Photons have the largest range of energy and central in a variety of energy conversions. Photons interact with electric and magnetic entities. For example, electric dipole which in turn are excited by optical phonons or fluid particle vibration, or transition dipole moments of electronic transitions. In heat transfer physics, the interaction kinetics of phonon is treated using the perturbation theory (the Fermi golden rule) and the interaction Hamiltonian. The photon-electron interaction is H p h − − e = − − e c m e ( a + a † † ) a e ⋅ ⋅ p e = − − ( ℏ ℏ ω ω p h , α α 2 ε ε o V ) 1 / 2 ( s p h , α α ⋅ ⋅ e c x e ) ( a + a † † ) ( c e i κ κ ⋅ ⋅ x + c † † e − − i κ κ ⋅ ⋅ x ) , where p e is the dipole moment vector and a and a are the creation and annihilation of internal motion of electron. Photons also participate in ternary interactions, e.g., phonon-assisted photon absorption/emission (transition of electron energy level). The vibrational mode in fluid particles can decay or become excited by emitting or absorbing photons. Examples are solid and molecular gas laser cooling.