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We report the characterization of an achromatic focusing metasurface at oblique incident angles. We show that in addition to the inherent off-axis aberrations that occurs due to the hyperbolic phase profile of the metasurface, the focusing performance is significantly degraded due to the meta-atoms' angular dispersion. To obtain insights into how the angular and spectral bandwidth of meta-atoms relate to the metasurface focusing performance, point-dipole models are used which incorporate different aspect's of the meta-atoms' angular response. It is emphasized that despite the meta-atoms being designed under the assumption that they support a single dipolar resonance, other resonances exist within the meta-atom geometry and become stronger at oblique incidence. These resonances disturb the designed phase and amplitude responses, resulting in lower focusing efficiency at higher incident angles. The modelling of higher order modes leads to good agreement with the experimental measurements, confirming that angular dispersion of the meta-atoms is the dominant mechanism in determining off-axis aberrations.

Broadband achromatic subdiffraction focusing is in urgent need in application of imaging. However, the previously published broadband achromatic metalenses are restricted by diffraction effect or limited efficiency. In this communication, a new gradient refractive index (GRIN) lens with a modified refractive index (RI) profile of classical Luneburg lens is proposed and designed based on a radial gradient periodic structure. Highly efficient achromatic subdiffraction focusing with full width at half maximum (FWHM) around $0.36\lambda $ and large numerical aperture (NA) of 1.26 has been accomplished. The sample of the proposed GRIN lens is manufactured by 3-D printing technology. Experimental results of the near- and far-field are well consistent with those of theoretical predictions and numerical simulations. This GRIN lens could yield subdiffraction focusing spot with high focusing efficiency (above 74%) from 8 to 16 GHz. Directive far-field radiation (side lobes below −7 dB over an ultrabroadband frequency range with bandwidth ratio of 120% (4–16 GHz)) is also achieved. The demonstrated GRIN lens has a great potential to be applied in the subdiffraction imaging system in the future.

Propagation effects in the interstellar medium and intrinsic profile changes can cause variability in the timing of pulsars, which limits the accuracy of fundamental science done via pulsar timing. One of the best timing pulsars, PSR J1713+0747, has gone through two ‘dip’ events in its dispersion measure (DM) time series. If these events reflect real changes in electron column density, they should lead to multiple imaging. We show that the events are well fitted by an underdense corrugated sheet model, and look for associated variability in the pulse profile using principal component analysis. We find that there are transient pulse profile variations, but they vary in concert with the DM, unlike what is expected from lensing due to a corrugated sheet. The change is consistent in shape across profiles from both the Green Bank and Arecibo radio observatories, and its amplitude appears to be achromatic across the 820-MHz, 1.4-GHz, and 2.3-GHz bands, again unlike expected from interference between lensed images. This result is puzzling. We note that some of the predicted lensing effects would need higher time and frequency resolution data than used in this analysis. Future events appear likely, and storing baseband data or keeping multiple time–frequency resolutions will allow more in-depth study of propagation effects and hence improvements to pulsar timing accuracy.

There had been remarkable progress in developing third-generation electron storage rings as the main sources of very bright photon beams. Fourth-generation storage rings based on the multi-bend achromat lattice concept may be able to surpass the brightness and coherence that are attained using present third-generation storage rings. In this paper, we survey ongoing work around the world to develop concepts and designs for fourth-generation electron storage rings.

We examine the effect of the broadband wake on the longitudinal and transverse beam distributions in the low-emittance Hybrid Multi-bend Achromat (HMBA) storage ring. We utilize the Vlasov equation and a multi-particle tracking method to examine the equilibrium longitudinal beam distributions due to the broadband wake. The beam distributions from the Vlasov method is shown to agree well with the multi-particle tracking results. Multi-particle tracking simulations are also performed to investigate the longitudinal and transverse beam instabilities due to the broadband wake in the ring. In view of our results, our designed ring with $$Z/n=0.1\Omega$$ is shown to make the producion of a beams possible.

