Multiple-scattering Media Research Articles

Complex-valued scatter compensation in nonlinear microscopy

Nonlinear, i.e., multiphoton microscopy is a powerful technique for imaging deep into biological tissues. Its penetration depth can be increased further using adaptive optics. In this work, we present a fast, feedback-based adaptive-optics algorithm, termed C-DASH, for multiphoton imaging through multiple-scattering media. C-DASH utilizes complex-valued light shaping (i.e., joint shaping of amplitude and phase), which offers several advantages over phase-only techniques: it converges faster, it delivers higher image quality enhancement, it shows a robust performance largely insensitive to the axial position of the correction plane, and it has a higher ability to cope with, on the one hand, scattering media that vary over time and, on the other hand, scattering media that are partially absorbing. Furthermore, our method is practically self-aligning. We also present a simple way to implement C-DASH using a single reflection off a phase-only spatial light modulator. We provide a thorough characterization of our method, presenting results of numerical simulations as well as two-photon excited fluorescence imaging experiments. Published by the American Physical Society 2024

Full transmission of vectorial waves through 3D multiple-scattering media.

A striking prediction from the random matrix theory (RMT) in mesoscopic physics is the existence of "open channels": waves that use multipath interference to achieve perfect transmission across an opaque disordered medium even in the multiple-scattering regime. Realization of such open channels requires a coherent control of the complete incident wavefront and has only been achieved for scalar waves in two dimensions (2D) so far. Here, we utilize a recently proposed "augmented partial factorization" full-wave simulation method to compute the polarization-resolved scattering matrix from 3D vectorial Maxwell's equations and demonstrate the existence of open channels in 3D disordered media. We examine the spatial profile of such open channels, demonstrate the existence of a bimodal transmission eigenvalue distribution, and study the effects of incomplete polarization control and finite-area illumination. The simulations provide full access to all spatiotemporal properties of the complex wave transport in 3D disordered systems, filling the gap left by experimental capabilities.

Control of structured light beams focusing through anisotropic multiple-scattering media via multi-focus-based digital optical phase conjugation

A framework to focus structured light beams through an anisotropic multiple-scattering medium (AMSM) with multi-focus-based digital optical phase conjugation is proposed. In this work, the measured full vector transmission matrix (VTM) in conjunction with a well-designed multifocal target field can be used to calculate the required input field, which consists of two orthogonally linear polarization components. The polarization, amplitude and phase of the light before and after the AMSM are then shaped and controlled by encoding the input field into a double-channel computer generated hologram that is displayed on a vector spatial light modulator. The desired output field composed of multifocal spots can be obtained through the AMSM. We demonstrated several examples, generating vector beams, array vector beams and vortex beams, to experimentally validate the feasibility of our approach. Additionally, the peak to background ratio (PBR) of the generated multifocal structured light can be predicted theoretically by introducing the idea of critical focus number. The simulated and experimental results show that the generated structured light with a clear optical ring and high PBR can be realized through the AMSM. Consequently, our method provides an effective way to control and optimize structured light beams focusing through the AMSM.

Parallel optical hash function based on the interaction between linearly polarized light and multiple-scattering media.

A method is proposed for constructing a cryptographic hash function based on the interaction between linearly polarized light and multiple-scattering media in a parallel fashion. It is well known that an unpredictable noise-like speckle pattern will appear when a light beam passes through a scattering medium. By leveraging this natural optical-encoding mechanism, we developed a paralleled algorithm to construct an optical hash function. It was shown by numerical simulation to have a high security level. Furthermore, in the proposed conceptual optical-digital setup, a strategy for multiplexing linearly polarized light was introduced to accelerate data processing.

Numerical Parametric Study of Coda Wave Interferometry Sensitivity to Microcrack Angle and Length in a Multiple Scattering Medium

Numerical Parametric Study of Coda Wave Interferometry Sensitivity to Microcrack Angle and Length in a Multiple Scattering Medium

Monte-Carlo and sensitivity transport models for domain deformation

We address the question of evaluating shape derivatives of objective functions for radiative-transfer engineering involving semi-transparent media. After recalling the standard Monte-Carlo approach to sensitivity estimation and its current limitations, a new method is presented for the specific case of geometrical sensitivities. This method is then tested on configurations with multiple-scattering and absorbing (non-emitting) semi-transparent medium. A new geometrical sensitivity algorithm is presented with full details in order to extend, on several examples, its implementation in complex geometries.

