Observation of induced shear acoustic phonons by Brillouin scattering

The Brillouin scattering measurement is an efficient nondestructive and noncontact method which enables the simultaneous measurement of longitudinal and shear wave velocities at hypersonic frequencies. However, the measurement accuracy of shear wave velocities is low because of the weak Brillouin scattering from the thermal phonons. In this study, therefore, we have tried to overcome this problem by making use of the induced coherent shear phonons. We have adopted the Reflection Induced θA (RIθA) scattering geometry for Brillouin scattering measurement. To induce shear acoustic phonons, we used an uniaxially aligned ZnO film transducer developed in our laboratory, which can be fabricated on any solid materials without the epitaxy technique. As a result, we obtained the intense Stokes peak in case of silica glass sample which is larger than that obtained from the thermal phonons. It means that observation of induced shear acoustic phonons was achieved. Because the RIθA geometry enables the simultaneous measurement of longitudinal and shear phonons in plane, this technique opens the new feature for the nondestructive elasticity measurement.