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  • 1. Rida fatme MS Physics
  • 2. Lasers & its Types  A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Types  Gas lasers  Chemical lasers  Excimer lasers  Solid-state lasers  FEL lasers
  • 3. He Ne Laser  A helium-neon laser, usually called a He-Ne laser, is a type of small gas laser. He-Ne lasers have many industrial and scientific uses, and are often used in laboratory demonstrations of optics.  He-Ne laser is a four-level laser.  Its usual operation wavelength is 632.8 nm, in the red portion of the visible spectrum.  It operates in Continuous Working (CW) mode.
  • 4. Construction of He-Ne laser  The setup consists of a discharge tube of length 80 cm and bore diameter of 1.5cm.  The gain medium of the laser, as suggested by its name, is a mixture of helium and neon gases, in a 5:1 to 20:1 ratio, contained at low pressure (an average 50 Pa per cm of cavity length ) in a glass envelope.  The energy or pump source of the laser is provided by an electrical discharge of around 1000 volts through an anode and cathode at each end of the glass tube. A current of 5 to 100 mA is typical for CW operation.  The optical cavity of the laser typically consists of a plane, high- reflecting mirror at one end of the laser tube, and a concave output coupler mirror of approximately 1% transmission at the other end.  He Ne lasers are normally small, with cavity lengths of around 15 cm up to 0.5 m, and optical output powers ranging from 1 mW to 100 mW.
  • 5. Construction Of He-Ne Laser
  • 6. Working  A description of the rather complex He.Ne excitation process can be given in terms of the following four steps.  (a)When the power is switched on, An energetic electron collisionally excites a He atom to the state labeled 21 S . A He atom in this excited state is often written He*(21 S), where the asterisk means that the He atom is in an excited state.  (b) The excited He*(21 S) atom collides with an unexcited Ne atom and the atoms exchange internal energy, with an unexcited He atom and excited Ne atom, written Ne*(3s), resulting. This energy exchange process occurs with high probability only because of the accidental near equality of the two excitation energies of the two levels in these atoms. Thus, the purpose of population inversion is fulfilled
  • 7. Description of Energy level diagram  When the excited Ne atom passes from metastable state(3s) to lower level(2p), it emits photon of wavelength 632 nm.  This photon travels through the gas mixture parallel to the axis of tube, it is reflected back and forth by the mirror ends until it stimulates an excited Ne atom and causes it to emit a photon of 632nm with the stimulating photon.  The stimulated transition from (3s) level to (2p) level is laser transition.  This process is continued and when a beam of coherent radiation becomes sufficiently strong, a portion of it escape through partially silvered end.  The Ne atom passes to lower level 1s emitting spontaneous emission. and finally the Ne atom comes to ground state through collision with tube wall and undergoes radiation lesss transition.
  • 8. Applications  The Narrow red beam of He-Ne laser is used in supermarkets to read bar codes.  The He- Ne Laser is used in Holography in producing the 3D images of objects.  He-Ne lasers have many industrial and scientific uses, and are often used in laboratory demonstrations of optics.
  • 9. The End