Comment on “Color astrophotography with a 100 mm-diameter f/2 polymer flat lens” [Appl. Phys. Lett. 126 , 051701 (2025)

Manufacturing diffractive lenses with a high numerical aperture (NA) is often a challenging task. The challenge stems from the fundamental limit of lithography techniques and the diffraction limit. Photolithography and femtosecond ablation are some of the well-established rapid lithography techniques for manufacturing large-area diffractive lenses for the visible region. First, when high NA diffractive lenses are designed, the outermost width of the zone becomes a sub-lithography limit (~ 2 μm) while still being super-wavelength. In advanced photolithography and most femtosecond ablation methods, the lithography limit is sub-wavelength, but scalar diffraction is not applicable, and the device becomes polarization sensitive. In this study, a holographic solution to overcome the above limitations is proposed. Fresnel incoherent correlation holography (FINCH) is a super-resolution incoherent imaging technique. In this project, a FINCH-inspired optical configuration is proposed to image beyond the lithography and diffraction limit of the diffractive lens. In a regular imaging system, the light from an object is collected by a diffractive lens and imaged, and recorded by an image sensor in the image plane. In this work, the intensity distribution is not recorded at the image plane but at a plane where the light modulated by the diffractive lens interferes with the unmodulated light outside the diffractive lens. This intensity distribution has spatial frequencies beyond the limit of the NA of the diffractive lens, resulting in super-resolution. Using the newly developed Lucy-Richardson-Rosen algorithm (LR²A), the image is reconstructed. We believe that the developed technique will improve the performance of imaging systems based on high-NA diffractive lenses.

There are mainly two complementary imaging modes in transmission electron microscopy (TEM): Conventional TEM (CTEM) and scanning TEM (STEM). In the CTEM mode the specimen is illuminated with a plane electron wave, and the direct image formed by the objective lens is recorded in the image plane. STEM is based on scanning the specimen surface with a focused electron beam and collecting scattered electrons with an extended disk or ring-shaped detector. Here we show that combination of CTEM imaging with STEM illumination generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. This new imaging mode improves imaging characteristics, is more robust against chromatic aberration, exhibits direct structural imaging with superior precision, visualizes light elements with excellent contrast, and even allows us to overcome the conventional information limit of a microscope.

In standard intensity imaging, apart from the availability of prior information about an image, the resolution is limited by the width of the aperture. The region of support of the autocorrelation of the pupil function is the measured spatial-frequency bandwidth of the imaging system, and thus the size of the pupil function determines the resolution limit. This relationship between the size of the pupil function and the resolution limit is generally taken to describe a fundamental limit for resolution. Contrary to conventional wisdom, the resolution is actually limited only for fields with zero higher-order cumulants. For fields with nonvanishing higher-order cumulants, higher resolution can be obtained by integrating higher powers of instantaneous intensity in the image plane and combining these images appropriately. The result is that resolution is limited only by the time required for the integral of the higher power of intensity to approximate the expected value. These claims are demonstrated, and the variance of the integrated intensity-squared image as a function of the temporal spectrum and integration time is analyzed. Simulations are provided that show imaging of spatial-frequency information outside the support of the pupil function autocorrelation for non-Gaussian fields.

The atmosphere of the earth restricts the resolution of conventional astrophotography to about 1 arcsec. Much higher resolution can be obtained by using speckle methods. The speckle masking method (triple correlation method) yields images of general astronomical objects with diffraction-limited resolution, for example, 0.03 arcsec resolution for a 3.6-m telescope. True images are obtained since speckle masking reconstructs both the modulus and the phase of the object Fourier transform. Therefore, speckle masking is a solution of the phase problem in speckle interferometry. The limiting magnitude of speckle masking is about 20m. Speckle spectroscopy is a speckle method that yields objective prism spectra with diffraction-limited angular resolution. Finally, speckle masking can recon-struct high-resolution images from optical long-baseline interferograms. A 1-km telescope array on the earth would yield images with 10 arcsec resolution. With a 40-km array in space a fantastic resolution of 10^-6 arcsec can be achieved at λ-200 nm. We show speckle masking observations of NGC 3603 and Eta Carinae and computer simulations of optical aperture synthesis.

