Of Lasers And Lightning: Thwarting Thor With Technology

Thor does battle with a man shooting lasers from his hands

Most of us don’t spend that much time thinking about lightning. Every now and then we hear some miraculous news story about the man who just survived his fourth lightning strike, but aside from that lightning probably doesn’t play that large a role in your day-to-day life. Unless, that is, you work in aerospace, radio, or a surprisingly long list of other industries that have to deal with its devastating effects.

Humans have been trying to protect things from lightning since the mid-1700s, when Ben Franklin conducted his fabled kite experiment. He created the first lightning rod, an iron pole with a brass tip. He had speculated that the conductor would draw the charge out of thunderclouds, and he was correct. Since then, there haven’t exactly been leaps and bounds in the field of lightning rod design. They are still, essentially, a metal rods that attract lightning strikes and shunt the energy safely into the earth. Just as Ben Franklin first did in the 1700s, they are still installed on buildings today to protect from lightning and do a fine job of it. While this works great for most structures, like your house for example, there are certain situations where a tall metal pole just won’t cut it.

Passive Lightning Protection (and the Radioactive Option)

Sometimes, the thing you’re trying to protect is, well, a tall metal pole. Radio towers make excellent lightning rods, and it’s hard to guarantee that the clouds will choose to discharge their pent-up electrons on a nearby pole instead of the tower itself. The type of lightning protection used on a tower or antenna depends on the application — many Ham Radio operators use lightning arresters to protect their equipment. These are small boxes that act as a passthrough for the antenna feedline. They are directly grounded, and in the event lightning strikes the antenna, are designed to provide a quick path to the earth for all that extra charge.

Many of us have secondary systems in place as well — automatic antenna disconnects, for example — just in case some excess energy “leaks through” the arrester. All this is designed to protect the expensive equipment in the shack, not the antenna itself, which you would probably need to replace after a direct lightning strike. What if we wanted to prevent lightning strikes altogether?

Lightning rod with radioactive tip
The radioactive tip of an old lightning rod. Source: Management of Radioactive Disused Lightning Rods (PDF)

Well, conventional lightning rods do help. A properly installed Lightning Protection System (LPS) can reduce the chance that an antenna or tower is struck by providing lots of enticing targets that the bolt can safely strike. Scientists have even tried to find ways to make those alternative targets a bit more alluring.

Back in the early 1900s, it was thought that slapping a bit of radioactive material on the top of the rod would help to attract lightning. The idea was that the radioactive material would partially ionize the surrounding air, making the area even more attractive. Several countries adopted their use in the 1970s and soon found that, in practice, this didn’t work as well as theory dictated. There was not a significant enough improvement over the conventional variety, especially considering the obvious health and safety complications that stray radioactive sources can cause. By 1990, many countries had banned their sale, and they have since been discontinued.

Radioactive or not, Lightning Protection Systems can get bulky. Take an airfield, for example. If we want to protect planes during takeoff and landing, we would need to cover a huge area with lightning rods and grounding lines… a huge area that becomes impassable to aircraft, for obvious reasons.

Lighting The Way

A recently-published paper just may be able to provide an alternative. It details the Laser Lightning Rod (LLR) project which aims to, as its name suggests, create lightning rods out of columns of light. Essentially, an extremely powerful laser is pointed at the sky, intersecting a conventional lightning rod along the way. The beam ionizes the air within it’s volume, creating a “wire” of sorts that guides lightning strikes into the lightning rod. The LLR team has proposed the system for use protecting buildings, rockets, and airports, and has even speculated that a series of lasers could be used around an airport to protect a large area (and the lasers could, of course, be selectively switched off when a plane approaches). The laser in question is a complex system, seeded by bursts from an emitter built by the TRUMPF corporation. The beam is amplified to around 800W, pulsing at 1kHz with each burst lasting around 1ps. The absolute maximum power of the system is not given, but Jean-Pierre Wolf, the team’s leader, told CNN that “a single pulse at peak power is equal to that produced by all the nuclear power plants in the world” — which sounds like it might be a slight exaggeration, but I wasn’t able to find an exact figure in the paper.

