High spectral resolution of GaAs/AlAs phononic cavities by subharmonic resonant pump-probe excitation

TL;DR

This study demonstrates high spectral resolution of GaAs/AlAs phononic cavities using subharmonic resonant pump-probe excitation, revealing detailed acoustic mode characteristics and high Q-values suitable for optomechanics.

Contribution

The paper introduces a subharmonic resonant pump-probe technique combined with high-sensitivity interferometry to precisely measure confined acoustic modes in GaAs/AlAs cavities, achieving high spectral resolution and spatial mapping.

Findings

Resolved cavity modes up to 180 GHz

Measured Q-values up to 2.7 x 10^4

Achieved Q-frequency product of ~5 x 10^{14}

Abstract

We present here precise measurement of the resonance frequency, lifetime and shape of confined acoustic modes in the tens of GHz regime in GaAs/AlAs superlattice planar and micropillar cavities at low temperature ($\sim 20\,\textrm{K}$). The subharmonic resonant pump-probe technique, where the repetition rate of the pump laser is tuned to a subharmonic of the cavity resonance to maximize the amplitude of the acoustic resonance, in combination with a Sagnac interferometer technique for high sensitivity ($\sim 10 \,\textrm{fm}$) to the surface displacement, has been used. The cavity fundamental mode at $\sim 20\,\textrm{GHz}$ and the higher order cavity harmonics up to $\sim 180\,\textrm{GHz}$ have been clearly resolved. Mechanical Q-values up to $2.7 \times 10^4$ have been measured in a planar superlattice, and direct spatial mapping of confined acoustic modes in a superlattice cavity micropillar has been demonstrated. The Q-frequency product obtained is $ \sim 5 \times 10^{14}$ demonstrating the suitability of these superlattice cavities for optomechanical applications.