The relatively high atmospheric propagation of millimeter-waves (MMW) was found to be one of the most critical reasons for the development of reliable sensors for MMW detection. According to previous research works, it has been already shown that incident MMW radiation on a glow discharge detector (GDD) can increase the discharge current. Hence, the electrical mode of detection can be employed to detect the presence of MMW radiation. In this article, a new design of a row detector using GDDs as pixel elements, and the influence of MMW incidence on GDD’s discharge current, were acquired using an elementary data acquisition (DAQ) platform. The DAQ system computes the averaged Fast Fourier Transform (FFT) spectrum of the time signal and returns the FFT results as magnitude based on the level of detection. An FFT-based signal acquisition proved to be a better alternative to the lock-in detection that was commonly used in MMW detection systems. This improved detection circuit provides enhanced noise filtering, thereby resulting in better MMW images within a short time. The overhead expense of the entire system is very low, as it can avoid lock-in amplifier stages that were previously used for signal enhancement. A scanning mechanism using a motorized translation stage (step motor) is involved to place and align the row detector in the image plane. The scanning can be carried out vertically to perform the imaging, by configuring the step motor after selecting the desired step size and position. A simplified version of the MMW detection circuit with a dedicated over-voltage protection facility is presented here. This made the detection system more stable and reliable during its operation. The MMW detection circuit demonstrated in this work was found to be a milestone to develop larger focal plane arrays (FPA) with very inexpensive sensor elements.

Fast, volumetric structural and functional imaging of cellular and sub-cellular dynamics inside the living brain is one of the most desired capabilities in the neurosciences, but still faces serious challenges. Specifically, while few solutions for rapid 3D scanning exist, it is generally much easier to facilitate fast in-plane scanning than it is to scan axially at high speeds. Remote focusing in which the imaging plane is shifted along the optical axis by a tunable lens while maintaining the position of the sample and objective is a promising approach to increase the axial scan speed, but existing techniques often introduce severe optical aberrations in high-NA imaging systems, eliminating the possibility of diffraction-limited single-cell imaging. Here, we demonstrate near diffraction-limited, volumetric two-photon fluorescence microscopy in which we resolve the deep sub-micron structures of single microglia cells with axial scanning performed using a novel high-NA remote focusing method. Image contrast is maintained to within 7% compared to mechanical sample stepping and the focal volume remains nearly diffraction-limited over an axial range greater than 86 µm.

Controlled fabrication of single and multiple nanostructures far below the diffraction limit using a method based on laser induced periodic surface structure (LIPSS) is presented. In typical LIPSS, multiple lines with a certain spatial periodicity, but often not well-aligned, were produced. In this work, well-controlled and aligned nanowires and nanogrooves with widths as small as 40 nm and 60 nm with desired orientation and length are fabricated. Moreover, single nanowire and nanogroove were fabricated based on the same mechanism for forming multiple, periodic structures. Combining numerical modeling and AFM/SEM analyses, it was found these nanostructures were formed through the interference between the incident laser radiation and the surface plasmons, the mechanism for forming LIPSS on a dielectric surface using a high power femtosecond laser. We expect that our method, in particular, the fabrication of single nanowires and nanogrooves could be a promising alternative for fabrication of nanoscale devices due to its simplicity, flexibility, and versatility.

Planar lenses are attractive photonic devices due to its minimized size and easy to integrate. However, planar lenses designed in traditional ways are restricted by the diffraction limit. They have difficulties in further reducing the focal spot size beyond the diffraction limit. Super-oscillation provides a possible way to solve the problem. However, lenses based on super-oscillation have always been affected by huge sidelobes, which resulted in limited field of view and difficulties in real applications. To address the problem, in the paper, a far-field sub-diffraction lens based on binary amplitude-phase mask was demonstrated under illumination of linearly polarized plane wave at wavelength 632.8 nm. The lens realized a long focal length of 148λ (94 µm), and the full width at half maximum of the focal line was 0.406λ, which was super-oscillatory. More important is that such a flat lens has small sidelobes and wide field of view. Within the measured range of [-132λ, + 120λ], the maximum sidelobe observed on the focal plane was less than 22% of the central peak. Such binary amplitude-phase planar lens can also be extended to long focal length far-field sub-diffraction focusing lens for other spectrum ranges.