In this communication, we propose a robust broadband anomalous refractor (BAR), which minimizes chromatic aberration. The design is based on engineering the dispersion curve of spoof surface plasmon polaritons (SSPPs) and manipulating the wavefront of the transmitted waves. We begin by deriving deflection conditions such that the discrete scatterers of the refractor need to have linear dispersion curves in the operating frequency band. The rich dispersion properties of the SSPP make it a good candidate for meeting the broadband deflection condition. Next, we design symmetric metallic blade structures (MBSs) to efficiently transform free-space waves into SSPPs and to realize the broadband linear dispersion relationship. The BAR is comprised of these MBSs with different strip heights. A prototype is designed, fabricated, and measured. Both the simulated and experimental results demonstrate excellent fixed-direction deflection in the 6.9–9.1 GHz band for the normal incidence case. Furthermore, the BAR still performs well when its outer profile is deformed to some extent, which is desirable in practical applications. This alternative approach to designing achromatic devices at microwave frequencies can be readily extended to higher frequencies.

We design and fabricate ultra-broadband achromatic metalenses operating from the visible into the short-wave infrared, 450–1700 nm, with diffraction-limited performance. A hybrid 3D architecture, which combines nanoholes with a phase plate, allows realization in low refractive index materials. As a result, two-photon lithography can be used for prototyping while molding can be used for mass production. Experimentally, a 0.27 numerical aperture (NA) metalens exhibits 60% average focusing efficiency and 6% maximum focal length error over the entire bandwidth. In addition, a 200 μm diameter, 0.04 NA metalens was used to demonstrate achromatic imaging over the same broad spectral range. These results show that 3D metalens architectures yield excellent performance even using low-refractive index materials, and that two-photon lithography can produce metalenses operating at visible wavelengths.

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

An investigation of the damping wiggler effect to reduce the emittance in the Pohang Accelerator Laboratory (PAL), a fourth-generation storage ring (4GSR) that uses a multi-bend achromat, is presented. A 4GSR lattice which has reduced emittance and increased dynamic aperture to amplify the synergy with two existing light sources (PLS-II and PAL-XFEL) at PAL is described.

Polarization array based polarization Michelson wind field detection interferometer is a new type of interferometer for detecting atmospheric temperature and wind field velocity. We proposed a theoretical model and design of the novel static polarization wind imaging interferometer (NSPWII). It consists of a group of polarizers and waveplates, a polarization beamsplitter, a field widened Michelson interferometer, a pyramid prism, and a polarization array. Based on the principle of polarization interference, a polarization array composed of four polarizers with 45° polarization directions differences is directly in front of the detector, and four modulated light beams from the pyramid prism pass through the four polarizers. Then, interferograms with four different intensity are imaged on the detector simultaneously, which further provides the atmospheric temperature and wind field velocity. The advantages of this instrument are static (no moving parts), achromatic, and temperature compensated. It is capable of measuring the upper atmospheric wind field in real time with a high precision.

Achromatization of a three-component diffraction system consisting of one thick and two thin hologram optical elements is considered in the work. Analytical expressions are obtained for correcting the chromatic aberration of the position of a thick focusing hologram optical element by two scattering thin hologram optical elements in a given spectrum range. It is shown that achromatization is achieved for such a three-component system using two thin hologram elements located symmetrically on both sides of the thick element and having a value of the working diffraction order greater than the ratio of the focal length to the distance from the thin element to the image plane (at a given wavelength). The proposed three-component holographic system can be used to convert both an imaginary image into a real image and a real into an imaginary image in predetermined spectral regions of the visible, ultraviolet or infrared ranges of the spectrum.

PURPOSE: To compare ray-tracing aberrometry, Hartmann-Shack wavefront analysis, automated refraction, and manifest refraction in patients with echelette diffractive intraocular lenses (IOLs) and patients with monofocal IOLs with negative spherical aberration. METHODS: Pseudophakic patients implanted with an echelette diffractive IOL (Tecnis ZXR00; Johnson & Johnson Vision) and a control group consisting of patients implanted with a negative spherical aberration monofocal IOL (Tecnis ZCBOO, Johnson & Johnson Vision) were included in this study. Ray-tracing aberrometry (iTrace; Tracey Technologies Corp.), Hartmann-Shack wavefront analysis (LADARWave; Alcon Laboratories, Inc.), automated refraction (Topcon KR-8800; Topcon Medical Systems, Inc.), and manifest refraction spherical equivalent were performed 1 to 3 months postoperatively. RESULTS: Thirty-two eyes implanted with a ZXR00 IOL and 30 eyes implanted with a ZCBOO IOL were enrolled in this study. The ZXR00 IOL group yielded more myopic results with automated refactions (−0.62 ± 0.41 diopters [D]), Hartmann-Shack wavefront analysis (−0.85 ± 0.40 D), and ray-tracing aberrometry (−0.45 ± 0.64 D), compared to manifest refraction (−0.12 ± 0.44 D) ( P < .001). Hartmann-Shack wavefront analysis showed a statistically significant myopic shift (−0.39 ± 0.47 D) in the ZCBOO group compared to ray-tracing aberrometry, automated refraction, and manifest refraction spherical equivalent (−0.14 ± 0.56, −0.14 ± 0.50, and −0.06 ± 0.44 D, respectively; P < .001). CONCLUSIONS: Manifest refraction techniques unique to echelette technology should be used to avoid over-minus end points. Autorefractors and aberrometers commonly use near-infrared light; thus, myopic results are expected with echelette achromatic technology. [ J Refract Surg . 2020;36(5):334–339.]

