Lasers basics mechanism and principles


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Lasers basics mechanism and principles

  2. 2. • In 1917, Albert Einstein first theorizedabout the process which makes laserspossible called "Stimulated Emission."
  3. 3. LASER is an acronym for light amplification by StimulatedEmission of radiation.When radiation interacts with matter we have three processes togenerate laser light.(1) Optical Absorption(2) Spontaneous Emission(3) Stimulated Emission
  4. 4. Characteristics of LasersThe most important characteristics of lasers are1. High Directionality → Angular spread 10 micro radians2. High Monochromacity3. High Coherence → (a). Spatial coherence(b). Temporal coherence4. High Intensity:The number of photons coming out from a laser per secondper unit area is given by2rhPnυπ=
  5. 5. Incandescent vs. Laser Light• Many wavelengths• Multidirectional• Incoherent• Monochromatic• Directional• Coherent
  6. 6. Spontaneous Emission• Incoherent• Less intensity• Poly chromatic• Less directionality• More angular spread• No need of externalenergyStimulated emission• Coherent• High intensity• Mono chromatic• High directionality• Less angular spread• External energy isrequired
  7. 7. Spontaneous &Stimulated emission
  8. 8. • Stimulated emission
  9. 9. Stimulated emission
  10. 10. Energylevel diagram
  11. 11. • Video of laser with diffraction gratingLasers and Diffraction Gratings_xvid.avi
  12. 12. absorptionSpontaneousemissionStimulatedemissionE1E2N1N2)(υρ Supplied energyEinstein’s Co-efficients• Consider two energy levels E1 and E2.• N1 and N2 be the number of atoms per unit volume present at thelevels E1 and E2 respectively.
  13. 13. radiation.ginteractinofdensityenergy(v)&,absorptionstimulatedoftcoefficienEinstientheisBalityproportionofconstanttheWhere)(B(v)&NtoalproportionisrateabsorptionStimulated:Absorption(1)121121ρρρvN=
  14. 14. emission.sspontaneouoftcoefficienEinstientheisAalityproportionofconstanttheWhere)2(ANtoalproportionisrateemissionsSpontaneou:EmissionsSpontaneou(2)212212−−−−−= N
  15. 15. emission.stimulatedoftcoefficienEinstientheisBalityproportionofconstanttheeWher)3...().........(B)(&NtoalproportionisrateemissionStimulated:EmissionStimulated(3)212212vNvρρ=
  16. 16. For system in a equilibrium1)()()()()()()(211221212121122121212121212212212121212212121−=−=−==−+=BBNNBAvBBNNAvBNBNANvANBvNBvNANBvNBvNρρρρρρρ
  17. 17. )6.....(}.........1)kThexp(1{8(v)bygivenisdensityradationtheradiation,bodyblackoflawsplanckfrom)5.....(..........1)exp()(.E&Elevelsenergyofsdegeneracyareg&gWhere)exp(lawondistributimanBoltstoAccording33212112212121212121−=−==υυπρυρυchkThggBBBAvkThggNN
  18. 18. Comparing equations (5)& (6))8........(8)7........(1332121212121212112chBABgBgggBBυπ===
  19. 19. 1)kThexp(R}1)kThexp(1{8)8()()8(R8)()(3333332121212212−=−→===υυυπυπρυπρρchchvcheqfromBvARBvNANRnThe equation shows ratio of spontaneousEmission Rate to stimulated emission rate.
  20. 20. Population inversionTo achieve more stimulated emission population of theexcited state N2 should be made larger than the lower stateN1 and this condition is called population inversion.E1E2N1N212 NN >
  21. 21. Three level Laser systemNEE0E1E2 Fast decayLaser transitionpumpingMeta stable level
  22. 22. Four level laser systemNEE0E1E2Fast decayLaser transitionpumpingE3Meta stable state
  24. 24. Types of LASERS• Solid state Lasers(Ruby laser)• Gas Lasers(He-Ne laser)• Liquid lasers( Europium laser)• Semiconducting lasers( Ga As laser)• Dye lasers(Coumarian laser )
  25. 25. Ruby LASER1. Maiman in 1960.2. Solid State Laser.3. Active Medium: Al2O3doped with 0.05% Cr3+ions(10cmlong & 0.5cm diameter).4. Resonant Cavity: Fully reflecting surface & partiallyreflecting surface.5. Pumping System: Helical Xenon flash lamp.6. Three level laser system.7. Wave Length: 694.3nm.8. Pulsed Laser.9. Widely used in Echo technique & Pulsed Holography
  26. 26. Ruby laser
  27. 27. NEE0E1E2 Fast decayLaser transition69430ApumpingMeta stable levelEnergy level diagram of Ruby laserShort lived state
  28. 28. He-Ne LASER1.Ali Javan in 1961.2.Gas Laser..3.Active Medium: Helium & Neon Mixture 10:1ratio... Neon at 0.1mm of Hg and He at 1mm of Hg.4.Resonat Cavity: Fully & partially reflected surfaces…5.Pumping System: Discharge electrodes…6.Four level Laser System.7.Wave Length:632.8nm.8.Red color Continuous Laser.9.Widely used in Interferometer Experiments &Holography.
