Laser ppt by jithin m.p,amrita


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Laser ppt by jithin m.p,amrita

  1. 1. LASERLight Amplification by Stimulated Emission of Radiation By JITHIN MP AM.AR.P2PHY12006 S1 M.Sc PHYSICS
  2. 2. contents Laser and it’s properties Population inversion Einstein’s coefficient and Einstein’s relation Main parts of a laser Three level and four level laser Different types of a laser Applications of laser Conclusion
  3. 3. Induced absorption (stimulated absorption) The process in which an atom sized system in lower energy state is raised in to higher energy state by electro magnetic radiation which is quanta of energy is equal to the difference of energy of the two states is called stimulated absorption. i.e., hν=E2-E1E2 E2E1 E1 Before After
  4. 4. Spontaneous emissionIn the atom initially at upper state E2, itcan brought to E1 by emitting photonof energy hν.This is known asspontaneous emission. Before After emission During E2 E1 Atom in excited state Atom in ground state
  5. 5. Stimulated emissionAccording to Einsteins, under certain condition it is possibleto force an excited atom emit a photon by another photonand the incident light wave must be in same phase .hence weget an enhance beam of coherent light Excited state After emission E2 E1 Ground state ie,
  6. 6. Population inversionpopulation inversion occurs when a system (such as a groupof atoms or molecules) exists in a state with more members inan excited state than in lower energy states. The concept is offundamental importance in laser science because theproduction of a population inversion is a necessary step in theworkings of a standard laser.
  7. 7. Einsteins coefficient and Einsteins relation Let N1 & N2 be the no. of atoms in the ground state and excited state and is the energy density per unit volume Then the ratio of absorption per unit volume Ratio of spontaneous emission per unit volume Ratio of stimulated emission per unit volume Where B12,B21 and A21 are Einsteins coefficient under thermal equilibrium, the rate of absorption = rate of emission
  8. 8. N0. N0. 1
  9. 9. Main parts of a laserActive medium or working substancePumping source or energy sourceOptical resonator
  10. 10. Active medium or working substanceThis is the basic material in which atomic and molecular transitions take place leading to laser action.It is the medium where the stimulated emission take placeDepending the active medium lasers are classified in to different types like solid, gas, dye or liquid, semiconductor laser
  11. 11. Pumping source or energy sourceWith the help of energy source the system can be raised to an excited state, with the help of this source the no. of atoms in higher energy state may be increased and hence the population inversion is achieved. the energy source may also be called pumping source.
  12. 12. Optical resonator  It is specially designed cylindrical tube  Set of mirrors at the ends of which are silvered one end being completely silvered at which the other is partially silvered  Photons are emitted parallel to the axis of the active medium undergo multiple reflections between them  So, the light intensity can be increased Energy source Working substanceFully Partiallysilvered silvered
  13. 13. Three level and four level laser The simplest kind is three level laser which uses and assembly of atom or molecules that have three energy states E1,E2,E3. Where, E1-> ground state E2->meta stable state E3->higher excited stateE3 Excited state E2 Pumping active Meta stable stateE1 Ground state
  14. 14. Four level laserE1->ground state,E2->intermediate,E3->metastable,E4->excited state Excited state E4 Pumping active E3 Meta stable state E2 Intermediate E1 Ground state
  15. 15. Different types of lasersThere are basically four types of lasersSolid state laserGas laserLiquid laser or dye laserSemi conductor laser
  16. 16. Solid state laser In this a ruby like crystal is used which acts as an active medium. It is basically cylindrical in shape. This crystal is surrounded by a xenon flash lamp T. This flash lamp is of helical shape. In this arrangement this lamp acts as a pumping arrangement. Both the ends E1 and E2 of the crystal are properly polished. Similar to the gas lasers, the surface M1 will do the complete reflection but on the other hand M2 will reflect partially. Whenever we will pass the current through the arrangement a laser beam of red color having large intensity will come out.
  17. 17. Gas laserCO2 & He-Ne lasers are the best e.g. gas laser. The CO2 lasers was one ofthe earliest gas laser to be developed, and still of the main useful.The He-Ne laser contain a mixture of helium & neon. This mixture ispacked in to glass tube and it acts as an active medium. Two electrodes areconnected in to high voltage D.C source.Two parallel mirrors are placed in front of each other. both mirrors arepresent inside the tube only one mirror M1 shows the complete reflectionand mirror M2 shows partial reflection. when we pass the electric current through the tube, a continues lightwave will start flowing the tube with constant frequency.
  18. 18. Liquid laser or dye laserIn liquid lasers organic dyes are used as active medium inside the glass tube. The complete circulation of dye is done in the tube with the help of a pump. From this organic dye laser light will emerge out.
  19. 19. Semiconductor laser In these lasers junction diodes are used. Thedoping of p-n junction diode is done. Both theacceptors and donors are doped. These areknown as ILD(Injection Laser Diodes).Whenever the current is passed then the lightmodulation from the ILD can be seen. This isused in various electronic equipments
  20. 20. Properties of laser It is highly coherent It is monochromatic in nature Laser beam is hardly divergent
  21. 21. Applications Modulated laser beam have been used for communication In medical field High power laser have been used for cutting & drilling holes in hard metal and diamonds They have been used in the production and research with holograms, they are also used in high speed photography and fiber optics
  22. 22. conclusion Lasers are device which amplify light and produce beams of light which are very intense, directional andPure in colour. Laser action is preceded by three processes namely absorption, spontaneous emission and stimulated emission. They can solid state ,gas, semiconductor or liquid. Laser can be used for many applications ,helped people develop in many things in our daily life.