  Fluorescence imaging is indispensable to biology and neuroscience. The need
for large-scale imaging in freely behaving animals has further driven the
development in miniaturized microscopes (miniscopes). However, conventional
microscopes / miniscopes are inherently constrained by their limited
space-bandwidth-product, shallow depth-of-field, and the inability to resolve
3D distributed emitters. Here, we present a Computational Miniature Mesoscope
(CM$^2$) that overcomes these bottlenecks and enables single-shot 3D imaging
across an 8 $\times$ 7-mm$^2$ field-of-view and 2.5-mm depth-of-field,
achieving 7-$\mu$m lateral resolution and better than 200-$\mu$m axial
resolution. Notably, the CM$^2$ has a compact lightweight design that
integrates a microlens array for imaging and an LED array for excitation in a
single platform. Its expanded imaging capability is enabled by computational
imaging that augments the optics by algorithms. We experimentally validate the
mesoscopic 3D imaging capability on volumetrically distributed fluorescent
beads and fibers. We further quantify the effects of bulk scattering and
background fluorescence on phantom experiments.
