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Imperial College Safety Unit - Introduction to laser safety - 1 Introduction to laser Imperial College Safety Unit - Introduction to laser safety - 2 What is a laser? Imperial College Safety Unit - Introduction to laser safety - 3 The word “laser” is an acronym which stands for Light Amplification by Stimulated Emission of Radiation. Light energy is amplified to extremely high intensity by a process called stimulated emission. The energy generated by the laser is in or near the optical portion of the electromagnetic spectrum. How does a laser work? Imperial College Safety Unit - Introduction to laser safety - 4 Electrons surrounding atoms are excited into higher energy states to create a “population inversion”. The excited electrons release their energy in the form of photons which can, in turn, collide with other excited electrons and cause them to release an identical photon - this is called stimulated emission. As more energy is put in so more photons are released. By reflected the photons back and forth in a mirrored system the amount of energy can be increased. Some of the energy is allowed to escape through a partially coated mirror to create a “laser beam”. Types of laser Gas lasers • including He-Ne and carbon dioxide lasers Dye lasers Solid state lasers Imperial College Safety Unit - Introduction to laser safety - 5 • including neodymium-YAG (Nd:YAG) lasers Semiconductor lasers • diode lasers Chemical lasers Laser light Laser light has the following properties: Imperial College Safety Unit - Introduction to laser safety - 6 • • • • it is monochromatic it is very intense it has low divergence it is coherent. Lasers can have different types of beam output • continuous wave (CW), or • pulsed. Laser “speckle” is caused by scattered laser radiation interfering with incident laser radiation.