Strong Optical-Mechanical Coupling in a Vertical GaAs/AlAs Microcavity for Subterahertz Phonons and Near-Infrared Light

TLDR

The study predicts that pillar GaAs/AlAs microcavities will exhibit picogram effective masses, near‑perfect acoustic extraction, and μW–mW threshold powers for stimulated phonon emission, paving the way for phonon lasing via parametric instability. The authors generate intense, monochromatic acoustic phonons using picosecond laser excitation and monitor their elastic strain evolution, while detecting them optically through strong phonon backaction on the high‑Q cavity mode. The cavities simultaneously confine photons and phonons of matching wavelength, yielding large optomechanical coupling (~THz/nm) and enabling picogram‑mass pillar structures with near‑perfect acoustic extraction and μW–mW thresholds for stimulated phonon emission, suggesting phonon lasing via parametric instability.

Abstract

We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-Q optical cavity mode. Large optomechanical factors are reported (~THz/nm range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range μW-mW, opening the way for the demonstration of phonon "lasing" by parametric instability in these devices.