Question

what is laser

Answer 1

A laser is a beam of monochromatic light in which all the waves within the beam are in phase and coherent with each other. Laser is actually an acronym and stands for Light Amplification by Stimulated Emission of Radiation. This accurately describes how a laser works, in that the atoms within the "lasing chamber" are excited such that all their electrons are in the same energy level.

When the electrons decay to a lower energy state they emit photons of a characteristic wavelength, which then stimulate the decay of other electrons, which emits more photons of the same wavelength, but which are coherently in phase with the triggering photons.