Lesion Imaging and Target Detection in Multiple Scattering (LITMUS) Media.

We present an ultrasound algorithm [lesion imaging and target detection in multiple scattering (LITMUS)] suited to image lesions (hypoechoic) or targets (hyperechoic) in highly complex structures. In such media, standard ultrasound imaging techniques fail to detect lesions or targets due to aberrations and the loss of linearity between propagation distance and propagation time, caused by multiple scattering of ultrasound waves. The present algorithm (LITMUS) has the capability to predict the location as well as the size of such lesions/targets by using the multiple scattered ultrasound signals to its advantage. In this experimental and computational study, we use an ultrasound linear array. Lesions/targets are embedded at varying depths inside multiple scattering media with varying density of scatterers. In the simulations, plastic scatterers are used as the source of multiple scattering in a propagation medium (water). In the experiments, melamine sponges are used, with air alveoli as the scattering source. For multiple locations along the transducer, the incoherent backscattered intensity of the backscattered signals is extracted and the linear growth of the diffusive halo over time is tracked. Sudden changes in this growth indicate the presence of a region with reduced heterogeneity, indicative of the presence of a lesion/target. This methodology is combined with a depression detection algorithm to predict the size and location of the lesion/targets with high fidelity, despite the presence of strong heterogeneity and multiple scattering.

Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold

A method of reference-free speckle spectroscopy based on the statistical analysis of intensity spatial fluctuations of the spectrally-selected multiple-scattered fluorescence radiation is examined in the case of the finite-band spectral selection of fluorescence light emitted by the laser-pumped random medium, and detection conditions far from the ideal case. Intensity fluctuations are recorded during point-to-point scanning of the surface of a random multiple-scattering medium, which is characterized by the dependences of the second- and third-order statistical moments of intensity on the wavelength of detected spectrally selected light. In turn, the statistical moments of intensity fluctuations are determined by the average propagation path of fluorescent radiation in the medium. This makes it possible to analyze the features of the light-medium interactions at a scale of the order of the transport mean free path of radiation propagation in the medium. Depending on the spectral selection conditions, the method is applicable for characterizing micro- or nano-structured fluorescent layers with thicknesses from tens of micrometers to several millimeters. In the examined case, the finite-band spectral selection results in the values of coherence length of the detected fluorescence radiation compared with the ensemble-averaged absolute value of the path-length difference between the stochastically interfering and spectrally selected partial contributions to the fluorescence field. In addition, non-ideal detection conditions (usage of a multimode optical fiber in the light-collecting unit) cause additional strong damping of the detected speckle intensity fluctuations. These factors lead to a remarkable suppression of spatial fluctuations of the fluorescence intensity in the course of spatially- and spectrally-resolved surface scanning of the laser-pumped probed random medium. Nevertheless, with appropriate procedures of the intrinsic noise reduction and data correction, the obtained spectral dependencies of the normalized third-order statistical moment of the band-limited fluorescence intensity clearly indicate the fluorescence propagation features in the probed multiple-scattering random media (such as a strong influence of the scattering strength and multiple self-absorption–re-emission events on the average propagation path of light in the medium).The possibilities of noise reduction and data correction in the case of applying the band-limited reference-free spectroscopic instrumentation with low spectral and spatial resolution are illustrated by the experimental results obtained using the Rhodamine-6G-doped and continuous wave (CW)-laser-pumped layers of the densely packed titania and silica particles.

Realistic phase screen model for forward multiple-scattering media.

Existing random phase screen (RPS) models for forward multiple-scattering media fail to incorporate ballistic light. In this Letter, we redesign the angular spectrum of the screen by means of Monte Carlo simulation based on an assumption that a single screen should represent all the scattering events a photon experiences between two adjacent screens. Three examples demonstrate that the proposed model exhibits more realistic optical properties than conventional RPS models in terms of attenuation of ballistic light, evolution of beam profile, and angular memory effect. The proposed model also provides the flexibility to balance the computing accuracy, speed, and memory usage by tuning the screen spacing.

