Broadband Imaging Research Articles

Computing Metasurfaces Enabled Broad-Band Vectorial Differential Interference Contrast Microscopy

Differential interference contrast (DIC) microscopy provides the ability to visualize transparent phase samples such as living cells and tissues, which plays an essential role in applications in modern biology and medicine. However, existing DIC microscopy requires the introduction of complicated phase-contrast devices and is still limited to one-dimensional imaging. To mitigate these challenges, we propose a two-dimensional (2D) vectorial DIC microscopy based on computing metasurfaces to extract the 2D edge information for weakly scattering cells. Here, the Wollaston prism in a conventional DIC microscope is replaced by the computing metasurface, enabling our vectorial DIC microscope system to be miniaturized because of its compactness and multifunctionality. Imaging experiments with phase samples verify the capability to clearly observe a 2D vectorial DIC microscopy image with high contrast and its application in biological imaging. Particularly, because the designed computing metasurface is based on the Pancharatnam–Berry phase, our scheme may provide real-time, broad-band, and high-contrast phase imaging of living biomedical systems.

A slow bar in the lenticular barred galaxy NGC 4277

Aims.We characterised the properties of the bar hosted in lenticular galaxy NGC 4277, which is located behind the Virgo cluster.Methods.We measured the bar length and strength from the surface photometry obtained from the broad-band imaging of the Sloan Digital Sky Survey and we derived the bar pattern speed from the stellar kinematics obtained from the integral-field spectroscopy performed with the Multi Unit Spectroscopic Explorer at the Very Large Telescope. We also estimated the co-rotation radius from the circular velocity, which we constrained by correcting the stellar streaming motions for asymmetric drift, and we finally derived the bar rotation rate.Results.We found that NGC 4277 hosts a short (Rbar = 3.2−0.6+0.9kpc), weak (Sbar = 0.21 ± 0.02), and slow (ℛ = 1.8−0.3+0.5) bar and its pattern speed (Ωbar = 24.7 ± 3.4 km s−1kpc−1) is amongst the best-constrained ones ever obtained with the Tremaine–Weinberg (TW) method with relative statistical errors of ∼0.2.Conclusions.NGC 4277 is the first clear-cut case of a galaxy hosting a slow stellar bar (ℛ > 1.4 at more than a 1σconfidence level) measured with the model-independent TW method. A possible interaction with the neighbour galaxy NGC 4273 could have triggered the formation of such a slow bar and/or the bar could be slowed down due to the dynamical friction with a significant amount of dark matter within the bar region.

Spatial resolution of omni-resonant imaging.

Omni-resonance refers to the broadening of the spectral transmission through a planar cavity, not by changing the cavity structure, but by preconditioning the incident optical field. As such, broadband imaging can be performed through such a cavity with all the wavelengths simultaneously resonating. We examine here the spatial resolution of omni-resonant imaging and find that the spectral linewidth of the cavity resonance determines the spatial resolution. Surprisingly, the spatial resolution improves at longer wavelengths because of the negative angular dispersion intrinsic to Fabry-Pérot resonances, in contrast to conventional diffraction-limited optical imaging systems where the spatial resolution improves at shorter wavelengths. These results are important for applications ranging from transparent solar windows to nonlinear resonant image processing.

A slow lopsided bar in the interacting dwarf galaxy IC 3167

ABSTRACT We present surface photometry and stellar kinematics of IC 3167, a dwarf galaxy hosting a lopsided weak bar and infalling into the Virgo cluster. We measured the bar radius and strength from broad-band imaging and bar pattern speed by applying the Tremaine–Weinberg method to stellar-absorption integral-field spectroscopy. We derived the ratio of the corotation radius to bar radius (${\cal {R}}=1.7^{+0.5}_{-0.3}$) from stellar kinematics and bar pattern speed. The probability that the bar is rotating slowly is more than twice as likely as that the bar is fast. This allows us to infer that the formation of this bar was triggered by the ongoing interaction rather than the internal processes.