Block diagram of how a laser lightning rod works
Smoke (okay, hopefully not) and mirrors: a diagram of the laser lightning rod. Source: The laser lightning rod project EPJAP CC-BY 4.0
Laser lightning rod system deployed at Santis
The LLR system deployed at Säntis. Source: The laser lightning rod project EPJAP CC-BY 4.0

The team has built a prototype of the system, which they deployed at a communications tower on the peak of Säntis, the tallest mountain in the Swiss Alps. As can be expected, the tall metal structure at the peak of the tallest mountain in the region is no stranger to lightning strikes. In fact, in an average year it’s hit roughly 100 times.

The LLR team hauled a staggering 29 tons of materials and equipment to the mountaintop (sound a bit familiar? Check out this recent Hacker Challenge on Twitter). After about two weeks of setup and testing, the laser was ready to go. In mid-July, the first series of experiments started, and the team expects to have some numbers to crunch when the trials end sometime in September. In the meantime, they’re just hoping for some nasty weather.

High-powered lasers might be a bit overkill for the vast majority of today’s lightning-protection needs (unless you’re building the world’s safest amateur radio shack, have millions of dollars, and can convince your local government to let you shoot lasers at the sky) but this research is indisputably interesting. After all, is there anything that isn’t instantly cooler when you throw lasers into the mix?  We’ve even seen laser headlights! As with many new technologies, we’ll be watching this one closely (with the proper laser safety eye protection, of course) and looking forward to the day when, rather than sounding like something out of a Weather Control Matrix in Star Trek, it becomes a viable and maybe even ubiquitous Lightning Protection System.

45 thoughts on “Of Lasers And Lightning: Thwarting Thor With Technology

  1. Pilots bitch about getting blasted with 5mw laser pointers. They are going to love getting hit with the equivalent of all the nucellar power plants in the world if the thing misfires..

    1. Is there something like the inverse square law for lasers? Wondering if we’re going to be zapping low-flying satellites with this thing. I’m not suggesting we’ll cut through metal at that range, but sensitive optics?

      1. Yes, it’s still inverse square, same geometry just lower dispersion. Earth moon earth bounces with lasers off the retroreflectors we’ve left there are like 15km in diameter when they get back.

      2. If that was an issue, I’d think they’d also shut the laser off when a satellite is passing overhead, as they would for an aircraft, since they have predictable orbits. The only satellites I suppose that would suffer from problems would be spy satellites, and blinding those doesn’t seem like a problem to me…

        1. The paper talks about turning lasers off for safe passage of aircraft in the airport use case. At higher elevations, beam divergence would probably attenuate the risk fairly quickly. Part of what they’re wanting to explore is how long the streamer paths they can make will be. I think they only need 100m or so to close the gap to the cloud enough to effectively control the location of the lightning strike. So if the beam diverged significantly at a distance of 1km, that’d likely give plenty of protection for planes flying higher, and various height restrictions are common in controlled airspaces. I didn’t read the paper in enough detail to give specifics, but the extremely high peak power levels coupled with ultra-short pulse lengths are to overcome normal attenuation mechanisms that are there to begin with.

          They’re also (surprisingly, to me at least) working at near-infrared wavelengths (~~1 um), a range in which I think metal airframes would be quite reflective.