Angular Memory Effect of Transmission Eigenchannels.

The optical memory effect has emerged as a powerful tool for imaging through multiple-scattering media; however, the finite angular range of the memory effect limits the field of view. Here, we demonstrate experimentally that selective coupling of incident light into a high-transmission channel increases the angular memory-effect range. This enhancement is attributed to the robustness of the high-transmission channels against perturbations such as sample tilt or wave front tilt. Our work shows that the high-transmission channels provide an enhanced field of view for memory-effect-based imaging through diffusive media.

Magnetic-field effects on one-dimensional Anderson localization of light

Transport of coherent waves in multiple-scattering media may exhibit fundamental, non intuitive phenomena such as halt of diffusion by disorder called Anderson localization. For electromagnetic waves, this phenomenon was observed only in one and two dimensions so far. However, none of these experiments studied the contribution of reciprocal paths nor their manipulation by external fields. In order to weaken the effect of reciprocity of coherent wave transport on Anderson localization in one dimension (1D), we studied light propagation through stacks of parallel Faraday-active glass slides exposed to magnetic fields up to 18 Tesla. Measurements of light transmission statistics are presented and compared to 1D transfer-matrix simulations. The latter reveals a self-organization of the polarization states in this system leading to a saturation of the Faraday rotation-induced reciprocity breaking, an increase of the localization length, and a decrease of transmission fluctuations when reciprocity is broken. This is confirmed experimentally for samples containing small numbers of slides while for larger samples a crossover from a 1D to a quasi-1D transport regime is found.

Iterative Method to Obtain Raman Spectra of Organic Dyes by Their Chaotic Generation in Multiple-Scattering Media

An iterative method is developed to obtain vibrational spectra of laser organic dyes from their secondary radiation spectra in multiple-scattering media, which manifests as a result of coupled process of chaotic generation (CG) and stimulated Raman scattering (SRS). The developed method increases significantly the capability to detect weak Raman lines by using batch processing of a set of experimental SRS-CG spectra, which makes it possible to optimize the deconvolution of these spectra and to average vibrational spectra obtained from the set of experimental SRS-CG spectra. The method is tested on spectra of the SRS-CG laser dye pyrromethene 597 in a vesicular film. The obtained results agree well with Raman spectra calculated by the Hartree–Fock method.

Method for Separation of Blood Vessels on the Three-Color Images of Biological Tissues

A new technology was developed to improve the visibility of blood vessels on images of tissues of hollow human organs(the alimentary tract and respiratory system) based on the relation between the color components of the image, the scattering properties of the tissue, and its hemoglobin content. A statistical operator was presented to convert the three-color image of the tissue into a parametric map objectively characterizing the concentration of hemoglobin in the tissue regardless of the illumination and shooting conditions. An algorithm for obtaining conversion parameters for image systems with known spectral characteristics was presented. An image of a multilayer multiple-scattering medium modeling bronchial tissue was synthesized and was used to evaluate the efficiency of the proposed conversion system. It was shown that the conversion made it possible to increase the contrast of the blood vessels by almost two orders of magnitude, to significantly improve the clarity of the display of their borders, and to eliminate almost completely the influence of background and nonuniform illumination of the medium in comparison with the original image.

Measurement of vector transmission matrix and control of beam focusing through a multiple-scattering medium based on a vector spatial light modulator and two-channel polarization holography

An experimental system for measuring the complex vector transmission matrix (VTM) of an anisotropic multiple-scattering medium (AMSM) is proposed. In this system, a simple vector spatial light modulator unit composed of a conventional transmittance spatial light modulator and a small-angle birefringent beam splitter is introduced to realize programmable and quantitative control of both the amplitudes and phases of two orthogonal polarization components of the input vector beam point by point. At the same time, a two-channel angular-multiplexing holographic polarization recording geometry is applied to realize the synchronous holographic measurement of the two orthogonal polarization components of the scattered light field. Using this system, we measured the VTM of an AMSM composed of the ZnO scattering layer. At the same time, we also demonstrated that the system can be directly applied to realize focusing a vector beam through the AMSM based on the measured VTM.

