Laser is light amplification by stimulated emission of radiation. He-Ne laser, carbon dioxide laser and Argon laser are examples of gas lasers. In He-Ne laser a mixture of He and Ne gas is taken in a discharge tube. Pumping mechanism employed is direct electron excitation and inelastic atom-atom collisions. The wavelength in this case is 632.8 nm. Ruby laser and Nd:YAG laser are exadmples of solid state lasers. Ruby rod is used in ruby laser with optical pumping. Wavelength of laser light is around 694.3 nm. Nd:YAG laser emit light in the near infrared region. Semiconductor laser is another laser system which is very economical. Some other laser systems are ion and metal vapour laser, excimer laser, liquid dye laser, free electron laser, chemical laser and heater laser.
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