Photoemission properties of the variable component GaInAsSb heterojunction nanopillar array cathode

zhidong Wang, Lei Liu, zhihao Cao, Jian Tian, and Xingyue Zhangyang

DOI: 10.1364/JOSAA.506364 Received 21 Sep 2023; Accepted 15 May 2024; Posted 15 May 2024  View: PDF

Abstract: The GaxIn1-xAsySb1-y heterojunction NPAs exhibit different properties depending on thematerial composition. Changing the Ga composition significantly affects the quantum efficiencyand broadening of the heterojunction nanopillar array, while varying the As composition affectsthe peak position of its quantum efficiency. The quantum efficiency of the heterojunction isnotably influenced by changes in the height of the top layer of the heterojunction, and when thereis a difference in quantum efficiency between the two materials, the quantum efficiency of theheterojunction exhibits extremum values. Furthermore, external electric fields significantly affectthe quantum efficiency of nanopillar arrays, providing important references and theoreticalfoundations for designing and optimizing resonantly enhanced GaInAsSb nanopillar arrayphotonic cathodes.

Analysis of far-field radiation pattern by a current loop in hyperbolic material

Aamir Hayat, Hafiza Khalid, and Muzamil Shah

DOI: 10.1364/JOSAA.519811 Received 24 Jan 2024; Accepted 15 May 2024; Posted 15 May 2024  View: PDF

Abstract: In this article, we investigate the radiations from a current loop in the hyperbolicmaterials. To encounter the arbitrary orientation of the loop, the results are presented when theloop axis is aligned parallel and perpendicular to the optic axis. Closed-form expressions aswell as numerical results are presented for both ordinary and extraordinary waves. The resultsindicate a strong dependence on the size of the loop, in contrast to the case of uniaxial dielectricmaterials. When the loop axis is parallel to the optic axis the pattern is quite similar to that ofuniaxial dielectric materials, however, a significant change in the pattern is observed when theoptic axis turns perpendicular to the loop axis. The results show a significant role of the size ofthe loop in the hyperbolic material as compared to the uniaxial dielectric material.

Does the quasi-static polarizability have principal axes?

Vadim Markel

DOI: 10.1364/JOSAA.523449 Received 11 Mar 2024; Accepted 14 May 2024; Posted 14 May 2024  View: PDF

Abstract: Beyond strict statics, the dipole polarizability tensor is a complex symmetric matrix. Such matrices may not be diagonalizable by an orthogonal similarity transformation (a rigid rotation of the reference frame). In this paper, we provide examples of polarizability tensors, which have no real principal axes and discuss the conditions under which this counter-intuitive phenomenon can occur.

Statistical insights of polarization speckle via von Mises-Fisher distribution on the Poincaré sphere

SOURAV CHANDRA, Rajeev Singh, and Rakesh Singh

DOI: 10.1364/JOSAA.519685 Received 22 Jan 2024; Accepted 14 May 2024; Posted 14 May 2024  View: PDF

Abstract: Polarization speckle generated via random scattering of light, are ubiquitous in natural and engineered systems. They not only manifest intensity fluctuations but also reveal a spatially fluctuating, random polarization distribution. The precise morphology of the polarization speckle pattern serves as a deterministic signature of the light's state of polarization fluctuation within a scattering medium. Given the inherent randomness of polarization speckle patterns, a statistical approach emerges as the most pragmatic method for their analysis. Stokes parameters, implemented as temporal or spatial averages are utilized for this purpose. However, within a polarization speckle field featuring a specific spatial average of Stokes parameters, the polarization state exhibits spatial variations across the speckle pattern. These random polarization fluctuations can be effectively modeled using a particular probability density function (PDF), visually represented on the Poincaré sphere. In this work, we propose and experimentally demonstrate a statistical analysis of polarization speckles using von Mises-Fisher (vMF) distribution on the Poincaré sphere. A complete theoretical basis is developed to investigate the spatial fluctuation of the state of polarization in the polarization speckle using vMF distribution on the Poincaré sphere, including the spatial mean direction, and spatial concentration parameter. Behaviour of the marginal vMF distribution on the axes of the Poincaré sphere and its association with the probability density function of the normalized at-the-point Stokes parameters for three different polarization speckles are examined by experiment and simulation. The experimental results are in good agreement with simulation results and confirm the usefulness of the developed theoretical framework for the analysis of the polarization speckles. Characterization of spatial polarization fluctuation offers significant applications such as in polarimetric analysis, optical sensing, as well as same analogy can be used in quantum optics.

