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Lasers for mpctc

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Basics of lasers
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Lasers for mpctc

  1. 1. LASER
  2. 2. What is Laser? Light Amplification by Stimulated Emission of Radiation • A device produces a coherent beam of optical radiation by stimulating electronic, ionic, or molecular transitions to higher energy levels • When they return to lower energy levels by stimulated emission, they emit energy.
  3. 3. Properties of Laser • Monochromatic • Coherent • Directional
  4. 4.  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. 5. Basic concepts for a laser • Absorption • Spontaneous Emission • Stimulated Emission • Population inversion
  6. 6. Absorption • Energy is absorbed by an atom, the electrons are excited into vacant energy shells.
  7. 7. Spontaneous Emission • The atom decays from level 2 to level 1 through the emission of a photon with the energy hv. It is a completely random process.
  8. 8. Stimulated Emission atoms in an upper energy level can be triggered or stimulated in phase by an incoming photon of a specific energy.
  9. 9. Stimulated Emission The stimulated photons have unique properties: – In phase with the incident photon – Same wavelength as the incident photon – Travel in same direction as incident photon
  10. 10. Population Inversion • A state in which a substance has been energized, or excited to specific energy levels. • More atoms or molecules are in a higher excited state. • The process of producing a population inversion is called pumping. • Examples: →by lamps of appropriate intensity →by electrical discharge
  11. 11. Lasing Action 1. 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.
  12. 12. Two-level Laser System • Unimaginable as absorption and stimulated processes neutralize one another.
  13. 13. 14 Lasing Action Diagram Energy Introductio Ground State Excited State Metastable State Spontaneous Energy Emission Stimulated Emission of Radiation
  14. 14. How a laser works?
  15. 15. 1. High-voltage electricity causes the quartz flash tube to emit an intense burst of light, exciting some of Cr3+ in the ruby crystal to higher energy levels. 2. At a specific energy level, some Cr3+ emit photons. At first the photons are emitted in all directions. Photons from one Cr3+ stimulate emission of photons from other Cr3+ and the light intensity is rapidly amplified.
  16. 16. 3. Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification. 4. The photons leave through the partially silvered mirror at one end. This is laser light.
  17. 17. Three-level Laser System • Initially excited to a short-lived high- energy state . • Then quickly decay to the intermediate metastable level. • Population inversion is created between lower ground state and a higher-energy metastable state.
  18. 18. Three-level Laser System mµλ 6943.0= s7 3 10τ − ≈ s3 2 103τ − ⋅≈ Ruby laser 23 ττ <<
  19. 19. Four-level Laser System • Laser transition takes place between the third and second excited states. • Rapid depopulation of the lower laser level.
  20. 20. 1.06 mλ µ= 4 2τ 2.3 10 s− ≈ × 2 0.6328 mλ µ= 100nsτ2 ≈ 10nsτ1 ≈ Four-level Laser System Nd:YAG laser He-Ne laser 23 ττ <<
  21. 21. Laser Construction • A pump source • A gain medium or laser medium. • Mirrors forming an optical resonator.
  22. 22. Laser Construction
  23. 23. Pump Source • Provides energy to the laser system • Examples: electrical discharges, flashlamps, arc lamps and chemical reactions. • The type of pump source used depends on the gain medium. →A helium-neon (HeNe) laser uses an electrical discharge in the helium-neon gas mixture. →Excimer lasers use a chemical reaction.
  24. 24. Gain Medium • Major determining factor of the wavelength of operation of the laser. • Excited by the pump source to produce a population inversion. • Where spontaneous and stimulated emission of photons takes place. • Example: solid, liquid, gas and semiconductor.
  25. 25. 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.
  26. 26. Laser Types • According to the active material: solid-state, liquid, gas, excimer or semiconductor lasers. • According to the wavelength: infra-red, visible, ultra-violet (UV) or x-ray lasers.
