Do photons get absorbed by electrons and new ones remitted as they travel across the

[eon_rider]

I'm reading that photons get absorbed by electrons which then emit new photons. (electrons in cosmic gasses or other mediums) So the photons that reach us are not the photons that started out the journey.

 

Is this true?

[stubighead]

I can tell you that photons can interact with electrons and may result in the production of further photons. The original photon may or may not be completely absorbed and may just be deflected off its course. Its all about transfer of energy. So if the photons you are talking about have to pass through matter on their way to us then they may not be the original photons produced by whatever.

 

However many will be as a photon is very small and can easily pass through matter without interacting at all. (think x-rays taken in a hospital, the xrays (photons) have to pass straight through the patient without any interaction to produce a good picture. In this case any xrays deflected or absorbed or created by interaction can result in picture degradation due to them not being original xrays or being off original course.

 

Im not a cosmologist but those are the basic interactions of photons with matter - complete absorption by an electron or nucleus, or deflection by an electron. Either can result in a new photon being created.

 

stu

[swansont]

There's no way to tell if a photon is the same one, because you can make an exact (as far as one can tell) duplicate. Once the photon interacts and changes its energy it has to be considered a different one, and there's no way to make two separate measurements on a randomly encountered photon - the measurement changes or destroys the photon.

[eon_rider]

Wow.

 

That's fantastic.

Very clear. Very cool.

 

Thank you both,

 

best,

 

Eon.

 

PS. It seems a few photons, over vast distances, might be the last members in a relay race from "very far away" to us. But most photons would be the original ones.

[Norman Albers]

X-rays scatter only slightly from bone, so that's why images are not strong. Have you seen the series of small-angle reflector plates used to focus astronomical X-rays? We are in the same realm as my thread "light..dark..matter" where I started talking about this with Swansont. Stubighead makes a clear statement. I am still clueless as to Swansont's last offering about atoms emitting to their local structural vibrations.

[swansont]

X-rays scatter only slightly from bone, so that's why images are not strong. Have you seen the series of small-angle reflector plates used to focus astronomical X-rays? We are in the same realm as my thread "light..dark..matter" where I started talking about this with Swansont. Stubighead makes a clear statement. I am still clueless as to Swansont's last offering about atoms emitting to their local structural vibrations.

 

I don't see where I used "local," "structural" or "vibration" here. So I can't make heads or tails of your objection.

[Norman Albers]

It doesn't have to re-emit a photon; the energy can go elsewhere in the system. Or it may emit one after it gets to a lower energy state.

. This is where I lose your context (this quote from the other thread).

[Klaynos]

When an electron drops down an energy level it doesn't have to emit a photon, it can emit a phonon or some other way to lose it's energy, I havn't studied these much so can't really say much more, they're called non-radioative decays or something like that

[swansont]

When an electron drops down an energy level it doesn't have to emit a photon, it can emit a phonon or some other way to lose it's energy, I havn't studied these much so can't really say much more, they're called non-radioative decays or something like that

 

(non-radiative)

 

That's basically it. You have a vibrational state than can give up its energy through mechanical means (phonons). It can also give up part of its energy (i.e. drop to a lower state but not the ground state) and then emit a lower energy photon. This is basically what happens in the material in a fluorescent light bulb. The original transition is in the UV, this gets absorbed and visible light comes out.

[Norman Albers]

Good, now we are getting to the missing pieces in my understanding. My books deal not so much with solids, and I am acquainted with vibration-rotation states. The phenomenology in solids is what I need to see. When do we deal with electrons, and when do we see modes involving the mass of the nucleii?

[trvlrpsmyrph]

K.I.S.S. (keep it simple scholar)

[Norman Albers]

I was driving at phonon exitations when using the concepts of local structural vibrations. These are what I understand poorly. My confusions still are: how does visible light warm things, if being warm means having spectral energy at lower regimes, microwave and IR? Why is an object opaque or transparent?

[swansont]

I was driving at phonon exitations when using the concepts of local structural vibrations. These are what I understand poorly. My confusions still are: how does visible light warm things, if being warm means having spectral energy at lower regimes, microwave and IR? Why is an object opaque or transparent?

 

An object is transparent if there are no optical absorption transitions in the range in question. For many solids you get absorption because of the band structure and the molecular complexity of the material meaning that there are a lot of possible transitions.

