Precise control of high-frequency ultrasounds in thin crystals for the development of tunable narrowband and directional γ-ray sources

This work presents a complete methodology for the precise characterization of the acoustic field inside crystal-based devices driven by high-frequency ultrasounds toward the generation of tunable narrowband and directional γ-radiation via undulation of ultra-relativistic charged particles. Such γ-ray sources have long been anticipated by the scientific community, as they promise new powerful tools for the study of high-energy physical phenomena and the development of novel nuclear technologies. In such devices, a piezoelectric transducer induces tens of MHz harmonic waves inside a silicon monocrystal. Ultra-relativistic charged particles traversing the crystal get trapped within the channels formed by the extremely strong electric fields of the acoustically modulated lattice planes, undergoing undulation and emitting γ-radiation. Precise characterization of the acoustic field in the crystal is crucial for the determination of the expected characteristics of the secondarily generated γ-rays. For this purpose, fast laser refraction imaging is used here to image the acoustic waves by exploiting the spatial redistribution of a laser beam's optical intensity, caused by the acoustic field. A dedicated computational model is developed for the estimation of spatial distribution of the pressure and lattice deformation inside the crystal. This methodology provides a framework for future novel γ-ray sources in high-energy facilities.