A panchromatic view of star cluster formation in a simulated dwarf galaxy starburst

ABSTRACT We present a photometric analysis of star and star cluster (SC) formation in a high-resolution simulation of a dwarf galaxy starburst that allows the formation of individual stars to be followed. Previous work demonstrated that the properties of the SCs formed in the simulation are in good agreement with observations. In this paper, we create mock spectral energy distributions and broad-band photometric images using the radiative transfer code skirt 9. We test several observational star formation rate (SFR) tracers and find that 24 $\mu$m, total infrared and Hα trace the underlying SFR during the (post)starburst phase, while UV tracers yield a more accurate picture of star formation during quiescent phases prior to and after the merger. We then place the simulated galaxy at distances of 10 and 50 Mpc and use aperture photometry at Hubble Space Telescope resolution to analyse the simulated SC population. During the starburst phase, a hierarchically forming set of SCs leads inaccurate source separation because of crowding. This results in estimated SC mass function slopes that are up to ∼0.3 shallower than the true slope of ∼−1.9 to −2 found for the bound clusters identified from the particle data in the simulation. The masses of the largest clusters are overestimated by a factor of up to 2.9 due to unresolved clusters within the apertures. The aperture-based analysis also produces a relation between cluster formation efficiency and SFR surface density that is slightly flatter than that recovered from bound clusters. The differences are strongest in quiescent SF environments.

Three-dimensional acoustic metamaterial Luneburg lenses for broadband and wide-angle underwater ultrasound imaging

This paper introduces spherical and ellipsoidal metamaterial lenses designed based on the Luneburg lens and transformation optics for underwater ultrasound imaging, which enhances signals over a broadband frequency range and detects objects at a wide-angle. The meta-atoms were analyzed with dispersion curves, equi-frequency contours, and effective acoustic parameters to design the lenses and predict the focusing performance. The three-dimensional lenses made of stainless steel were demonstrated numerically and experimentally in an underwater environment to determine the focal length and full width at half maximum. The spherical lens is omnidirectional. The focal length and the full width at half maximum of the spherical lens are 0λ and 0.6λ at 80 kHz, respectively. The ellipsoidal lens is thinner on the x-axis than that of the spherical lens. This lens has broadband properties by achieving the focal length and the full width at half maximum of 1.5λ to 0λ and 0.95λ to 0.59λ at frequencies between 60 kHz and 160 kHz, respectively. These lenses can potentially be applied to sound navigation ranging or medical transducers, providing the opportunities to view the underwater world with improved resolution at broadband and wide-angle.

MUSUBI (MegaCam Ultra-deep Survey: u*-band Imaging) Data for the COSMOS and SXDS Fields

The Subaru Hyper Suprime-Cam (HSC) Strategic Survey is the latest-generation multiband optical imaging survey for galaxy evolution and structure formation. The “Ultra-deep” component of the HSC survey provides grizy broadband images over ∼3.4 deg2 to detection limits of ∼26–28 AB, along with narrowband images, in the COSMOS and SXDS fields. These images provide an unprecedented combination of depths and area coverage, for studies of galaxies up to z ∼ 7. However, the lack of coverage at <4000 Å implies an incomplete sampling of the rest-frame UV at z ≲ 3, which is critically needed for understanding the buildup of stellar mass in later cosmic time. We conducted a multiyear CFHT u*-band imaging campaign in the two HSC Ultra-deep fields with CFHT MegaCam. By including shallower archival data, we reached 5σ depths of u* = 28.1 and 28.4 (AB) at the centers of the COSMOS and SXDS fields, respectively, and u* = 27.7 and 27.8 in the central 1 deg2 fields. The image quality is ≳ 0.″90, fairly good for the u* band. Both the photometric and astrometric quality of our data are excellent. We show that the combination of our u*-band and HSC data can lead to high-quality photometric redshifts at z = 0–3, and robust measurements of rest-frame UV on galaxies at 0.4 < z < 0.6 for distinguishing green-valley galaxies from star-forming and quiescent galaxies. We publicly release our reduced u*-band images and reference catalogs, which can be used readily for scientific studies.

Broadband Graphene Field-Effect Coupled Detectors: From Soft X-Ray to Near-Infrared

Here, we report a broadband graphene-silicon field-effect coupled detector (FCD) sensitive to photons spanning from soft X-ray to Near-Infrared region. Unlike traditional charge-coupled devices (CCD) relying on serial charge transfer between potential wells, the FCD integrates photo-sensing, charge integration, field-effect amplification, and random readout in one pixel. The charge integration in the potential well of the semiconductor substrate and field-effect coupled amplification in graphene transistor result in a highly sensitive broadband response. In the X-ray region, the device displays a high sensitivity of 1088 CGy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">air</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> and a fast response time < ~5 ms. Linear array imaging reveals the potential of our devices for array-based broadband imaging. Our FCD offers a viable strategy to monolithically integrate 2D materials into conventional solid-state imaging technology, exploring the next-generation broadband photodetectors for high-quality imaging and super vision technology.

