5/21/2025 at 7:49:56 PM
I see a number of comments here misunderstanding the power of this laser. Laser facilities like this one are designed for incredibly short pulses that are femtoseconds long, and total energy per pulse is typically on the order of tens of joules, roughly equivalent to a few seconds of your phone flashlight. They can’t destroy much of anything on human scales. They are made to do physics research, and there is absolutely no pathway from a 2 petawatt laser that delivers a few joules a minute to a 2 petawatt laser that hits full output power for a few seconds: that would be 10^16 times more energy, and of course that brief pulse would use more electricity than all the US uses in a year and completely destroy the University of Michigan in spectacular fashion (very roughly equivalent to a five megaton nuclear explosion.)If you’re interested in the most energy per pulse, you want the “most energetic” laser, which is the NIF at LLNL. That’s about 2 megajoules per pulse or half a kilowatt hour. Definitely enough to kill a mosquito, but it doesn’t even register on the scale of Death Star style lasers from fiction.
And if you want the most destructive power, those are all military lasers. Which can absolutely destroy things science fiction style, but on a fairly small scale and with some important limitations.
by owenversteeg
5/21/2025 at 10:45:48 PM
Fun fact: these laser pulses are so short they are no longer a single wavelength. They have a spectrum due to the uncertainty principle. And at this short of a time scale, it’s pretty broad.by killjoywashere
5/22/2025 at 3:43:53 AM
I might regret asking, but could you explain this? (At a physics 101 level)by callc
5/22/2025 at 4:24:27 AM
Time and energy are “conjugated” quantities: the more one is sharp, the more the other one is broad (it’s the same concept as Fourier transforming a Gaussian: the more it’s peaked the more the transform is broad). In order for the time duration of the pulse to be so short, it must have a broad uncertainty in energy, which for light is the same as a wide spectrum of colors.That’s why it’s very tricky to find materials for mirrors and lenses when working with these short pulses: they must work well over a large range of frequencies. If they happen to absorb some more than others not only they would burn, but they would also change the temporal profile of the pulse.
by ziofill
5/22/2025 at 8:20:06 AM
Thanks very much ziofill. Is this the same thing as the Heisenberg Uncertainty Principle? Or is there something else similar for time and energy?by callc
5/22/2025 at 3:41:02 PM
Yes, it's the same thing in the sense that even if you work with a single photon the same applies (if you want its wavefunction to be narrow in time, its energy uncertainty must be broad)by ziofill
5/21/2025 at 8:25:56 PM
The article said 2 Petawatts for 25 quintillionths of a second. That's about 50mJ.That's about the amount of power used in your phone's flash when taking a picture, not a few seconds, but the LED being on for about 50-100 milliseconds.
by ta1243
5/21/2025 at 8:39:51 PM
Not sure if the article is accurate (the accuracy of numbers in written text took a nosedive concurrent with the rise of LLMs), but the capabilities page of the laser’s website claims 23 femtoseconds pulse duration, 2 PW power, 50 J energy, and 1 shot per minute. 50 J is roughly a 3W light for 15 seconds.by owenversteeg
5/21/2025 at 9:51:28 PM
> Not sure if the article is accurate (the accuracy of numbers in written text took a nosedive concurrent with the rise of LLMs)Written text accuracy took a nosedive in the early '00s as newspapers couldn't afford to hire journalists with a scientific background, followed by universities not hiring scientists to write press releases any more. GIGO - garbage in, garbage out.
by mschuster91
5/21/2025 at 9:27:12 PM
>And if you want the most destructive power, those are all military lasers. Which can absolutely destroy things science fiction style, but on a fairly small scale and with some important limitations.https://en.wikipedia.org/wiki/Project_Excalibur
Once upon a time we tried developing a nuclear-pumped X-ray laser for use in strategic defense, which if my napkin math is correct was probably in the neighborhood of NIF in terms of energy output (despite the conversion efficiency being terrible). Notable is that NIF continues existing after it fires.
by rl3
5/21/2025 at 10:31:27 PM
Also NIF is actually 192 laser beams with about 3 football fields of lab grade warehouse to house all those laser beams optics for beam pumping, shaping, etc.Not sure you can move NIF like you would move excalibur
by doctorwho42
5/21/2025 at 11:14:15 PM
Finally, a use for aircraft carriers.by dmurray
5/22/2025 at 3:03:51 AM
Back in graduate school, I TA'd an electrostatics course. We were going through the details of the basic parallel-plate capacitor, and so Prof. Peter Hagelstein (of the project you listed above) used the example of how much energy was stored in a football-field sized set of parallel-plate capacitors with oil as a high-breakdown dielectric.The students were dutifully copying the lecture while I was sitting there with my mouth agape realizing that he was working through a simplified example of what energy storage was required for the X-ray laser. IIRC Those guys had their own substation, and would charge the capacitors. The switch would get thrown and the sublasers would shoot at the molybdenum target, which would laze in the X-ray spectrum (and the molybdenum would vaporize, I think.)
Afterwards, I asked him how on earth the energy was transferred from the caps to the sublasers: He just smiled and said "very carefully".
by jpmattia
5/21/2025 at 9:25:09 PM
> completely destroy the University of Michigan in spectacular fashionSure, Ann Arbor may be destroyed, but that's a sacrifice I'm willing to make. For Science. /insert Lord Farquaad meme here
by yongjik
5/22/2025 at 12:08:55 AM
Go greenby unzadunza
5/22/2025 at 3:30:32 AM
For the most energetic, half a kilowatt hour makes me think of a high setting microwave for 30 minutes. Must be enough to roast a chicken?by coolcase
5/22/2025 at 4:12:39 AM
Choose how ablated you want your chickenby other_herbert
5/21/2025 at 7:54:16 PM
So.. We just need to figure out wormholes and make an infinite loop the laser goes through and harness its true power!!by babyent
5/21/2025 at 8:07:24 PM
I understand that you're being silly, but even in this silly theory land how is that supposed to work? While the laser is in a loop it's not hitting anything, and if you let it out it's the same as when you put it in.by Dylan16807
5/21/2025 at 8:27:26 PM
I figure it's a matter of stacking/charging the laser in that loop with a lot of pulses, then letting that all out at once? Like, what if we shot pulses into the orbit of a mini black hole, but then managed to unwind it back out into a single direction?by z2
5/21/2025 at 9:19:17 PM
In that case the problem is you're only charging the loop with about 1 watt of laser on average. It's going to take two weeks just to reach a megajoule. So you can do one really cool shot, and then you have to wait months.by Dylan16807
5/21/2025 at 8:12:33 PM
You're right, I am being silly because I am too uneducated to really make sense of any of it.I love smart people who work on this stuff, a lot of what I take for granted is due to their efforts :)
by babyent
5/21/2025 at 9:29:20 PM
Laser facilities like this one are designed for incredibly short pulses that are femtoseconds long"Look at the facts. Very high power, portable, limited firing time, unlimited range. All you'd need is a big spinning mirror and you could vaporize a human target from space."
by reaperducer