Near-infrared Bandpasses Research Articles

Grating-based metasurfaces for ultra-narrow near-infrared bandpass filtering with wide out-of-band suppression

Here, we present a straightforward strategy for designing silicon grating-based metasurfaces tailored for narrow near-infrared bandpass filtering. By selecting appropriate structural parameters for the grating and including periodic groove perturbations within each grating slit, transverse guided mode resonances (GMRs) propagating perpendicular and parallel to the grating slit are created to provide wide out-of-band suppression and high-Q filter responses, respectively. The destructive and constructive interference between radiations from groove perturbations are then introduced to eliminate all GMRs except one, producing a single-band bandpass filter. Simply adjusting the period of the groove perturbations allows precise tuning of the passband’s central wavelength across the operational spectral range from 1350 nm to 1750nm, throughout which the passband exhibits a Q-factor exceeding 9,000 and the attenuation level outside the passband remains below 1%. Furthermore, our proposed narrow bandpass filters are found to be robust against the potential fabrication imperfections, such as variations in groove size and position.

Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey

Context. The highly debated effect of metallicity on the absolute magnitudes of classical Cepheid variables needs to be properly quantified for determining accurate and precise distances based on their Leavitt Law. Aims. Our goal is to obtain homogeneous optical and near-infrared light curves of Milky Way Cepheid variables complementing their already collected high-resolution spectroscopic metallicities as part of the C-MetaLL survey. Together with Gaia parallaxes, we investigate period-luminosity-metallicity relations for Cepheid variables at multiple wavelengths. Methods. We present homogeneous multiband (grizJHKs) time-series observations of 78 Cepheids including 49 fundamental mode variables and 29 first-overtone mode variables. These observations were collected simultaneously using the ROS2 and REMIR instruments at the Rapid Eye Mount telescope. Multiwavelength photometric data were used to investigate pulsation properties of Cepheid variables and derive their period–luminosity (PL) and period–Wesenheit (PW) relations. Results. The Cepheid sample covers a large range of distances (0.5 − 19.7 kpc) with varying precision of parallaxes, and thus astrometry-based luminosity fits were used to derive PL and PW relations in optical Sloan (griz) and near-infrared (JHKs) filters. These empirically calibrated relations exhibit large scatter primarily due to larger uncertainties in parallaxes of distant Cepheids, but their slopes agree well with those previously determined in the literature. Using homogeneous high-resolution spectroscopic metallicities of 61 Cepheids covering −1.1 < [Fe/H] < 0.6 dex, we quantified the metallicity dependence of PL and PW relations which varies between −0.30 ± 0.11 (in Ks) and −0.55 ± 0.12 (in z) mag dex−1 in grizJHKs bands. However, the metallicity dependence in the residuals of the PL and PW relations is predominantly seen for metal-poor stars ([Fe/H] < −0.3 dex), which also have larger parallax uncertainties. The modest sample size precludes us from separating the contribution to the residuals due to parallax uncertainties, metallicity effects, and reddening errors. While this Cepheid sample is not optimal for calibrating the Leavitt law, upcoming photometric and spectroscopic datasets of the C-MetaLL survey will allow the accurate derivation of PL and PW relations in the Sloan and near-infrared bandpasses, which will be useful for the distance measurements in the era of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time and upcoming extremely large telescopes.

Visible-blind near-infrared organic photodetectors

The presently available commercial photodetectors have a broadband photoresponse and require different external optical filters to block the undesired light outside the detection spectrum window, e.g., near-infrared (NIR) detection. The use of an NIR bandpass has technical limitations in curved or flexible large-area photodetectors, as an NIR bandpass depends critically on the difference in the interference of the optical path in the filter. This work reports the effort to develop a high-performance filter-free organic photodetector (OPD) with a double bulk heterojunction (BHJ) structure. The visible-blind NIR photodetection is realized by eliminating the photocurrent generated in the front visible light-absorbing BHJ optical depletion layer, due to the suppression of electron transport by incorporating a copper thiocyanate-based electron-blocking layer in the OPD. Only excitons generated in the rear NIR-absorbing BHJ contribute to photocurrent in the OPD, thereby achieving visible-blind NIR photodetection. The double BHJ OPD has a high responsivity of 0.38 A/W at 1050 nm and a specific detectivity of >1013 Jones over the wavelength range from 800 to 1050 nm, making it an ideal candidate for applications in optical communication, food quality detection, wellness monitoring, and NIR image sensors.

