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  1. 1. LASER
  2. 2. Introduction  In early 1960s Quantum physics made enormous contribution to technology by introducing a Laser a device that creates an intense beam of light is called as laser beam. The word laser is an acronym that stands for “light amplification by the stimulated emission of radiation”. Lasers are essentially highly directional, highly intense, highly monochromatic and highly coherent optical sources.
  3. 3. • Stimulated emission was postulated by Einstein as early as in 1917. • In 1960 , a solid state ruby laser is developed by Maiman on this principle. • In 1961, a gas state He-Ne laser is developed by Ali javan and others in Bell telephone laboratory.
  4. 4. Working Principle  Laser action is quantum process that occur in a material medium if its exposed radiation of photon of energy hv. Atoms and molecules have discrete energy level when they absorbs or emit the photon they make transition between energy level. There are two energy level one in ground state and other is excited state these level are quantized energy level there is no intermediate level the atoms are present one of these level and when beam of Photon particles incident on it there is certain phenomenon occurs.
  5. 5. Absorption
  6. 6.  There is two energy level E1 is represents ground state & E2 will represents the excited state. The atoms in ground state are remain ground state until an external radiation incident on it. The Photon with appropriate frequency is incident on atom which is ground state they are excited on the excited state. This is called as absorption According to principle of conservation of energy. hv = E2 - E1 Absorption
  7. 7. Spontaneous Emission
  8. 8. In Spontaneous emission atoms are in excited level they are jump on the ground state by emitting the electromagnetic radiation. The frequency of emitted radiation v is directly proportional to the energy differences between two energy level or energy difference is inversely propotional to wavelength of radiation from v = c/λ Spontaneous Emission
  9. 9. Stimulated Emission
  10. 10. In Stimulated emission the external triggering is required to decay the atoms in ground state. This phenomenon which is studied by Einstein in 1917.  According to this phenomenon the photon which is incident the atoms whose are in excited state when they are transition to the ground state they emit the photon which is same phase with incident radiation photon. Stimulated Emission
  11. 11. Hence we get monochromatic, coherent source of light from LASER. Thus along with an incident triggering photon one more photon is also produced if this two photon are further used in triggering more and more excited atoms one identical multiple photon 4, 8, … etc. such amplification is called as amplification of light by stimulated emission of radiation. Stimulated Emission
  12. 12. Few points discussed • At thermal equilibrium condition nos. atom in the ground state is larger than exited state in that case there incident radiation incident on the atoms so that there is absorption takes place hence its called as attenuation of light • But in non equilibrium condition the nos. of atom in the exited state is larger than ground state so when radiation incident on it result in stimulated emission is called as Optical amplification.
  13. 13. • Einstein showed that both the process like stimulated absorption and stimulated emission has equal probability. • According to Boltzman Distribution Law : N2/N1 = exp [-(E2 – E1)/kT] N2 :- Nos. of atom in excited state. N1 :- Nos. of atom in ground state. E2 :- Energy level of excited level E1 :- Energy level of ground level k :- Boltzman Constant T :- Temperature
  14. 14. •Case :- I If T is positive E2 > E1 therefore N2 < N1 Absorption Dominates. •Case :- II If T is Negative N2 > N1 Stimulated Emission Dominates.
  15. 15. LASER System
  16. 16. Population Inversion • To increases the nos. of atom in excited state than ground state N2 > N1 for laser action such process is called as population Inversion. • To raise atoms from ground state to excited state by external energy source is called as pumping
  17. 17. Active Medium The Active medium is the material used in a laser. The Active is consists of collection of atoms molecule or ions. The active medium is solid liquids or gaseous state
  18. 18. Active Medium in Stable Optical Resonantor
  19. 19. In The process of Optical amplification is achieved by placing the active medium in Two mirror M1 & M2 called as optical reflector such system of mirrors used to obtain optical feedback is called as mirror cavity resonator or optical resonator.
  20. 20. Properties of Laser Monochromaticity Coherence Intensity & Power Directionality
  21. 21. Monochromaticity
  22. 22. • Laser light high monochromatic light source than conventional light source . • Eg. The Spectral Width Neon light is approximately 5A0 whereas the He – Ne Laser gives spread of 10-8 A0 at 6328A0 i.e. Laser light highly monochromatic. • Laser light spectral width of the order 10-6 A0 which is extremely small as compared with the width of the order 0.1 A0 of sodium light. • Light from conventional source is more or less sharp but for laser light is sharp Monochromaticity
  23. 23. Monochromaticity
  24. 24. • Laser light is highly coherent. • The stimulated emission give rise of coherence of radiated beam. • The emitted photon train of laser light which maintain constant phase. • When the two wavetrain interfere they producing steady interference. • On the other hand ordinary light whose coherence length of wave train emitted by a light less than meter. Coherence
  25. 25. • Laser light is produced highly intense beam than conventional light source. • Laser light is emitted by continues wavetrain which is highly intense is focused on very small area. •I = (10/λ)2 P • The unit of Intensity W/m2 Intensity & Power
  26. 26. • Laser light is highly directional than ordinary light source they travel a greater distance without divergence or spreading. • The divergence can be less than 10-5 radians the width is also narrow so they should focus extremely sharp focus. • On the other hand ordinary light diverges more as it propagates • The directionality of laser is measured in terms of full angle beam divergence Directionality
  27. 27. He Ne Laser
  28. 28. Energy Level Diagram
  29. 29. Application of Laser
  30. 30. • Laser is used for various metallic welding purposes when laser is focus on small area its start melt because of high temperature so the metal can easily join with another metal. • Eg. CO2 Laser at 10.6 µm have a power of order 6kW it welding 0.25 inch thick steel its cheaper than ordinary welding. • Nd : YAG laser 1.06 µm with output 100 mJ/pulse is more compact because of low peak power pulses of 10-3 to 10-2s width and suitable for welding. Laser Welding
  31. 31. • Laser is also used for cutting purpose of material like textiles industries for cutting cloth, in aeroplane industries for cutting aluminium sheet, wood plastic glass ceramics. Using a jet with the laser the efficiency of laser cutting can be increased. • This process of High accuracy & fine precision. Laser Cutting
  32. 32. Holography
  33. 33. Recording of hologram
  34. 34. Reconstruction of Image
  35. 35. • Holography is wide application in holographic, Interferometry, holographic microscope etc a hologram is for data storage its also used to recording three dimensional image and cinemas. Application of Holography
  36. 36. • Laser is used in medical purpose because its high precision and accuracy. • He – Ne laser is trophic Ulcer treatment and preparation of hologram. • CO2 Laser has application in brain oviduct and spinal surgery. • Argon Laser is used in angioplasty brain and eye surgery. • Nitrogen Laser is used in DNA analysis & genetic engineering Laser in Medical