The FRagment Separator FRS at GSI is primarily a powerful in-flight separator for short-lived exotic nuclei based on multiple magnetic rigidity analysis and atomic energy-loss in shaped matter. The versatile ion-optical system of the FRS can also be operated as a high-resolution spectrometer and can be used for precise momentum measurements. Other experiments require high rates of exotic nuclei which is accomplished through thick targets and high optical transmission. Here, two developments are presented: A new mode for high-resolution momentum measurements and a high-transmission mode for exotic isotopes spatially separated and energy bunched with achromatic and monoenergetic degraders.

BigRIPS is a powerful two-stage in-flight separator for the research with exotic nuclei studied in frontier experiments since more than a decade. The ion-optical system is very versatile due to the multi-stage structure of BigRIPS combined with the ZeroDegree spectrometer or the Superconducting Ring Cyclotron (SRC). Various optical modes can be flexibly realized according to the purpose of experiments. Two categories of developments are presented here. One is a new operating mode of BigRIPS aiming at higher ion-optical resolving power. BigRIPS itself has a two-stage structure. Spatial isotope separation is made at both the first and second stages. In the standard operating mode of BigRIPS, at the second stage the two spatial separations with energy degraders are subtractive in their resolving powers. Here, we present the additive mode. With the resulting increased spatial separation power, the isotopic background can be substantially reduced. Higher ion-optical resolving powers of the first and second BigRIPS degrader stages are also investigated with the goals to reduce further the background and to yield access to new isotopes of heavier elements. The other development is a dispersion-matched system with BigRIPS for high-resolution spectrometer experiments. The BigRIPS and ZeroDegree spectrometer are presently two independent, coupled achromatic systems. A new dispersion-matched mode of BigRIPS and ZeroDegree will enable novel experiments. For high-resolution spectroscopy experiments with high-intensity light projectiles, SRC and BigRIPS can be operated as a dispersion-matched system. The described different ion-optical developments are a base for a new category of experiments exploring exotic nuclei and mesic atoms. Characteristic future experiments with these new ion-optical developments are exemplified in this report.

A new, to the best of our knowledge, method for designing a thick-lens achromatic doublet based on the concept of a caustic surface to correct both third- and fifth-order spherical aberration is presented. We consider two different wavelengths brought into coincidence at the back focal length instead of the effective focal length as it is usually done, to calculate the radii of curvature assuming predefined values for axial thicknesses and their indices of refraction for both lenses. Alternatively, we apply Taylor’s series around the optical axis, and to vanish the approximate caustic surface, we obtain the values for the conic constants, which reduce at third- and fifth-order spherical aberration. Two designs for cemented doublets are provided assuming that the lenses are cemented. Finally, we propose a method to qualitatively test doublet lenses by using null screens, considering to place the detection plane at arbitrary positions.

We demonstrate a simple single grating beam modulation technique, which enables the use of a highly intense neutron beam for differential phase and dark-field contrast imaging and thus spatially resolved structural correlation measurements in full analogy to interferometric methods. In contrast to these interferometric approaches our method is intrinsically achromatic and provides unprecedented flexibility in the choice of experimental parameters. In particular the method enables straight forward application of quantitative dark-field contrast imaging in time-of-flight mode at pulsed neutron sources. Utilizing merely a macroscopic absorption mask unparalleled length scales become accessible. We present results of quantitative dark-field contrast imaging combining microstructural small angle scattering analyses with real space imaging for a variety of materials.