Empirical 2MASS–WFC3/IR Filter Transformations Across the H-R Diagram from Synthetic Photometry

Near-infrared bandpasses on spaceborne observatories diverge from their ground-based counterparts as they are free of atmospheric telluric absorption. Available transformations between respective filter systems in the literature rely on theoretical stellar atmospheres, which are known to have difficulties reproducing the observed spectral energy distributions of cool giants. We present new transformations between the Two Micron All Sky Survey JHK S and Hubble Space Telescope WFC3/IR F110W, F125W, and F160W photometric systems based on synthetic photometry of empirical stellar spectra from four spectral libraries. This sample comprises over 1000 individual stars, which together span nearly the full H-R diagram and sample stellar populations from the solar neighborhood out to the Magellanic Clouds, covering a broad range of ages, metallicities, and other relevant stellar properties. In addition to global color-dependent transformations, we examine band-to-band differences for cool, luminous giant stars in particular, including multiple types of primary distance indicators.

Film structure and optical characteristics of a-Si:H prepared with a rotary table type layer-by-layer sputtering method for application in short-wave near-infrared filters

The structure and optical properties of a hydrogenated amorphous silicon (a-Si:H) film for a short-wave near-infrared bandpass filter (BPF), fabricated using the rotary table type layer-by-layer (LbL) sputtering method, were evaluated. Although the extinction coefficient k tended to increase as the film thickness per cycle increased, the bonded hydrogen composition increased owing to an increase in the hydrogen partial pressure of the reactive plasma area, thereby decreasing k to 1 × 10−3 or less. Meanwhile, the occurrence of (Si–H2)n bonds was suppressed. Consequently, in contrast to reactive sputtering, it was found that the a-Si:H achieved via LbL sputtering has a high refractive index, low absorption characteristics, and high thermal durability suitable for BPFs, due to the chemical annealing effect.

Blanco DECam Bulge Survey (BDBS)

Red clump (RC) stars are one of the best stellar tracers of the structure of the Milky Way (MW) bulge. Here we report a new view of the double RC through luminosity and color distributions of RC stars in nine bulge fields (l = 0.0°, ±4.5°; b = −6.0°, −7.5°, −9.0°) from the Blanco DECam Bulge Survey (BDBS), which covers near-ultraviolet to near-infrared bandpasses. The bright and faint RCs show contrasting distributions in (u − g)0 and (u − i)0 colors but similar distributions in (J − Ks)0 with a variation depending on the Galactic longitude, where the bright RC is typically redder than the faint RC. In particular, the RC stars are clearly divided into the bluer and redder populations when using the (u − g)0 color ((u − g)0 < 2.5 for the bluer RC; (u − g)0 ≥ 2.5 for the redder RC). The bluer stars show a single clump on the faint RC regime, whereas the redder stars form double clumps on both the bright and faint RCs. The bright clump of the redder stars is dominant in the positive longitude fields, while the faint clump of those red stars is significant at negative longitudes. We also confirm that the bluer and redder stars have different peak metallicity through comparison with spectroscopy (Δ[Fe/H] ∼ 0.45 dex). Therefore, our results support a scenario whereby the MW bulge is composed of a spheroid of metal-poor stars and a boxy/peanut shape (X-shape) predominantly made up of metal-rich stars.

Dynamically tunable reflecting near-infrared bandpass filter based on a hybrid graphene–nanometallic structure

A dynamically tunable reflecting near-infrared bandpass filter based on a hybrid graphene–nanometallic structure is demonstrated by numerical simulation. The proposed filter is constructed by unit cells with a graphene monolayer embedded into the nanometallic grating structure. The gradual transition of the graphene monolayer from a very thin metal to dielectric plays the key role in tuning the reflection spectrum of the structure. Spectral analysis clearly shows a passband blueshift with increasing graphene Fermi energy. The filter parameters are investigated by varying graphene Fermi energy through external voltage gates. The modulation depth, center frequency, bandwidth, and quality factor of the filter could be tuned. We achieved stable modulation depth as high as 0.735, and a quality factor as high as 3.4. The center frequency can be tuned in a broad range from 210 to 230 THz and with bandwidth tuning from 60 to 95 THz. The effect of the nanogap size and environment refractive index is also numerically investigated. These results are very promising for future use and integration of the proposed filters as a key element of optical communication systems and infrared sensing.