        2. With the cloud cover and atmospheric moisture in general you would expect from a lighting storm I think the laser would be well and truly scattered or absorbed before it left the atmosphere. I doubt it would remain of much threat to satellite, though its all going to be very wavelength dependent – if its a wavelength with great absorbtion in Nitrogen, water, oxygen – something common in the air, then the laser power doesn’t need to be that high to generate the ionisation they desire and most all of it should get absorbed safely before getting out to a great distance, but if they are using something with less absorption in air you would need more power in the first place to get the desired effect and quite a bit could get out, and that would be more of a threat to spacecraft. So finding that sweet spot in the middle where its not absorbed so strongly you don’t get enough penetration to really make a good conductive path, but it is absorbed strongly enough it doesn’t pose a threat above. Ironically the opposite of most large lasers shot upwards – those experiements were all about ballistic missile and satellite destruction, so getting absorbed too much by air and not making it to space is a bad thing…

          Seems like a bonkers idea though – spending all that energy to direct lighting, when in truth very few human made structures are ever bothered by lighting with current protections. Not saying it doesn’t happen, but serious harm from lighting striking human made stuff is pretty damn rare if any protections are in place at all.

      3. Yes – you can’t get the beam in a perfectly parallel column, so it spreads out like light from any other source. So the inverse square law still applies – except it’s as if the beam starts at a distance well behind the laser, a hypothetical spot where the beam would have been a single point.

        I was a little disappointed that Trumpf’s press release was so short on details. Doesn’t even give the wavelength, let alone power output. But nine meters long and five tonnes is a lot even compared to a typical industrial cutting laser.

        1. Reading the paper, it seems likely that a lot of the weight quoted was the ~ 20 x 900kg concrete blocks used as ballast to keep the container housing the container being blown off the mountain.

          1. Ah, thanks for the correcting note – I hadn’t read the press release where it mentioned the size of the laser itself, was responding to the line in the article that said they hauled 29 tons of gear and equipment up the mountain. Yeesh, 9 meters and 5 tons for just the laser itself is pretty crazy. I imagine some of the optical components have to be pretty large to withstand the peak power levels, and likely a lot of metal to hold everything together to the level of precision needed.

      4. Presumably the ionisation that the laser causes, also absorbs or scatters laser light, making the falloff faster? Plasmas are generally pretty good at absorbing light of all wavelengths. I think I’ve even seen (but can’t remember where) a low-divergence high-power laser which creates a blob of plasma near the aperture, which then just absorbs all the power and doesn’t really go anywhere

        That might be why in the graphic above they show a focused cone of laser, not a straight parallel beam (so not enough intensity to cause ionisation in the wide, low intensity bit at the base, but higher intensity as it goes past the pole and into the air – so it’ll spread out into the same cone afterwards, and drop off in intensity pretty quickly

        1. It turns out that’s the point of the ultra-short pulse length. The ionization that blocks the beam is a secondary mechanism that takes a little while to happen (I gather on the order of nanoseconds). With all the beam power delivered in 1ps, it can create the initial ionization and propagate for quite a distance, before the secondary ionization occurs that would block the beam. Pretty crazy; whether or not it works for lightning control, it’s an amazing piece of optical hardware :-0

  2. Seen once: a fireball (plasma) entering the open window on a hot and dry afternoon: it literally bumped on the wooden staircase, passed by me and two friends, and vanished / burst with a very dry sound and a light flash against a central heating radiator downstairs, or the electric outlet next to it. The fuses tripped, all plugged electronic appliances in the house were fried: TV, radio, microwave oven…
    It took about two seconds to travel before exploding. Since it bumped, it seemed to have a mass. Its color was yellowish, definitely not blueish like an electric arc. That day was very heavy weather, punctuated by muffled sound of thunder in altitude.

    1. Quite a lot of people have seen such things. But somehow no one has yet caught one on cellphone video or security camera, sadly.
      According to local legend, a ball lightning also was seen during a thunderstorm at the local radio station’s antenna.

      1. I saw regular lightning strike a radio station antenna one time and I was listening to the station when it happened. I was just a kid and it was a heck of a storm and I was looking out the window and I had the (am) radio going and Bang, a giant flash of lightning lit up the sky and the tower was clearly visible as the target in the night sky. And the radio station went dead. It remained that way for a few days too as I remember.