Dispersion problem has always constrained the development of see-through near-eye displays with diffractive waveguide. Here, we propose a design method and optical systems for achromatic surface microstructure composed with a triple-carved-sub-grating. The triple-carved-sub-grating with specified period is designed based on rigorous coupled wave theory, corresponding to Red, Green and Blue (RGB) wavelengths, respectively, with diffraction efficiencies of 1st(-1st) orders reach 47.5% under TE polarization. The surface microstructure with period of 18.9um is realized by integrating the three sub-gratings together, and it is verified numerically that the diffractive angle of RGB wavelengths is 35{\deg} and the crosstalk is less than 4.5% under the normal incidence of TE polarization, which imply the surface microstructure diffracts the certain RGB wavelengths achromatically. Via proper duplication it could be utilized as the combining optics of diffractive-waveguide near-eye display and head-up display because of its light and compact features., Comment: 5 pages, 1 figure

A theory of correcting residual change in focal length with wavelength is presented for high-harmonic diffractive lenses. The theory is based on a multiple-order diffractive (MOD) lens in combination with a stepped plate called an Arizona total energy color corrector (AZTECC) lens. Results indicate that best performance in terms of on-axis focused irradiance versus wavelength is found when low-dispersion glass is used for the AZTECC lens. A single-order diffractive Fresnel lens (DFL) in combination with the AZTECC lens makes the system achromatic over a wide bandwidth.

A method for designing afocal achromatic doublet is presented. We have implemented an exact ray trace through a separated doublet lens considering a plane wavefront propagating along the optical axis. The analytic equation of both the caustic surface and the back focal length for separated doublet lenses are provided. Demanding that the back focal length tends to infinity, we impose the conditions to design afocal optical systems, obtaining sixth and fourth degree polynomials as a function of the radii of curvature. In order to produce an afocal achromatic optical system, we solve numerically a set of two nonlinear equations assuming two spectral lines. Therefore, we have two unknowns which are the curvature radii for both the front surface and the rear surface. The contribution of this work is to provide simple formulas for designing optical beam expander or reducer devices based on separated doublets.

International audience; The European Synchrotron Radiation Facility (ESRF) operates a 6 GeV fourth generation light source, the ESRF-Extremely Brilliant Source (EBS). This storage ring is the first to implement the hybrid multibend achromat lattice (HMBA) that provides a reduction of the horizontal emittance of approximately a factor 30 with respect to the former double bend achromat structure. By combining several innovative concepts, the HMBA lattice allows the achievement of ultralow emittance while maintaining excellent lifetime and dynamic aperture performance. In this paper, beam commissioning experience and results of the new ESRF storage ring will be presented with an emphasis on the specific challenges relating to the HMBA lattice. The issues, methods, and concepts developed during the commissioning period and first months of operation are discussed.

We present a simple method to measure the two principal planes and the effective focal length of an imaging optical system. It is based on measurements of transverse magnification of the image and both the object and image positions from two arbitrary reference points. A simple linear equation is derived to find the distances of the principal planes from the reference points, which enables the computation of the effective focal length. Experimentally, the method only needs a standard optical bench, thus avoiding the use of a nodal slide. The accuracy obtained for a practical example with an optical system composed of two achromatic doublets is smaller than 1 mm, or better than 2%, for all three measured values (two principal planes and the one effective focal length) as compared with the results of optical ray tracing performed with OSLO software.

Broadband achromatic metalens imaging is of great interest in various applications, such as integrated imaging and augmented/virtual reality display. Current methods of achromatic metalenses mainly rely on the compensation of a linear phase dispersion implemented with complex nanostructures. Here, we propose and experimentally demonstrate a polarization-insensitive achromatic metalens (PIA-ML) based on computational wavefront coding. In this method, simple circular or square nanopillars are individually coded such that the focal depths at wavelengths at both ends of the achromatic bandwidth overlap at the designed focal plane, which removes the limitation of requiring a linear phase dispersion. An optimized PIA-ML that works in the full optical communication band from 1300 to 1700nm was obtained using a particle swarm optimization algorithm. Experimental results show that both focusing and imaging of the fabricated metalens are consistent with theoretical predictions within the broadband wavelength range, which provides a new methodology for ultra-broadband achromatic imaging with simple-shaped nanostructures.

We demonstrated three kinds of broadband terahertz achromatic metasurfaces with linear phase gradients including a deflector, a beam splitter and an axicon, whose phase and dispersion were simultaneously engineered by changing the geometric parameters of the unit cells. The devices presented here may inspire novel achromatic metasurfaces and promote the development of broadband terahertz devices.