Deep SBP+ 2.0: Physics-driven generation capability enhanced framework to reconstruct space-bandwidth product-expanded image from two image shots

Chen Li, zhibo xiao, and Shouyu Wang

DOI: 10.1364/JOSAA.516572 Received 20 Dec 2023; Accepted 13 May 2024; Posted 14 May 2024  View: PDF

Abstract: The space-bandwidth product (SBP) limitation makes it difficult to obtain an image with both high spatial resolution and a large field of view (FoV) through commonly used optical imaging systems. Though FoV and spectrum stitch provide solutions for SBP expansion, they rely on spatial and spectral scanning, which lead to massive image captures and low processing speed. To solve the problem, we previously reported a physics-driven deep SBP-expanded framework (Deep SBP+) [JOSA A 40, 833-840 20 ]. Deep SBP+ can reconstruct the image with both high spatial resolution and a large FoV from a low-spatial-resolution image in a large FoV and several high-spatial-resolution images in sub-FoVs. In physics, Deep SBP+ reconstructs the convolution kernel between the low- and high-spatial-resolution images and improves the spatial resolution through deconvolution. But Deep SBP+ needs multiple high-spatial-resolution images in different sub-FoVs, inevitably complicating the operations. To further reduce the image captures, we report an updated version of Deep SBP+ 2.0, which can reconstruct an SBP expanded image from a low-spatial-resolution image in a large FoV and another high-spatial-resolution image in a sub-FoV. Different from Deep SBP+, the assumption that the convolution kernel is a Gaussian distribution is added to Deep SBP+ 2.0 to make the kernel calculation simple and in line with physics. Moreover, improved deep neural networks have been developed to enhance the generation capability. Proven by simulations and experiments, the receptive field is analyzed to prove that a high-spatial-resolution image in the sub-FoV can also guide the generation of the entire FoV. Furthermore, we also discuss the requirement of the sub-FoV image to obtain an SBP-expanded image of high quality. Considering its SBP expansion capability and convenient operation, the updated Deep SBP+ 2.0 can be a useful tool to pursue images with both high spatial resolution and large FoV.

Evolution of the polarization singularities in partially coherent beams on propagation through turbulence

William Raburn and Gregory Gbur

DOI: 10.1364/JOSAA.522600 Received 29 Feb 2024; Accepted 13 May 2024; Posted 13 May 2024  View: PDF

Abstract: In recent years, topological singularities of wavefields have been considered as8structures that can improve a variety of optical technologies, including remote sensing and9free-space optical communications. However, atmospheric turbulence can distort the features10of singularities over long propagation distances, limiting their use in many cases. One solution11being considered is the reduction of spatial coherence of light, as partially coherent beams12have shown increased resistance to turbulence under a broad range of situations. In this paper,13we look at the evolution of polarization singularities that arise in a particular projection of a14partially coherent vector beam, and how the position and number of singularities are affected15by atmospheric turbulence. We find that there are projections where the singularities persist on16propagation, suggesting their possible use in applications.

Color-appearance-matched data in high-dynamic-range luminance conditions

Jisoo Hwang, YESEUL BAEK, Youngshin Kwak, and YEJIN HONG

DOI: 10.1364/JOSAA.515516 Received 20 Dec 2023; Accepted 10 May 2024; Posted 10 May 2024  View: PDF

Abstract: We report color-appearance-matched data under high-dynamic-range luminance conditions. Theexperimental method and apparatus proposed in a previous study (J. Hwang et al., J. Opt. Soc. Am. A, 36 1940 (2019))were used to measure perceptual color shifts in the R, G, B, Y, RB, BG, GY, and YR groups of 16 samples under fourdual-illumination conditions at luminance levels of (300 cd/m2 and 4,500 cd/m2), (20 cd/m2 and 300 cd/m2), (80 cd/m2and 4,500 cd/m2), and (20 cd/m2 and 4,500 cd/m2). We observed a decrease in lightness for all samples, and hue shiftstoward blue in R, red in reddish YR, and green in BG samples when the luminance changed from low to high.Correlated changes in lightness and chroma, that is, an increase in lightness change and a decrease in chroma changeunder the highest luminance contrast (20 cd/m2 and 4,500 cd/m2), were observed for the Y, GY, and YR samples.

