Figure 3. Ultrafast degenerate IR pump–probe spectroscopy on MEG.

Normalized probe differential transmission ΔT/T in ultrafast degenerate 1.8-μm IR pump–probe spectroscopy as a function of pump–probe delay recorded at a pump fluence of 80 μJ cm⁻² and a substrate temperature of 10 K for a MEG sample with ∼63 layers. The black solid line is a guide for the eye. The sign changes in the differential transmission at ∼1 and ∼20 ps indicate the presence of interlayer energy transfer from the top layers to the first HD layer in MEG. (Inset: schematic diagram of interlayer Coulombic energy transfer from a hot LD to a cold HD layer in MEG. The pump selectively injects hot electrons in all layers of MEG except the first HD layer, in which interband absorption is Pauli blocked).