It is generally assumed that correcting chromatic aberrations in imaging requires optical elements. Here, we show that by allowing the phase in the image plane to be a free parameter, it is possible to correct chromatic variation of focal length over an extremely large bandwidth, from the visible (Vis) to the longwave infrared (LWIR) wavelengths using a single diffractive surface, i.e., a flat lens. Specifically, we designed, fabricated and characterized a flat, multi-level diffractive lens (MDL) with thickness {\pounds} 10{\mu}m, diameter ~1mm, and focal length = 18mm, which was constant over the operating bandwidth of l=0.45{\mu}m (blue) to 15{\mu}m (LWIR). We experimentally characterized the point-spread functions, aberrations and imaging performance of cameras comprised of this MDL and appropriate image sensors. We further show using simulations that such extreme achromatic MDLs can be achieved even at high numerical apertures (NA=0.81). By drastically increasing the operating bandwidth and eliminating several refractive lenses, our approach enables thinner, lighter and simpler imaging systems., Comment: arXiv admin note: substantial text overlap with arXiv:1907.06251

Green stimuli are more difficult to detect than red stimuli in the retinal periphery, as reported previously. We examined the spatial characteristics of chromatic mechanisms using stimuli, modulated from an achromatic background to each pole of the “red–green” cardinal axis in DKL space at 20 deg eccentricity. The “blue–yellow” cardinal axis was also studied for comparison. By measuring both grating discrimination at the resolution limit (resolution acuity) and spatial summation, assessed by the Michaelis–Menten function, we demonstrated a marked “red–green” asymmetry. The resolution acuity was worse and spatial summation more extended for “green” compared to “red” stimuli, while showing significant individual variations. Ricco’s area was also measured, but not determined for “green” spots because of the poor small stimuli detection. These results cannot be explained by differences in L- and M-cone numerosity and/or spatial arrangement, but rather have postreceptoral origin, probably at the cortical level.

Polarization entanglement based cryptography uses the photon pairs generated in a spontaneous paramet- ric down-conversion process and guarantees the security through the violation of Bell’s inequality. Certain experimental parameters affects the entanglement fidelity and leads to a possible information leakage. The optical path difference of photons born at different crystals contributes to reduced fidelity, due to the extra birefringence of the nonlinear crystal. Although previous studies suggested methods to erase the distinguishability of photons by introducing compensation crystals, the phase difference, which is due to the lateral ray distribution is not studied. We used two commercially available collection optics; an aspheric and an achromatic lens. With these collection optics, the effect of collection optics on the entanglement fidelity is studied. We developed a simulation of such a system and found that aspheric collection optics is more suitable to achieve high fidelity.

The results of psychophysical studies suggest that color in a visual scene affects luminance contrast perception. In our brain imaging studies we have found evidence of an effect of chromatic information on luminance information. The dependency of saturation on brain activity in the visual cortices was measured by functional magnetic resonance imaging (fMRI) while the subjects were observing visual stimuli consisting of colored patches of various hues manipulated in saturation (Chroma value in the Munsell color system) on an achromatic background. The results indicate that the patches suppressed luminance driven brain activity. Furthermore, the suppression was stronger rather than weaker for patches with lower saturation colors, although suppression was absent when gray patches were presented instead of colored patches. We also measured brain activity while the subjects observed only the patches (on a uniformly black background) and confirmed that the colored patches alone did not give rise to differences in brain activity for different Chroma values. The chromatic information affects the luminance information in V1, since the effect was observed in early visual cortices (V2 and V3) and the ventral pathway (hV4), as well as in the dorsal pathway (V3A/B). In addition, we conducted a psychophysical experiment in which the ability to discriminate luminance contrast on a grating was measured. Discrimination was worse when weak (less saturated) colored patches were attached to the grating than when strong (saturated) colored patches or achromatic patches were attached. The results of both the fMRI and psychophysical experiments were consistent in that the effects of color were greater in the conditions with low saturation colors.

We examine the chromatic properties of ghost images appearing in expanded viewing angle polarization-type head-up display systems. We propose an achromatic polarization correction method to suppress ghost images in the whole visible spectral range. The method is based on the use of two half-wave plates of orthogonal optical axis–one being laminated on the combiner, the other attached to the head-up display (HUD) projector. We show that in this configuration the dispersion of the two waveplates cancel each other. Based on the results, a ghost image free colour HUD is demonstrated with 13 ° × 40 ° FOV. We present our modeling and experimental results and our demonstration HUD system.

