LASERS A short introduction on how “lasing” is achieved

Applications of Lasers 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