  27. 27. 28 Argon fluoride (Excimer-UV) Krypton chloride (Excimer-UV) Krypton fluoride (Excimer-UV) Xenon chloride (Excimer-UV) Xenon fluoride (Excimer-UV) Helium cadmium (UV) Nitrogen (UV) Helium cadmium (violet) Krypton (blue) Argon (blue) Copper vapor (green) Argon (green) Krypton (green) Frequency doubled Nd YAG (green) Helium neon (green) Krypton (yellow) Copper vapor (yellow) 0.193 0.222 0.248 0.308 0.351 0.325 0.337 0.441 0.476 0.488 0.510 0.514 0.528 0.532 0.543 0.568 0.570 Helium neon (yellow) Helium neon (orange) Gold vapor (red) Helium neon (red) Krypton (red) Rohodamine 6G dye (tunable) Ruby (CrAlO3 ) (red) Gallium arsenide (diode-NIR) Nd:YAG (NIR) Helium neon (NIR) Erbium (NIR) Helium neon (NIR) Hydrogen fluoride (NIR) Carbon dioxide (FIR) Carbon dioxide (FIR) 0.594 0.610 0.627 0.633 0.647 0.570-0.650 0.694 0.840 1.064 1.15 1.504 3.39 2.70 9.6 10.6 Key: UV = ultraviolet (0.200-0.400 µm) VIS = visible (0.400-0.700 µm) NIR = near infrared (0.700-1.400 µm) WAVELENGTHS OF MOST COMMON LASERS Wavelength (µm)Laser Type
  28. 28. Solid-state Laser • Example: Ruby Laser • Operation wavelength: 694.3 nm (IR) • 3 level system: absorbs green/blue •Gain Medium: crystal of aluminum oxide (Al2O3) with small part of atoms of aluminum is replaced with Cr3+ ions. •Pump source: flash lamp •The ends of ruby rod serve as laser mirrors.
  29. 29. Liquid Laser • Example: dye laser • Gain medium: complex organic dyes, such as rhodamine 6G, in liquid solution or suspension. • Pump source: other lasers or flashlamp. • Can be used for a wide range of wavelengths as the tuning range of the laser depends on the exact dye used. • Suitable for tunable lasers.
  30. 30. Schematic diagram of a dye laser dye laser A dye laser can be considered to be basically a four-level system. The energy absorbed by the dye creates a population inversion, moving the electrons into an excited state.
  31. 31. Gas Laser • Example: Helium-neon laser (He-Ne laser) • Operation wavelength: 632.8 nm • Pump source: electrical discharge • Gain medium : ratio 5:1 mixture of helium and neon gases
  32. 32. Excimer Laser • cool laser. • Incredibly precise. • laser eye surgery. Excimer laser used for eye surgery.
  33. 33. Semiconductor laser Semiconductor laser is a laser in which semiconductor serves as photon source.
  34. 34. Applications of laser • Industry & Commercial a. cutting, welding, marking b. CD player, DVD player c. Laser printers, laser pointers d. Photolithography e. Laser light display
  35. 35. Applications of laser • Medical a. eye surgery b. cosmetic surgery
  36. 36. Applications of laser • Scientific a. Spectroscopy b. Lunar laser ranging c. Photochemistry d. Nuclear fusion
  37. 37. Military Applications of Laser
  38. 38. Applications Non-Weapon Compact systems EOCM Lasers HPL-DEW Directed Energy Systems Battlefield Lasers Compact, low power Lasers. - LRF / Target Designator - Underwater Ranging - Laser Bathymetry - Laser Trackers - Ring Laser Gyro - Laser Proximity fuse - Submarine Laser Communication Moderate Power Laser for Anti sensor /Anti-Personnel use. - Soft kill – Low Intensity Warfare - Disabling of EO sensors IR camera, CCD etc - Damage to front-end optics - Dazzling of Military Operators - Range – upto 20 km - EOCM class Laser types : Pulsed solid state lasers like Nd:YAG/Glass, Alexandrite High power Lasers. - Burning holes in critical structure like fuel tank of aircrafts,H’copters, Missiles - Damage to vulnerable points like: Sensors, Optics of Helicopters, Aircrafts & Missiles - Range 5-20 km - Laser types : Chemical, Dynamic Gas lasers - CO2 , HF/DF, COIL, FEL
  39. 39. LASER RANGE FINDER •Laser range finders (LRFs) are vital components of high precision targeting engagements. •The precise and accurate range-to-target information is an essential variable in the fire control solution of today’s sophisticated weapons. •During the Persian Gulf War (Aug 90 to Feb 91), the effective use of Laser based devices were amply demonstrated. •LRFs (along with laser target designators and laser-guided smart bombs) were perhaps the most used and reliable devices that used Laser technology.
