Types of laser

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basic defintions of laser, fundamentals of laser, types of laser, He-Ne laser,merits and demerits of laser

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Types of laser

  1. 1. T YPES OF PREPARED BY V.REVATHIAMBIKA LECTURER IN PHYSICS
  2. 2. 7/28/2012INTRODUCTION OF LASER L – LIGHT A – AMPLIFICATION S – STIMULATED E – EMISSION R - REDIATION A. L. SCHAWLOW and C. H. TOWNES IN 1958 2 RUBY LASER by T. H. MAIMANN IN 1960
  3. 3. 7/28/2012BASIC IDEA Consider a group of atoms exposed stream of photons, each with energy h . Let us assume two energy levels E1 and E2 of an atom.  During transition from one energy state to another, the light is absorbed (or) emitted by particles. Under this action, 3 processes can occur.  They are,  Stimulated absorption 3  Spontaneous emission  Stimulated emission
  4. 4. 7/28/2012 MECHANISMS OF LIGHT EMISSIONFor atomic systems in thermal equilibrium with theirsurrounding, the emission of light is the result of:AbsorptionAnd subsequently, spontaneous emission of energyThere is another process whereby the atom in an upper energylevel can be triggered or stimulated in phase with the anincoming photon. This process is:Stimulated emissionIt is an important process for laser actionTherefore 3 process 1. Absorptionof light emission: 2. Spontaneous Emission 4 3. Stimulated Emission
  5. 5. LASER FUNDAMENTALS 7/28/2012 The light emitted from a laser is monochromatic, that is, it is of one color/wavelength. In contrast, ordinary white light is a combination of many colors (or wavelengths) of light. Lasers emit light that is highly directional, that is, laser light is emitted as a relatively narrow beam in a specific direction. Ordinary light, such as from a light bulb, is emitted in many directions away from the source. The light from a laser is said to be coherent, which means that the wavelengths of the laser light are in phase in space and time. Ordinary light can be a mixture of many wavelengths. These three properties of laser light are what can make it more hazardous than ordinary light. Laser light can deposit a lot of energy within a small area. 5
  6. 6. 7/28/2012 INCANDESCENT VS. LASER LIGHT1. Many wavelengths 1. Monochromatic2. Multidirectional 2. Directional3. Incoherent 3. Coherent 6
  7. 7. 7/28/2012 COMMON COMPONENTS OF ALL LASERS1. Active Medium The active medium may be solid crystals such as ruby or Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, or semiconductors such as GaAs. Active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source.2. Excitation Mechanism Excitation mechanisms pump energy into the active medium by one or more of three basic methods; optical, electrical or chemical.3. High Reflectance Mirror A mirror which reflects essentially 100% of the laser light.4. Partially Transmissive Mirror A mirror which reflects less than 100% of the laser light and transmits the remainder. 7
  8. 8. LASER COMPONENTS 7/28/2012Gas lasers consist of a gas filled tube placed in the laser cavity. A voltage (the external pumpsource) is applied to the tube to excite the atoms in the gas to a population inversion. The lightemitted from this type of laser is normally continuous wave (CW). 8
  9. 9. LASING ACTION 7/28/20121. Energy is applied to a medium raising electrons to an unstable energy level.2. These atoms spontaneously decay to a relatively long-lived, lower energy, metastable state.3. A population inversion is achieved when the majority of atoms have reached this metastable state.4. Lasing action occurs when an electron spontaneously returns to its ground state and produces a photon.5. If the energy from this photon is of the precise wavelength, it will stimulate the production of another photon of the same wavelength and resulting in a cascading effect.6. The highly reflective mirror and partially reflective mirror continue the reaction by directing photons back through the medium along the long axis of the laser.7. The partially reflective mirror allows the transmission of a small amount of coherent radiation that we observe as the “beam”.8. Laser radiation will continue as long as energy is applied to the lasing medium. 9
  10. 10. 7/28/2012 LASING ACTION DIAGRAM Excited State Spontaneous Energy Emission Metastable StateIntroduction Stimulated Emission of RadiationEnergy Ground State 10
  11. 11. 7/28/2012 PRINCIPLE OF LASER ACTION Due to stimulated emission the photons multiply in each step giving rise to an intense beam of photons that are coherent and moving in the same direction . hence the Light Is Amplified By Stimulated Emission Of Radiation 11
  12. 12. 7/28/2012 PUMPING METHODS OPTICAL PUMPING DIRECT ELECTRON EXCITATION INELASTIC ATOM – ATOM COLLISION DIRECT CONVERSION 12 CHEMICAL PROCESS
  13. 13. PROPERTIES OF LASER Monochromatic Concentrate in a narrow range of wavelengths (one specific colour). Coherent All the emitted photons bear a constant phase relationship with each other in both time and phase Directional A very tight beam which is very strong and concentrated.
