Focusing polychromatic light through strongly scattering media

TL;DR

This paper demonstrates a method to focus polychromatic light through scattering media using feedback optimization, revealing how spectral bandwidth depends on feedback characteristics and modeling the spectral mode transmission.

Contribution

It introduces a feedback-based focusing technique for polychromatic light through scattering media and models the spectral mode transmission effects.

Findings

Optimized focus intensity relates to initial speckle contrast.

Spectral bandwidth depends on feedback signal characteristics.

Model confirms the relationship between spectral modes and focus enhancement.

Abstract

We demonstrate feedback-optimized focusing of spatially coherent polychromatic light after transmission through strongly scattering media, and describe the relationship between optimized focus intensity and initial far-field speckle contrast. Optimization is performed using a MEMS spatial light modulator with camera-based or spectrometer-based feedback. We observe that the spectral bandwidth of the optimized focus depends on characteristics of the feedback signal. We interpret this dependence as a modification in the number of spectral modes transmitted by the sample, and introduce a simple model for polychromatic focus enhancement that is corroborated by experiment with calibrated samples.