I De Broglie relation - new student

[mainguy]

Hi physics folk,

Thought you guys would be able to clarify something, self study learner here getting into quantum.
So I've just learned about the De Broglie relation and The Photoelectric effect and am bamboozled (in a good way).

The notion being that light is absorbed in packets. However I'm unclear on this, if E = hf, surely you could arrange four photons (each with 1/4 of the excitation energy of the electron) so they overlap perfectly on the electron and thus excite it, or is it literally impossible in any scenario?

Also I was thinking about whether this quantum property is intrinsic to light. If you have an atom moving relative to an observer at 0.5c, away from a beam of photons shining on the atom, then the observer notes that the moving atom sees a frequency given by the classic doppler shift, e.g. Photons with a lower frequency.

Meanwhile in the atom's frame it notes a different frequency, given by the special relativistic doppler shift. That is, the two disagree on the photons striking the electron.

However if we add the time dilation factor to the observer frame the agreement is of course perfect. However does this not indicate that the wave packet energy is not intrinsic to the wave, that is waves of a different frequency can appear to create the same excitation?

 

[.Scott]

In order for 4 low-energy photons to create the same effect as 1 hi-energy photon, the electron orbital would have to have some way of storing the energy - even for only a femtosecond. No such mechanism exists.

As for your second question: it's all about the available energy. So what counts is what the atom sees. If we see a low-energy photon, but it sees a high-energy one, that higher energy will be available to the electron.

 

[kith]

The notion being that light is absorbed in packets. However I'm unclear on this, if E = hf, surely you could arrange four photons (each with 1/4 of the excitation energy of the electron) so they overlap perfectly on the electron and thus excite it, or is it literally impossible in any scenario?

Multiphoton processes are indeed possible, see https://en.wikipedia.org/wiki/Two-photon_absorption. Such effects belong to non-linear optics and occur only at sufficiently high intensities.

 

[.Scott]

Multiphoton processes are indeed possible, see https://en.wikipedia.org/wiki/Two-photon_absorption. Such effects belong to non-linear optics and occur only at sufficiently high intensities.

Thanks for shining light on that for us. ;)

 

[mainguy]

Multiphoton processes are indeed possible, see https://en.wikipedia.org/wiki/Two-photon_absorption. Such effects belong to non-linear optics and occur only at sufficiently high intensities.

great thanks man!