The Carnegie Supernova Project. I. Third Photometry Data Release of Low-redshift Type Ia Supernovae and Other White Dwarf Explosions

Abstract We present final natural-system optical (ugriBV) and near-infrared (YJH) photometry of 134 supernovae (SNe) with probable white dwarf progenitors that were observed in 2004–2009 as part of the first stage of the Carnegie Supernova Project (CSP-I). The sample consists of 123 Type Ia SNe, 5 Type Iax SNe, 2 super-Chandrasekhar SN candidates, 2 Type Ia SNe interacting with circumstellar matter, and 2 SN 2006bt-like events. The redshifts of the objects range from to 0.0835; the median redshift is 0.0241. For 120 (90%) of these SNe, near-infrared photometry was obtained. Average optical extinction coefficients and color terms are derived and demonstrated to be stable during the five CSP-I observing campaigns. Measurements of the CSP-I near-infrared bandpasses are also described, and near-infrared color terms are estimated through synthetic photometry of stellar atmosphere models. Optical and near-infrared magnitudes of local sequences of tertiary standard stars for each supernova are given, and a new calibration of Y-band magnitudes of the Persson et al. standards in the CSP-I natural system is presented.

The Frontier Fields: Survey Design

The Frontier Fields are a director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combine the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters - Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370 - were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and pre-existing ancillary data. These clusters have been targeted by the HST ACS/WFC and WFC3/IR with coordinated parallels of adjacent blank fields for over 840 HST orbits. The Spitzer Space Telescope has dedicated > 1000 hours of director's discretionary time to obtain IRAC 3.6 and 4.5 micron imaging to ~26.5, 26.0 ABmag 5-sigma point-source depths in the six cluster and six parallel Frontier Fields. The Frontier Field parallel fields are the second-deepest observations thus far by HST with ~29th ABmag 5-sigma point source depths in seven optical - near-infrared bandpasses. Galaxies behind the Frontier Field cluster lenses experience typical magnification factors of a few, with small regions near the critical curves magnified by factors 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ~30-33 magnitudes over very small volumes. Early studies of the Frontier Fields have probed galaxies fainter than any seen before during the epoch of reionization 6 < z < 10, mapped out the cluster dark matter to unprecedented resolution, and followed lensed transient events.

On-chip copper-dielectric interference filters for manufacturing of ambient light and proximity CMOS sensors.

Filter technologies implemented on CMOS image sensors for spectrally selective applications often use a combination of on-chip organic resists and an external substrate with multilayer dielectric coatings. The photopic-like and near-infrared bandpass filtering functions respectively required by ambient light sensing and user proximity detection through time-of-flight can be fully integrated on chip with multilayer metal-dielectric filters. Copper, silicon nitride, and silicon oxide are the materials selected for a technological proof-of-concept on functional wafers, due to their immediate availability in front-end semiconductor fabs. Filter optical designs are optimized with respect to specific performance criteria, and the robustness of the designs regarding process errors are evaluated for industrialization purposes.

Development of visible and NIR imaging equipment for small animals with smart pad.

The portable visible and near-infrared (NIR) imaging equipment for a pre-clinical test with small animals was designed and developed in this paper. The developed equipment is composed of a CCD camera, a focusing lens, an objective lens, a NIR band pass filter and a NIR filter driving motor. An NIR ray is mainly used for imaging equipment because it has high light penetration depth in biological tissue. Therefore, NIR fluorescent agents are available for chemical conjugation to targeting molecules in vivo. This equipment can provide a visible image, NIR image and merged image simultaneously. A communication system was specifically established to check obtained images through a smart pad in real time. It is less dependent on space and time than the conventional system.

Application of day and night digital photographs for estimating maize biophysical characteristics

In this study, an inexpensive camera-observation system called the Crop Phenology Recording System (CPRS), which consists of a standard digital color camera (RGB cam) and a modified near-infrared (NIR) digital camera (NIR cam), was applied to estimate green leaf area index (LAI), total LAI, green leaf biomass and total dry biomass of stalks and leaves of maize. The CPRS was installed for the 2009 growing season over a rainfed maize field at the University of Nebraska-Lincoln Agricultural Research and Development Center near Mead, NE, USA. The vegetation indices called Visible Atmospherically Resistant Index (VARI) and two green–red–blue (2g–r–b) were calculated from day-time RGB images taken by the standard commercially-available camera. The other vegetation index called Night-time Relative Brightness Index in NIR (NRBINIR) was calculated from night-time flash NIR images taken by the modified digital camera on which a NIR band-pass filter was attached. Sampling inspections were conducted to measure bio-physical parameters of maize in the same experimental field. The vegetation indices were compared with the biophysical parameters for a whole growing season. The VARI was found to accurately estimate green LAI (R2 = 0.99) and green leaf biomass (R2 = 0.98), as well as track seasonal changes in maize green vegetation fraction. The 2g–r–b was able to accurately estimate total LAI (R2 = 0.97). The NRBINIR showed the highest accuracy in estimation of the total dry biomass weight of the stalks and leaves (R2 = 0.99). The results show that the camera-observation system has potential for the remote assessment of maize biophysical parameters at low cost.

