[Paper Review] Universal sensitivity of speckle intensity correlations to wavefront change in light diffusers

KyungDuk Kim, Hyeonseung Yu+2 more|arXiv (Cornell University)|Oct 5, 2016

Random lasers and scattering media3 citations

TL;DR

This paper proposes that speckle intensity correlations in light diffusers universally reflect wavefront changes of an incident coherent beam, enabling the diffuser to act as a simple interferometer. Using random matrix theory and experiments with a microfluidic wavefront modulator, the authors demonstrate that intensity correlations are independent of the diffuser's specific properties and depend solely on phase changes, enabling robust, reference-free wavefront sensing in applications from biomedicine to metrology.

ABSTRACT

Here, we present a concept based on the realization that a complex medium can be used as a simple interferometer. Changes in the wavefront of an incident coherent beam can be retrieved by analyzing changes in speckle patterns when the beam passes through a light diffuser. We demonstrate that the spatial intensity correlations of the speckle patterns are independent of the light diffusers, and are solely determined by the phase changes of an incident beam. With numerical simulations using the random matrix theory, and an experimental pressure-driven wavefront-deforming setup using a microfluidic channel, we theoretically and experimentally confirm the universal sensitivity of speckle intensity correlations, which is attributed to the conservation of optical field correlation despite multiple light scattering. This work demonstrates that a complex media is a simple interferometer, and presents opportunities to replace complicated reference-beam-assisted interferometers with a simple and compact scattering layer in various applications in metrology, analytical chemistry, and biomedicine.

Motivation & Objective

• To explore whether speckle intensity correlations in complex media can serve as a universal probe for wavefront changes.
• To address the challenge of wavefront sensing in turbid or scattering media without requiring a reference beam.
• To demonstrate that intensity correlations are independent of the specific diffuser properties, relying only on phase changes of the incident beam.
• To establish a theoretical and experimental foundation for using diffusers as simple, compact interferometers.

Proposed method

• Theoretical analysis using random matrix theory to model wave propagation through disordered media and predict intensity correlation behavior.
• Numerical simulations to validate the universality of intensity correlation sensitivity to wavefront changes across different diffuser configurations.
• Experimental setup using a pressure-driven microfluidic channel to dynamically deform the wavefront and modulate the incident beam.
• Measurement of speckle intensity correlations before and after wavefront deformation to extract phase change information.
• Comparison of theoretical predictions with experimental results to confirm the universality of the correlation response.
• Use of statistical analysis to show that intensity correlations depend only on phase changes, not on the specific scattering medium.

Experimental results

Research questions

• RQ1 Can speckle intensity correlations in a light diffuser universally detect changes in the wavefront of an incident coherent beam?
• RQ2 Is the sensitivity of intensity correlations to wavefront changes independent of the specific properties of the diffuser?
• RQ3 To what extent can a complex medium like a diffuser replace traditional reference-beam interferometers in wavefront sensing?
• RQ4 How does the conservation of optical field correlation under multiple scattering enable universal wavefront detection via intensity correlations?
• RQ5 Can this method be experimentally validated in a practical, compact setup without requiring a reference beam?

Key findings

• Speckle intensity correlations are universally sensitive to wavefront changes and independent of the specific light diffuser used.
• Theoretical predictions based on random matrix theory accurately describe the observed intensity correlation behavior across different diffuser types.
• Experimental results using a microfluidic wavefront modulator confirm that intensity correlations reflect phase changes with high fidelity.
• The method enables reference-free wavefront sensing, eliminating the need for complex interferometric setups.
• The sensitivity of intensity correlations to phase changes is robust and reproducible across multiple trials and diffuser configurations.
• The conservation of optical field correlation during multiple scattering underpins the universal behavior of intensity correlations in response to wavefront changes.