Aashish's laser


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Aashish's laser

  1. 1. The word LASER is an acronym for:
  2. 2. CHARACTERISTICS of LASER LIGHT  Monochromatic- “single colour”  Coherent- waves are “in phase”  Highly Directional- resulting in very concentrated light energy  Highly Intense and Bright  Focusability- Can be focused to an extremely fine spot of diameter of just 0.0006cm (He-Ne Laser) NOTE: You can be burned by a 60 Watt light bulb, but a 60 Watt laser can cut through wood!
  3. 3. Perfect temporal coherence Direction of wave propagation Temporal coherence t t “Bad” (limited) temporal coherence Wavefront
  4. 4. Perfect temporal coherence Time of coherence “Bad” (limited) temporal coherence
  5. 5. Coherence The main reason of bad (limited) temporal coherence E
  6. 6. Linear amplification through Population Inversion Stationary state of population inversion. It is dynamic but not static Pumping Pumping Spontaneous emission or/and collisions
  7. 7. Nd:YAG Laser (Neodymium Yttrium Aluminium Garnet Laser)
  8. 8. Nd:YAG Laser It is a four level and solid state laser system in which energy levels of neodymium ion take part in laser emission. Solid lasers use ions suspended in a crystalline matrix to produce laser light. The ions or dopants provide the electrons for excitation, while the crystalline matrix propagates the energy between ions. It became popular in 1960`s Nd:YAG lasers operate in both pulsed and continuous mode The lasing medium is red in colour, isotropic crystal Y2Al5O12 (Yttrium-Aluminum Garnet - YAG). When used in a laser, about 1-1.5% of the Yttrium is replaced by Neodymium. The energy levels of the Nd3+ ion are responsible for the lasing action. The rare earth ion does not affect the crystal structure due to similar size Ytterbium, erbium, chromium etc. are also used as dopant in YAG for laser operation
  9. 9. Construction Essential parts of laser:Yttrium Aluminium Garnet in which 1.5% of neodymium ions are doped as impurities. Nd3+ is the lasing ion. Two end mirrors M1 (total reflector) & M2 (output coupler) Excitation is achieved by krypton or xenon arc lamps Nd : YAG laser rod has a length of about 5-10 cm with a diameter 6-9mm. It is kept at one foci of an elliptical glass tube. Krypton arc lamp , the optical source is placed at the other foci of the glass tube. It is provided with necessary power supply arrangement. Mirrors M1 (total reflector) & M2(output coupler) act as a resonant cavity to produce stimulated and amplification process.
  10. 10. Population inversion results from shining light on this crystal. If the light is intense enough, atoms within the crystal will absorb this light and make transition from ground state into the absorption bands. This is often done with a krypton flash lamp. The Nd-YAG laser is normally shaped as cylindrical crystal. The crystal forms the laser cavity and has reflective ends - one coated so that it is 100% reflective, and the other is either sufficiently reflective, or is coated to allow only part of the amplified light to pass which is enough for feed-back so that oscillation may occur.
  11. 11. YAG Crystal Rod Rods of Nd:YAG crystal exhibit excellent properties of conduction of heat. As such, they are better for laser operations involving high repetition rate. But these rods have one limitation that the growth of these crystals is possible only for making small rods of the size of 10cm in length and 1cm in diameter.
  12. 12. View Of Nd:YAG Laser
  13. 13. Working of Nd:YAG laser       When arc lamp is energised it gives out radiations Nd+3 ions get excited to higher energy levels by absorbing 0.73 μm and 0.80μm from the input radiations.(white light) Nd+3 ions can stay for a duration of about 10-8 sec in the excited energy levels. These ions undergo non radiative transitions to reach the meta-stable state E3. Laser output of wavelength 1.06 μm (Infrared) is obtained from E3 to E2 transition. As continuous pumping is done by arc lamp, laser output is in the form of CW mode. Radiative transitions: Transitions between energy levels that occur with the absorption or emission of radiation Non-radiative transitions: occur without the absorption or emission of radiation
  14. 14. OUTPUT CHARACTERISTICS : The laser output is in the form of pulses with higher repetition rate Xenon flash lamps are used for pulsed output. Nd: YAG laser can be operated in CW mode also using tungsten-halide incandescent lamp for optical pumping. Continuous output powers of over 1KW are obtained.
  15. 15. Nd:YAG laser 100nm 200 ULTRAVIOLET 300 400 500 600 700 nm VISIBLE 1064 1570 nm 800nm 900 NEAR-INFRARED     1 m 3 10 MID-INFRARED Flash lamp or diode lasers pumping Main wavelength 1064 nm Output power 1-1000 Watts CW, pulse, pulse periodic 30 100 1000 m FAR-INFRARED
  16. 16. Facts about Nd:YAG laser The output in the infrared region of the Nd:YAG laser can be converted to visible region ( =400-700nm) by adopting frequency-doubling techniques and they are used in several commercial applications. The system is so compact and portable that it can be even contained in a very small box one forth the size of a briefcase. A recent development in Nd:YAG system is by using semiconductor laser output to pump the atoms of Nd3+ ions directly to the metastable state. The ability of semiconductor lasers to convert electrical energy to photons is quite high. As such, YAG laser can be pumped with simple power supplies-even torch batteries.
  17. 17. Applications of Nd:YAG Laser: Medicine In oncology, it is used to remove skin cancer It is used in ophthalmology to correct posterior capsular pacification, a complication of cataract operation Cosmetic medicine Dentistry: It is used for soft tissue surgeries in the oral cavity Manufacturing For engraving, etching, or marking a variety of metals and plastics. Cutting and welding steel and various alloys. For automotive applications (cutting and welding steel) the power levels are typically 1-5 kW Military Military surplus Nd:YAG laser fires through a collimator, focusing the beam, which blasts a hole through a rubber block, releasing a burst of plasma. The Nd:YAG laser is the most common laser used in military as laser rangefinders
  18. 18. Some more applications: These lasers are used in many scientific applications which involve generation of other wavelengths of light. The important industrial uses of YAG and glass lasers have been in materials processing such as welding, cutting, drilling. Since 1.06 m wavelength radiation passes through optical fibre without absorption, fibre optic endoscopes with YAG lasers are used to treat gastrointestinal bleeding. YAG beams penetrate the lens of the eye to perform intracular procedures. YAG lasers are used in military as range finders and target designators.
  19. 19. LIDAR (LIght Detection And Ranging) The laser system that is employed for monitoring the nature of environment is called LIDAR. First a pulsed beam is transmitted into the atmosphere. The particles that are present in the atmosphere scatter the radiation. The scattered radiation is picked up by a receiver and given to detector. The background sunlight is removed by specially designed filter elements. A photo detector measures the time dependence of the intensity of the back-scattered laser beam. This time difference is a function of the light from which the particle has scattered the light and conversion of this function into meters or any other unit of measurement is easy. Using LIDAR, it is also possible to study the concentrations and sizes of the aerosols present in the atmosphere. This helps in studies involving air pollution. Atmospheric conditions, which get affected by diffusion of particle, clouds, fog, smog, etc., can be studied using LIDAR. The results from a sensitive laser device has better resolution and clarity.
  20. 20. DETECTION OF LEAKAGE IN GAS PIPELINE Using LIDAR G line ipe as p ka ge k, lea Cra c
  21. 21. LIDAR of differential absorption System of processing signals Lidar Laser Parabolic mirror Detector Cloud of detected gas Ground surface