Effect of probe pulse duration in picosecond ultrasonics

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