Achromatic focusing is essential for broadband operation, which has recently been realised from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element. Here, we propose an achromatic metalens with C-shaped unit elements working from 0.3 to 0.8 THz with a bandwidth of approximately 91% over the centre frequency. The designed metalens possesses a high working efficiency of more than 68% at the peak and a relatively high numerical aperture of 0.385. We further demonstrate the robustness of our C-shaped metalens, considering lateral shape deformations and deviations in the etching depth. Our metalens design opens an avenue for future applications of terahertz meta-devices in spectroscopy, time-of-flight tomography and hyperspectral imaging systems.

In this paper, an achromatic LED projection headlamp (ALPH) is proposed for compensating color dispersion on the cut-off line of the light pattern. The ALPH consists of a white light LED, an elliptical reflector, a stop, an achromatic doublet lens (ADL). The ALPH is optimized and designed by computer programs firstly and its prototype is verified in experiments. According to the simulation results, the distance between the cut-off lines of the red light and the blue light is about 5.4 mm at 25 m and much less than that of the conventional LED projection headlamp. The measurements of the spectrometer and the illuminometer show that the ALPH can effectively enhance the consistency of the light pattern of the red and blue light and reduces the color dispersion near the cut-off line simultaneously. Moreover, all test points conform with the ECE R112 regulation except for only one point. By the determination of the integrating sphere, the optical efficiency of the prototype is 59%.

A theory of a broadband thin-film polarizing beam splitter based on an anisotropic cycloidal diffraction grating is proposed. The achromatization of the grating is provided by creating two-layer chiral structures with an opposite twist sense. Such a system has almost 100% efficiency. The calculations were carried out by the Jones matrix method. The resulting efficiency and bandwidth are higher than the previously known results.

The shape of the human spectral sensitivity function depends on how it is measured. In the increment threshold (IT) technique, sensitivity is typically measured as the inverse of threshold for detection of increments of monochromatic light presented for relatively long durations on achromatic pedestals. Spectral sensitivity functions derived from IT techniques have long been used to reveal contribution from opponent color channels. Although IT functions have been studied extensively, little attention has been given to functions derived from decrement thresholds (DT), partly due to technical challenges of producing appropriate stimuli. Comparison of IT and DT spectral sensitivities may be of interest because there are known asymmetries in the visual system between on- and off-pathways and between increment and decrement responses within these pathways. Consequently, spectral sensitivity functions obtained using DT measures may reveal a different complement of contributing mechanisms than those that produce IT functions. We report here that IT and DT derived spectral sensitivities were essentially identical over much of the visible spectrum. However, decrement sensitivity was slightly greater than increment sensitivity in the shorter wavelengths at modest light levels. This difference was not present at higher light levels, implicating rod pathways as a possible source of the difference. In sum, it appears that under conditions shown to reveal strong contribution from opponent mechanisms, decrement functions are either 1) determined by a similar complement of spectrally opponent mechanisms as those that define increment spectral sensitivities or 2) that the present conditions are insensitive to underlying asymmetries.

The feeling of being dazzled that is evoked by images consisting of an achromatic uniform center surrounded by regions with a luminance gradient was investigated. The effects of type of color saturation gradient in the peripheral region on the feeling of being dazzled were examined. Stimulus configuration was also varied. For the stimulus configuration of a disk-annulus, the feeling of being dazzled was lower for an increasing saturation gradient from the center to the periphery than for decreasing and no-saturation gradients when the center and the periphery maximum luminances were the same. This suggests that the presence of a chromaticity difference between the disk and the surrounding annulus strengthens the feeling of being dazzled. Similar results were obtained for the stimulus configuration of a star shape. For the stimulus configuration of a cross shape, quite different results were obtained; the chromaticity discontinuity had little or opposite effect. These results suggest that chromaticity border and stimulus configurations are factors in the feeling of being dazzled that is evoked by images with luminance gradient.