We report on high-accuracy, high-resolution (< 20mas) stellar measurements obtained in the near infrared (≃ 2.2 microns) at the 200 inch telescope using two elliptical (3m x 1.5m) sub-apertures located 3.4m apart. Our interferometric coronagraph, known as the Palomar Fiber Nuller (PFN), is located downstream of the adaptive optics (AO) system and recombines the two separate beams into a common singlemode fiber. The AO system acts as a fringe tracker, maintaining the optical path difference (OPD) between the beams around an adjustable value, which is set to the central dark interference fringe. AO correction ensures high efficiency and stable injection of the beams into the single-mode fiber. A chopper wheel and a fast photometer are used to record short (< 50ms per beam) interleaved sequences of background, individual beam and interferometric signals. In order to analyze these chopped null data sequences, we developed a new statistical method, baptized Null Self-Calibration (NSC), which provides astrophysical null measurements at the 0.001 level, with 1 σ uncertainties as low as 0.0003. Such accuracy translates into a dynamic range greater than 1000:1 within the diffraction limit, demonstrating that the approach effectively bridges the traditional gap between regular coronagraphs, limited in angular resolution, and long baseline visibility interferometers, whose dynamic range is restricted to ≃ 100:1. As our measurements are extremely sensitive to the brightness distribution very close to the optical axis, we were able to constrain the stellar diameters and amounts of circumstellar emission for a sample of very bright stars. With the improvement expected when the PALM-3000 extreme AO system comes on-line at Palomar, the same instrument now equipped with a state of the art low noise fast read-out near IR camera, will yield 10^(-4) to 10^(-3) contrast as close as 30 mas for stars with K magnitude brighter than 6. Such a system will provide a unique and ideal tool for the detection of young (<100 Myr) self-luminous planets and hot debris disks in the immediate vicinity (0.1 to a few AUs) of nearby (< 50pc) stars.

Astronomical imaging with micro-arcsecond (µas) angular resolution could enable breakthrough scientific discoveries. Previously proposed µas x-ray imager designs have been interferometers with limited effective collecting area. Here we describe x-ray telescopes achieving diffraction-limited performance over a wide energy band with large effective area, employing a nested-shell architecture with grazing-incidence mirrors, while matching the optical path lengths between all shells. We present two compact nested-shell Wolter Type 2 grazing-incidence telescope designs for diffraction-limited x-ray imaging: a micro-arcsecond telescope design with 14 µas angular resolution and 2.9m2 of effective area at 5 keV photon energy (λ=0.25nm), and a smaller milli-arcsecond telescope design with 525 µas resolution and 645cm2 effective area at 1 keV (λ=1.24nm). We describe how to match the optical path lengths between all shells in a compact mirror assembly and investigate chromatic and off-axis aberrations. Chromatic aberration results from total external reflection off of mirror surfaces, and we greatly mitigate its effects by slightly adjusting the path lengths in each mirror shell. The mirror surface height error and alignment requirements for diffraction-limited performance are challenging but arguably achievable in the coming decades. Because the focal ratio for a diffraction-limited x-ray telescope is extremely large (f/D∼105), the only important off-axis aberration is curvature of field, so a 1 arc sec field of view is feasible with a flat detector. The detector must fly in formation with the mirror assembly, but relative positioning tolerances are on the order of 1 m over a distance of some tens to hundreds of kilometers. Although there are many challenges to achieving diffraction-limited x-ray imaging, we did not find any fundamental barriers.

Thermal imagers and used therein infrared array sensors are subject to calibration procedure and evaluation of their voltage sensitivity on incident radiation during manufacturing process. The calibration procedure is especially important in so-called radiometric cameras, where accurate radiometric quantities, given in physical units, are of concern. Even though non-radiometric cameras are not expected to stand up to such elevated standards, it is still important, that the image faithfully represents temperature variations across the scene. The detectors used in thermal camera are illuminated by infrared radiation transmitted through a specialized optical system. Each optical system used influences irradiation distribution across an sensor array. In the article a model describing irradiation distribution across an array sensor working with an optical system used in the calibration set-up has been proposed. In the said method optical and geometrical considerations of the array set-up have been taken into account. By means of Monte-Carlo simulation, large number of rays has been traced to the sensor plane, what allowed to determine the irradiation distribution across the image plane for different aperture limiting configurations. Simulated results have been confronted with proposed analytical expression. Presented radiometric model allows fast and accurate non-uniformity correction to be carried out.

Modern (sub)millimeter interferometers, such as ALMA and NOEMA, offer high angular resolution and unprecedented sensitivity. This provides the possibility to characterize the morphology of the gas and dust in distant galaxies. To assess the capabilities of the current software in recovering morphologies and surface brightness profiles in interferometric observations, we tested the performance of the Spergel model for fitting in the uυ-plane, which has been recently implemented in the IRAM software GILDAS (uv_fit). Spergel profiles provide an alternative to the Sérsic profile, with the advantage of having an analytical Fourier transform, making them ideal for modeling visibilities in the uυ-plane. We provide an approximate conversion between the Spergel index and the Sérsic index, which depends on the ratio of the galaxy size to the angular resolution of the data. We show through extensive simulations that Spergel modeling in the uυ-plane is a more reliable method for parameter estimation than modeling in the image plane, as it returns parameters that are less affected by systematic biases and results in a higher effective signal-to-noise ratio. The better performance in the uυ-plane is likely driven by the difficulty of accounting for a correlated signal in interferometric images. Even in the uυ-plane, the integrated source flux needs to be at least 50 times larger than the noise per beam to enable a reasonably good measurement of a Spergel index. We characterized the performance of Spergel model fitting in detail by showing that parameter biases are generally low (&lt;10%) and that uncertainties returned by uv_fit are reliable within a factor of two. Finally, we showcase the power of Spergel fitting by reexamining two claims of extended halos around galaxies from the literature, showing that galaxies and halos can be successfully fitted simultaneously with a single Spergel model.

Recently introduced angular-memory-effect based techniques enable non-invasive imaging of objects hidden behind thin scattering layers. However, both the speckle-correlation and the bispectrum analysis are based on the statistical average of large amounts of speckle grains, which determines that they can hardly access the important information of the point-spread-function (PSF) of a highly scattering imaging system. Here, inspired by notions used in astronomy, we present a phase-diversity speckle imaging scheme, based on recording a sequence of intensity speckle patterns at various imaging planes, and experimentally demonstrate that in addition to being able to retrieve the image of hidden objects, we can also simultaneously estimate the pupil function and the PSF of a highly scattering imaging system without any guide-star nor reference.

For the middle wave 640×512 cooled thermal IR focal plane array with 15 μm pixel pitch, a design of 3.7～4.8 μm refractive infrared switchable dual-field-of-view imaging system is described, which makes use of a mechanical holder to switch two lenses into and out of the whole optical system to change the focal length from 45mm to 135mm. The system includes a telescope and a relay sub-system to avoid vignetting caused by the presence of the cold shield. Preliminary calculations are carried out first to determine the focal powers and first-order parameters of each lens and then the aberration equations are solved to achieve the initial configuration of the system as the starting point. During the optimization, in order to correct varied aberrations, such as spherical aberrations, coma, astigmatism, and chromatic aberrations, more lenses, glasses and aspherical surfaces are employed. In consideration of decreasing the manufacture cost and fabrication difficulties, only germ, silicon and one ZnS single lens are allowed to make use of, and the highest order of aspherical coefficients is no more than 8 th . Meanwhile, the separation between the two lenses fixed in the mechanical holder must be controlled strictly to make sure no ray will be obscured by them when they are switched out of the system. Between the telescope and the relay system, the relay system and the image plane, there are two mirrors to fold the system, so reserved space must be valued in the optical path. Finally, a total of ten lenses with two aspherical surfaces and two mirrors are used in the design, making the system cost effective and compact. At the end, the design results are given. The modulation transfer function (MTF) of each field-of-view is above 0.5 in all focal positions at the spatial frequency of 33lp/mm, which approaches the diffraction limits and the energy permeance ratio is greater than 80%, showing excellent performance.

To develop the detection ability of ultimate stars, and use more dark stars as referenced stars of deep space aircraft navigation, a catadioptric star sensor with a proved Cassegrain configuration with three pieces of emending lens optical system is designed. In this system, the proved Cassegrain configuration is used to reduce the spherical aberration and coma out of optical axis and bring the focus and large size of entrance pupil at the same time; emending lens close to the image plane is mainly eliminating the remaining aberrations of catoptric configuration, the telecentric image plane design among the emending configuration is also benefit to the irradiance unification in full of field and decrease the sensitivity of image sensor setting. This system has a 180 mm focal length and F-number is 2, view of field is 33, the effective pupil area is 5106 mm2, energy centroid aberration is smaller than 2.5 m, lateral color is better than 3.5 m among 450~800 nm spectrum, over 80% energy of spot in less than 33 pixel, and modulation transfer function (MTF) is approaching to diffraction limit. The inner baffles of reflected lens and outer two-group baffles are introduced, through modeling and analyzing the stray light of system in the Lighttools, the designed result shows that in the range of 2 to 40 incident angle of stray light, the point resource transmittance is between 10-6 to 10-4. These results can provide a good reference for further star sensors with deep space catadioptric configuration star sensor.