Dual‐frequency‐selective surfaces for near‐infrared bandpass filters

AbstractA bandpass filter resonating at ∼1.4 μm and based on a dual‐frequency‐selective surface design is fabricated and characterized on a silicon substrate. The filter consists of square apertures arranged in a square lattice and separated by magnesium‐fluoride dielectric layers. Simulations indicate minimal change in spectral reflectance versus overlay misalignment. The measured reflectance shows almost zero minima and a sharp roll‐off. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 95–98, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20387

Radio Galaxies atz= 1.1 to 3.8: Adaptive Optics Imaging and ArchivalHubble Space TelescopeData

We have undertaken a program of high-resolution imaging of high-redshift radio galaxies (HzRGs), using adaptive optics on the Canada-France-Hawaii Telescope. We report on deep imaging in J, H, and K bands of six HzRGs in the redshift range 1.1 to 3.8. At these redshifts, near-infrared bandpasses sample the rest-frame visible galactic light. The radio galaxy is resolved in all the fields and is generally elongated along the axis of the radio lobes. These images are compared with archival Hubble Space Telescope Wide-Field Planetary Camera 2 optical observations of the same fields and show that the HzRG morphology in rest-frame ultraviolet and visible light is generally very similar: a string of bright compact knots. Furthermore, this sample?although very small?suggests that the colors of the knots are consistent with light from young stellar populations. If that is the case, a plausible explanation is that these objects are being assembled by mergers at high redshift.

Galaxy clustering in the Herschel Deep Field

ABSTRA C T We present a study of the angular correlation function as measured in the William Herschel Deep Field, a high galactic latitude field which has been the subject of an extensive observing campaign from optical to infrared wavelengths. It covers 50 arcmin 2 and with it we are able to investigate the scaling of the angular correlation function to B , 28; R; I , 26, K , 20 and H , 22:5: We compare our measurements to results obtained from the smaller Hubble Deep Field. To interpret our results, we use a model which correctly predicts colours, number counts and redshift distributions for the faint galaxy population. We find that at fixed separation the amplitude of v (u ) measured in BRI bandpasses is lower than the predictions of a model containing no luminosity evolution and stable clustering growth in proper coordinates. However, in the near-infrared bandpasses, our measurements are consistent with the predictions of an essentially non-evolving K-selected galaxy redshift distribution. In the range B , 27‐28 we find that our correlation amplitudes are independent of magnitude, which is consistent with the observed flattening of the number count slope and correspondingly slower increase of the cosmological volume element expected at these magnitudes. If our luminosity evolution models provide a correct description of the underlying redshift distributions (and comparisons to available observations at brighter magnitudes suggest they do), then our measurements in all bandpasses are consistent with a rapid growth of galaxy clustering O0 , e , 2 in the normal parametrization) on the sub-Mpc scales which our survey probes. We demonstrate that this rapid growth of clustering is consistent with the predictions of biased models of galaxy formation, which indicate that a rapid rate of clustering growth is expected for the intrinsically faint galaxies which dominate our survey.

The Near-Infrared Fundamental Plane of Elliptical Galaxies

We present results from a near-infrared K-band imaging survey of 59 elliptical galaxies in five nearby clusters. We measure photometric parameters for each galaxy using surface photometry and draw velocity dispersions from the literature. Three observables define a near-infrared fundamental plane (FP) of elliptical galaxies with Re ∝ σ1.44±0.04Σe−0.79±0.04. The scatter in the near-infrared relation is small at 16.5% in distance, which is equivalent to, or less than, the scatter of the optical FP. We suggest that the small deviation of the near-infrared FP relation from the optical FP is due to the reduction of metallicity effects in the near-infrared bandpass. While the small scatter of the optical FP could be consistent with compensating effects of age and metallicity, the similarly small scatter of the near-infrared FP is nearly independent of metallicity and hence places a strong constraint on possible age spreads among elliptical galaxies at every point along the FP. We suggest that the departure of the near-infrared FP from the pure virial form Re ∝ σ2Σe−1, and the corresponding observed relation (M/L) ∝ M0.16 ± 0.01, may be explained by slight systematic departures of the structure and dynamics of elliptical galaxies from a homology.