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Acoustic phonons are coherent movements of atoms of the lattice out of their equilibrium positions. If the displacement is in the direction of propagation, then in some areas the atoms will be closer, in others farther apart, as in a sound wave in air (hence the name acoustic).
Namely, a concerted emission of phonons can lead to coherent sound and an example of concerted phonon emission is the emission coming from quantum wells. This stands in similar paths with the laser where a coherent light can build up by the concerted stimulated emission of light from a lot of atoms .
where is the characteristic length of the system and represents the fraction of specularly scattered phonons. The p {\displaystyle p} parameter is not easily calculated for an arbitrary surface. For a surface characterized by a root-mean-square roughness η {\displaystyle \eta } , a wavelength-dependent value for p {\displaystyle p} can be ...
Three of these modes (corresponding to the parallel space) are acoustic phonon modes, while the remaining three are diffusive phason modes. In incommensurately-modulated crystals, phasons may be constructed from a coherent superposition of phonons of the unmodulated parent structure, though this is not possible for quasicrystals. [1]
Picosecond ultrasonics is a type of ultrasonics that uses ultra-high frequency ultrasound generated by ultrashort light pulses. It is a non-destructive technique in which picosecond acoustic pulses penetrate into thin films or nanostructures to reveal internal features such as film thickness as well as cracks, delaminations and voids.
The line shape of the phonon side band is that of a Poisson distribution as it expresses a discrete number of events, electronic transitions with phonons, during a period of time. At higher temperatures, or when the chromophore interacts strongly with the matrix, the probability of multiphonon is high and the phonon side band approximates a ...
The generation of the conjugate wave can be seen as the decay of a photon into two phonons, as seen on the diagram. The two phonons have opposite wave vectors k and -k (they will propagate in opposite directions) and a frequency two times smaller than that of the photon. [1] Parametric pumping techniques can be performed in several media: [1]
The electron-longitudinal acoustic phonon interaction is an interaction that can take place between an electron and a longitudinal acoustic (LA) phonon in a material such as a semiconductor. Displacement operator of the LA phonon