Laser Diode is another popular diode for its kind. This is an optical diode which emits light but with stimulated process. The name LASER implies Light Amplification by Stimulated Emission of Radiation.
Stimulated Emission
This is a PN junction diode whose action starts when a light ray is incident on it. With a light ray, when photons get incident on an atom, the atom gets excited and it reaches an upper level which can be termed as a Higher Energy Level.
The atom when shifts from the higher energy level to a Lower Energy Level, it releases two photons which are similar in characteristics to the incident photon and are in equal phase to it. This process is called as Stimulated Emission. An atom can generally stay in this excited state for 10-8 secs of time.
So, the above process sets the principle for laser diode.