Effect of probe pulse duration in picosecond ultrasonics

Abstract

Picosecond ultrasonics is a powerful tool for nanoscale metrology, giving access to dimensions and mechanical, thermal, and optical properties of nanomaterials. By monitoring the temporal evolution of the interaction of light with coherent acoustic phonons, also known as Brillouin oscillations, phonon lifetime and optical absorption can be measured. However, the extraction of these quantities can be inaccurate due to the common assumption of the infinite coherence length of probe pulses. Here, we demonstrate the effect of probe pulse duration on picosecond ultrasonic measurements numerically and experimentally. We establish a model that shows how the probe coherence length affects the measured signal loss and how we can overcome this limitation and measure an upper limit of the acoustic attenuation factor. The model is verified experimentally on a GaAs bulk substrate by varying the probe pulse duration, showing a strong effect for sub-100 fs pulses. Finally, we applied to CH3NH3PbBr3, where we reveal a high acoustic attenuation factor, which is in line with recent claims of strong anharmonicity in halide perovskites.

Long-Lived Coherent Acoustic Phonons in Epitaxially Grown III-V Adiabatic Cavities

“…The coherent acoustic phonons (CAPs) lifetime determines phonon energy damping time and attenuation factor [30]. An adequate phonon lifetime and coherence allow robust control and help preserve and store information [31].…”

Excitation and detection of acoustic phonons in nanoscale systems

“…19 Phonon lifetimes are crucial for efficient device performance, as they are closely linked to the quality factor, and therefore to the energy damping time and attenuation factor. 19,221,222 For sufficiently long phonon lifetimes and phonon coherence, information can be preserved, allowing for the robust control and storage of information. 223 A phonon's lifetime refers to the timescale over which a phonon is scattered or attenuated.…”