Pupil engineering for extended depth-of-field imaging in a fluorescence miniscope

Abstract

Significance: Fluorescence head-mounted microscopes, i.e., miniscopes, have emerged as powerful tools to analyze in-vivo neural populations but exhibit a limited depth-of-field (DoF) due to the use of high numerical aperture (NA) gradient refractive index (GRIN) objective lenses.

Aim: We present extended depth-of-field (EDoF) miniscope, which integrates an optimized thin and lightweight binary diffractive optical element (DOE) onto the GRIN lens of a miniscope to extend the DoF by $2.8\times$ between twin foci in fixed scattering samples.

Approach: We use a genetic algorithm that considers the GRIN lens' aberration and intensity loss from scattering in a Fourier optics-forward model to optimize a DOE and manufacture the DOE through single-step photolithography. We integrate the DOE into EDoF-Miniscope with a lateral accuracy of $70\mu m$ to produce high-contrast signals without compromising the speed, spatial resolution, size, or weight.

Results: We characterize the performance of EDoF-Miniscope across 5- and $10\text{-}\mu m$ fluorescent beads embedded in scattering phantoms and demonstrate that EDoF-Miniscope facilitates deeper interrogations of neuronal populations in a $100\text{-}\mu m$-thick mouse brain sample and vessels in a whole mouse brain sample.

Conclusions: Built from off-the-shelf components and augmented by a customizable DOE, we expect that this low-cost EDoF-Miniscope may find utility in a wide range of neural recording applications.

Keywords: computational imaging; extended depth-of-field; fluorescence microscopy; miniscope.