Introduction

The word laser is an acronym (an abbreviation pronounced as an ordinary word) of Light Amplification by Stimulated Emission of Radiation. Lasers are devices that produce or amplify a beam of narrow, low-divergence light with a well-defined wavelength within the optical region of the electromagnetic spectrum, covering the infrared, the visible and the ultraviolet. Historically, the laser is very different from other 20th century inventions as it first appeared as an imaginary literary creation.