  14. 14. PART 2: 7/28/2012LASER HAZARDS 14
  15. 15. TYPES OF LASER HAZARDS 7/28/20121. Eye : Acute exposure of the eye to lasers of certain wavelengths and power can cause corneal or retinal burns (or both). Chronic exposure to excessive levels may cause corneal or lenticular opacities (cataracts) or retinal injury.2. Skin : Acute exposure to high levels of optical radiation may cause skin burns; while carcinogenesis may occur for ultraviolet wavelengths (290-320 nm).3. Chemical : Some lasers require hazardous or toxic substances to operate (i.e., chemical dye, Excimer lasers).4. Electrical : Most lasers utilize high voltages that can be lethal.5. Fire : The solvents used in dye lasers are flammable. High voltage pulse or flash lamps may cause ignition. Flammable materials may be ignited by direct beams or specular reflections from high power continuous wave (CW) infrared lasers. 15
  16. 16. 7/28/2012 LASER CLASSThe following criteria are used to classify lasers:1. Wavelength. If the laser is designed to emit multiple wavelengths the classification is based on the most hazardous wavelength.2. For continuous wave (CW) or repetitively pulsed lasers the average power output (Watts) and limiting exposure time inherent in the design are considered.3. For pulsed lasers the total energy per pulse (Joule), pulse duration, pulse repetition frequency and emergent beam radiant exposure are considered. 16
  17. 17. 7/28/2012 LASER COMPONENTS Optical Resonator Output Beam Active Medium High Reflectance Output Coupler Mirror (HR) Mirror (OC) Excitation Mechanism 17Laser-Professionals.com
  18. 18. 7/28/2012 18
  19. 19. OPTICAL RESONATOR Two parallel mirrors placed around the gain medium. Light is reflected by the mirrors back into the medium and is amplified . The design and alignment of the mirrors with respect to the medium is crucial. Spinning mirrors, modulators, filters and absorbers may be added to produce a variety of effects on the laser output.
  20. 20. COMPARISON CHART FOR ALL THE LASERSCharacter Nd-YAG laser He-Ne laser CO2 laser Semiconductistics or (Ga-As) laserType Doped insulator Gas laser Molecular Semiconductor laser(solid state laser) gas laser laserActive Yttrium Aluminium Garnet Mixture of Mixture of P-N junctionmedium (y3Al5O12) Helium and CO2, N2 and diode Neon in the Helium (or) ratio 10:1 water vapourActive Neodymium(Nd3+ ions) Neon CO2 Recombinationcentre of electrons & holesPumping Optical pumping Electrical Electric Direct pumpingmethod pumping disharge methodOptical Ends of the rods polished Pair of Metallic Junction ofresonator with silver and two concave mrror of gold diopdes- mirrors. One of them is to mirrors (or) silicon polished totally reflected and the mirrors
  21. 21. 7/28/2012TYPICAL APPLICATION OF LASERThe detection of the binary data stored in the form of pits on the compact discis done with the use of a semiconductor laser. The laser is focused to adiameter of about 0.8 mm at the bottom of the disc, but is further focused toabout 1.7 micrometers as it passes through the clear plastic substrate tostrike the reflective layer. The reflected laser will be detected by aphotodiode. Moral of the story: without optoelectronics there will no CDplayer! 21
  22. 22. DIFFERENCE BETWEEN A PHOTOGRAPHY & HOLOGRAPHYS.No photography Holography1. Photography is a 2-dimensional Holography is a 3-dimensional recording process recording process2. Ordinary light can be used for Only laser beam should be used for recording recording (or) constucting a hologram3. It is based on lens systems It is a lensless systems4. Amplitude alone can be recorded Both Amplitude and phase can be recorded5. Image is recorded totally Image is recorded bit by bit6. Image has poor resolution Image has very high solution7. To get the positive of the image it To get the positive of the image it needs printing needs printing8. No need of vibration less table Needs of vibration less table
  23. 23. 7/28/2012COMMON LASER SIGNS AND LABELS 23
  24. 24. 7/28/2012 LASER SAFETY EYEWEAR 24Laser-Professionals.com
  25. 25. 7/28/2012 INTERNATIONAL LASER WARNING LABELS INVISIBLE LASER RADIATION AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION CLASS 4 LASER PRODUCT WAVELENGTH 10,600 nm MAX LASER POWER 200 W EN60825-1 1998 Symbol and Border: Black Legend and Border: Black Background: Yellow Background: Yellow 25Laser-Professionals.com
  26. 26. 7/28/2012 CDRH CLASS WARNING LABELS Laser Radiation VISIBLE LASER RADIATION- AVOID EYE OR SKIN EXPOSURE TO Do Not Stare Into Beam DIRECT OR SCATTERED RADIATION Argon Ion Helium Neon Laser Wavelength: 488/514 nm 1 milliwatt max/cw Output Power 5 W CLASS II LASER PRODUCT CLASS IV Laser Product Class II Class IIIa with small beam Class IIIa with expanded beam Class IIIb Class IV 26Laser-Professionals.com

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