:Light Amplification by Stimulated Emission of Radiation

A device produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels
When they return to lower energy levels by stimulated emission, they emit energy.

PROPERTIES

Monochromatic
Concentrate in a narrow range of wavelengths (one specific colour).

Coherent
All the emitted photons bear a constant phase relationship with each other in both time and phase

Directional
A very tight beam which is very strong and concentrated.