  40. 40. LASER RANGE FINDER Requirement : For Acquiring and Locating a target before any tactical decision is taken in the battlefield scenario. Works on the principle of a RADAR. A collimated pulse is directed towards a target and the reflected light is received and detected. Range = C×t/2 where t is the round trip time
  41. 41. LASER TARGET ILLUMINATOR •This is a device which illuminates a target/group of targets or area with laser radiation. • The use of laser illuminators are varied, including use as a non-lethal weapon or as a source of laser energy for laser guided weapons to home in on. Suitable Lasers: 1. Nd: YAG laser 2. Diode Pumped Solid State laser 3. Semiconductor laser
  42. 42. LASER DAZZLER • The Laser Illuminator temporarily impairs an adversary’s ability to fire a weapon or to otherwise threaten friendly forces. • The laser briefly illuminates an opponent with harmless, low-power laser light from a Semiconductor laser or a Solid State laser.
  43. 43. A weapon which uses a seeker to detect laser energy reflected from a target marked by a laser, and through signal processing provides guidance commands to a control system which guides the weapon to the point from which the laser energy is being reflected LASER GUIDED WEAPON (LGW)
  44. 44. LGWs A laser-guided GBU-24 strikes its target
  45. 45. •Higher Accuracy •Less Munitions Required •Less Civilian Casualties •Greater Target Damage •Simple to Convert From Old Munitions WHY LGWs
  46. 46. High Energy Laser Weapons
  47. 47. Laser DEW
  48. 48. Lethal Laser Weapons Pump Power Laser Medium LASER LASER A Directed Energy Lethal Weapon (DEW) exploits the High Power Laser Radiation for causing the intended Damage to the Target. Destroys Targets by Melting & Weakening the Structures, Igniting the Explosive Fillers etc. Beam Director for Remote Focusing Speed of Light Delivery of Speed of Light Delivery of Lethal Energy Lethal Energy Converts Chemical / Electrical Energy into Light Energy
  49. 49. Capabilities – High Power Laser DEWs • Engagement at the speed of light Reduces challenges of late detection and maneuvering threats • Precision application of energy Small engagement spot size on threat target lowers risk of collateral damage • High resolution target imaging and target tracking High kill probability – beam on target until kill is confirmed • Low cost per kill Only fuel is consumed, no hardware is launched • Stealth - invisible beam • Deep magazine with rapid recharging Limitations • Line-of-Sight Dependence • Weather conditions • Minimal Effects on Hardened Structures and Armored Vehicles
  50. 50. International Status Avenger Laser System, USA ZEUS USA Thor - Israel  Remote Neutralization of Unexploded Ordnance, Surface Landmines and Improvised Explosive Devices (IED’s)  Effective Standoff Operational Range – (200-250) meters
  51. 51. UAVs / DRONES Structure Material -Aluminum / Steel -Wood -Carbon Fiber Composites -Glass Fiber Reinforced Plastics Damage Mechanism -Heating (structure weakening) -Combustion (Burning)
  52. 52. ABL to Destroy Ballistic Missiles US defence along with DARPA is developing a 20MW DF laser for destroying the ICBM
  53. 53. Interesting Facts.. •Laser Target Designators were used during the Persian Gulf War to direct Precision Guided Munitions such as the GBU – 12 and the Hellfire laser guided bombs. •Stealth F-117 aircraft was also laser assisted for attacks against Baghdad. •Apache helicopters armed with hellfire destroyed 2 radar sites in Western Iraq. •Out of the 20,000 PGMs used in the Persian Gulf War, more than 60% were laser guided. •Laser Guided bunker buster bombs destroyed the hide-outs of Osama in Tora Bora in Afghanistan.