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Laser system

A laser is a device that produces monochromatic, coherent light through stimulated emission of photons from the atoms or molecules of a lasing medium, which have been excited from the ground state to a higher energy level. Lasers are employed in a wide variety of uses: medical devices, communications, scientific research, holography, and laser light shows. A laser device includes a gain medium situated within a laser cavity defined by two end mirrors and a pump source used to pump the gain medium to an energy state sufficient to support lasing operation. Many types of lasers have been developed: solid state lasers that utilize an optically-pumped gain media such as Nd:YAG, semiconductor lasers that are pumped by an electrical current applied directly across the semiconductor material, and gas lasers in which a gas such as HeNe or argon is disposed within an electrical discharge tube. Liquid lasers most commonly contain of a gain medium of organic dye salts which are dissolved in solvents such as methanol or water. The gain medium is excited by light produced typically by flashlamps or another laser. These dye lasers exhibit gain across a broad region of the visible to near infrared spectrum. The high gain cross section and broad tunability make these lasers attractive for a number of uses. However, these dye lasers exhibit a very short upper-state lifetime and low saturation fluence which makes them unsuitable for high energy applications. A semiconductor laser provides a low driving voltage as compared to a solid-state laser device or a gas laser device, while it is small-size and lightweight. Therefore, it has been extensively used as a laser beam source for an optical disk system, an optical communication system. However, the optical output obtained from one semiconductor laser is limited to approximately several milliwatts to several hundreds of milliwatts in CW (constant wave) operation. It is thus quite difficult to apply the semiconductor laser to the aforementioned fields. Since the laser beam of the semiconductor laser has a great divergent angle, high accuracy is required for the configuration and arrangement of optical elements. Solid-state lasers (SSL) have received particular attention in recent years. Such lasers typically include a solid-state lasing medium (crystal or glass) doped with suitable rare-earth ions that are optically pumped with light emitting from one or more semiconductor diodes to produce coherent light.