ABSTRACT
The basis for laser physics can be traced back to Albert Einstein when he published his treatise on the quantum theory of radiation in 1917.1 In this paper, he theorized the existence of a phenomenon by which a photon can stimulate an atom or molecule and produce multiple identical photons. The process by which electricity is converted into light is called ‘stimulated emission’ and microwaves were the first portion of the energy spectrum used to demonstrate this effect. It was not until the mid 1950s that Gordon and colleagues2 developed the laser based on Einstein’s principles, and three years later Schawlow and Townes3 developed the theory of light amplification by the stimulated emission of radiation, which is more simply referred to by the acronym ‘laser’. In this context, radiation merely refers to light, not the ionizing radiation associated with x-rays. Lasers are essentially devices that produce intense beams of light energy which have three physical characteristics that differentiate them from normal light:(1) monochromaticity; (2) collimation; and (3) coherence. In other words, the light of any particular laser is of the same wavelength and the waves are in phase both temporally and spatially.
