Question

What are i) spontaneous emission ? and ii) and stimulated emission?

Answer 1

Spontaneous Emission :

It is a process in which a transition of an atom/molecule/subatomic particles take place from an excited energy state to a lower energy state ( i.e. ground state) and emits quantum in the form of photon.

Spontaneous emission is responsible for most of the light we see all around us.

Stimulated Emission:

It is a process by which an incoming photon of a specific frequency can interact with an exited atomic electron , causing it to drop to a lower energy state.

This is a principle behind the working of a laser.