Fig. 1: Layer-selective, double-pump excitation of coherent phonons in a GaAs/AlAs SL detected using ultrafast X-rays.
From: Coherent phonon flatband generated in GaAs/AlAs superlattices via layer-selective optical pumping
a Schematic of the experimental setup. A pair of ultrafast 800 nm optical pulses with variable relative delays excite the coherent phonons in GaAs/AlAs SL, while a 10 keV X-ray pulse at glancing incidence resolves the temporal evolution of the SL lattice response via stroboscopic X-ray diffraction. b Structure of GaAs/AlAs SL. With an 800 nm pump, only the GaAs layers are excited since the AlAs layers are optically transparent. The optical penetration depth exceeds the total SL thickness. c The reciprocal space map (RSM) of the static (unpumped) GaAs/AlAs SL near the (1 1 3) Bragg peak of the GaAs substrate. The white arrow marks the GaAs (1 1 3) substrate peak, while the orange arrows point to the Bragg peaks of the GaAs/AlAs SL. The H and L are in the relative lattice unit (r.l.u.) of the folded Brillouin zone (FBZ) of the SL. The even orders of the SL Bragg peaks are structurally allowed but substantially weaker than the odd orders. The color of the L = +/− 1 SL Bragg peaks is saturated in panel (c) to highlight the higher-order SL peaks.
