(I am not sure what is the best subforum for this doubt, please move the thread if necessary) When we study the interaction of the electromagnetic waves with a charged particle (let's say an electron) we can find two totally different approaches in the literature. If we are talking about light or lower frequency radiation, a classical view is often employed and it is said that the electron oscillates due to the electric field of the wave. However, for higher frequencies (gamma and X-rays) the e.m. field is viewed as particles that hit the electron (the Compton effect). Since both radiations are of the same nature and they differ only in the frequency, and all the intermediate frequencies are possible, it is reasonable to think that there should exist a smooth transition between the "electric-like" behavior and the "particle-like" behavior, but I have trouble to figure it out. I cannot imagine how it is. For example, if we irradiate a conducting medium or a plasma with UV light (between visible and X-rays), is the interaction with the charges best described by the classical approach or by Compton scattering?. Are both effects present as different, simultaneous phenomena or there is something in between? If we could irradiate the electrons with a coherent X-ray beam (I think it can be achieved in a synchrotron, but not sure), could we get an ordered oscillation instead of Compton effects? If we have a visible or radio-frequency radiation very dim so that the photon flux is very low, would the interactions be "compton-like"? Any explanation, reference or link that could help to understand this transition would be most appreciated!