# Facing the phase problem in Coherent Diffractive Imaging via Memetic Algorithms

## TL;DR

This paper introduces a memetic algorithm-based method to solve the phase problem in Coherent Diffractive Imaging, enabling atomic-resolution imaging and revealing details like oxygen columns in electron diffraction data.

## Contribution

The paper presents a novel hybrid genetic algorithm approach that effectively retrieves phase information in CDI, demonstrated on simulated and experimental electron diffraction data.

## Key findings

- Successfully retrieved atomic potential and oxygen columns in SrTiO3
- Proved effectiveness on simulated and real electron diffraction data
- Enhanced phase retrieval capabilities for atomic-resolution imaging

## Abstract

Coherent Diffractive Imaging is a lensless technique that allows imaging of matter at a spatial resolution not limited by lens aberrations. This technique exploits the measured diffraction pattern of a coherent beam scattered by periodic and non-periodic objects to retrieve spatial information. The diffracted intensity, for weak-scattering objects, is proportional to the modulus of the Fourier Transform of the object scattering function. Any phase information, needed to retrieve its scattering function, has to be retrieved by means of suitable algorithms. Here we present a new approach, based on a memetic algorithm, i.e. a hybrid genetic algorithm, to face the phase problem, which exploits the synergy of deterministic and stochastic optimization methods. The new approach has been tested on simulated data and applied to the phasing of transmission electron microscopy coherent electron diffraction data of a $\text{SrTiO}_\text{3}$ sample. We have been able to quantitatively retrieve the projected atomic potential, and also image the oxygen columns, which are not directly visible in the relevant high-resolution transmission electron microscopy images. Our approach proves to be a new powerful tool for the study of matter at atomic resolution and opens new perspectives in those applications in which effective phase retrieval is necessary.