[Paper Review] Intensity speckle presents the density matrix of light

KyeoReh Lee, YongKeun Park|arXiv (Cornell University)|Sep 26, 2017

Random lasers and scattering media48 references3 citations

TL;DR

This paper demonstrates that intensity speckle patterns directly encode the full density matrix of light, including amplitude, phase, polarization, and coherence properties. By extending the speckle-correlation scattering matrix (SSM) method, the authors extract the complete coherency matrix from a single intensity snapshot, enabling full characterization of complex light states with higher efficiency than conventional techniques like Stokes polarimetry.

ABSTRACT

We show that an intensity speckle can be directly interpreted as the properties of incident light - amplitude, phase, polarization, and coherency over spatial positions. Revisiting the speckle-correlation scattering matrix (SSM) method [Lee and Park, Nat. Comm. 7, 13359 (2016)], we successfully extract the intact information of incident light from an intensity speckle snapshot as the form of coherency matrix. The idea is verified experimentally by introducing the peculiar states of light that exhibit uneven amplitude, phase, polarization, and coherency features. We also find substantial practical advantage of the proposed method compared to the conventional coherency matrix measuring techniques such as Stokes polarimetry. We believe this physical interpretation of an intensity speckle could open a new avenue to study and to utilize the speckle phenomenon in vast subfields of wave physics.

Motivation & Objective

• To establish a physical interpretation of intensity speckle as a direct representation of the light's density matrix.
• To overcome limitations of conventional coherency matrix measurement techniques, such as Stokes polarimetry, which require multiple measurements and lack full coherence information.
• To demonstrate experimentally that speckle patterns can preserve and encode spatially varying amplitude, phase, polarization, and coherence features of incident light.
• To validate the method using engineered light states with non-uniform coherence and polarization profiles.
• To establish a practical, single-shot alternative for measuring the full coherency matrix of light fields.

Proposed method

• The speckle-correlation scattering matrix (SSM) method is extended to extract the full coherency matrix from a single intensity speckle pattern.
• The method relies on cross-correlating intensity speckle patterns from multiple scattering configurations to reconstruct the incident light's density matrix.
• Theoretical modeling shows that intensity speckle patterns contain complete information about the coherency matrix, including off-diagonal elements representing coherence.
• Experimental validation uses tailored light states with spatially varying amplitude, phase, polarization, and coherence to test the method's fidelity.
• The approach avoids phase-sensitive detection by using only intensity measurements, enabling robust and simple implementation.

Experimental results

Research questions

• RQ1 Can intensity speckle patterns be interpreted as a direct representation of the full density matrix of light?
• RQ2 How accurately can the coherency matrix be reconstructed from a single intensity speckle snapshot using the SSM method?
• RQ3 What are the practical advantages of this method over conventional techniques like Stokes polarimetry in measuring coherence properties?
• RQ4 Can the method resolve complex, spatially non-uniform light states with varying amplitude, phase, polarization, and coherence?
• RQ5 Does the method preserve full information about the incident light’s coherence, including off-diagonal elements of the density matrix?

Key findings

• The intensity speckle pattern contains complete information about the incident light’s coherency matrix, including amplitude, phase, polarization, and spatial coherence features.
• The SSM method successfully reconstructs the full coherency matrix from a single intensity snapshot, achieving high-fidelity characterization of complex light states.
• The method demonstrates superior practicality compared to Stokes polarimetry by eliminating the need for multiple measurements and phase-sensitive detection.
• Experimental results confirm the method's ability to resolve spatially varying coherence and polarization profiles in engineered light fields.
• The approach enables full characterization of light fields with minimal hardware requirements, opening new pathways for wave physics applications.