Intensity-Correlation Synthetic Wavelength Imaging in Dynamic Scattering Media

Abstract

Imaging through dynamic scattering media, such as biological tissue, presents a fundamental challenge due to light scattering and the formation of speckle patterns. These patterns not only degrade image quality but also decorrelate rapidly, limiting the effectiveness of conventional approaches, such as those based on transmission matrix measurements. Here, we introduce an imaging approach based on second-order correlations and synthetic wavelength holography (SWH) to enable robust image reconstruction through thick and dynamic scattering media. By exploiting intensity speckle correlations and using short-exposure intensity images, our method computationally reconstructs images from a hologram without requiring phase stability or static speckles, making it inherently resilient to phase noise. Experimental results demonstrate high-resolution imaging in both static and dynamic scattering scenarios, offering a promising solution for biomedical imaging, remote sensing, and real-time imaging in complex environments.

Figures (4)

• Figure 1: Experimental setup overview. Overview of the measurement process. The two lasers are combined at a fiber beamsplitter, ensuring that both wavelengths, $\lambda_1$ and $\lambda_2$, are present in both the signal and reference arms. Two measurement configurations are depicted: reflection (solid green) and transmission (dashed green). The reference arm collimator is adjusted using a motorized translation stage and rapidly moved with a piezo stage for phase randomization (PR). (a) SWL hologram (simulation) generated from 3 sets of intensity images at the surface of the scatterer. (b) Hologram after numerical backpropagation to the hidden object plane, revealing the object. (c) Photographs of the sample objects (3D-printed letters) with a scale bar of 5 mm.
• Figure 2: Recovering an object hidden by two scattering planes (ground glass diffusers): The columns show (as indicated in the figure) the measured intensity, synthetic wave (SW) amplitude and phase, and object reconstruction. (a), (b) and (c) are all performed in reflection: (a) Static object with phase randomization (PR) applied in the reference path. (b) Same scene as (a), with random motion of one scatterer and no PR in the reference arm. (c) Dynamic scatterer with PR applied in the reference arm. (d) is performed in transmission for a dynamic scatterer with PR applied in the reference arm. Scale bar: 5 mm. The synthetic wavelength used for this was $\Lambda = 0.68~\mathrm{mm}$
• Figure 3: Recovering an object hidden by volume scatterers: The columns display intensity, reconstruction for each wavelength, and object reconstruction by fusing information from both, as indicated at the top of each column. Reflection($\Lambda_1= 2;\Lambda_2= 3$ mm): (a) Static object with phase randomization (PR) applied in the reference path. (b) Dynamic scatterer with PR applied in the reference arm. Transmission($\Lambda_1= 3 , \Lambda_2 = 5$ mm): (c) Dynamic scatterer with PR applied in the reference arm. Scale bar: 5 mm.
• Figure 4: Diffraction-limited resolution: (a) Measured diffraction beam waist size (dots) for a a point-source (optical fiber tip) and the theoretical Abbe limit (solid line) as a function of the numerical back-propagation distance. The dashed line and plateau arises due to the limited NA of the fiber tip, which constrains the system's numerical aperture (NA) from short distances up to approximately 150 mm. (b) An $x-z$ cutout of the back-propagated synthetic field for the fiber tip at 200 mm from the diffuser with $\Lambda = 1.28$ mm. The corresponding measurement point in (a) is highlighted with a red border.