# Coherence measurements of scattered incoherent light for lensless identification of an object's location and size

## TL;DR

This paper demonstrates that measuring the complex spatial coherence function of scattered incoherent light enables lensless identification of an object's size and position, using wavefront sampling with a digital micromirror device.

## Contribution

It introduces a novel lensless method for object localization and sizing by coherence measurements, utilizing a DMD for real-time wavefront sampling.

## Key findings

- Coherence measurements can identify object size and position.
- Experimental results match numerical simulations based on Fresnel propagators.
- DMD enables rapid, potentially real-time, coherence-based imaging.

## Abstract

In absence of a lens to form an image, incoherent or partially coherent light scattering off an obstructive or reflective object forms a broad intensity distribution in the far field with only feeble spatial features. We show here that measuring the complex spatial coherence function can help in the identification of the size and location of a one-dimensional object placed in the path of a partially coherent light source. The complex coherence function is measured in the far field through wavefront sampling, which is performed via dynamically reconfigurable slits implemented on a digital micromirror device (DMD). The impact of an object -- parameterized by size and location -- that either intercepts or reflects incoherent light is studied. The experimental results show that measuring the spatial coherence function as a function of the separation between two slits located symmetrically around the optical axis can identify the object transverse location and angle subtended from the detection plane (the ratio of the object width to the axial distance from the detector). The measurements are in good agreement with numerical simulations of a forward model based on Fresnel propagators. The rapid refresh rate of DMDs may enable real-time operation of such a lensless coherency imaging scheme.