Three-dimensional surface reconstruction from reflectance direction fields with orthogonal multicolor filters

Hiroshi Ohno

DOI: 10.1364/JOSAA.521452 Received 12 Feb 2024; Accepted 10 May 2024; Posted 13 May 2024  View: PDF

Abstract: A three-dimensional (3D) freeform surface reconstruction method is proposed,specifically designed to handle complex surfaces, even those with steep inclinations. Thismethod utilizes a one-shot color mapping imaging system to obtain reflectance direction fieldsusing a stripe multicolor filter positioned in two orthogonal orientations. This imaging systemcan capture reflectance directions that are identifiable by corresponding colors. The multicolorfilter consists of multiple stripe regions, each with a different transmission spectrum.Theoretically, an equation that describes the relationship between reflectance direction fieldsand the reflective 3D surface can be derived based on the geometrical optics. By solving thisequation using a deep neural network (DNN) as a gradient descent method without any trainingdata, the 3D surface can be accurately reconstructed, even for surfaces with steep inclinations.The effectiveness of this method is validated through numerical demonstrations on several 3Dsurfaces, including complex ones with concave and convex areas, as well as steep inclinations.

Twisted vortex Gaussian Schell-model beams, generalized ABCD systems, and multidimensional Hermite polynomials

Milo Hyde, Benjamin Wilson, and Santasri Bose-Pillai

DOI: 10.1364/JOSAA.525568 Received 03 Apr 2024; Accepted 08 May 2024; Posted 09 May 2024  View: PDF

Abstract: We derive the cross-spectral density (CSD) function for a twisted vortex partially coherent beam at the output of a general ABCD system in terms of multidimensional Hermite polynomials (MDHPs). MDHPs, which to our knowledge have not been applied in classical optics, offer notational and computational advantages over prior CSD function representations, which use common (one-dimensional) Hermite polynomials. We explain how to compute MDHPs using the recurrence relation given in the literature and include MATLAB code to generate MDHPs of any order. Lastly, we validate our work experimentally by comparing the measured spectral density of a twisted vortex beam at the output of an asymmetric optical system to predictions from our theoretical CSD function.

Identifying the twist factor of twisted partially coherent optical beams

Jiajie Li, Jun Chen, Guo-zhen Qi, and Jinzhen Li

DOI: 10.1364/JOSAA.522975 Received 04 Mar 2024; Accepted 07 May 2024; Posted 07 May 2024  View: PDF

Abstract: Twisted partially coherent light, characterized by its unique twist factor, offers a novel control over the statistical properties of random light. However, the recognition of the twist factor remains a challenge due to the low coherence and the stochastic nature of the optical beam. This paper introduces a method for the recognition of twisted partially coherent beams by utilizing a circular aperture at the source plane. This aperture produces a characteristic hollow intensity structure due to the twist phase. A deep learning model is then trained to identify the twist factor of these beams based on this signature. The model, while simple in structure, effectively eliminates the need for complex optimization layers, streamlining the recognition process. This approach offers a promising solution for enhancing the detection of twisted light and paves the way for future research in this field.

