Reality → Tech → Laser → Basics
The laser (acronym for Light Amplification by Stimulated Emission of Radiation) amplifies light of a specific frequency through an interaction of photons with electrons of the right atoms with the right energy levels that produces intensified emission of radiation of the same quality as the irradiation. This process, known as stimulated emission, is difficult to achieve because absorption and spontaneous emission are normally predominant when atoms are being irradiated [1] . To achieve amplified light radiation through a chain reaction of stimulated emission, it was necessary to find a way to generate unnatural 'population inversion', a condition where most atoms are in an excited state rather than in their natural state of equilibrium. The theoretical groundwork by Townes et al. was awarded with a Nobel Prize, and the first laser was constructed by Maiman.
In a 1917 paper, Einstein predicted, based on the principal of thermodynamical equilibrium, 'stimulated' emission as one of three possible ways of photon/electron interaction (the other two being adsorption and spontaneous emission). A photon emitted by stimulation would have the same frequency, phase, polarization, and direction of movement, as the stimulating photon.