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NATS 1870 Study Guide - Final Guide: Ruby Laser, Spontaneous Emission, Stimulated Emission

Natural Science
Course Code
NATS 1870
Robin Kingsburgh
Study Guide

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Review part1
How do lasers emit light?
!Know spontaneous emission vs stimulated emission
!Ruby laser: it contains chromium
oSurrounded by a flash tube: emits light
oChromium ions in ruby absorbs photons from flash tube
and jump to higher levels
oPopulation inversion created, as all electrons are in upper
oSome will spontaneously decay and emit photons
oThose photons which are reflected by the mirrors at either
end they stimulate emission from other chromium ions
oThis stimulated emission creates an amplification of the
oOne mirror reflects 100%, the other 95-99%, from the
second side some of the photon can escape and create
the laser beam
How does LED’S work?
!Doped semiconductors: silicon- crystal structure is
“doped” by adding an atom which has one more electron
(like arsenic)- this will allow and additional electrons to be
in the conduction band- that electrons will flow more
readily and carry current- n-type semiconductor
!Doping can also happen with a material with one less
electron this will generate a positive “hole” which can also
carry a current –p-type semiconductor
!Diode: when p- type and n-type are placed next to each
other it creates p-n junction
!Electrons will jump from –type to p-type and fill in the
positive hole
!As electrons is captured by hole- it is in a higher energy
state-spontaneously drops to a lower level and emits a
photon – generally it will be IR, but depending on the
materials and type of doping, it can be a visible
wavelength photon
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