Negative Reflection and Total Internal Reflection at the internal surface of Lithium NIobate crystal

Priyank Sain, Gopalkrishna Hegde, and Srinivas Talabattula

DOI: 10.1364/JOSAA.522592 Received 28 Feb 2024; Accepted 07 May 2024; Posted 07 May 2024  View: PDF

Abstract: In this paper, we analytically find out the expression for wave vector and Poynting vector in the reflection domain for negative uniaxial material. We investigate the impact of optical axis rotation and incident angle on the wave vector and Poynting vector reflected from the internal surface of Lithium Niobate crystal when the light is propagating from the denser anisotropic medium to the rarer isotropic medium. We derived the Brewster angle condition and discussed the walk-off between TE and TM polarized light. We explored where the wave vector and Poynting vector are parallel after reflection. In further analysis, we look into the phase differences between ordinary and extraordinary reflected light after total internal reflection from the internal surface of Lithium Niobate crystal. The necessary conditions for linear polarization and circular polarization have been established. The impact of optical axis orientation is also taken into consideration. The refractive index for the isotropic material for the desired polarization response has been found as 2.18, 2.1, and 2.03 at 632nm, 1550nm, and 3500nm respectively.

Three-Dimensional Freeform Reflector Design with a Microfacet Surface Roughness Model

Vì Kronberg, Martijn Anthonissen, Jan ten Thije Boonkkamp, and Wilbert IJzerman

DOI: 10.1364/JOSAA.522862 Received 01 Mar 2024; Accepted 04 May 2024; Posted 06 May 2024  View: PDF

Abstract: This manuscript will unify inverse freeform reflector design and surface light scattering to design freeform reflectors with a scattering surface. We use microfacets, which are small, tilted mirrors superimposed on a smooth surface. We form a simple model of surface roughness and light scattering based on the orientations of the microfacets. Using a least-squares solver to compute the smooth reflector as a starting point, we can subsequently alter the surface using an optimization procedure to account for the scattering. After optimization, the resulting reflector surface produces the desired scattered light distribution. We verify the resulting reflector using raytracing.

Extended-depth-of-field imaging with an ultra-thin folded lens

Lehan Zhang, shuo Wang, Dachao Li, zhu meng, yuhai li, Na Xie, Hongxia Zhang, and Dagong Jia

DOI: 10.1364/JOSAA.518441 Received 11 Jan 2024; Accepted 04 May 2024; Posted 06 May 2024  View: PDF

Abstract: An optical system with an extended depth of field (EDOF) is important in observation and measurement applications, in which achieving both compactness and a large depth of field (DOF) is a significant challenge using traditional optical elements. In this paper, we propose an innovative solution by intruducing an ultra-thin annular 4-folded lens with an EDOF to significantly enhance the DOF in a compact structure. The designed annular folded lens (AFL) has a effective focal length of 78.4 mm and a total thickness of only 8.5 mm. Simulation analysis shows that the proposed folded lens has a DOF of 380.55 m. To validate the practical feasibility of the AFL, we developed an AFL-based test system exhibiting a resolution of 0.11 mrad across a wide wavelength range of 486 nm to 656 nm. Additionally, we present experimental results from a miniature compact prototype, which further highlight the promising potential of folded lenses for imaging applications with EDOF.

Transparent coating on a color surface

Geoffrey Rogers

DOI: 10.1364/JOSAA.521759 Received 20 Feb 2024; Accepted 03 May 2024; Posted 06 May 2024  View: PDF

Abstract: When a laminate or transparent coating is applied to the surface of a colored slab, there may be a significant change in the color. A reason for the change in color is internal reflection at the slab surface and greater selective absorption. The current work develops a random walk model of reflection that includes internal reflection to predict the change in color. The probability density of photons that have diffused a particular path length within the slab is calculated and Bouger’s law is applied to each path. The flux is summed over all paths and the total probability flux through the surface is shown to be equal to the reflectance factor. The CIELAB colors are calculated from the reflectance, and the model shows that that there is not much change in hue but there is significant change in the saturation and value: the saturation increases and the value decreases. A comparison of the reflectance factor as predicted by the model is made with a Monte-Carlo simulation and shown to have good agreement.

