A petascale automated imaging pipeline for mapping neuronal circuits with high-throughput transmission electron microscopy.

Electron microscopy (EM) is widely used for studying cellular structure and network connectivity in the brain. We have built a parallel imaging pipeline using transmission electron microscopes that scales this technology, implements 24/7 continuous autonomous imaging, and enables the acquisition of petascale datasets. The suitability of this architecture for large-scale imaging was demonstrated by acquiring a volume of more than 1 mm3 of mouse neocortex, spanning four different visual areas at synaptic resolution, in less than 6 months. Over 26,500 ultrathin tissue sections from the same block were imaged, yielding a dataset of more than 2 petabytes. The combined burst acquisition rate of the pipeline is 3 Gpixel per sec and the net rate is 600 Mpixel per sec with six microscopes running in parallel. This work demonstrates the feasibility of acquiring EM datasets at the scale of cortical microcircuits in multiple brain regions and species.

Population pulsation resonances of excitons in monolayer MoSe2 with sub-1 µeV linewidths.

Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe_{2} using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2 µeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scales longer than 1 ns. The ultranarrow resonance (<0.2 µeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.