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Intense laser experiments provide evidence that light can stop electrons

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Re: Intense laser experiments provide evidence that light can stop electrons

#21

Post by danbruc »

jerry40 wrote: post #18
ISL wrote: post #10

The HN title is incorrect -- perhaps the first direct evidence is Compton's original work, showing that electrons scatter photons. If electrons scatter photons, then photons scatter electrons. Every time a photon scatters off an electron, there exists a reference frame in which the electron is brought to rest. I'm certain that one could find an earlier argument than Compton scattering, too. Maxwell surely would have…

> If electrons scatter photons, then photons scatter electrons. Does it mean that photons are able to scatter photons?

Photon photon scattering is a thing [1] but I am not sure whether that is implied by the interaction of light and electrical charged particles acting both ways. I slightly tend to think that is not implied but I am not a physicist.

[1] https://en.wikipedia.org/wiki/Two-photon_physics

Re: Intense laser experiments provide evidence that light can stop electrons

#22

Post by jerry40 »

danbruc wrote: post #21
jerry40 wrote: post #18

Earlier quoted context omitted.

> If electrons scatter photons, then photons scatter electrons. Does it mean that photons are able to scatter photons?

Photon photon scattering is a thing [1] but I am not sure whether that is implied by the interaction of light and electrical charged particles acting both ways. I slightly tend to think that is not implied but I am not a physicist. [1] https://en.wikipedia.org/wiki/Two-photon_physics

Interesting! Thanks

Re: Intense laser experiments provide evidence that light can stop electrons

#23

Post by madengr »

ISL wrote: post #10

The HN title is incorrect -- perhaps the first direct evidence is Compton's original work, showing that electrons scatter photons. If electrons scatter photons, then photons scatter electrons. Every time a photon scatters off an electron, there exists a reference frame in which the electron is brought to rest. I'm certain that one could find an earlier argument than Compton scattering, too. Maxwell surely would have…

What’s the difference between this and radiation pressure on charges (which is classical physics)?

Re: Intense laser experiments provide evidence that light can stop electrons

#25

Post by sofasurfer »

noobermin wrote: post #12

This is a potentially impactful experimental result in my niche field, the physics of relativistic laser phenomena. People have been running simulations and imaging what RR would look like for years, and this looks like the first experimental result that shows it The money shot, fig. 9 is a bit underwhelming to me though, because it is supposed to show where the "classical model" diverges from the quantum model, and…

I’d say that the main conclusion is the observation of a statistically significant (> 3 sigma) radiation reaction effect which is pretty consistent with both the classical model and the quantum model. The data “hints” that the quantum one fits the data better, but not at a very significant level (1 sigma). Moving to higher electron energies and/or laser intensities will help make that difference clearer. The paper is not called “first observation of quantum radiation reaction” for a reason.

Re: Intense laser experiments provide evidence that light can stop electrons

#26

Post by raverbashing »

marknadal wrote: post #3

What on earth, light by definition is the quantifiable (quanta) of energy levels between electron orbital states. This is such a nonsensical title, as the electron would be changing electron states based off the energy level of the laser - of course! Any suggestions on what the title should be changed to?

> light by definition... of energy levels between electron orbital states

No, that's not the definition of light, photons or quanta.

The fact that electrons on an atom emit or "absorb" energy in a quantized way is a consequence of several basic elements of QM

Re: Intense laser experiments provide evidence that light can stop electrons

#27

Post by sofasurfer »

madengr wrote: post #23
ISL wrote: post #10

The HN title is incorrect -- perhaps the first direct evidence is Compton's original work, showing that electrons scatter photons. If electrons scatter photons, then photons scatter electrons. Every time a photon scatters off an electron, there exists a reference frame in which the electron is brought to rest. I'm certain that one could find an earlier argument than Compton scattering, too. Maxwell surely would have…

What’s the difference between this and radiation pressure on charges (which is classical physics)?

Good question! In radiation pressure the fact that the charges radiate energy isn’t included, it’s just the change in momentum due to to radiation being absorbed or reflected that produces a force. In radiation reaction the charges are accelerated and decelerated by the electric field of the light. Classical electrodynamics says the electrons must give off em radiation, and so must lose energy in the process, so must be an additional force associated with this emission. Physicists such as Dirac looked at classical radiation reaction in the early 20th century, but I don’t think it’s effect has been observed in the interaction of electrons with light before. At very high electron energies and/or laser intensities the classical description of radiation reaction should break down.

Re: Intense laser experiments provide evidence that light can stop electrons

#28

Post by pif »

jerry40 wrote: post #18
ISL wrote: post #10

The HN title is incorrect -- perhaps the first direct evidence is Compton's original work, showing that electrons scatter photons. If electrons scatter photons, then photons scatter electrons. Every time a photon scatters off an electron, there exists a reference frame in which the electron is brought to rest. I'm certain that one could find an earlier argument than Compton scattering, too. Maxwell surely would have…

> If electrons scatter photons, then photons scatter electrons. Does it mean that photons are able to scatter photons?

Yes, they are. They cannot interact directly, but they can via "virtual" electron/positron pairs (or actually any other pair of charged elementary particle + antiparticle).

Re: Intense laser experiments provide evidence that light can stop electrons

#30

Post by pif »

greendesk wrote: post #13

Can this phenomenon be used as a shield for spacecraft? If a laser travels inside a fiber cable, then the laser beam can wrap around the spacecraft. If the beam can stop electrons, it can potentially stop the larger particles traveling in space.

> the laser beam can wrap around the spacecraft.

If you want the laser beam carry enough impulse to stop a rock flying towards you at a few thousands km/h, good luck keeping the fiber in place! Every time the fibre tries to make the light change direction, the light tries to straighten the fibre, just like water running through a pipe.

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