  We present a variation of two-dimensional electronic spectroscopy that is
capable of mapping spatially-varying differences in electronic couplings using
a correlated map of excitation and detection frequencies, with sensitivity
orders of magnitude better than conventional spatially-averaged electronic
spectroscopies. The approach performs fluorescence-detection-based fully
collinear two-dimensional electronic spectroscopy in a microscope, combining
femtosecond time-resolution, sub-micron spatial resolution, and the sensitivity
of fluorescence detection. We demonstrate the approach on a mixture of
photosynthetic bacteria that are known to exhibit variations in electronic
structure with growth conditions. Spatial variations in the constitution of
mixed bacterial colonies manifests as spatially-varying peak intensities in the
measured two-dimensional contour maps, which exhibit well-resolved electronic
couplings between excited electronic states of the bacterial proteins.
