Effect Of Chromatic Aberration Research Articles

Ocular accommodation and wavelength: The effect of longitudinal chromatic aberration on the stimulus-response curve.

The longitudinal chromatic aberration (LCA) of the eye creates a chromatic blur on the retina that is an important cue for accommodation. Although this mechanism can work optimally in broadband illuminants such as daylight, it is not clear how the system responds to the narrowband illuminants used by many modern displays. Here, we measured pupil and accommodative responses as well as visual acuity under narrowband light-emitting diode (LED) illuminants of different peak wavelengths. Observers were able to accommodate under narrowband light and compensate for the LCA of the eye, with no difference in the variability of the steady-state accommodation response between narrowband and broadband illuminants. Intriguingly, our subjects compensated more fully for LCA at nearer distances. That is, the difference in accommodation to different wavelengths became larger when the object was placed nearer the observer, causing the slope of the accommodation response curve to become shallower for shorter wavelengths and steeper for longer ones. Within the accommodative range of observers, accommodative errors were small and visual acuity normal. When comparing between illuminants, when accommodation was accurate, visual acuity was worst for blue narrowband light. This cannot be due to the sparser spacing for S-cones, as our stimuli had equal luminance and thus activated LM-cones roughly equally. It is likely because ocular LCA changes more rapidly at shorter wavelength and so the finite spectral bandwidth of LEDs corresponds to a greater dioptric range at shorter wavelengths. This effect disappears for larger accommodative errors, due to the increased depth of focus of the eye.

Three-dimensional reconstruction based on micro-imaging under wavelength-tunable illumination.

The three-dimensional reconstruction technique has been widely applied across various fields, with imaging serving as a fundamental approach to achieve this reconstruction. In the present study, we employed micro-imaging to realize 3D reconstruction based on the "shape from focus" and the chromatic aberration effect. This approach eliminates the need for sample or imaging lens movement to locate the focal plane for obtaining clear images. Instead, by utilizing tunable illuminance, we can adjust the imaging distance through the chromatic aberration, thereby achieving accurate reconstructions. As a means of verification, a simple system was accordingly constructed with an adjustable illuminance range (500-750nm) at a magnification of 10× for imaging purposes. The fine reconstruction achieved high precision in micrometers; however, the depth of field emerged as an issue during the reconstruction process. To assess this method, a coin was employed, and the resulting reconstruction bias was determined to be as low as 0.01mm. These findings indicate that the proposed method is practical for surface reconstruction and its capabilities will be further enhanced through optical design improvements.

Altering chromatic aberration: how this latest trend in intraocular-lens design affects visual quality in pseudophakic patients

BackgroundChromatic aberration of the eye results from the dispersion of polychromatic light at the interfaces of ocular media. An intraocular lens (IOL) based approach utilizing the diffractive-multifocal principle has been proposed for its correction, but the clinical evidence on the impact of reducing or increasing chromatic aberration on the visual quality of pseudophakic patients remains scarce.MethodsIn this cross-sectional study, longitudinal chromatic aberration (LCA) effects were studied monocularly in 37 patients implanted with a monofocal lens. LogMAR corrected distance visual acuity (VA) and defocus curve at the + 1.0 D to − 2.0 D range were assessed. Contrast sensitivity (CS) was evaluated at far and at four spatial frequencies. Measurements were performed with the eye's natural conditions, as well as with increased and corrected (by the same amount) LCA, which was altered by introducing zero-power trial triplets.ResultsThe mean (± standard deviation) logMAR VA was − 0.11 ± 0.07 for the natural condition, − 0.13 ± 0.07 for the LCA-corrected eye, and − 0.06 ± 0.08 for the eye with increased LCA. A sharp decline of the defocus tolerance was found after the LCA correction with the VA value of 0.38 ± 0.15 logMAR at − 1.5 D. However, for the natural and increased LCA, it was 0.32 ± 0.16 logMAR and 0.25 ± 0.13 logMAR, respectively. CS was improved at all spatial frequencies after the LCA correction, which was closely followed by the natural-eye performance. Increased LCA resulted in reduced CS, mainly at higher spatial frequencies.ConclusionsWe demonstrated that elevating chromatic aberration above the natural level of monofocal patients extends their depth of focus while causing a measurable albeit minimal reduction in visual function. Still, the observed changes indicate that neither correction nor increase of LCA yields a substantial clinical effect on distance VA and CS in monofocal pseudophakia.

