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  • Created by: Emily
  • Created on: 10-01-13 16:55
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  • Lasers
    • Types of Emission
      • Spontaneous Emission
        • Electrons will drop down to a lower energy level at any point.
          • In a random direction
      • Stimulated Emission
        • Incoming photon stimulates an electron to drop to a lower energy level
          • Emitted photon is polarised in the same direction and travels in the same direction as the stimulating photon.
          • Same Amplitude and Frequency as the stimulating photon.
      • Absorption
    • Population Inversion
      • When a higher energy level is more populated than a lower energy level.
    • Metastable Level
      • Electrons spend a long time here before spontaneously dropping
    • Types of Lasers
      • Gas
        • Highly Inefficient
          • 90% Reflecting
          • 10% Emitting
        • Photons are reflected back and fourth within the amplyfing medium
          • 1 becomes 2, 2 becomes 4 - an exponential increase.
          • Until they emerge as a beam
          • Amplifying medium is the material with the population inversion.
      • Solid
        • Advantages
          • Cheap
          • Efficient
          • Huge Population Inversions can be achieved.
        • Uses
          • Blu ray/ CD reading
          • Barcode Reading
          • Data Transfer
          • Laser Surgery
    • 3 - level system
      • We pump energy into the system to promote electrons from the ground state to the top level.
        • One way of doing this is to shine light contain photons with energy Eu-El at the atoms.
        • Top  Level has to be very short lived.
          • Otherwise it will prevent further pumping.
    • 4 - level system
      • The stimulated emission transition is above ground state
        • Self emptying, spontaneous emission to the ground state.
          • Don't need such a ferocious rate of pumping
            • Pumping
              • Feeding energy into the amplifying medium of a laser to produce a population inversion.


Tilly - Team GR


Brilliant and very detailed. 

Could do with a bit more colour, but other than that really good information!

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