The word "LASER" is an acronym for "Light Amplification by Stimulated Emission of Radiation". Light that comes from a conventional light source radiates in all directions and in various wavelengths that reinforce or cancel each other. On the other hand, light from a laser beam travels in one direction in straight line and in a specific wavelength only; thus, the laser beam is a very narrow beam. Laser radiation may be released either as a pulse or a continuous wave radiation. Note that laser beams are not limited to visible wavelengths only. Though a laser beam produces only one wavelength, laser units can be designed over a wide range of frequencies, from infrared to ultraviolet regions. There are many types of lasers including gas lasers, fiber lasers, solid state lasers, dye lasers, diode lasers and excimer lasers.