Can free electrons absorb photons?

[AkiraBakaBaka]

When a photon hits an atom, it is absorbed by an electron. This electron becomes excited for a short time, then emits another photon and returns to normal.

 

Is it possible for this same process to occur with a free electron (not bound to an atom)? In other words, if a photon hit a lone electron in deep space, what would happen?

[UncleAl]

You would get scattering from photon-electron collision. There is a small literature on accelerating electrons with an intense laser beam. The interaction has a low cross-section.

[AkiraBakaBaka]

Thanks for the help!

 

I have learned that this particular collision falls under the category of 'Raman scattering'. There is a more specific interpretation called "Coherent Raman Effect on Incoherent Light" (CREIL) and appears to be somewhat controversial, for it could reinterpret Hubble's redshift-distance relation, the 'proof' that space is expanding!

[AkiraBakaBaka]

BTW, nice avatar UncleAl! :hihi:

[Qfwfq]

Is it possible for this same process to occur with a free electron (not bound to an atom)? In other words, if a photon hit a lone electron in deep space, what would happen?

The photon easily changes the atom's internal state but can't so easily change that of the free electron. This is the crux of the difference. Without changing the internal state of the electron it can't be "really" absorbed, a photon must be emitted just about immediately otherwise energy-momentum couldn't be conserved.

 

In practice, the photon may be scattered by the free electron but not actually absorbed by it.

[Kirk Gregory Czuhai]

The photon easily changes the atom's internal state but can't so easily change that of the free electron. This is the crux of the difference. Without changing the internal state of the electron it can't be "really" absorbed, a photon must be emitted just about immediately otherwise energy-momentum can't be conserved.

 

In practice, the photon may be scattered by the free electron but not actually absorbed.

Question? Could not the electron gain momentum, the photon lose energy and a neutrino be released to conserve momentum?

peace and love,

and,

love and peace,

(kirk) kirk gregory czuhai

http://KirkGregoryCzuhai.WS :hihi:

[Qfwfq]

It would have to be a nu-antinu pair and it would typically mean changing from an electron to another type of lepton, e. g. e- --> mu- nu antinu.

 

Offhand I couldn't give you more details, even with a strong enough photon the cross-section for it to happen would probably be quite low, you might find Perkins helpful to work it out, if you know the grounding.

[AkiraBakaBaka]

Question? Could not the electron gain momentum, the photon lose energy and a neutrino be released to conserve momentum?

peace and love,

and,

love and peace,

(kirk) kirk gregory czuhai

http://KirkGregoryCzuhai.WS ;)

 

If the free plasma electron were to be accelerated by the photon, it would emit bremsstrahlung or cyclotron radiation, which could possibly help explain the Cosmic Microwave Background (electrons in plasma clouds of intergalactic space being bombarded by light, perhaps, flooding the cosmos with this low level secondary radiation).

 

I like the explanation of light being scattered but not absorbed. What a strange place intergalactic space is...

[Qfwfq]

If the free plasma electron were to be accelerated by the photon, it would emit bremsstrahlung or cyclotron radiation

Actually, it would be just the inverse process, except for the fact that it couldn't conserve energy-momentum.

 

What you really need to do is to learn fairly basic RQFT, if you're feeling up to it, books like Schweber or Bjorken-Drell are good starters.

[Kirk Gregory Czuhai]

Actually, it would be just the inverse process, except for the fact that it couldn't conserve energy-momentum.

 

What you really need to do is to learn fairly basic RQFT, if you're feeling up to it, books like Schweber or Bjorken-Drell are good starters.

 

sir: !

 

i am trying to figure out what the RQ in RQ field theory (i presume) means, help?!

 

so apparently a free electron canNOT? :friday: be scattered by a photon? emitting a lower energy photon, gaining energy, and emitting a neutino to conserve momentum?

[GAHD]

sir: !

 

i am trying to figure out what the RQ in RQ field theory (i presume) means, help?!

 

so apparently a free electron canNOT? :friday: be scattered by a photon? emitting a lower energy photon, gaining energy, and emitting a neutino to conserve momentum?

 

I'm not shure but I'll take a stab; Raman Quantum Feld theory?

[Kirk Gregory Czuhai]

You would get scattering from photon-electron collision. There is a small literature on accelerating electrons with an intense laser beam. The interaction has a low cross-section.

