Laser beam material processing, Mechanical Engineering

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LASER BEAM MATERIAL PROCESSING

 

Light Amplification of Stimulated Emission of Radiation (LASER) is generated when a lasing medium is excited by a source of energy. Gases like argon, helium, neon and carbon dioxide are used as a lasing medium. In addition, Neodymium - Doped Yttrium Aluminium Garnet (Nd:YAG) is the most widely used solid state lasing medium. At the heart of the lasing phenomenon is the ability of photons to stimulate the emission of other photons, each having the same wavelength and direction of travel as the original. According to quantum theory, atoms and molecules have discrete energy levels and can change from one level t o anot her in discontinuous jumps. The energy change required for a jump is provided by the atom's absorption or emission of a burst of electromagnetic radiation. The radiation frequencies involved and the energy spacings between levels are characteristic of the atom, and thus differ from element to element.

Generally, atoms or molecules remain quiescent at their lowest energy level, or ground state. But, if these particles are excited into higher energy states by an intense flash of light, an electrical Charge, or other means they will in dropping back to the normal ground state, emit incoherent light in the process. (This is what happens in fluorescent lamps and some types of street lights). In a laser cavity, such emitted photons are trapped between highly polished and parallel mirrors, forcing them to bounce back and Forth in the cavity. Whenever, a photon of any particular wavelength passes close to another excited particle, the second particle will also be stimulated to emit a photon that is identical in wavelength phase and spatial coherence to the first. Both phot ons are now capable of stimulating the emission of more photons like themselves and these too, become part of the growing wave between mirrors. The wave length of each photon is related to its energy E. Lasing begins when enough photons are present and if one of the mirrors is partially transparent, a highly disciplined, intense, now coherent beam is emitted.


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