Can a beam of photons accelerate an atom or object?

[PJMath]

Not quite sure how to ask this, but here goes: I think I understand how a photon impacting an atom can increase the energy level of an electron in the atom. When I read about "light pressure", I thought, is there a way for, say, a stream of photons to accelerate an atom by continually impacting the atom until it moved or changed its velocity? Is this what light pressure does to an object? Thanks for any insights.

 

[phinds]

Not quite sure how to ask this, but here goes: I think I understand how a photon impacting an atom can increase the energy level of an electron in the atom. When I read about "light pressure", I thought, is there a way for, say, a stream of photons to accelerate an atom by continually impacting the atom until it moved or changed its velocity? Is this what light pressure does to an object? Thanks for any insights.

Yes, "light sails" do move things because light has momentum even though it has no mass

 

[anorlunda]

Definitely yes. This is the key principle of the two-stage thermonuclear warhead, radiation pressure up to 1,400 million bars!

You may also have seen news about the lightsail project last week.
https://en.m.wikipedia.org/wiki/Thermonuclear_weapon#Radiation_pressure

 

[berkeman]

https://upload.wikimedia.org/wikipe...s_radiometer.jpg/220px-Crookes_radiometer.jpg

 

[jbriggs444]

https://upload.wikimedia.org/wikipe...s_radiometer.jpg/220px-Crookes_radiometer.jpg

But a Crookes radiometer is not primarily affected by light pressure. It turns against the light pressure.

 

[jtbell]

https://en.wikipedia.org/wiki/Crookes_radiometer#Explanations_for_the_force_on_the_vanes

 

[ZapperZ]

Not quite sure how to ask this, but here goes: I think I understand how a photon impacting an atom can increase the energy level of an electron in the atom. When I read about "light pressure", I thought, is there a way for, say, a stream of photons to accelerate an atom by continually impacting the atom until it moved or changed its velocity? Is this what light pressure does to an object? Thanks for any insights.

Charged particles, including heavy ions, are accelerated in particle accelerators using RF fields. So that, technically, are photons.

Zz.

 

[berkeman]

https://en.wikipedia.org/wiki/Crookes_radiometer#Explanations_for_the_force_on_the_vanes

Very interesting, thanks! I definitely had the wrong picture in my head about how it worked.

1. The final piece of the puzzle, thermal transpiration, was theorized by Osborne Reynolds[5] in an unpublished paper that was refereed by Maxwell, who then published his own paper which contained a critique of the mathematics in Reynolds's unpublished paper.[6] Maxwell died that year and the Royal Society refused to publish Reynolds's critique of Maxwell's rebuttal to Reynolds's unpublished paper, as it was felt that this would be an inappropriate argument when one of the people involved had already died.[3] Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward due to the tangential force of the movement of the rarefied gas moving from the colder edge to the hotter edge.[3]

But so are they saying that with a fully evacuated version that has mirrors on the vanes, that you won't get rotation if you shine a strong laser on one side of one of the vanes? I suppose that the small vane pivot friction is too big to overcome with just light (as opposed to a solar sail in frictionless space)...

 

[PJMath]

Definitely yes. This is the key principle of the two-stage thermonuclear warhead, radiation pressure up to 1,400 million bars!

You may also have seen news about the lightsail project last week.
https://en.m.wikipedia.org/wiki/Thermonuclear_weapon#Radiation_pressure

Thanks for the response. Can you also recommend any books/articles/etc. that I can read to obtain a better understanding of this topic? For example, at what point or energy level might a stream of photons go from simply heating up an object to affecting its velocity?

 

[anorlunda]

Thanks for the response. Can you also recommend any books/articles/etc. that I can read to obtain a better understanding of this topic? For example, at what point or energy level might a stream of photons go from simply heating up an object to affecting its velocity?

Ah, you may need to reprase your question. The literal answer is and and all energy levels. I think you're getting hung up on unscientific notions of "significant" heating and "significant" velocity change.