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Phonon (Read 1808 times)
Gerrit-Jan Linker
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Phonon
21.05.09 at 11:19:28
 
Phonon
 
Atoms in materials are always in motion.  In crystals, the atomic motions must satisfy periodic boundary condition and become collective. These collective vibrations are called phonons.  
 
Usually atomic motion is as random phase. At different locations in the crystal the atomic motions are at different stages of the periodic motion. When atoms move in-phase the phonon is called coherent.
 
A phonon is a quantized mode of vibration occurring in a rigid crystal lattice.
 
Phonons play a major role in many of the physical properties of solids, including a material's thermal and electrical conductivities.
 
Phonons are a quantum mechanical version of normal modes in classical mechanics.
 
Usually, at thermal equilibrium, phonons of different modes with different wavevectors coexist with phases random to each other. It is VERY UNLIKELY that all the atoms vibrate toward the same direction and at the same speed.
 
However, shining a (femtosecond) light pulse whose duration is shorter than the half period of the phonon will induce in-phase (COHERENT) motion of the atoms over a macroscopic spatial region. This is (historically) called COHERENT optical PHONONS or just coherent phonons.
 
See also:
Coherence
http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1336971750/0#0
 
Source:
http://en.wikipedia.org/wiki/Phonon
http://www.nims.go.jp/ldynamics/en/Whats_Coherent_Phonon.html
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« Last Edit: 14.05.12 at 07:03:33 by Gerrit-Jan Linker »  

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