Resonance fluorescence
(重定向自Resonant fluorescence)
Resonance fluorescence is fluorescence from an atom or molecule in which the light emitted is at the same frequency as the light absorbed.
A photon is absorbed, causing an electron to jump to a higher energy level from which, after a delay, it falls back to its original level, emitting a photon having the same energy as the one absorbed. The emission direction is random.