Orientation-Based Solar Noise Impact on Underwater and Free-Space Optical Wireless Communication System: Experimental Investigations

SAROJ MAHAPATRA, Manotosh Howlader, Sanjib Kumar Roy, and Shailendra Varshney

DOI: 10.1364/JOSAA.518008 Received 08 Jan 2024; Accepted 27 Apr 2024; Posted 29 Apr 2024  View: PDF

Abstract: Solar noise, when it interferes with the received signal at the system receiver (Rx) of an optical wireless communication (OWC) system, degrades its performance. The detrimental effect of solar noise on OWC systems has been well-established and available in the literature. This work experimentally demonstrates solar noise interference in the OWC system by pointing the system Rx in various orientations in air and water mediums, e.g., 0° (Rx pointing horizontally leftward), 45°, 90° (Rx pointing vertically downward), 135°, 180° (Rx pointing horizontally rightward), 225°, 270° (Rx pointing vertically upward), and 315°. The experimental outcomes depict the signal’s noise content, spectral leakage, and roll-off rate variation at multiple Rx orientations. We also demonstrate the solar noise interference in transmitting an image through the outdoor underwater OWC link by pointing the system Rx in various orientations. Experimental demonstration confirms that the same OWC system never behaves identically in the presence of solar noise if the system Rx keeps changing its orientation during the maneuver.

Evaluating the Beam Shape Coefficients of Bessel-Gauss Beams with Radial Quadrature: a comparison with Angular Spectrum Decomposition and Finite Series Methods

Siqi Tang, Mengyang Wang, and Jianqi Shen

DOI: 10.1364/JOSAA.520876 Received 08 Feb 2024; Accepted 27 Apr 2024; Posted 29 Apr 2024  View: PDF

Abstract: The Bessel-Gauss beam (BGB) stands as a physically realizable beam extensively employed in applications such asmicromanipulation and optical trapping. In these contexts, the assessment of beam shape coefficients (BSCs) becomes imperative.Previous researches reveal that the BSCs of the BGBs obtained with different methods deviate from each other under certaincircumstances. In this paper, the formulation of BSCs employs the radial quadrature (RQ) method and a comparative analysis isconducted with counterparts formulated using the angular spectrum decomposition (ASD) and the finite series (FS) technique.Contribution stemming from evanescent waves and the situation of the BSCs blowing-ups are discussed, offering a deep insight ofpertinent BSC evaluation methods. The paper provides alternative approach for calculating the BSCs of the BGBs.

Vision-based algorithm for on-line TIG welding deviation detection of stainless steel welded pipes

Huaishu Hou, Tong Wang, Jinhao Li, Yong Zhang, and Chenhuai Tang

DOI: 10.1364/JOSAA.509496 Received 17 Oct 2023; Accepted 26 Apr 2024; Posted 26 Apr 2024  View: PDF

Abstract: Tungsten inert gas (TIG) welding is the main welding process in the production ofstainless steel welded pipe. According to the morphological characteristics of the weldingmolten pool image during the TIG welding process of stainless steel welded pipes, the exactposition of the tungsten needle tip is calculated using image moments. Extract the weld regionin the contour of the molten pool, interpolate the contour curve based on the cubic B splinecurve interpolation method, utilize the characteristics of the S-G filter, remove the interferencecoordinates in the contour curve through the de-trending of the contour curve, extract the weldfeature points, and realize the accurate identification of weld seams. The experimental resultsshow that the method can accurately calculate the welding deviation in the welding process.

Twin stagnation free phase retrieval with vortex phase illumination

Muskan Kularia, Manidipa Banerjee, and Kedar Khare

DOI: 10.1364/JOSAA.516339 Received 19 Dec 2023; Accepted 26 Apr 2024; Posted 26 Apr 2024  View: PDF