In this paper, an achromatic total internal reflection (TIR) prism set, consisting of two stacked prisms, is designed to reduce the lateral color aberration of a mini projector with light-emitting-diode (LED) light sources. Two different types of the prism set are proposed. Type 1 prism set is the first prism with a small Abbe number material stacked with the second prism with a large Abbe number material. By analyzing the optical properties of the proposed ATIR prism sets, we are able to choose an appropriate optical material combination of the prism set. For type 1 prism set, the corresponding lateral color aberration is 0. 65 μ m and the size is 2306 mm3. Nevertheless, the type 1 suffers from efficiency loss of 15.5%. For type 2 prism set, the corresponding lateral color aberration is 0. 61 μ m and the compact prism size is 3000 mm3. Although the size of type 2 prism set is larger than that of type 1, the efficiency loss can be as low as 1 %.

Optical metalens has been attracting more and more attention in recent years. To date, it is still difficult to simultaneously achieve wide field and broadband imaging in the visible region, which is very important in many applications, such as cameras, microscopy, and other imaging devices. In this paper, we design a double-layer metalens to achieve achromatic imaging over a field of view (FOV) of 60° in the visible light range of 470 nm to 650 nm, and its performance is verified by numerical simulations. The numerical aperture (NA) of the metalens is 0.61 and the average focusing efficiency is > 50% at normal incidence. The metalens has an additional advantage of polarization insensitivity.

In this paper, optical simulation of double rapid adiabatic passage (RAP) is investigated in three evanescently coupled waveguides with longitudinally varying detunings of the propagation constants. Unlike the time-dependent detuning which is kept linearly increased or decreased when the RAP is applied in two-state atomic systems, here all possible situations of the corresponding space-dependent detunings with or without sign flips are considered. At the maximum of the couplings in the waveguide structure, the detunings tend to become zero and the sign flips are supposed to occur. Theoretical analysis shows that different light evolutions such as light splitting, complete light transfer, or complete light return can be realized adiabatically, depending on the choices of the detunings. Moreover, two of the above three phenomena can be observed simultaneously in the waveguide structure under some circumstances. The theoretical analysis is confirmed by numerical calculations. Due to the robustness of the double RAP, the technique can be applied to design optical devices such as achromatic beam splitters or beam couplers.

In this work we propose an open-top like common-path intrinsically achromatic optical diffraction tomography system. It operates as a total-shear interferometer and employs Ronchi-type amplitude diffraction grating, positioned in between the camera and the tube lens without an additional 4f system, generating three-beam interferograms with achromatic second harmonic. Such configuration makes the proposed system low cost, compact and immune to vibrations. We present the results of the measurements of 3D-printed cell phantom using laser diode (coherent) and superluminescent diode (partially coherent) light sources. Broadband light sources can be naturally employed without the need for any cumbersome compensation because of the intrinsic achromaticity of the interferometric recording (holograms generated by –1st and +1st conjugated diffraction orders are not affected by the illumination wavelength). The results show that the decreased coherence offers much reduced coherent noise and higher fidelity tomographic reconstruction especially when applied nonnegativity constraint regularization procedure.

Various metasurfaces are proposed to abnormally modulate the elastic waves, but most of the elastic metasurfaces are wave-dispersive. In this paper, we theoretically design an achromatic meta-slab with subunits of different thickness, which can keep the refraction angle unchanged with the incident frequency. The designed meta-slab eliminates the wave dispersion without changing its configuration. Unlike the metasurface whose phase shift gradient is a constant, the designed meta-slab has a phase shift gradient that depends on the wavelength of the incident wave. Consequently, the meta-slab can compensate the wave path difference produced by the incident waves with different wavelengths. Through phase compensation, the meta-slab possesses an achromatic property. To show this property, we conduct corresponding finite element simulations for wave propagation and obtain good results consistent with the theoretical design. Our design broadens the working bandwidth of the meta-slab without changing its configuration, which makes it significant in the applications of vibration isolation, energy harvesting and health monitoring.

International audience; The Center for Optics and Photonics of the National Astronomical Research Institute of Thailand, together with the Institut d'Optique Graduate School and the Centre de Recherche Astrohpysique de Lyon (CRAL), is currently developing the Evanescent Wave Coronagraph (EvWaCo). The coronagraph relies on the tunneling effect to produce a fully achromatic focal plane mask (FPM) with an adjustable size. The full instrument comprises a coronagraph and adaptive optics system that will be mounted on the Thai National Telescope and is specified to reach a raw contrast of 10−4 at an inner working angle of 3 Airy radii. The coronagraph will be used to perform high contrast observations of stellar systems during on-sky observations over the spectral domain [600 nm, 900 nm]. In this paper, we present the opto-mechanical design of the EvWaCo prototype and the performance measured in laboratory conditions. We also discuss the potential applications for space-based observations and the development plan under this project in the next five years.