        In the city, I saw a strike on one of the metal power towers. The lights flickered and the world was mostly back to normal. It turned out that it took out my cable modem and the outside NIC of my home brew security device. I was very happy at the time I had build rather than bought as the first generation of home routers were around $300 and had no user serviceable parts. My old PC running Linux just needed a new $35 card.

        I was surprised I sustained even that much damage. In town there are so many good paths to ground you just don’t see that mush destruction very often. Now out in the very rural area we live in now, if lightning strikes a pole, there is going to be a lot of damage. Just not as many places for it to safely go.

    2. Ball lightning is one of those strange phenomenon that many people have seen but scientists seem to resolutely refuse to believe in, for the most part.
      Personally I think it’s real, and would love a proper scientific explanation. Weather is weird, and it gets even weirder when you toss in a few billion Amperes of electricity.

      1. Nicola Tesla believed in it but he was trying to avoid it as it damaged the equipment. i believe it was something like 2 separate tesla coils tuned to different frequencies ( some odd relationship between the frequencies almost 3rd harmonic but with a low beat frequency) at some time the first coil would do something to the other coil and this caused “all the stored energy in the coil to discharge very rapidly”. this can reliably cause a ball lightning event.

  3. Max peak power: Not a lot of info, but to an order of approximation, duty cycle is 1e-12/1e-3 = 1e-9. If average output power is 800W, peak would be 8e2/1e-9 = 8e11 watts. 800 Gigawatts is a lot, but a single large nuclear plant puts out ~2 GW.


    Huh, it looks like they may not be exaggerating; total global nuclear capacity is only 393 GW. I was expecting a lot more. Data from here: https://www.nei.org/resources/statistics/world-nuclear-generation-and-capacity

    It’s an intriguing approach, but yeesh, 29 *tons* of gear for just one? I know, it’s a prototype, but still…

    OTOH, you could probably have just one for a whole area (like an airport) and route the beam around to various exit points with underground tubes and mirrors. Any kind of optics, even mirrors can be problematic when you get to those kind of power levels, though.

    It occurred to me to wonder if you could get away with just a big honkin’ TEA laser, but checking, I found that they have much longer pulse durations and much lower peak power levels. (Great article about simple DIY nitrogen TEAs with other useful links here: http://technology.niagarac.on.ca/people/mcsele/lasers/LasersTEA.htm)

    Overall. I find this super-nteresting; I hope Hackaday will post a followup article, once the results from the test results are in!

      1. Yeah, I think you’re right. I did skim some of the paper, and it seems that the picosecond pulse duration is key to getting the range they’re looking for. I forget the details, but I gather there’s some sort of secondary ionization avalanche that happens over longer time periods, that results in much greater absorption of the beam energy. So if your beam power is stretched out in time, the secondary ionization ends up eating a lot of the beam power fairly close to the laser. TEA lasers typically have pulse widths of 10s to 100s of nanoseconds, so they’re way too slow to avoid that problem.

        (TEA lasers are also in the UV part of the spectrum, whereas the system the paper describes is in the NIR, at about ~~1um. I imagine that’d have a big impact on absorption as well.)

  4. Looks like a 1000W (1J * 1khz) picosecond laser. SWEET! For anyone interested in the “nuclear power plant” comment, they are discussing peak power over one pulse width. 1J/1ps= 1J/1E-12 s = 1e12 J/S= 1 Trillion Watts of Energy or 1 Terawatt (TW). What I don’t know if that is the seed laser pump power or the output of the THG (Third Harmonic Generator). Usually you can expect 50% loss at each harmonic, expecting around a 250W UV picosecond laser beam.

    With all that said, this system better be protecting losses in excess of 100s of Millions of dollars in equipment loss over a 3-5 year period. I cant see how a system like this could cost less than 1-2 Million + operating costs.

