(L&PTD)

Invention of Laser is regarded as one of the most significant scientific achievement of the last century. It was variously referred to as "the light fantastic" and "a solution looking for problems". It represents yet another possible but unstable state in which matter can exist by the passage of very strong electric current or highly ionizing radiation through matter. 

When de excitation of molecules and atoms from this unstable state to stable ground state by dissipation of their excess energy takes place in a resonator, monochromatic, coherent light emission - laser - results.