Suppose a human is lying on a beach. He/she starts to feel warm after exposing his/her skin to the sunlight. I assume that feeling is due to the ability of the human body of "measuring" the increasing in temperature of the skin.
Now I want to understand what are the physical processes involved in this increasing in temperature. Imagine a group of photons impinging on the skin in a certain interval of time. I tried to list the possible interactions from a particle physics perspective between photons and the human tissue and I concluded that the possible interactions may be:
- Compton scattering
- Rayleigh scattering
- Pair production
The first 3 seems to be reasonable, but the fourth one requires an energy threshold too high: there are no incident photons that may have that energy. I conclude that by looking at the spectrum of sunlight that actually reaches the earth's surface below the atmosphere. So I think that the pair production does not play a role in this situation.
Are there any other interaction processes between photons and tissue molecules involved in the increasing of temperature of the human tissue?
After listing the processes I wonder what actually increases the temperature: is the temperature increasing because the photons-molecules interactions lead to a transition of molecules to excited vibrational states? or maybe transitions to excited rotational states?
I thought that another possibility is that the photons interactions are increasing the kinetic energy of the water molecules in the skin or maybe are increasing the lattice vibration of other tissue (skin, bones or others). Are this processes happening simultaneously? One of this processes (for example transition to rotational excited states) is dominant over the others ?
I'm looking to a qualitative answer, without going into too much details of the Biology of the human body. I just want to create an approximate picture of this situation in my mind. I want to create a mental "video" from the instant in which a photon or a group of photons impinges in the skin to the moment in which tissue molecules are affected and the temperature starts rising up.
I thank in advance anyone who answers this question.