With the novel capabilities of engineering the optical wavefront at the nanoscale, the dielectric metalens has been utilized for fluorescence microscopy imaging system. However, the main technical difficulty is how to realize the achromatic focusing and light modulation simultaneously by a single-layer metalens in the two-photon excitation STED (TPE-STED) endomicroscopy imaging system. Herein, by combining the spatial multiplexing technology and vortex phase modulation, a single-layer multitasking vortex-metalens as a miniature microscopy objective on the end of fiber was proposed. The multitasking vortex-metalens with 36-sectors interleaving (diameter of 100 μm) could focus the excitation beam (1050 nm) and depletion beam (599 nm) to the same focal distance, modulate a doughnut-shaped depletion spot with vortex phase and reshape the focal spots to further make improvement in the quality and symmetry. According to the TPE-STED theory, a symmetrical effective fluorescent spot with the lateral resolution of 30 nm was obtained by the proposed metalens. Thus, with the advantage of ultra-compact and lightweight, we prospect that the subminiature multitasking metalens will help guide future developments in high-performance metalenses toward high-resolution and real-time images for deep biological tissue in vivo and enable scientific high-end miniature endomicroscopy imaging system.

The evanescent wave coronagraph uses the principle of frustrated total internal reflection (FTIR) to suppress the light coming from the star and study its close environment. Its focal plane mask is composed of a lens and a prism placed in contact with each other to produce the coronagraphic effect. In this paper, we present the experimental results obtained using an upgraded focal plane mask of the Evanescent Wave Coronagraph (EvWaCo). These experimental results are also compared to the theoretical performance of the coronagraph obtained through simulations. Experimentally, we reach a raw contrast equal to a few $10^{-4}$ at a distance equal to 3 ${\lambda}/D$ over the full I-band (${\lambda}_c =$ $800$ $nm$, ${\Delta}{\lambda}/{\lambda} \approx 20\%$) and equal to 4 ${\lambda}/D$ over the full R-band (${\lambda}_c =$ $650$ $nm$, ${\Delta}{\lambda}/{\lambda} \approx 23\%$) in unpolarized light. However, our simulations show a raw contrast close to $10^{-4}$ over the full I-band and R-band at the same distance, thus, confirming the theoretical achromatic advantage of the coronagraph. We also verify the stability of the mask through a series of contrast measurements over a period of 8 months. Furthermore, we measure the sensitivity of the coronagraph to the lateral and longitudinal misalignment of the focal plane mask, and to the lateral misalignment of the Lyot stop., Comment: 27 pages, 19 figures, accepted by AJ

The achromaticity and wide-angle property of quarter-wave plates (QWPs) are crucial for the color uniformity and image resolution of the future displays such as virtual reality (VR) pancake lens and augmented reality (AR) waveguide/focusing systems. However, most reported achromatic wide-angle QWPs designs composed by stacks of different birefringent plates are too complicated with limited achromaticity and wide-angle performance. The multi-twist retarders (MTR) QWPs presented in previous work already showed its potential to achieve high achromaticity in RGB using one monolithic film in normal incidence, but the incompetent polarization control in blue-violet limits its application in LED-based polarization-sensitive AR/VR headsets. In this work, we theoretically investigate a new type of MTR QWPs achieving super achromaticity from violet to red with average ellipticity 43° and simultaneously maintaining wide-viewing angle up to ±45°, which enables a precise polarization control within the field-of-view (FOV) of current AV/VR headset. The new proposed MTR QWP is also reported to obtain average reflection luminance leakage 0.15~% and maximum leakage 0.23~%, making it a promising element to reduce polarization leakage and enhance image resolution in the next-generation displays.

Spatial light modulators produce beams with a desired phase pattern, which directly affects the beam’s power spatial distribution. We demonstrate an approach for creating holographic spatial light modulators, which are permanently recorded in a photosensitive glass and do not require electric power in order to operate. The essence of the approach is that by means of holographic recording, an arbitrary phase pattern is encoded into a transmitting volume Bragg grating. Upon Bragg reconstruction, the phase pattern is reconstructed in the diffracted beam. These spatial light modulators are tunable and could be achromatic in broad spectral range.