Rapid and simple measurement of hypersonic wave velocity by Brillouin scattering with induced phonons

Abstract

Brillouin scattering is a non-contact method to measure wave velocities in the GHz range. One problem of the Brillouin scattering technique is weak light scattering from thermal phonons, which results in the long measurement time and necessity of a complex tandem Fabry-Perot interferometer. To overcome this problem, we have proposed techniques to make use of induced strong coherent phonons from a high frequency transducer. In this study, we have tried to induce strong longitudinal coherent phonons by a ScAlN film transducer (composition of the film : Sc0.41Al0.59N), which has a high electromechanical coupling coefficient. The transducer was fabricated on the quartz sample and composed of the ScAlN film grown by an RF magnetron sputtering and electrodes. The transducer was deposited on one side of the sample. Due to the induced phonons, the scattered light became much stronger than those of thermal phonons and could be observed by a simple confocal Fabry-Perot interferometer. The measured frequency shift of the Brillouin scattering peak was equal to the excitation frequency of the ScAlN transducer (883 MHz). This technique enables easy, rapid and simple measurement of wave velocity in the GHz range, which can be applied for the 2D velocity imaging of the sample.