Coherent Light-Matter Interactions: Shining New Light on Nanotechnology

Science and technology are strongly influenced by light-matter interactions in materials that comprise real optoelectronic devices. The designs of these devices can be enhanced using knowledge of the fundamental electronic dynamics and dephasing processes. Ultrafast pulsed laser experiments provide a snapshot of these fundamental processes, and tailoring the excitation pulses allows for coherent control of the light-matter interactions. The latter is especially useful because such interactions are often characterized by spectral or temporal signatures that are ambiguous in conventional optical experiments. For example, isolating signatures of coupled and uncoupled resonances leads to structural information in molecules. Similarly in solid state nanostructures, decoherence processes are frequently masked by the effect of disorder. In this talk I showcase optical two-dimensional Fourier-transform spectroscopy, which uses precise control of a multi-pulse excitation sequence, to separate competing contributions onto a two-dimensional frequency plane (as shown in the figure). This provides an “interaction fingerprint” that can characterize different spectral broadening mechanisms and reveals coherent coupling differently from incoherent relaxation. The technique is applied to excitonic (electron-hole pair) interactions in GaAs quantum wells and quantum dots at low temperature, to explore the interplay of disorder and many-body correlations.