Generation and Optimization of Spectral Cluster Maps to Enable Data Fusion of CaSSIS and CRISM Datasets

Four-band color imaging of the Martian surface using the Color and Stereo Surface Imaging System (CaSSIS) onboard the European Space Agency’s ExoMars Trace Gas Orbiter exhibits a high color diversity in specific regions. Not only is the correlation of color diversity maps with local morphological properties desirable, but mineralogical interpretation of the observations is also of great interest. The relatively high spatial resolution of CaSSIS data mitigates its low spectral resolution. In this paper, we combine the broad-band imaging of the surface of Mars, acquired by CaSSIS with hyperspectral data from the Compact Reconnaissance Imaging Spectrometer (CRISM) onboard NASA’s Mars Reconnaissance Orbiter to achieve a fusion of both datasets. We achieve this using dimensionality reduction and data clustering of the high dimensional datasets from CRISM. In the presented research, CRISM data from the Coprates Chasma region of Mars are tested with different machine learning methods and compared for robustness. With the help of a suitable metric, the best method is selected and, in a further step, an optimal cluster number is determined. To validate the methods, the so-called “summary products” derived from the hyperspectral data are used to correlate each cluster with its mineralogical properties. We restrict the analysis to the visible range in order to match the generated clusters to the CaSSIS band information in the range of 436–1100 nm. In the machine learning community, the so-called UMAP method for dimensionality reduction has recently gained attention because of its speed compared to the already established t-SNE. The results of this analysis also show that this method in combination with the simple K-Means outperforms comparable methods in its efficiency and speed. The cluster size obtained is between three and six clusters. Correlating the spectral cluster maps with the given summary products from CRISM shows that four bands, and especially the NIR bands and VIS albedo, are sufficient to discriminate most of these clusters. This demonstrates that features in the four-band CaSSIS images can provide robust mineralogical information, despite the limited spectral information using semi-automatic processing.

High efficiency and scalable fabrication of fresnel zone plates using holographic femtosecond pulses

Abstract To meet the growing demand for photonic integration and device miniaturization, planar diffractive Fresnel zone plates (FZPs) are widely applied in integrated optical systems. However, challenges remain in fabricating FZPs with high efficiency and satisfying the requirement for cross-scale fabrication. This paper details a high efficiency method for fabricating ultrathin FZPs of different scales on metal films by using holographic femtosecond lasers. The FZPs are split into a series of element patterns that are printed in order by using corresponding modulated femtosecond pulses. The fabricated FZPs are spliced by the printed element structures with no FZP size limitation in theory. FZPs with an area varying across three orders of magnitude are presented to demonstrate the capability of cross-scale fabrication. The fabricated FZPs possess an excellent broadband focusing and imaging ability in the visible spectrum. Furthermore, the fabrication of other functional ultrathin lenses, such as axial multifocal zone plates, petal-like zone plates, and FZP arrays, is described, revealing the wide potential for the flexible and scalable fabrication method in on-chip integrated optical systems.

Design Study of Broadband and Ultrahigh-Resolution Imaging Spectrometer Using Snapshot Multimode Interference in Fiber Bundles

Imaging spectrometry plays a significant role in various scientific realms. Although imaging spectrometers based on different schemes have been proposed, the pursuit of compact and high-performance devices is still ongoing. A compact broadband and ultrahigh-resolution imaging spectrometer (CBURIS) is presented, which comprises a microlens array, multiple fiber bundles, a microscope, and a two-dimensional detector array. The principle of the device is to spatially sample and integrate the field information via the front microlens array and then further process with the fiber bundles and imaging system based on the multimode interference theory. From both the theoretical and numerical analysis, this CBURIS design is a superior concept that not only achieves a 0.17° spatial resolution and ultrahigh spectral resolution (resolving power exceeds 2.58 × 106 at 1.55 µm) from the visible to mid-infrared region but also has the advantages of snapshot measurement, thermal stability, and a compact footprint compared with most existing imaging spectrometers.

Band-tunable achromatic metalens based on phase change material.

Achromatic metalens have the potential to significantly reduce the size and complexity of broadband imaging systems. A large variety of achromatic metalens has been proposed and most of them have the fixed achromatic band that cannot be actively modified. However, band-tunable is an important function in practical applications such as fluorescence microscopic imaging and optical detection. Here, we propose a bilayer metalens that can switch achromatic bands by taking the advantage of the high refractive index contrast of Sb2S3 between amorphous and crystalline state. By switching the state of Sb2S3, the achromatic band can be reversibly switched between the red region of visible spectrum (650-830 nm) and the near-infrared spectrum (830-1100 nm). This band-tunable design indicates a novel (to our knowledge) method to solve the problem of achromatic focusing in an ultrabroad band. The metalens have an average focusing efficiency of over 35% and 55% in two bands while maintaining diffraction-limited performance. Moreover, through proper design, we can combine different functionalities in two bands such as combining achromatic focusing and diffractive focusing. The proposed metalens have numerous potential applications in tunable displaying, detecting devices and multifunctional devices.

Theoretical Design of Graphene-Based Bi-Functional Tunable Terahertz Metasurfaces

Tunable multifunctional metasurface has wide application such as optical electromagnetics and material science. In this paper, a terahertz (THz) metasurface based on double graphene split-ring resonators (GSRRs) are theoretically demonstrated, integrating dual-band absorption and plasmon-induced transparency (PIT) filtering effect. The structure is composed of a monolayer of graphene arrays with periodic patterns and a metal ground surface partitioned by a silicon dioxide dielectric layer. When the initial structure of unit cell is three-layer sandwich structure (bottom metal plate), its dual-frequency absorption spectra appears two peaks at 2.50 THZ and 3.38 THz, which are 99.98% and 97.94%, respectively. Then the mechanism of double band absorption is explained by analyzing the distribution of surface current and electric intensity of the absorbent material. When the initial arrangement of the cell is a double layer structure (without the bottom metal plate), the PIT effect will occur when the incident wave is y-polarized. And in a certain range to achieve more than 90% of the transmission. In addition, CST simulations demonstrate that the designed model supports changing the operating frequency by adjusting the Fermi energy of graphene The dual-function terahertz metasurface proposed in this work has broad application prospects in broadband communication, terahertz imaging and industrial sensors.

Star formation in two irradiated globules around Cygnus OB2

Context. The ultraviolet irradiation and the action of stellar winds of newly formed massive stars on their parental molecular environment often produces isolated or small clouds, some of which become sites of star formation themselves. Aims. We investigate the young stellar populations associated with DR 18 and ECX 6-21, which are two isolated globules irradiated by the O-type stars of the Cygnus OB2 association. Both are HII regions containing obvious tracers of recent and ongoing star formation. We also study smaller isolated molecular structures in their surroundings. Methods. We combined near-infrared broad- and narrow-band imaging with broad-band imaging in the visible and with archive images obtained with the Spitzer Space Telescope. We used the joint photometry to select young stellar objects (YSOs), simultaneously estimating their intrinsic properties and classifying them according to the characteristics of their infrared excess. We also present low-resolution visible spectroscopy of selected sources. Results. We reproduce previous findings of an extended population of YSOs around both globules, dominated by the more evolved classes, associated with the general Cygnus OB2 population. Both globules contain their own embedded populations, with a higher fraction of the less-evolved classes. Masses and temperatures are estimated under the assumption of a common age of 1 Myr, which has been found to appropriately represent the general Cygnus OB2 YSO population but is most probably an overestimate for both globules, especially ECX 6-21. The early-B star responsible for the erosion of DR 18 is found to be part of a small aggregate of intermediate-mass stars still embedded in the cloud, which probably contains a second site of recent star formation, also with intermediate-mass stars. We confirm the two main star forming sites embedded in ECX 6-21 described in previous works, with the southern site being more evolved than the northern site. We also discuss the small globule ECX 6-21-W (=G79.8 + 1.2), and propose that its non thermal radio spectrum is due to synchrotron emission from an embedded jet, whose existence is suggested by our observations. Conclusions. The extreme youth of some of the YSOs suggests that star formation in both globules started after they became externally irradiated. The populations of both globules are not found to be particularly rich, but they contain stars with estimated masses similar or above that of the Sun in numbers that hint at some differences with respect to the star formation process taking place in more quiescent regions where low-mass stars dominate, which deeper observations may confirm.

Mid-infrared biomimetic moth-eye-shaped polarization-maintaining and angle-insensitive metalens.

Metalenses can potentially reduce the size and complexity of existing cameras, displays, and other optical devices, owing to their capability of flexible manipulation of the polarization, amplitude, and phase of light. However, metalenses capable of maintaining polarization and broadband wavefront shaping under arbitrarily polarized excitation have not been studied. In this study, we present the first demonstration of a biomimetic moth-eye-shaped metalens for polarization-maintaining, broadband and angle-insensitive focusing under an arbitrarily polarized excitation in the mid-infrared waveband (3.1-8.0 µm). Modulation and focusing efficiencies of 92% and 90%, respectively, were achieved. Moreover, a bifocal moth-eye-shaped metalens operating at normal and oblique incidences was realized. Compared to previously reported metalenses, the one proposed in this study exhibited a better focusing under oblique incidence, ensuring light transmission as effectively as a traditional lens. This study paves the way for the development of polarization-maintaining, broadband, and angle-insensitive microscale optical devices and imaging systems.

