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Lecture 19

PHY 102 Lecture 19: Lecture 19 - How does a laser work

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PHY 102

Lecture #19 – How does a laser work? 4/5/2017 ELECTRON ENERGY LEVELS Band gap = NO TRANSITIONS allowed Band of energy levels = electrons exist, can transition Conductors – conduct electricity - Electrons don't enter the band gap - Move around in other energy levels Insulators – do not conduct electricity - Band gap is very large o Electrons cannot pass this gap and thus, cannot be excited to the conduction band - Electrons sit on valence band (band of energies where electrons are permitted to move) Semiconductor – may or may not conduct electricity - Band gap between valence band and conduction band is small ABSORPTION & EMISSION OF PHOTONS Photon energy = E photon E final E initialhf = hc/ Energy levels of electrons bound to atoms = discrete, unique to each atom - Absorption = atom absorbs energy of photon o Promotes to higher energy orbital - Emission = atom emits energy of photon o Electron falls from higher energy to lower energy orbital LASER Light Amplification by Stimulated Emission of Radiation - Laser beams are o Coherent o Intense o Single frequency o Narrow - Generated in several ways - Wide applications in science, tech, biomedical applications Generation of Laser 1. Energy Absorption = Pumping o Absorbs light energy/electrical energy o Atoms in material mo
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