|
Acoustic phase conjugation is a set of techniques meant to perform phase conjugation on acoustic waves.〔(A. P. Brysev et al., ''Wave phase conjugation of ultrasonic beams'', Physics-Uspekhi (1998) )〕 == Techniques == Acoustic phase conjugation can appear in a solid when the sound velocity is modulated by an electromagnetic field. 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 time smaller than that of the photon.〔 Parametric pumping techniques can be performed in several media:〔 * In piezoelectric crystals, a nonlinear piezoelectric effect will produce a modulation of fractions of a percent. * In magnetic crystals, a modulation of dozens of percent can be reached through the magneto-acoustic coupling, which can be improved by combining the magnetostriction and spin reorientation transition effects or using the magnetoacoustic resonance. A "supercritical" or "giant" amplification, up to 80 dB, can be obtained beyond the threshold of instability of phonons in magnetoacoustic media. * In semiconductors, parametric interaction between phonons and plasmon can be generated by an alternative electric field or a modulated optical pump. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Acoustic phase conjugation」の詳細全文を読む スポンサード リンク
|