Glass is a typical insulator: electrons inside their atoms has band gaps, which are setting limits for low-frequency photons and prohibits energy conveying for them.

Therefore, light just passes through (transparency).

Metals, on the other hand, as conductors has NO band gaps, so in theory (as I took it) any photon regardless of its frequency may give away its energy to electrons.

My question is: does any photon therefore will (definitely) excite such electrons?

Simply speaking: are there any quantum mechanical processes\phenomena that allows a single photon pass through "NO band gaping" orbitals in conductors? And does these processes\phenomena (if there are any) depends on photon's frequency?


1 Answer 1


You are basically asking if light can pass through metal. The answer is plasmons.

Plasmon is a quantum of plasma oscillation. Light consists of photons (optical oscillation), and plasma oscillation consists of plasmons. Plasmons are oscillations of the free electron gas density.

Plasmons play a large role in the optical properties of metals and semiconductors. Frequencies of Light below the plasma frequency are reflected by a material because the electrons in the material screen the electric field of the light. Light of frequencies above the plasma frequency is transmitted by a material because the electrons in the material cannot respond fast enough to screen it. In most metals, the plasma frequency is in the ultraviolet, making them shiny (reflective) in the visible range.


  • $\begingroup$ No - not exactly, I'm afraid. I asked if photon can pass, or reflect, or scatter any other way from electron within metal without losing its energy. $\endgroup$ Nov 29, 2019 at 23:16
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    $\begingroup$ @VictorNovak that is elastic scattering. Elastic scattering is the only way (of interaction) for photons to keep their energy level. en.wikipedia.org/wiki/Elastic_scattering this is about photon elastic scattering inside metals arxiv.org/abs/cond-mat/9307033 $\endgroup$ Nov 29, 2019 at 23:27
  • $\begingroup$ That seems helpful, thank you! $\endgroup$ Nov 29, 2019 at 23:43

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