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Theory of Second‐Harmonic Generation by Soft Ultrasonic Shear Waves in Transforming A‐15 Compounds
Author(s) -
Agyei A. K.
Publication year - 1981
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221050204
Subject(s) - physics , amplitude , sine wave , oscillation (cell signaling) , non sinusoidal waveform , shear waves , distortion (music) , dispersion (optics) , love wave , mechanical wave , longitudinal wave , shear (geology) , optics , quantum mechanics , wave propagation , materials science , chemistry , waveform , amplifier , biochemistry , optoelectronics , cmos , voltage , composite material
A theory of second‐harmonic generation by pulsed “soft” ultrasonic shear waves in a transforming A‐15 compound, A 3 B, is presented which accounts for the generation observed in V 3 Si by Testardi. It is shown that this phenomenon, which is forbidden on the basis of static symmetry considerations, is possible under conditions of quasi‐static distortion of the crystal by the free A‐atom oscillations excited by the front of the driving‐wave pulse. Under these conditions not only should the driving‐wave‐amplitude dependence of the second‐harmonic waves be cubic at low drive levels and linear at high drive levels, as observed by Testardi, but the generated waves should also be amplitude modulated by a sine curve (in the absence of damping) of a period equal to the free‐oscillation period of the A atoms. This latter effect can thus be used to measure the soft‐phonon frequency as a function of temperature and the phonon dispersion at very low wave numbers.