Spontaneous Emission:
We know that when a quantum mechanical system such as atom, molecule or subatomic particle (electron, proton etc.) absorbs extra energy, it goes in a excited energy state. To return to its normal or ground state, it emits the absorbed extra energy in the form of photon at an undetermined time. This unpredictable release of photon energy is known as spontaneous emission.
Stimulated Emission:
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase, frequency, polarization, and direction of travel that are all identical to the photons of the incident wave.
Difference between Stimulated Emission and Spontaneous Emission:
