Journal of The Optical Society of America A-optics Image Science and Vision最新文献

This study presents the first experimental characterization of the phase structure function (PSF) and the spatial coherence radius of a laser beam propagating through underwater Rayleigh-Bénard (RB) turbulence, using a two-channel moiré-based wavefront sensor. A collimated laser beam (λ=532nm, diameter=33mm) was passed horizontally through a temperature-controlled water tank, where convective turbulence was induced by vertical temperature differences (0-6°C). Measurements were performed at multiple vertical (21, 100, and 179 mm) and lateral (21 and 100 mm) positions to examine spatial variations in turbulence. Wavefront phases were reconstructed from moiré fringe patterns, and the PSF was computed in two orthogonal directions transverse to the laser beam's propagation. The results revealed that underwater RB turbulence is both anisotropic and inhomogeneous in the cross-plane transverse to the beam propagation direction. While the turbulence intensity increases with the imposed temperature difference, the anisotropy observed in the PSF becomes more apparent at larger separation distances r. The analytical oceanic turbulence optical power spectrum model showed excellent agreement with the experimental PSF within the inertial subrange. Additionally, the spatial coherence radius was found to decrease with increasing temperature difference and was consistently smaller near the tank boundaries. These findings provide unique experimental validation for underwater turbulence models and offer insights critical to the design of robust underwater optical communication systems.

Utilizing the extended Huygens-Fresnel principle, field correlations of a Gaussian vortex beam propagating in the vertical turbulent oceanic link are examined analytically and evaluated by simulation in the Atlantic Ocean at low- and mid-latitude and high-latitude summer. Our formulation is based on the coherence length of a spherical wave operating at the depth range between 3000 and 3500 m. Variations in the rate of dissipation of turbulent kinetic energy per unit mass of fluid ε, the rate of dissipation of the mean-squared temperature χ_T, and the ratio of temperature to salinity contributions to the refractive index spectrum ω are taken into account at these depths in the underwater turbulent medium. The field correlation obtained using the coherence length found with the help of the depth-dependent power spectrum is expressed in detail. When the topological charge is selected considering the source size and propagation distance, it is seen that the normalized field correlation of the Gaussian vortex beam gives better results as compared to Gaussian beams.

All past demonstrations of wavefront-guided scleral lenses have relied on the full-surface method (FSM) of lens manufacture, which requires the wavefront correction to be integrated into the design of a traditional scleral lens prior to lens manufacture. A novel patch-cutting method (PCM) of manufacture would rely on carving the wavefront correction into the anterior surface of a previously manufactured scleral lens. This study compared wavefront corrections manufactured with the FSM and PCM. Two duplicates of four unique wavefront-guided scleral lens designs were manufactured using both the FSM and PCM, resulting in a total of 16 test lenses. All lenses were optically profiled, and comparisons were made between each wavefront-guided lens and its design, its within-method of manufacture duplicate, and across methods of manufacture. This study demonstrated that utilizing the PCM does not induce variability in the manufacturing process beyond what is already observed in the FSM.

This tutorial covers human cone spectral sensitivities and their linear transformations, the color matching functions. We focus on the mean or standard functions and the individual differences that occur between observers and how we can correct for those differences. The differences arise mainly because of genetically determined spectral shifts of the L- and M-cone photopigment curves, variability in the optical densities of the lens and macular pigments, and variability in the optical densities of the three photopigments. These can lead to people seeing colors on displays and on printed or dyed material differently even though, according to color standards, they should all appear the same. Such discrepancies have become more apparent and their correction more urgent with the emergence of narrow-band light sources and primaries that expand the color gamut. The discrepancies can be reduced by using better color standards, but to eliminate them completely requires corrections be made for individual differences.

Fluorescence molecular tomography (FMT) is a noninvasive imaging technique that enables the quantitative three-dimensional reconstruction of fluorescent probe distributions in vivo. However, FMT reconstruction is limited in accuracy and reliability due to light scattering and the ill-posed inverse problem. In this paper, the adaptive Bayesian augmented Lagrangian (ABAL) algorithm is proposed, which adaptively adjusts the regularization parameter to promote sparsity and enhance robustness to noise, while significantly improving computational efficiency. By integrating sparse Bayesian learning (SBL) with the augmented Lagrangian (AL) framework, the approach addresses the computational challenges and non-convexity introduced by the iterative adjustment of regularization parameters in SBL. The inverse problem is reformulated as a weighted L₁ minimization with adaptive regularization and solved via the AL method, enhancing computational efficiency and mitigating the risk of local minima. Moreover, the adaptive regularization mechanism enables the method to dynamically adjust to data-specific characteristics, avoiding over-regularization or under-regularization and improving both stability and reconstruction accuracy. To evaluate the effectiveness of our method, a series of numerical simulations and implantation experiments were conducted. Results confirm that the ABAL method can achieve relatively accurate reconstruction performance compared to other approaches, with an average minimum localization error (LE) of 0.358 mm and an average Dice coefficient of 0.775. These results show relatively high localization accuracy, shape recovery, and robustness of the ABAL method in FMT reconstruction, indicating its potential for practical FMT application.

Over the last century, the study of color differences has attracted considerable attention, with numerous attempts to develop increasingly accurate perceptual metrics that, however, have progressed incrementally but never achieved full adequacy. Although research eventually moved from color spaces to appearance spaces, color was still examined without accounting for its surrounding context, even though visual context has long been known to strongly influence chromatic appearance. This work attempts to address the following question: is it meaningful to pursue marginal improvements in color-difference metrics that treat color in isolation, when embedding color within a visual context can produce appearance changes far greater than the precision gained by the most recent formulas? More broadly, is it still appropriate to measure color differences without accounting for their visual context? The results underscore the necessity for the development of a color metric that takes into account the spatial computations of the scene, thereby aligning more closely with the mechanisms of human vision.

Phase contrast is a technique that allows the visualization of phase variations of an object by transforming them into intensity variations at the image plane when a phase filter is set at the Fourier plane of the optical system. Ideally, only the zero frequency of the object's Fourier transform must be affected by the phase filter to have an intensity image that follows the object's phase variations. The implementation of the technique in real systems requires a filter with a defined spatial size, and therefore, more Fourier frequencies can be phase shifted. In this work, we investigate the impact of the phase filter shape and size on the image contrast. Phase objects with binary and quadratic phase distribution are analyzed. The shape of the filter was modified from an abrupt binary to a smooth phase variation. We specifically examined four types of filters: disk, stepped conical, continuous conical, and Gaussian. Size variations were achieved by varying the radii of the filters, while maintaining their constant maximum phase values. The results demonstrate that the shape and size of the filter affect the obtained image, showing that filters with smooth variation maintain their capability for contrast even for radii larger than that of the main lobe of the object Fourier transform. Experimental results using a phase spatial light modulator to control the phase, form, and radius variation of the phase filter are presented. High consistency is achieved between numerical and experimental results.

A Poincaré-like sphere for spatial coherence characteristics leading to "visual algorithms" is introduced. Deterministic and random Jones transformations, as well as coherence optimization between lights at two spatial locations, can be apprehended with simple geometric transformations analogous to the ones used with the standard Poincaré sphere for polarization. The joint representation of polarization and coherence characteristics in a single global polarization intrinsic coherence Poincaré sphere allows one to easily identify remarkable physical situations.

Fluorescent molecules emit light in a dipole radiation pattern that can be used to infer their orientation through defocused fluorescence microscopy. Proper measurement of the orientation requires mathematical modeling of the radiation pattern expected for a dipole in the geometry of interest and subsequent comparison against experimental data. We point out an ambiguity in common calculations of these patterns that appears to compromise orientation measurements for molecules that are especially near dielectric surfaces. This results in a rotation of the measured emission dipole toward the surface for near-interface molecules, which can be mistaken for a preferentially horizontal orientation among the emitters. The proper treatment for on-surface emitters requires consideration of finite-sized current elements between two dielectric media, and we show that the theoretical ambiguity can be lifted via finite-element modeling. A prescription is provided for correcting measured orientations at arbitrary interfaces.

Propagation of an orbital angular momentum beam-the Laguerre-Gaussian (LG) beam-through anisotropic non-Kolmogorov atmospheric turbulence is analyzed using three approaches: the extended Huygens-Fresnel (EHF) principle, the perturbation method, and computational wave-optics simulations (WOS). Two LG beams (modes 1 and 2) are evaluated on how their characteristics change with varying turbulence parameters. Beam irradiance profiles and spot sizes are computed, with the goal of assessing the relative stability of different modes. For the Kolmogorov power-law exponent, the results obtained via the perturbation method show good agreement with those from the EHF principle and WOS but only within the weak-to-moderate fluctuation regime. For stronger turbulence fluctuations, the results obtained via the perturbation method begin to deviate, whereas the EHF principle and WOS remain in good agreement. It is also shown that this type of alignment does not hold in other power-law exponents. Results obtained by the EHF principle and WOS show both the LG modes exhibit deformation under turbulence, though the lower-order mode shows a more pronounced rate of change, and the higher-order mode remains more confined and symmetric. The results obtained by the perturbation method are confirmed or rejected in different scenarios. Results obtained for two LG beams, and via all three methods, show saturation of the degree of ellipticity after some anisotropy ratios.