­ject of laser fil­a­men­ta­tion and laser light­ning con­duc­tors for more than 20 years. It was the suc­cess of our lab­o­ra­to­ry exper­i­ments and the fact that we had access to a new laser tech­nol­o­gy capa­ble of pro­duc­ing ultra­short, intense laser puls­es with a rate of 1,000 laser shots per sec­ond that encour­aged us to launch the project.”

A highly collaborative project

The tech­nol­o­gy itself was devel­oped by TRUMPF Sci­en­tif­ic Lasers, based in Munich. “We turned to them and asked them to make the most pow­er­ful laser that was pos­si­ble with their tech­nol­o­gy, and we ordered a 1‑Joule-laser. We then formed a con­sor­tium with Swiss light­ning experts at the EPFL, with Prof. André Mysy­row­icz, who had ini­ti­at­ed the project 20 years ago and inter­vened here in a con­sul­tant capac­i­ty, and Ari­ane­Group.” The lat­ter is direct­ly inter­est­ed in this type of sys­tem for the pro­tec­tion of air­ports and of course the Ari­ane rocket.

In addi­tion to the fact that the laser is more pow­er­ful than any the team had access to before, the site they chose for their exper­i­ments was also cru­cial. “The Sän­tis moun­tain is one of the most light­ning-struck sites in Europe. Also, light­ning always strikes in the same place there, so it’s ide­al for the type of exper­i­ment in which we want­ed to max­imise our chances of the laser inter­act­ing with the light­ning. Light­ning exper­i­ments are very com­pli­cat­ed, it can take months or even years for a light­ning bolt to strike a par­tic­u­lar spot,” explains Aurélien Houard.

The laser itself is expen­sive, so the con­sor­tium applied for fund­ing from the Euro­pean Com­mis­sion. “This was a long process because the funds we applied for are for col­lab­o­ra­tive research (requir­ing at least three coun­tries and three part­ners) and for so-called ‘break­through research’ that can ben­e­fit society.”

“To apply, we had to demon­strate that the laser could con­trol elec­tric dis­charges in the lab­o­ra­to­ry over sev­er­al metres, which we did suc­cess­ful­ly,” explains Aurélien Houard. “How­ev­er, we were not sure that the tech­nique would work over much longer dis­tances, as is the case with nat­ur­al light­ning, because the val­ues of the elec­tric fields are com­plete­ly different.”

Efforts that paid off

At the start of the project, TRUMPF’s devel­op­ment of the laser took two years because it turned out to be more dif­fi­cult than the researchers had orig­i­nal­ly thought. They then had to test the device and make sure it was capa­ble of pro­duc­ing fil­a­ments over dis­tances of 100 metres. But when they want­ed to start their exper­i­ments, the Covid epi­dem­ic arrived, and the researchers had to stop every­thing. “We had to post­pone the whole cam­paign for a year, which meant find­ing addi­tion­al fund­ing,” recalls Aurélien Houard.

The dif­fi­cul­ties were not only finan­cial but also prac­ti­cal. It was a mat­ter of bring­ing a laser that weighed five tonnes and was nine metres long to the top of a moun­tain. “The sum­mit was only acces­si­ble by cable car and we had to dis­man­tle the laser to get it there. Once up there, we had to build an infra­struc­ture to house a tele­scope that would focus the laser in the atmos­phere. This required mul­ti­ple heli­copter trips and hop­ing for good weath­er con­di­tions – not too much wind and snow – so that we could install all our instru­ments. It then took us about a month to get every­thing working.”

Light­ning exper­i­ments are very com­pli­cat­ed. It can take months or even years for light­ning to strike a par­tic­u­lar spot!

The team also had to obtain per­mis­sion from the local author­i­ties before fir­ing its laser into the air: a 5‑km-wide no-fly zone had to be organ­ised each time the laser was acti­vat­ed. Their efforts paid off though: “We were lucky enough to observe the light­ning deflect­ed in two dis­tinct pho­tos at the same time – which is rare, as clouds on top of moun­tains often con­ceal light­ning. We detailed these obser­va­tions in Nature Pho­ton­ics and our pub­li­ca­tion attract­ed a lot of media interest.”

How­ev­er, there is still a lot of work to be done, accord­ing to the researcher. “While we have been able to show that a laser beam can deflect light­ning, we can­not yet eas­i­ly quan­ti­fy that the pro­tec­tion pro­vid­ed by the laser is equiv­a­lent to that of a con­ven­tion­al Franklin-type light­ning rod. To do this, we need to be sure that when the laser is turned on, the light­ning will want to pass through the path traced by the beam filaments.”

“Franklin light­ning rods have been around for hun­dreds of years and have been exten­sive­ly test­ed and mod­elled, but our laser is new, and we don’t yet under­stand all the physics behind it,” con­cludes Aurélien Houard.

Isabelle Dumé


  • https://​llr​-fet​.eu
  • https://​www​.epjap​.org/​a​r​t​i​c​l​e​s​/​e​p​j​a​p​/​f​u​l​l​_​h​t​m​l​/​2​0​2​1​/​0​1​/​a​p​2​0​0​2​4​3​/​a​p​2​0​0​2​4​3​.html


Aurélien Houard

Aurélien Houard

Researcher at LOA* at ENSTA Paris (IP Paris)

Aurélien Houard's research activities focus on the study of femtosecond laser filamentation and on the applications of laser filaments such as the generation of THz radiation or remote UV laser emission, laser aerodynamic control, acoustic wave generation or the triggering and guiding of electric arcs by laser. His work on the “generation of THz radiation by laser filamentation in the air” received the École Polytechnique thesis prize. Hired as a researcher at the Applied Optics Laboratory* (a joint research unit (UMR) of CNRS / École Polytechnique / ENSTA Paris), he became head of the “Laser-Matter Interaction" team and obtained his Habilitation to direct research. He is also author or co-author of 87 papers in international peer-reviewed journals and has given 25 invited conference presentations. He is currently the coordinator of a major European project to develop a laser lightning conductor in collaboration with the University of Geneva, EPFL and Ariane Group.

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