 

IF UncleAl, would ever "talk" to me again!

where is this "small literature?"

would not the electron HAVE TO emit also a neutrino to conserve momentum?

[Qfwfq]

i am trying to figure out what the RQ in RQ field theory (i presume) means, help?!

Relativistic Quantum.... Field Theory. Feynman diagrams and a few equations. You wouldn't need to go through quite all the formalities such as Fock space or renormalization, just the backbone, like.

 

so apparently a free electron canNOT? :friday: be scattered by a photon? emitting a lower energy photon, gaining energy, and emitting a neutino to conserve momentum?

It's enough for there to be two photons. One of these may be the field of a nearby massive charged particle but that isn't what you mean be a free electron. A free electron may absorb a photon and emit one, this is often called Compton scattering and doesn't require any neutrino emission.

[Kirk Gregory Czuhai]

Relativistic Quantum.... Field Theory. Feynman diagrams and a few equations. You wouldn't need to go through quite all the formalities such as Fock space or renormalization, just the backbone, like.

 

It's enough for there to be two photons. One of these may be the field of a nearby massive charged particle but that isn't what you mean be a free electron. A free electron may absorb a photon and emit one, this is often called Compton scattering and doesn't require any neutrino emission.

my physics is old, rusted out, and i have hardly a physics text at my disposal norwish to omg, google physics!

may i however ask about this Compton scattering; has it been thourghly

considered in cosmological models? i mean in other words does not this

Compton scattering give ANOTHER cause for red-shift of spectra in addition

to gravitational red-shift?

AND IF SO, can anyone give a reference hopefully from the web where the

amounts of these two red shifts are discussed?

seems to me that if Compton scattering is of a significant amount in the

universe and not accounted for basing all red shift of spectra on gravitational effects would overestimate the age of the universe.

comments please?

not that it matters a whole lot to my overall happiness knowing ignorance

is such bliss.:hihi:

[Qfwfq]

may i however ask about this Compton scattering; has it been thourghly considered in cosmological models? i mean in other words does not this Compton scattering give ANOTHER cause for red-shift of spectra in addition to gravitational red-shift?

 

....

 

seems to me that if Compton scattering is of a significant amount in the universe and not accounted for basing all red shift of spectra on gravitational effects would overestimate the age of the universe.

I'm sure cosmologists know about Compton scattering and I'm sure they can distinguish it from Doppler shift by the spectrum.

 

You see, if a source is receding from the observer at a given velocity each emitted wavelength will be shifted by a definite amount for the observer. The spectra remain recognizeable and that's how they know what gasses there are around a star. If they couldn't recognize the spectra and compare them with the unshifted ones they couldn't even say the spectra are shifted.

 

Compton scattering is a collision and it changes the distribution very much. Totally different effect from Doppler.

[Kirk Gregory Czuhai]

I'm sure cosmologists know about Compton scattering and I'm sure they can distinguish it from Doppler shift by the spectrum.

 

You see, if a source is receding from the observer at a given velocity each emitted wavelength will be shifted by a definite amount for the observer. The spectra remain recognizeable and that's how they know what gasses there are around a star. If they couldn't recognize the spectra and compare them with the unshifted ones they couldn't even say the spectra are shifted.

 

Compton scattering is a collision and it changes the distribution very much. Totally different effect from Doppler.

but at least classically i would expect that the electromagnetic field of the photon as it travels would interact somehow with the free electrons! quantum mechanically one would say the free electrons would have overlapping energy levels? would this not shift the spectra in a very small almost continuous way similiar to the dopler shift for each interaction?

love and peace,

and,

peace and love,

(kirk) kirk gregory czuhai

p.s. NOW some people are objecting to me placing the urls i have in my signature? WHAT THE?!!!

[Qfwfq]

quantum mechanically one would say the free electrons would have overlapping energy levels?

Actually, for any free particle the energy and momentum have a continuous spectrum, unlike in the case of bound states (e. g. electron orbitals).

 

would this not shift the spectra in a very small almost continuous way similiar to the dopler shift for each interaction?

Compton scattering can occur with arbitrarily small variation of wavelength and it depends on the angle. In any case it is a form of scattering and the observed effects are quite unlike the Doppler shift.

 

NOW some people are objecting to me placing the urls i have in my signature? WHAT THE?!!!

They are indeed quite outside the purposes of this site, which is available very much by virtue of paid advertisements. Only staff can decide whether or not to admit an advertisement, or a link to one, or to anything concerning payment.