A Retrofittable Photoelectron Gun for Low-Voltage Imaging Applications in the Scanning Electron Microscope.

Low-voltage scanning electron microscopy is a powerful tool for examining surface features and imaging beam-sensitive materials. Improving resolution during low-voltage imaging is then an important area of development. Decreasing the effect of chromatic aberration is one solution to improving the resolution and can be achieved by reducing the energy spread of the electron source. Our approach involves retrofitting a light source onto a thermionic lanthanum hexaboride (LaB6) electron gun as a cost-effective low energy-spread photoelectron emitter. The energy spread of the emitter's photoelectrons is theorized to be between 0.11 and 0.38 eV, depending on the photon energy of the ultraviolet (UV) light source. Proof-of-principle images have been recorded using this retrofitted photoelectron gun, and an analysis of its performance is presented.

Spectral Effects and Range of Focus in a Multizonal-Refractive Intraocular Lens Compared with a Standard Trifocal Diffractive Design.

This study was performed to compare the optical performance of a multizonal presbyopia-correcting intraocular lens (IOL) and a conventional trifocal model. The optical quality and simulated visual acuity (VA) of 570 Precizon Presbyopic NVA (OPHTEC BV) and AcrySof IQ PanOptix (Alcon) were compared. The Precizon features a refractive design consisting of alternating optical zones that converge the incident light into two principal foci and a transitional zone for intermediate vision. By contrast, the PanOptix applies a diffractive (non-apodized) profile to achieve trifocality. Simulated VA was derived from the modulation transfer function. Chromatic aberration effects were also studied. The diffractive and multizonal-refractive lenses yielded comparable simulated VAs at far focus (0.00 logMAR). All curves showed a reduction in expected VA with an increase in negative defocus. At -1.0 D, the multizonal-refractive IOL's VA dropped by 0.05 logMAR, but for the diffractive model, it was one line (0.11 logMAR). The multizonal-refractive lens's VA prediction at the secondary peak was 0.03 logMAR-minimally better than the 0.06 logMAR of the diffractive lens at -2.5 D. The refractive lens exhibited a 24% decrease in polychromatic optical quality due to material dispersion. The performance of PanOptix was more substantially affected, showing a 44% loss at 50 lp/mm at far, with minimal effects at other distances. The multizonal-refractive lens does not fall short of the established trifocal IOL, and it can be used to extend the visual range of pseudophakic patients. Although the multizonal-refractive lens has lower material dispersion, the diffractive model corrects chromatism beyond far focus.

A flexible lateral chromatic aberration correction method for a color-encoded fringe projection system

A flexible correction method is proposed for improving the performance of a color-encoded fringe projection system which suffers from lateral chromatic aberration (LCA) effects. The method uses a white plate with discrete markers and orthogonal fringe patterns projected on its surface to establish the relationships between depth information and pixel deviations among three color channels, and then corrects color-encoded fringe patterns affected by LCA with the acquired relationship for three-dimensional (3D) reconstruction. Compared with the methods that use a translation stage to accurately locate the plate to several parallel positions, the proposed method is flexible because the plate can be placed at arbitrary positions and directions in the measuring volume without an extra translation stage. Two experiments, including 3D shape measurement of a white plate and 3D shape measurement of a regular spherical object are carried out to verify the effectiveness and accuracy of the proposed method.

Influence of optical aberrations on depth-specific spatial frequency domain techniques.

Spatial frequency domain imaging (SFDI) and spatial frequency domain spectroscopy (SFDS) are emerging tools to non-invasively assess tissues. However, the presence of aberrations can complicate processing and interpretation. This study develops a method to characterize optical aberrations when performing SFDI/S measurements. Additionally, we propose a post-processing method to compensate for these aberrations and recover arbitrary subsurface optical properties. Using a custom SFDS system, we extract absorption and scattering coefficients from a reference phantom at 0 to 15mm distances from the ideal focus. In post-processing, we characterize aberrations in terms of errors in absorption and scattering relative to the expected in-focus values. We subsequently evaluate a compensation approach in multi-distance measurements of phantoms with different optical properties and in multi-layer phantom constructs to mimic subsurface targets. Characterizing depth-specific aberrations revealed a strong power law such as wavelength dependence from ∼40 to ∼10 % error in both scattering and absorption. When applying the compensation method, scattering remained within 1.3% (root-mean-square) of the ideal values, independent of depth or top layer thickness, and absorption remained within 3.8%. We have developed a protocol that allows for instrument-specific characterization and compensation for the effects of defocus and chromatic aberrations on spatial frequency domain measurements.

Achromatic and athermal catadioptric long wave infrared freeform prism with a diffractive surface

Freeform prisms have an alignment-free structure that can be used in imaging system to guarantee optical performance and stability. Chromatic aberration and thermal effect would hardly be corrected owing to a single substrate material for the freeform prism. Using a progressive design strategy, we designed an achromatic and athermal catadioptric infrared freeform prism with refractive-diffractive optics. The designed modulation transfer function (MTF) values of all fields approach the diffraction limits. Sensitivity analysis was conducted to verify the fine manufacturability. Experiments are carried out to manufacture this freeform prism.

Potential continuous zooming scheme based on high-power broadband laser

Continuous zooming is efficient in mitigating the cross-beam energy transfer effect and improving implosion hydrodynamic efficiency in the application of inertial confinement fusion. In this paper, a novel continuous zooming scheme is proposed, based on the chromatic aberration effect of the lens groups to gradually reduce the size of the focal spot at the target position by focusing the broadband laser pulse. This scheme is simulated theoretically on the Shenguang-II upgrade (SG-II UP) facility, and the results show that the focal spot size is positive and linear for the beam wavelength. When the fundamental wave bandwidth was 5 nm, the focal spot radius was reduced by 15.21% without changing the geometric parameters of the SG-II upgrade, and the focal spot radius was reduced by 27.73% after optimization. In addition, the conversion efficiency is compensated for in the harmonic converter. This paper supports a new perspective for the realization of high-power laser zooming.

Elliptical-Shaped Fresnel Lens Design through Gaussian Source Distribution

A novel three-dimensional elliptical-shaped Fresnel lens (ESFL) analytical model is presented to evaluate and maximize the solar energy concentration of Fresnel-lens-based solar concentrators. AutoCAD, Zemax and Ansys software were used for the ESFL design, performance evaluation and temperature calculation, respectively. Contrary to the previous modeling processes, based on the edge-ray principle with an acceptance half-angle of ±0.27° as the key defining parameter, the present model uses, instead, a Gaussian distribution to define the solar source in Zemax. The results were validated through the numerical analysis of published experimental data from a flat Fresnel lens. An in-depth study of the influence of several ESFL factors, such as focal length, arch height and aspect ratio, on its output performance is carried out. Moreover, the evaluation of the ESFL output performance as a function of the number/size of the grooves is also analyzed. Compared to the typical 1–16 grooves per millimeter reported in the previous literature, this mathematical parametric modeling allowed a substantial reduction in grooves/mm to 0.3–0.4, which may enable an easy mass production of ESFL. The concentrated solar distribution of the optimal ESFL configuration was then compared to that of the best flat Fresnel lens configuration, under the same focusing conditions. Due to the elliptical shape of the lens, the chromatic aberration effect was largely reduced, resulting in higher concentrated solar flux and temperature. Over 2360 K and 1360 K maximum temperatures were found for ESFL and flat Fresnel lenses, respectively, demonstrating the great potential of the three-dimensional curved-shaped Fresnel lens on renewable solar energy applications that require high concentrations of solar fluxes and temperatures.

Beamline design with weak-focusing magnetic field for applications of laser-driven proton beams

<sec>With the development of high-power laser technology, laser plasma acceleration has developed rapidly due to its excellent acceleration structure. Nearly one-hundred-MeV proton beams and several GeV electron outputs are obtained. The laser-driven proton beams have excellent quality of μm-scale sizes and ps-scale pulse lengths. Owing to the existence of the accelerating laser field, direct application is difficult, so the proton beams need to be transmitted to the application terminal through the beamline. However, the wide energy spectrum and large divergence angle bring difficulties in transmitting the beam. The weak focusing in the constant gradient magnetic field is neglected in the transmission of laser-driven particle beams because of the relatively weak focusing force. But weak focusing has special advantages: simultaneous focusing in the horizontal direction and the vertical direction, energy analysis in the horizontal direction, focusing force in the horizontal and vertical direction distributed by the field index <i>n</i>, and smaller influence of chromatic aberration effect.</sec><sec>In this paper, we propose the beam transmission with weak-focusing magnet. The requirements for the focusing of proton beams with the same energy and different divergence angles in the <i>X</i> direction and <i>Y</i> direction in the weak-focusing magnetic field are explored by studying the linear beam dynamics of the beams. Then the conditions of precise energy analysis for particle beams with large divergence angle can be determined. For beams with 2% energy spread, the lengths of the drift space before and after the weak-focusing magnet and deflection radius are scanned to find out the minimum beam size and the shortest pulse length after transmission. It is found that a certain combination of drift space and deflection radius can minimize the beam size or the pulse length. Focusing and energy selection can be achieved while compressing the pulse length and effectively reducing the size of the beamline, which has significant advantages. When the deflection radius is 0.65 m, the proton beam with 20 MeV energy, 2% energy spread, and an initial divergence angle of ±50 mrad has the root-mean-square size of 108 μm in both the <i>X</i> direction and the <i>Y</i> direction, and a pulse length of 154 ps at the application terminal.</sec><sec>Comparing with common beam transmission elements such as quadrupole lenses and deflection magnets, the laser-accelerated ion beam benefits from the integration of focusing and energy analysis of weak-focusing magnetic fields (focusing and energy analysis exist at the same time and continuously change with deflection angle), as well as the horizontal and vertical focusing forces can be distributed by the magnetic field index <i>n</i> (the larger the <i>n</i>, the stronger the focusing force in the vertical direction is and the weaker the focusing force in the horizontal direction). When the proton beam is transmitted in a weak-focusing magnetic field, the advantages of the focusing element and the energy selection element are combined, so the influence of the chromatic aberration effect can be reduced, the pulse length can be compressed, and the beamline size can be effectively reduced.</sec>

The influence of chromatic aberration on the dose-limited spatial resolution of transmission electron microscopy

The effect of chromatic aberration (CC) on the spatial resolution in transmission electron microscopy (TEM) was studied in thick specimens in which the sample becomes the limiting factor in the resolution. The sample influences the energy spread of the electron beam, allows only a limited electron dose, and modulates electron scattering events. The experimental set-up consisted of a thin silicon nitride membrane and a silicon wedge containing gold nanoparticles. The resolution was measured as a function of electron dose and sample thickness for different sample configurations and for different microscopy modalities including regular TEM, energy filtered TEM (EFTEM) and CC-corrected TEM. Comparison with an analytical model aided the understanding of the experimental data applied over varied conditions. The general trend for all microscopy modalities was a transition from a noise-limited resolution at low electron dose to a CC-limited resolution at high-dose in the absence of beam blurring. EFTEM required an accurate energy slit offset and an optimal energy spread to energy-slit width ratio to surpass regular TEM. The key advantage of CC correction appeared to be the best possible resolution for larger sample thickness at low electron dose outperforming EFTEM by about fifty percent. Several hypothetical sample configurations relevant to liquid phase electron microscopy were evaluated as well to demonstrate the capabilities of the analytical model and to determine the most optimal microscopy modality for this type of experiment. The analytical model included an automated optimization of the EFTEM settings and may aid in optimizing the sample-limited resolution for experimental analysis and planning.

Multispectral small-angle light scattering from particles.

Using a supercontinuum laser, reflective optics, and a spatial filter, we measure two-dimensional small-angle light-scattering patterns for a variety of microparticles including spheres, salt, sand, and volcanic dust. The measurements are done at 13 wavelengths from 450-850 nm, where the absence of refractive optical elements minimizes the effects of chromatic aberration. Qualitative particle-material sensitivity is demonstrated by layering differently colored patterns. Last, the multispectral capability of our device demonstrates a new possibility to probe different q-space regimes for a given particle in a single measurement.

Phase characterisation of metalenses

Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications.