  5. Not only does lightning suck for people in the radio and aerospace industries, but heavy industrial equipment is way less protected than consumer equipment.

    Among other things this means the (relatively modern) mining plant i used to work at is susceptible to very short power interruptions stopping production. So much so that the company maintains their own network of lightning radars, and send warnings to the plants when there are storms along the local power generation and transmission infrastructure.

    In general i think most of us forget how protected most of our electronics is from crappy power. As well as what happens to less protected equipment when it has to contend with a good thunderstorm.

  6. However much I wish these guys success – who’s taking bets? My money is on the gods of thunder not noticing the little laser pointing at their mighty clouds.

    I say this because present role involves modeling the performance of the laser triggered spark gaps in Sandia’s Z-machine (with the posibility that we might make some bigger switches), and being one of the lightning/aerospace people.

    Laser triggered spark gaps are not new, and use ns scale UV pulses to set them off. They are tricky though and usually the triggered bit is short. Like in their references where they mention a 25mm gap being set off.

    Fun story though.

    1. You just have to ionize a narrow channel for an instant and the millions of volts field across it should get the point. Jitter is not a problem if you just want to make it go bang.

      1. That would work if you could ionise the channel long enough for current to flow in it and allow it to become polarised by the electric field. Then the cloud would unleash it’s bang. This takes quite a while for such high impedance systems. Natural lightning takes a goodly bit of a second. Let’s say 0.1 to get establish the charge distribution. It’s the emptying the already establised charge channel that’s quite quick at around 50 us.

        These are all rather long time scales compared to ps pulses.

        But still calling maybe nope on it working with such a small laser. Have a bash at working out how much energy is required to ionise a several km long channel of the beam diameter. If you had more than 1MJ of beam energy, ideally much more, then game on.

        In perfectly still air, with nicely behaving field gradients, and a large enough laser it would lean towards a solution to triggering a very long discharge. But with constantly moving air and out in the wild, might still be challenging.

        Off topic, but always wanted to try rocket triggered lightning. There, someone has already put all the energy into the copper when making it into a nice little ready to use arc channel starter. And you get to play with rockets too!

  7. i wonder… if you can force lighting to strike a specific spot somewhat at will (assuming there is consistent nasty weather to accommodate), could you harvest the power somehow? large scale electrolysis for fuel? I assume the infrastructure would be too expensive if you couldn’t get reliable strikes…

    1. You seem to want to put targeted lightning to good uses. Could it not also shorten the occasional zoom meeting by zapping a router/modem. Maybe your own if feeling altruistic, and then freeing you to explore a world that’s not a rectangle at arms length.

    2. You sure could, but the worth of a lightning bolt’s kilowatt hours of energy is not very high (I think I WAGged it at about $160). You’d also have to slow it down and charge up a capacitor or battery bank without blowing it up. Fortunately it’s DC so a suitable inductor would do it (large one). Also, intermittency would be a problem if you didn’t live in that Venezuelan town where storms come every night.

      1. You know I think I remember something like that – using a laser to draw a line from the cloud to the insurgent hiding behind a rock and make it appear as if is displeased with them.

  8. I think this project has been around in one form or another for decades. I remember it was guys experimenting with laser lightning rods who discovered non linear lasers.

  9. According to the diagram, it’s only a 1 Joule pulse. But it’s concentrated in a 1 ps pulse.

    Strangely, they also show a 1 KHz rep rate. Seems to me once every ten seconds would do the job, and result in much less power consumption and wear of the switches. Plus they could shut it off unless there were high electric fields detected.

  10. “The team has built a prototype of the system, which they deployed at a communications tower on the peak of Säntis, the tallest mountain in the Swiss Alps.”
    nope… Säntis is only 2502m tall… the tallest is 4634m in Swizerland…

    1. Yeah, not the highest mountain by a long shot. I think what was meant to be said was that it’s the highest communication tower – and hence a “tall thing that gets hit by lightning” :-)

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