Abstract: The recovery of complex-valued exit wavefront from its Fourier transform magnitude is challenging due to the stagnation problems associated with iterative phase retrieval algorithms. Among the various stagnation artefacts, the twin-image stagnation is the most difficult to address. The upright object and its inverted and complex-conjugated twin correspond to the identical Fourier magnitude data and hence appear simultaneously in the iterative solution. We show that the twin stagnation problem can be eliminated completely if a coherent beam with charge-1 vortex phase is used for illumination. Unlike the usual plane wave illumination case, a charge-1 vortex illumination intentionally introduces an isolated zero near the zero spatial frequency region, where maximal energy in the Fourier space is usually concentrated for most natural objects. The early iterations of iterative phase retrieval algorithms are observed to develop a clockwise or anti-clockwise vortex in the vicinity of this isolated zero. Once the solution latches onto a specific vortex profile in the neighborhood of this intentionally introduced intensity zero, the remaining parts of the solution quickly adjusts to the corresponding twin (upright or inverted) and further iterations are not observed to bring the other twin into the reconstruction. Our simulation studies with the well-known hybrid input-output (HIO) algorithm show that the solution always converges to one of the twins within a few hundred iterations when vortex phase illumination is used. Using a clockwise or anti-clockwise vortex phase as initial guess is also seen to lead to a solution consisting of the corresponding twin. The resultant solution still has some faint residual artifacts that can be addressed via the recently introduced complexity guidance methodology. There is an additional vortex phase in the final solution which can simply be subtracted out to obtain the original test object. The near guaranteed convergence to twin-stagnation free solution with vortex illumination as described here is potentially valuable for deploying practical imaging systems that work based on the iterative phase retrieval algorithms.

Routing light with different wavevectors using synthetic dimension

xin lyu, Kai Bai, and Meng Xiao

DOI: 10.1364/JOSAA.519506 Received 18 Jan 2024; Accepted 25 Apr 2024; Posted 26 Apr 2024  View: PDF

Abstract: Synthetic dimensions have drawn intense recent attention in investigating higher-dimensional topological physics and offering additional degrees of freedom for manipulating light. It has been demonstrated that synthetic dimension can help to concentrate light with different frequencies at different locations. Here, we show that synthetic dimension can also route light from different incident directions. Our system consists of an interface formed by two different photonic crystals. A synthetic dimension ξ is introduced by shifting the termination position of the photonic crystal on the right-hand side of the interface. We identify a correspondence between ξ and the interface state such that light incident from a specific direction can be collected. Thus, routing incident light from different directions is achieved by designing an interface with a proper distribution of ξ. Traditionally, this goal is achieved with a standard 4f optical system using convex lens, and our approach offers the possibility for such a capability within a few lattice sites of photonic crystals. Such an approach reduces the size of the system, making it easier for integration. Our work provides a new direction for routing light with different momentums and possibly contributes to applications such as lidar.

Integrating RGB-Thermal image sensors for non-contact automatic respiration rate monitoring

Fatema-Tuz-Zohra Khanam, Asanka Pereraa, Ali Al-Naji, Timothy D. McIntyre, and Javaan Chahl

DOI: 10.1364/JOSAA.520757 Received 01 Feb 2024; Accepted 23 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Respiration rate (RR) holds significance as a human health indicator. Presently,conventional RR monitoring system requires direct physical contact, which may causediscomfort and pain. Therefore, this paper proposes a non-contact RR monitoring systemintegrating RGB and thermal imaging through RGB-thermal image alignment. Theproposed method employs an advanced image processing algorithm for automatic regionof interest (ROI) selection. The experimental results demonstrated a close correlation and alower error rate between measured thermal, measured RGB and reference data. In summary,the proposed non-contact system emerges as a promising alternative to conventionalcontact-based approaches without the associated discomfort and pain.

Circularly coherent vortex beams optimized for propagation through turbulence

Arash Shiri, Rui Qi, and Gregory Gbur

DOI: 10.1364/JOSAA.521531 Received 19 Feb 2024; Accepted 23 Apr 2024; Posted 24 Apr 2024  View: PDF

Abstract: Self-focusing partially coherent beams with circular coherence have shown high potential for robust propagation through atmospheric turbulence. In this paper, we introduce a criteria to approximate the degrading effects of turbulence and we show that how the coherence of the source can be optimized to generate a beam with the highest stability in turbulence. To test our prediction, we analytically compare the turbulence propagation of the OAM spectrum of circularly coherent Gaussian vortex sources with three different coherence parameters. It is shown that by satisfying the introduced optimizing conditions, we can minimize the adverse effects of turbulence on the OAM spectrum.

