The difference between spontaneous emission and stimulated emission
Spontaneous emission: In atoms in an excited state, electrons can only stay on the excited state energy level for a short period of time, and then spontaneously jump to a lower energy level and emit a photon at the same time. This radiation is called spontaneous emission. .
Stimulated radiation: When the atom is in the excited state E2, if there is exactly a photon of energy (here E2>E1), under the influence of the incident photon, the atom will emit a same photon and jump to the lower energy level E1, This radiation is called stimulated radiation.
Difference: Unlike spontaneous radiation, radiation must occur under the influence of external light and emit a photon that is identical to the external photon. Stimulated radiation light is coherent light. The stimulated radiated light plus the original extraneous light makes the light intensity amplified in the direction of propagation. Spontaneous radiation is a spontaneous process that is not affected by the external radiation field. Each atom is independent of each other in the process of spontaneous transition. The spontaneous radiation generated by different atoms has a certain arbitrariness in frequency, phase, polarization direction and propagation direction.