  29. 29. DischargeelectrodesHe + Ne (10:1)0.1mm of HgDischarge tubeFully reflectingmirrorPartially reflectingmirrorLaser out put
  30. 30. Energy level Diagram of He-Ne Laser
  31. 31. Semiconductor Laser1.Semiconductor Laser is also called as DiodeLaser.2.The wave length of the emitted light depends uponthe Energy band gap of the material.3.Diode Lasers are always operated in forward bias..4.Working Principle: When we apply forward biasto a PN-Diode, charge carrier recombination takesplace.. Then in such a process the energy isemitted in the form of light radiation..5.Active Medium: Ga Al As diode or Ga AsP diode..6.Out put Wave length:GaAlAs:750-900nm,.GaAsP:1100-1600nm..7.Pulsed & Continuous Laser8.Extensively used in fiber optic communicationsystems because of low cost and small in size.
  32. 32. • Homo junction semiconductor laserP and n type are from same direct bandgapsemiconductorsEx:-p-Ga As ,n-Ga AsDraw backs:-1)Requires high threshold current densities2)O/p is in pulses3)Less directional4)Poor coherence
  33. 33. • Hetero junction semiconductor laserP and n type are from different directbandgap semiconductorsEx:-p-Ga As ,n-Al Ga AsDraw backs:-1)Requires less threshold currentdensities2)O/p is continuous3)High directional4)High coherence
  34. 34. gggEhchcEhE===λλυThe Energy band gap of a materialWhere c is the velocity of light & h is Plancks constant.
  35. 35. PNActiveregionPositiveMetal contactNegativeMetal contactForwardbiasing
  37. 37. MEDICAL
  38. 38. • Dermatology• Fractional skin resurfacing• The appearance of facial skin torestore a more youthful appearance• Only five days of healing are necessary
  39. 39. •stretch marks,sunspots,wrinkles,birthmarks, andhairs ,tattooremoval etc
  40. 40. •Endoscope surgery
  41. 41. ••An endoscope
  42. 42. LASIK• UV (193 nm) excimer laser is used toreshape the cornea and thus correct apatient’s eyesight• for near-sightedness and/or astigmatism.
  43. 43. • Laser Welding• Laser Cutting• Laser Trimming• Laser Marking• Barcode readers•INDUSTRIAL &COMMERCIALAPPLICATIONS
  44. 44. Laser cutting process on a sheet ofsteel.
  45. 45. • CO2 lasers are used for industrial cutting ofmany materials including mild steel,aluminum, stainless steel, titanium, paper,wax, plastics, wood, and fabric• When the material is exposed to laser itproduces intense heat, thus the material isheated and melted
  46. 46. • Cutting and peening of metals and othermaterial, welding, marking, etc.• surveying,• LIDAR / pollution monitoring,
  48. 48. Communication applications• Optical fibres• Barcode readers• Laser engraving of printing plate• Laser bonding of additive markingmaterials for decoration and identification,• Laser pointers• Holography
  49. 49. Fibre optic communication
  50. 50. • 3D laser scanners for accurate 3Dmeasurement.• Laser line levels are used in surveying andconstruction. Lasers are also used forguidance for aircraft.• .• In laser printers: gas and diode lasers playa key role in manufacturing high resolutionprinting plates and in image scanningequipment.
  51. 51. Laser Pointers and Handheld Lasers• Laser pointers are great tools for businesspresentations, academic lectures,speaking engagements, astronomy, star-pointing, etc.• Green laser pointers are 5 to 20 timesbrighter than traditional red laser pointers,so visibility is much better on projectionscreens
  52. 52. HOLOGRAPHY• Two photographs of a single hologramtaken from different viewpoints
  53. 53. Identigram as a security element in aGerman identity card
  54. 54. • Security holograms are very difficult toforge, because they are replicated from amaster hologram that requires expensive,specialized and technologically advancedequipment• They are also used in credit and bankcards as well as passports, ID cards,books, DVDs, and sports equipment.
  55. 55. Quality and applications of laserscanning for civil engineering
  56. 56. • The laser scanning is capable to provide3-dimensional information of thesurrounding environment for topographicsurveys with an accuracy equivalent totraditional land surveys
  57. 57. ATM MACHINE(Automated tellermachine)
  58. 58. COMPUTERS
  59. 59. A handheld barcode scannerA barcode reader (or barcodescanner) is an electronic device forreading printed barcodes.
  60. 60. Laser printer
  61. 61. • A laser printer is a common computerperipheral that rapidly produces highquality text and graphics on plain paper• Respiratory health risks• some printers emit sub-micrometreparticles which some suspect may beassociated with respiratory diseases
  62. 62. Lasers in military
  63. 63. Target designator
  64. 64. Common Laser Signs and Labels
  65. 65. THANK YOU