What is the Difference Between Spontaneous and Stimulated Emission?

Spontaneous and stimulated emission are two processes by which atoms in excited states can release energy in the form of photons. The main differences between these two processes are:

1. Interaction with other photons: Spontaneous emission occurs without interaction with other photons, while stimulated emission takes place when an excited electron interacts with another photon.
2. Direction and phase: In spontaneous emission, the direction and phase of the emitted photons are random. In contrast, in stimulated emission, the direction and phase of the emitted photons are "copied" from the other photon, resulting in a highly directional and coherent light.
3. External influence: Spontaneous emission does not require an external electromagnetic stimulus to release energy, whereas stimulated emission does require an incoming photon of the same frequency as the transition.
4. Occurrence: Spontaneous emission takes place regardless of the population inversion, while stimulated emission occurs only when the gain medium is pumped strongly enough and the population inversion exists.

These differences have significant implications in the application of these processes. For example, spontaneous emission is responsible for the light emission from devices like light-emitting diodes (LEDs), while stimulated emission is the principle behind the highly coherent and monochromatic light produced by lasers.

Comparative Table: Spontaneous vs Stimulated Emission

Spontaneous and stimulated emission are two processes in which an electron transitions from a higher energy level to a lower energy level, resulting in the emission of a photon. Here are the main differences between the two processes:

In summary, spontaneous emission occurs without the need for an external stimulus and is found in devices like LEDs and fluorescent tubes, while stimulated emission requires an external stimulus and is the key process in the formation of laser beams. The rate of spontaneous emission is independent of the spectral energy density per unit bandwidth, whereas the rate of stimulated emission depends on it.