# A Super-Condenser for Labelfree Nanoscopy

## TL;DR

This paper introduces a novel labelfree nanoscopy technique combining Fourier ptychography with waveguide microscopy, achieving high-resolution imaging by using a super-condenser with inclined darkfield illumination and advanced phase retrieval methods.

## Contribution

It presents a new super-condenser design utilizing Si3N4 waveguides for enhanced coherent illumination in Fourier ptychography, enabling larger imaging areas and improved phase retrieval.

## Key findings

- Successful in silico validation of the method
- In vitro experiments demonstrate high-resolution imaging
- Enhanced phase retrieval via multiplexed waveguide illumination

## Abstract

Labelfree nanoscopy encompasses optical imaging with resolution in the 100 nm range using visible wavelengths. Here, we present a labelfree nanoscopy method that combines Fourier ptychography with waveguide microscopy to realize a 'super-condenser' featuring maximally inclined coherent darkfield illumination with artificially stretched wave vectors due to large refractive indices of the employed Si$_3$N$_4$ waveguide material. We produce the required coherent plane wave illumination for Fourier ptychography over imaging areas 400 $\mathrm{\mu}$m$^2$ in size via adiabatically tapered single-mode waveguides and tackle the overlap constraints of the Fourier ptychography phase retrieval algorithm two-fold: firstly, the directionality of the illumination wave vector is changed sequentially via a multiplexed input structure of the waveguide chip layout and secondly, the wave vector modulus is shortend via step-wise increases of the illumination light wavelength over the visible spectrum. We validate the method via in silico and in vitro experiments and provide details on the underlying image formation theory as well as the reconstruction algorithm.