Metrological Optimization of Time-Domain Brillouin Scattering

Abstract

Acoustic phonons have been known to phase-match a monochromatic light source to disclose the Brillouin scattering over a century. Here, upon excitation of acoustic phonons, acoustically induced optical anisotropy such as birefringence conveys the information of partial branches of acoustic phonons as a function of the energy of laser sources. However, their metrological optimization, in terms of dephasing, spectral range, and amplitude, remains unclear in most of crystalline solids because the relevant data analytics requires the intercession of phononic coherence via the other information carriers such as electrons and photons. For example, such data analytics adheres to the photoelastic transduction which converts the probing laser parameters to those of acoustic phonon branches. Time-domain Brillouin scattering (TDBS) used for such acoustic phonon measurement is an experimental technique utilizing ultrafast lasers by precisely measuring the change in refractive index due to the generation and propagation of phonons. In this study, I have investigated the relationship between the refractive index changes in TDBS and the probing laser energy in piezoelectric quantum structure based on GaN. In particular, the large piezoelectric strain tensor coordinates the quantized strain with well-defined spatial profile of acoustic phonons, exhibiting prominent probing energy dependence of TDBS amplitude. In terms of optical parameters, this study aims to extract the real and imaginary parts of the refractive index based on which we can excavate the previously intractable procedure of maximizing TDBS amplitude by dilatation of probing energy conditions. This work could pave a new route to thermal manipulation of nanoscale semiconductor devices by overcoming the limitation of the low sensitivity of acoustic phonons in most of crystalline materials.