Lasers are constructed from three principal parts: an energy source called the pump source; a gain, or laser, medium where amplification takes place; and an optical resonator, usually formed by two or more mirrors. The first laser, built in 1960, used a ruby rod with polished ends and produced intense pulses of red light. Since then, various materials have been used as the active media in lasers, including solids, such as crystals, as well as gasses and liquids. What are superluminescent lasers? Discuss
Source: The Free Dictionary