Estimation of the elastic and piezoelectric tensors of sapphire and lithium niobate from Brillouin light backscattering measurements of a single crystal sample

International audienceBrillouin light scattering is a versatile measurement technique ofthe dispersion of bulk acoustic phonons in amorphous andcrystalline solids. It allows contactless and non-destructivecharacterization of the relevant material tensors of opticallytransparent materials, provided that the optical refractionindices, and in addition the dielectric tensor for piezoelectricmaterials, are known beforehand. The complete estimation of theanisotropic material tensors is often performed using manydifferent crystal orientations, and hence different samples of thesame crystal. In this paper, we consider the problem of measuringthose tensors using a single sample of an anisotropic singlecrystal with trigonal symmetry. A complete measurement requiressufficient experimental diversity in the phonon wavevectors whensampling the phonon velocity surfaces, hence the consideration of alarge number of directions away from crystallographic axes. Weestimate all six independent elastic constants of non-piezoelectricsapphire (⁠3m point group) with a single X-cut wafer and the sixindependent elastic constants together with the four independentpiezoelectric constants of piezoelectric lithium niobate (3 m pointgroup) with a single Y-cut wafer. The estimated tensors are inclose agreement with those reported in the literature based onresonant ultrasonic techniques

Brillouin Light Scattering Characterisation of Gray Tone 3D Printed Isotropic Materials

International audienceThree-dimensional direct laser writing technology enables one to print polymer microstructures whose size varies from a few hundred nanometers to a few millimeters. It has been shown that, by tuning the laser power during writing, one can adjust continuously the optical and elastic properties with the same base material. This process is referred to as gray-tone lithography. In this paper, we characterize by Brillouin light scattering the complex elastic constant C11 of different reticulated isotropic polymers, at longitudinal phonon frequencies of the order of 16 GHz. We estimate the real part of the C11 constant to vary from 7 to 11 GPa as a function of laser power, whereas its imaginary part varies between 0.25 and 0.6 GPa. The linear elastic properties are further measured at a fixed laser power as a function of temperature, from 20°C to 80°C. Overall, we show that our 3D printed samples have a good elastic quality with high Q factors only ten times smaller than fused silica at hypersonic frequencies