Register to reply

Why can't optical phonons travel far?

by joelio36
Tags: optical, phonons, travel
Share this thread:
Jan31-13, 11:39 AM
P: 22
I can't figure this out/find the answer. Why are acoustic phonons very low loss (i.e. earthquake P and S waves), but optical phonons die out rapidly?

Phys.Org News Partner Physics news on
Researchers study gallium to design adjustable electronic components
Gadolinium-based material that can be cooled by varying magnetic field
Experiments explain why some liquids are 'fragile' and others are 'strong'
Simon Bridge
Jan31-13, 08:55 PM
Sci Advisor
HW Helper
Simon Bridge's Avatar
P: 12,870
What mechanisms have you considered?
In what sense are phonons "low loss"? What does that mean exactly?
Feb2-13, 06:59 AM
P: 4
The energy loss is low is because of the low frequency/longer wavelength phonon - which does not coincide with the size of the molecules/atoms. The higher frequencies/shorter wavelength phonon is likely to coincide with the size of the molecules/atoms, and thus losing its energy through resonating the energy through all the molecules/atoms. This is the cause of energy attenuation.

Another factor is energy dissipation: By having the size of molecules/atoms coinciding close to that of the phonon, the phonon streams is more likely to be reflected/refracted and thus dissipated.

Both of these factors can help to explain why longer wavelength can travel far, low signal loss.

Another possible explanation is the phonon density: higher frequencies phonon matches with that of smaller atoms/molecular structures, which occurred at a higher density/number, and thus is able to spread the energy faster. Lower frequencies/longer wavelength need larger molecular structures (or multiple atom forming a macro-structures), which occur at a much lower densities, and thus is less able to spread the energy faster.

Another possible dissipative phenomena is electron-phonon coupling, which is more likely to happen for higher frequencies phonons.

These are my layman's perspective of what's happening, but from a specialist point of view (beyond me), u can refer to: (on resonance) (which correlate the wavelength of the phonon with the size of the molecule/atom)

and (on electron-phonon coupling)

Register to reply

Related Discussions
Optical phonons Atomic, Solid State, Comp. Physics 4
Excitation of optical branch phonons Atomic, Solid State, Comp. Physics 1
Optical and Acoustic Phonons? Atomic, Solid State, Comp. Physics 0
Polar coupling between electrons and optical phonons Quantum Physics 0
Optical Phonons and Monatomic Model Advanced Physics Homework 4