# Ptychographic modulation engine (PME): a low-cost DIY microscope add-on for coherent super-resolution imaging

## TL;DR

The paper introduces a low-cost, DIY ptychographic modulation engine add-on for microscopes that enables super-resolution, label-free quantitative phase imaging with a fourfold resolution enhancement over the diffraction limit.

## Contribution

It presents a simple, affordable microscope add-on that encodes high-resolution information through diffuser modulation, enabling super-resolution imaging without complex modifications.

## Key findings

- Achieved 4-fold resolution gain over diffraction limit.
- Enabled in-vivo cell imaging with post-capture focus adjustment.
- Provided a turnkey solution for high-resolution, large field-of-view bio-imaging.

## Abstract

Imaging of biological cells and tissues often relies on fluorescent labels, which offer high contrast with molecular specificity. The use of exogenous labeling agents, however, may alter the normal physiology of the bio-specimens. Complementary to the established fluorescence microscopy, label-free quantitative phase imaging provides an objective morphological measurement tool for bio-specimens and is free of variability introduced by contrast agents. Here we report a simple and low-cost microscope add-on, termed Ptychographic Modulation Engine (PME), for super-resolution quantitative phase imaging. In this microscope add-on module, we attach a diffuser to a 3D-printed holder that can be mechanically moved to different x-y positions. We then use two vibrational motors to introduce random positional shifts to the diffuser. The add-on module can be placed between the objective lens and the specimen in most existing microscope platforms. Thanks to the diffuser modulation process, the otherwise inaccessible high-resolution object information can now be encoded into the captured images. In the ptychographic phase retrieval process, we jointly recover the complex object wavefront, the complex diffuser profile, and the unknown positional shifts of the diffuser. We demonstrate a 4-fold resolution gain over the diffraction limit of the employed 2X objective lens. We also test our approach for in-vivo cell imaging, where we are able to adjust the focus after the data has been captured. The reported microscope add-on provides a turnkey solution for super-resolution quantitative phase imaging. It may find applications in label-free bio-imaging where both large field-of-view and high resolution are needed.

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Source: https://tomesphere.com/paper/1908.05761