L36 - SUMMARY FROM LAST CLASS Optical devices LASER: Light...

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Dr. P. Lucas U of A MSE 110 Optical devices SUMMARY FROM LAST CLASS LASER: Light Amplification by Stimulated Emission of Radiation. Stimulated emission: a photon stimulates an electronic transition in an excited active species which generates a second identical photon. The active species is enclosed between two mirrors in the laser cavity . The active species is pumped into a higher electronic state with a flash of light or an electric discharge to create a population of excited atoms A photon reflected back and forth between the mirrors induces stimulated emissions and generates an amplified coherent beam. The length of the laser cavity must be equal to an integral number of wavelength emitted by the active species in order to prevent destructive interferences. L = n λ A laser beam is therefore monochromatic , coherent and colinear . In a solid state Nd-YAG laser, 1% of the active species Nd 3+ is doped into the crystal structure and produce stimulated emission at 1.064 μm Diode lasers are based on emission of photon through electronic transition from the conduction to the valence band of semiconductors.
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Dr. P. Lucas U of A MSE 110 Semiconductors SEMICONDUCTOR DEVICES Semiconductors are elements from group IV: Ge, Si with 4 electrons on the outer shell Si:[Ne]2s 2 2p 2 . They form tetrahedral sp 3 hybrid orbitals each populated with one electron. Following the octet rule each sp 3 will share an electron with an adjacent atom and form 4 covalent bonds in tetrahedral configuration. Si and Ge semiconductor crystals therefore adopt the tetrahedral structure of diamond. This covalent network generates a full bonding band (valence) and a empty non-bonding band (conduction) separated by a small energy gap (E g ) which produce semiconducting properties.
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Dr. P. Lucas U of A MSE 110 Semiconductivity Some electrons get thermally excited across the band gap into the
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This note was uploaded on 11/19/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona- Tucson.

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L36 - SUMMARY FROM LAST CLASS Optical devices LASER: Light...

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