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126 points voxadam | 3 comments | | HN request time: 0s | source
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owenversteeg ◴[] No.44055538[source]
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.

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killjoywashere ◴[] No.44057017[source]
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.
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callc ◴[] No.44058577[source]
I might regret asking, but could you explain this? (At a physics 101 level)
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1. ziofill ◴[] No.44058777[source]
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.

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2. callc ◴[] No.44059922[source]
Thanks very much ziofill. Is this the same thing as the Heisenberg Uncertainty Principle? Or is there something else similar for time and energy?
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3. ziofill ◴[] No.44063157[source]
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)