Macroscopic assembled graphene nanofilms based room temperature ultrafast mid‐infrared photodetectors

AbstractGraphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious backscattering of hot‐electrons result in inadequate quantum yields, especially in the mid‐infrared range. Here, we report a macroscopic assembled graphene (nMAG) nanofilm/silicon heterojunction for ultrafast mid‐infrared photodetection. The assembled Schottky diode works in 1.5–4.0 μm at room temperature with fast response (20–30 ns, rising time, 4 mm2 window) and high detectivity (1.6 × 1011 to 1.9 × 109 Jones from 1.5 to 4.0 μm) under the pulsed laser, outperforming single‐layer‐graphene/silicon photodetectors by 2–8 orders. These performances are attributed to the greatly enhanced photo‐thermionic effect of electrons in nMAG due to its high light absorption (~40%), long carrier relaxation time (~20 ps), low work function (4.52 eV), and suppressed carrier number fluctuation. The nMAG provides a long‐range platform to understand the hot‐carrier dynamics in bulk 2D materials, leading to broadband and ultrafast MIR active imaging devices at room temperature.image

High-Frequency Vacuum Electron Devices

Vacuum electron devices at frequencies of millimeter waves and terahertz play highly important roles in the modern high-data rate and broadband communication system, high-resolution detection and imaging, medical diagnostics, magnetically confined nuclear fusion, etc [...]

Low-Dimensional Layered Light-Sensitive Memristive Structures for Energy-Efficient Machine Vision

Layered two-dimensional (2D) and quasi-zero-dimensional (0D) materials effectively absorb radiation in the wide ultraviolet, visible, infrared, and terahertz ranges. Photomemristive structures made of such low-dimensional materials are of great interest for creating optoelectronic platforms for energy-efficient storage and processing of data and optical signals in real time. Here, photosensor and memristor structures based on graphene, graphene oxide, bismuth oxyselenide, and transition metal dichalcogenides are reviewed from the point of view of application in broadband image recognition in artificial intelligence systems for autonomous unmanned vehicles, as well as the compatibility of the formation of layered neuromorphic structures with CMOS technology.

Hα emission in the outskirts of galaxies atz= 0.4

AbstractThis paper reports detections of Hα emission and stellar continuum out to approximately 30 physical kiloparsecs, and Hα directionality in the outskirts of Hα-emitting galaxies (Hα emitters) at $z$ = 0.4. This research adopts narrow-band selected Hα emitters at $z$ = 0.4 from the emission-line object catalog by Hayashi et al. (2020, PASJ, 72, 86), which is based on data in the Deep and Ultradeep layers of the Hyper Suprime-Cam Subaru Strategic Program. Deep narrow- and broad-band images of 8625 Hα emitters across 16.8 deg2 enable us to construct deep composite emission-line and continuum images. The stacked images show diffuse Hα emission (down to ∼5 × 10−20 erg s−1 cm−2 arcsec−2) and stellar continuum (down to ∼5 × 10−22 erg s−1 cm−2 Å−1 arcsec−2), extending beyond 10 kpc at stellar masses &amp;gt;109 $M_\odot$, parts of which may originate from stellar halos. Those radial profiles are broadly consistent with each other. In addition, we obtain a dependence of the Hα emission on the position angle because relatively higher Hα equivalent width has been detected along the minor-axis towards galaxy disks. While the Hα directionality could be attributed to biconical outflows, further research with hydrodynamic simulations is highly demanded to pin down the exact cause.

Broadband Near-Field Near-Infrared Spectroscopy and Imaging with a Laser-Driven Light Source

The scattering-type scanning near-field optical microscope (s-SNOM) has become a powerful imaging and nano-spectroscopy tool, which is widely used in the characterization of electronic and photonic devices, two-dimensional materials and biomolecules. However, in the published literature, nano-spectroscopy is mainly employed in the mid-infrared band, and the near-infrared (NIR) nano-spectroscopy with broadband spectral range has not been well discussed. In the present paper, we introduce a home-built near-field NIR spectroscopy and imaging set-up that is based on a laser-driven light source (LDLS). By mapping the Ge-Au periodic grating sample and the photonic topology device, a ~30 nm spatial resolution and the excellent capability of characterizing complex samples are demonstrated. Spectra obtained by experiment reveal the optical band-gap of Ge with a spectral resolution of 25 cm−1, and a spectral range from 900 to 2000 nm. This technology is expected to provide a novel and unique approach for near-field NIR spectroscopy and imaging.