Chromatic Aberration Effect in Refraction of Spin Waves

Chromatic Aberration Effect in Refraction of Spin Waves

Dark field proton radiography

A pre- and post-collimation scheme has been applied to high energy proton radiography to establish a dark field condition, which defaults to a state of no transmission until a scatterer is placed at the object plane. This technique, dark field proton radiography, provides two additional capabilities to a standard proton radiography setup. First, protons with a high degree of angular dispersion are removed from the beam, reducing the effects of chromatic aberrations and decreasing noise. Second, protons below the same threshold are removed from the beam downstream of the objects, effectively making the transmission highly sensitive to small amounts of scatter at the object plane. Initial results indicate that the system is highly sensitive to the presence of thinner materials and improves sensitivity to subtle areal density variations in thick objects.

A role of color vision in emmetropization in C57BL/6J mice

Spectral composition affects emmetropization in both humans and animal models. Because color vision interacts the effects of chromatic defocus, we developed a method to bypass the effects of longitudinal chromatic aberration by placing a spectral filter behind the optics of the eye, using genetic tools. Newborn C57BL/6J (B6) mice were reared in quasi-monochromatic red (585–660 nm) or blue (410–510 nm) light beginning before eye-opening. Refractive states and ocular dimensions were compared at 4, 6, 8, and 10 weeks with mice reared in normal white light. Cre recombinase-dependent Ai9 reporter mice were crossed with Chx10-Cre to obtain Chx10-Cre;Ai9 mice, expressing red fluorescent protein in retinal Cre-positive cells. Ai9 offsprings, with and without Cre, were reared under a normal visual environment. Refraction and axial components were measured as described above. Expression levels of M and S opsin were quantified by western blotting at 10 weeks. Compared with those reared in white light, B6 mice reared in red light developed relative hyperopia, principally characterized by flattening of corneal curvature. Emmetropization was not affected by blue light, possibly because the reduction in vitreous chamber depth compensated for the increase in corneal curvature. Compared with Cre-negative littermates, the refraction and axial dimensions of Chx10-Cre;Ai9 mice were not significantly different at the follow-up timepoints. M opsin levels were higher in Chx10-Cre;Ai9 mice at 10 weeks while S opsin levels were not different. Red light induced a hyperopic shift in mouse refractive development. Emmetropization was not impacted in mice with perturbed color vision caused by intrinsic red-fluorescent protein, suggesting that color vision may not be necessary in mouse emmetropization when other mechanisms are present.

Propagation characteristics of a spatially chirped Gaussian laser beam propagating through multiple lenses

Variation of curvature of laser beam changes characteristics of spatially chirped pulsed Gaussian (SCPG) laser beam primarily due to varying spectral divergence. Parametric dependence of different pulse parameters, e.g. angular chirp, pulse front tilt, pulse width, beam radius, radius of curvature etc., is presented for a SCPG laser beam propagating through single and pair of reflective or refractive optical system. Effect of chromatic aberration on characteristic of SCPG laser beam have also been presented under different propagation conditions. Different expressions for various parameters of pulsed Gaussian beam are extended using recursive relation for a sequence of multiple chromatic lenses generally used in large scale high energy high power laser system. Discussion is supported with few examples of lens system.

Lossless Monochromation for Electron Microscopy with Pulsed Photoemission Sources and Radio-Frequency Cavities

Resonant radiofrequency cavities enable exquisite time-energy control of electron beams when synchronized with laser driven photoemission. We present a lossless monochromator design that exploits this fine control in the one-electron-per-pulse regime. The theoretically achievable maximum beam current on target is orders of magnitude greater than state-of-the-art monochromators for the same spatial and energy resolution. This improvement is the result of monochromating in the time domain, unconstrained by the transverse brightness of the electron source. We show analytically and confirm numerically that cavity parameters chosen to minimize energy spread perform the additional function of undoing the appreciable effect of chromatic aberration in the upstream optics. We argue that our design has significant applications in both ultra-fast and non-time-resolved microscopy, provided photoelectron sources of sufficiently small size and laser sources of sufficiently high repetition rate. Our design achieves in simulations more than two orders of magnitude reduction in beam energy spread, down to single digit meV. Overcoming the minimum probe-size limit that chromatic aberration imposes, our design clears a path for high-current, high-resolution electron beam applications at primary energies from single to hundreds of keV.

Using S-Cone signals to detect the effects of longitudinal chromatic aberration

Using S-Cone signals to detect the effects of longitudinal chromatic aberration