All-optical generation, detection, and manipulation of picosecond acoustic pulses in 2D semiconductor/dielectric heterostructures

Abstract

Launching, tracking, and controlling picosecond acoustic (PA) pulses are fundamentally important for the construction of ultrafast hypersonic wave sources, ultrafast manipulation of matter, and spatiotemporal imaging of interfaces. Here, we show that GHz PA pulses can be all-optically generated, detected, and manipulated in a 2D layered MoS2/glass heterostructure using femtosecond laser pump–probe. Based on an interferometric model, PA pulse signals in glass are successfully decoupled from the coexisting temperature and photocarrier relaxation and coherent acoustic phonon (CAP) oscillation signals of MoS2 lattice in both time and frequency domains. Under selective interface excitations, temperature-mediated interfacial phonon scatterings can compress PA pulse widths by about 50%. By increasing the pump fluences, anharmonic CAP oscillations of MoS2 lattice are initiated. As a result, the increased interatomic distance at the MoS2/glass interface that reduces interfacial energy couplings can markedly broaden the PA pulse widths by about 150%. Our results open new avenues to obtain controllable PA pulses in 2D semiconductor/dielectric heterostructures with femtosecond laser pump–probe, which will enable many investigations and applications.