Abstract

The Luxemburg-Gorky Effect Revived for Elastic Waves: a Mechanism and Experimental Evidence

V.Yu.Zaitsev (Institute of Applied Physics RAS, Nizhny Novgorod, Russia ); V.E.Gusev (Laboratoire de Physique de l'Etat Condence, UPRESA-CNRS 6087, Universite du Maine, Le Mans, France); B.Castagnede (Laboratoire d'Acoustique, LAUM, UMR CNRS 6613, Universite du Maine, Le Mans, France)

e-mail: vyuzai@hydro.appl.sci-nnov.ru

For many nonlinear effects typical in optics and plasma physics direct acoustic analogies are known. Examples are wave phase-conjugation, stimulated scattering, maser effects. However, no acoustic analogies are known for the Luxemburg-Gorky (LG) effect, which represents one of the pioneering observations in nonlinear wave interactions. It consists of the transfer of modulation from the radiation of a powerful radio-station (originally, Luxemburg and Gorky-city stations) to another carrier wave. This cross-modulation is caused by perturbations in absorption of ionosphere plasma induced by the stronger wave. A majority of the later nonlinear research for waves of different nature focused, however, on effects of reactive, rather than dissipative nonlinearities. We propose a new mechanism for the linear and amplitude-dependent dissipation due to elastic wave-crack interaction, which we expect will be found to operate widely in seismics and ultrasonics. We have observed its strong manifestation in the form of cross-modulation of two longitudinal modes in a glass rod containing three corrugated thermal cracks, which is a direct elastic-wave analogue of the LG-effect. The counterpart acoustic mechanism implies, first, a drastic enhancement of the thermoelastic coupling at high-compliance microdefects. Second, the high stress-sensitivity of the defects leads to a strong stress-dependence of the resultant dissipation. The work was supported by RFBR (grant No 02-02-16237).

Section : 2