Spatiotemporal statistics of optical turbulence beyond Taylor’s frozen turbulence hypothesis

Dario Perez, Hishan Farfan, and MARCO SEPÚLVEDA

DOI: 10.1364/JOSAA.520550 Received 07 Feb 2024; Accepted 22 Apr 2024; Posted 25 Apr 2024  View: PDF

Abstract: Currently, limitations in modeling the temporal behavior of light propagating through atmosphericturbulence stem from the Taylor’s frozen turbulence hypothesis (TFTH). Indeed, under certain conditionsit has been reported to be unreliable, often leading to inaccurate predictions. On the other hand, inFluid Dynamics an alternative has been validated: the random sweeping hypothesis. Nevertheless, itsapplicability to optical turbulence has remained unexplored. This work introduces the first controlledexperiment testing this hypothesis on the spatiotemporal properties from image wander. The existenceof two characteristic times are observed, one associated to TFTH decorrelation and a second potentiallylinked to the sweeping hypothesis.

Universal Scale Laws for Colors and Patterns in Imagery

Rémi Michel and Mohamed Tamaazousti

DOI: 10.1364/JOSAA.516720 Received 27 Dec 2023; Accepted 22 Apr 2024; Posted 30 Apr 2024  View: PDF

Abstract: Distribution of colors and patterns in images is observed through cascades that adjustspatial resolution and dynamics. Cascades of colors reveal the emergent universal propertythat Fully Colored Images (FCIs) of natural scenes adhere to the debated continuous linearlog-scale law (slope −2.00 ± 0.01) (L1). Cascades of discrete 2 × 2 patterns are derived from pixel squares reductions onto the seven unlabeled rotation-free textures (0000, 0001, 0011, 0012,0101, 0102, 01 ). They exhibit an unparalleled universal entropy maximum of 1.74 ± 0.013 atsome dynamics regardless of spatial scale (L2). Patterns also adhere to the Integral FluctuationTheorem (1.00 ± 0.01) (L3), pivotal in studies of chaotic systems. Images with fewer colorsexhibit quadratic shift and bias from L1 and L3 but adhere to L2. Randomized Hilbert fractalsFCIs better match the laws than basic-to-AI-based simulations. Those results are of interest inNeural Networks, out of equilibrium physics and spectral imagery.

Quantitative evaluation of the impact of variation of optical parameters on the estimation of blood hematocrit and oxygen saturation for dual-wavelength photoacoustics

Subhadip Paul, Harishankar Patel, and Ratan Saha

DOI: 10.1364/JOSAA.521238 Received 08 Feb 2024; Accepted 19 Apr 2024; Posted 22 Apr 2024  View: PDF

Abstract: Photoacoustic (PA) spectroscopy is considered to be one of the most effective ways to measure the levelsof hematocrit (H) and oxygenation saturation (SO2) of blood, which are essential for diagnosing bloodrelated illnesses. This simulation study aims to investigate the impact of individual optical parametersi.e., optical absorption coefficient (µa), scattering coefficient (µs) and anisotropy factor (g) on the accuracyof this technique in estimating the blood properties. We first performed the Monte Carlo simulations,using realistic optical parameters, to obtain the fluence maps for various samples. The wavelengths ofthe incident light were chosen to be 532, 700, 1000 and 1064 nm. Thereafter, the k-Wave simulations wereexecuted incorporating those fluence maps to generate the PA signals. The blood properties were obtainedusing the PA signals. We introduced variations in µa, µs and g ranging from -10% to +10%, -10% to +10%and -5% to +1%, respectively at 700 and 1000 nm wavelengths. One parameter, at both wavelengths, waschanged at a time keeping others fixed. Subsequently, examined how accurately the blood parameterscould be determined at physiological hematocrit levels. A 10% variation in µa induces a 10% changein H estimation but no change in SO2 determination. Almost no change has been seen for µs variation.However, a 5% (-5% to 0%) variation in g factor resulted in approximately 160% and 115% changes in thePA signal amplitudes at 700 and 1000 nm, respectively leading to ≈ 125% error in hematocrit estimationand ≈ 14% deviation in SO2 assessment when nominal SO2 = 70% . It is clear from this study that thescattering anisotropy factor is a very sensitive parameter and its small change can result in large errors inthe PA estimation of blood properties. In future, in vitro experiments with pathological blood (inducingvariation in g parameter) will be performed and accordingly, evaluate the accuracy of the PA technique inquantifying blood H and SO2.