Continuous-variable quantum authentication of physical unclonable keys

We propose a scheme for authentication of physical keys that are materialized by optical multiple-scattering media. The authentication relies on the optical response of the key when probed by randomly selected coherent states of light, and the use of standard wavefront-shaping techniques that direct the scattered photons coherently to a specific target mode at the output. The quadratures of the electromagnetic field of the scattered light at the target mode are analysed using a homodyne detection scheme, and the acceptance or rejection of the key is decided upon the outcomes of the measurements. The proposed scheme can be implemented with current technology and offers collision resistance and robustness against key cloning.

Reciprocity relation for the vector radiative transport equation and its application to diffuse optical tomography with polarized light.

We derive a reciprocity relation for the 3D vector radiative transport equation that describes propagation of polarized light in multiple-scattering media. We then show how this result, together with translational invariance of a plane-parallel sample, can be used to efficiently compute the sensitivity kernel of diffuse optical tomography by Monte Carlo simulations. Numerical examples of polarization-selective sensitivity kernels are given.

Glucose detection in a highly scattering medium with diffuse photon-pair density wave

We propose a novel optical method for glucose measurement based on diffuse photon-pair density wave (DPPDW) in a multiple scattering medium (MSM) where the light scattering of photon-pair is induced by refractive index mismatch between scatters and phantom solution. Experimentally, the DPPDW propagates in MSM via a two-frequency laser (TFL) beam wherein highly correlated pairs of linear polarized photons are generated. The reduced scattering coefficient [Formula: see text] and absorption coefficient [Formula: see text] of DPPDW are measured simultaneously in terms of the amplitude and phase measurements of the detected heterodyne signal under arrangement at different distances between the source and detection fibers in MSM. The results show that the sensitivity of glucose detection via glucose-induced change of reduced scattering coefficient ([Formula: see text]) is 0.049%[Formula: see text]mM[Formula: see text] in a 1% intralipid solution. In addition, the linear range of [Formula: see text] vs glucose concentration implies that this DPPDW method can be used to monitor glucose concentration continuously and noninvasively subcutaneously.

Removing multiple scattering in underwater target detection

Recent advances have been made in the field of optics to image through multiple-scattering media in a regime where classical imaging techniques, which rely on the single-scattering approximation, fail. Using results generated by random matrix theory, it is possible to filter the response matrix generated by a source/receiver array to remove the multiple scattering components of the received signals. After removing the multiple scattering components, classical imaging techniques can be used to image with the single-scattering components. We show how this single-scattering filter can be adapted for underwater acoustical imaging in cases where multiple scattering effects are large compared to the reflection from the target. A full-wave 3-dimensional time-domain scaled model is used to characterize filter performance as a function of target strength and environmental coherence length for a shallow-water case. Preliminary results indicate that the filter can be used to detect a target located at least 2 mean f...

Coupled effect of stimulated Raman scattering and random lasing of dyes in multiple scattering medium

Random lasing (RL) and stimulated Raman scattering (SRS) of dye in multiple scattering media (MSM) appears simultaneously and each couple with other. This coupling has considerable influence on the SRS regularities of dye in MSM. The main feature of this impact is that RL radiation promotes the Raman lines revealing in the RL spectrum range as part of total radiation. SRS initiation occurs owing to the CARS-like mechanism provided by the two component pump: incident monochromatic radiation (laser pump) and RL radiation arising inside the MSM. It leads to important consequences: the RL spectrum must overlap with the spectral region of the possible Stokes lines of the dye; only those Stokes lines appear which are in a range of the RL spectrum; all conditions which promote RL assist SRS also. It is shown MSM promotes the best conditions for SRS and RL coupling due to optimal matching of RL localization regions and pump radiation.

Nonclassical light manipulation in a multiple-scattering medium.

We investigate the possibility of using a scattering medium as a highly multimode platform for implementing quantum walks. We demonstrate the manipulation of a single photon propagating through a strongly scattering medium using wavefront-shaping technique. Measurement of the scattering matrix allows the wavefront of the photon to be shaped to compensate the distortions induced by multiple scattering events. The photon can thus be directed coherently to a specific output mode. Using this approach, we show how entanglement of a single photon across different modes can be manipulated despite the enormous wavefront disturbance caused by the scattering medium.