Lasers
- 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
- Electrons will drop down to a lower energy level at any point.
- 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.
- Incoming photon stimulates an electron to drop to a lower energy level
- Absorption
- Spontaneous Emission
- 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.
- Highly Inefficient
- Solid
- Advantages
- Cheap
- Efficient
- Huge Population Inversions can be achieved.
- Uses
- Blu ray/ CD reading
- Barcode Reading
- Data Transfer
- Laser Surgery
- Advantages
- Gas
- 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.
- We pump energy into the system to promote electrons from the ground state to the top level.
- 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.
- Pumping
- Don't need such a ferocious rate of pumping
- Self emptying, spontaneous emission to the ground state.
- The stimulated emission transition is above ground state
- Types of Emission
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