Plasma frequency in Metals
Metals
• Metals have many free electrons that are not attached to individual
atoms (this is why they are good conductors of electricity)
• These free electrons move under the action of the light wave to cancel
out any field generated by the light (because they are free to move!)
• The oscillating free electrons generated an intense reflected wave, but
no transmitted wave. Metal mirrors reflect 90-99% of the light.
atoms (this is why they are good conductors of electricity)
• These free electrons move under the action of the light wave to cancel
out any field generated by the light (because they are free to move!)
• The oscillating free electrons generated an intense reflected wave, but
no transmitted wave. Metal mirrors reflect 90-99% of the light.
Plasma Frequency
•What happens if the light frequency is too high? i.e. if the light wave
oscillates too fast for the electrons to keep up?
• The free electrons can no longer reflect all the light, and the metal (or
gas plasma) becomes somewhat transparent.
• The frequency at which this happens is called the PLASMA
frequency
•What happens if the light frequency is too high? i.e. if the light wave
oscillates too fast for the electrons to keep up?
• The free electrons can no longer reflect all the light, and the metal (or
gas plasma) becomes somewhat transparent.
• The frequency at which this happens is called the PLASMA
frequency
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