 

As for the warming, you deposit energy and get an increase in vibration. The vibrational energy will be transmitted to other atoms until you reach the statistical distribution present at equilibrium.

[Norman Albers]

 

As for the warming' date=' you deposit energy and get an increase in vibration. The vibrational energy will be transmitted to other atoms until you reach the statistical distribution present at equilibrium.[/quote']

Do these vibrations extend into the visible range, then? I shall read on band structure, and I appreciate your help in putting together these pieces of understanding. Transparency must involve non-absorptive jiggling of available dielectric polarization to give the dielectric constant in the material, no?

[swansont]

Do these vibrations extend into the visible range, then?

 

Do you mean the transitions? Yes.

 

Transparency must involve non-absorptive jiggling of available dielectric polarization to give the dielectric constant in the material, no?

 

Polarizing the molecules due to the EM field affects the index, but I don't think this directly affects the absorption.

[Norman Albers]

Then does a dielectric medium not necessarily have Tyndall scattering? You have given me the missing keys of vibrational modes that you imply interact statistically. This answers the question!

[swansont]

Then does a dielectric medium not necessarily have Tyndall scattering? You have given me the missing keys of vibrational modes that you imply interact statistically. This answers the question!

 

Tyndall scattering happens in a colloidal material, i.e. off of particulates or larger conglomerations of molecules in suspension. I wouldn't expect that in some uniform material.

[VendingMenace]

Do you mean the transitions? Yes.

 

For swansont: Which molecular vibrational transitions are abosorb or emit visible light? Can you give an example? I can't think of any off the top of my head and would like to know what they are (cause that seems kinda cool -- so REALLY high energy vibrations).

[swansont]

For swansont: Which molecular vibrational transitions are abosorb or emit visible light? Can you give an example? I can't think of any off the top of my head and would like to know what they are (cause that seems kinda cool -- so REALLY high energy vibrations).

 

Sorry, I didn't mean to imply that the absorptions were purely vibrational. We were talking about depositing energy and one of the options is for that energy to go into exciting vibrational states, like in an indirect bandgap material, where the energy must go into phonons because emitting a photon wouldn't conserve momentum, or other processes where an electronic transition relaxes via vibrational state transitions.

[Norman Albers]

Is it so that the E&M energy of photons is fundamentally absorbed by electrons; is this either by quantum state transition of an atom or by available outer electrons? Then, are phonons vibrations involving the more massive nucleii or ions? I read they are in some sense acoustic.

[swansont]

Is it so that the E&M energy of photons is fundamentally absorbed by electrons; is this either by quantum state transition of an atom or by available outer electrons? Then, are phonons vibrations involving the more massive nucleii or ions? I read they are in some sense acoustic.

 

The electrons are bound to the nuclei, so the energy is absorbed by that system. But since e.g. when current is flowing it is typically the electrons, one usually associates the energy as being with them.

[Norman Albers]

I guess all things are fundamentally electric but are phonon vibrations characterized by currents?

[swansont]

I guess all things are fundamentally electric but are phonon vibrations characterized by currents?

 

Not as far as I know.

[5614]

Phonons are the quantisation of vibrations within a rigid lattice. How could they be characterised by currents?

 

An electric current, the absorption of a photon, they are all to do with the electrons... this doesn't mean everything is.

 

Phonons when referring to the quantisation of vibrations within a lattice are, as you suggested, involving the ions.

 

=====

 

What do you mean "I read they are in some sense acoustic", are you referring to acoustic and optical phonons?

 

Acoustic phonons: these are what I would call "normal" phonons in a basic monoatomic lattice. They have frequencies which become small at small wavelengths. They can be either transveres or longitudinal.

 

Optical phonons: These occurs in lattices which contain multiple (>1) unit cells (set of ordered ions). Due to the 2nd set of ions there are now two (sets?) of allowed frequencies for vibration. One referred to as the acoustic branch (similar to the vibrations seen with acoustic phonons) and the other the optical branch. The optical branch has a different form of wave motion.

 

Check out the 'Acousitcal phonons' and 'Optical phonons' section on this site:

http://www.chembio.uoguelph.ca/educmat/chm729/Phonons/cont.htm

 

This site shows a good optical (no pun) comparison of transverse optical and transverse acoustic vibrations in a diatomic lattice:

http://www.chembio.uoguelph.ca/educmat/chm729/Phonons/optmovie.htm

[Norman Albers]

I mean I don't know much here and appreciate your expositing!