Transcript LASERS.ppt

LASERS
A short introduction on how
“lasing” is achieved
Applications of Lasers
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To annoy people at the movies
Lasers in Industry
Lasers in Geography
Lasers in Astronomy
Lasers in Communication
3 ways radiation interact with the energy
levels of atoms
• Spontaneous Emission
– atom*

atom + photon
• Induced absorption
– atom + photon  atom*
• Induced/stimulated emission
– Responsible for laser creation
– Atom* + photon  atom + 2photons
– 2 photons travel in exactly the same direction
with the same energy and in phase
Importance of Induced Emission
• Laser = Light Amplification by Stimulated
Emission of Radiation
• Simple Model
– Why won’t this work?
• Population Inversion
– More atoms in upper/excited state than lower state
– Done by pumping the ground states to excited states
– Once pumped – decay rapidly (sp. em) to a
metastable state
– More atoms in a metastable state than ground state
– Achieves population inversion
Lasing Transition
• Can happen once
population inversion is
maintained
• Transition from
metastable state to the
ground state
• Atom* + photon 
atom + 2photons
3 level laser
• Ruby laser
• 1960 by
Theodore Maiman
4 level laser
• Relieves population
inversion difficulty
Summary
• How A laser Works