Mid-infrared Wavelengths Research Articles

Extremely Red Galaxies at z = 5–9 with MIRI and NIRSpec: Dusty Galaxies or Obscured Active Galactic Nuclei?

We study a new population of extremely red objects (EROs) recently discovered by the James Webb Space Telescope (JWST) based on their NIRCam colors F277W − F444W > 1.5 mag. We find 37 EROs in the Cosmic Evolution Early Release Science Survey (CEERS) field with F444W < 28 mag and photometric redshifts between 5 < z < 7, with median z=6.9−1.6+1.0 . Surprisingly, despite their red long-wavelength colors, these EROs have blue short-wavelength colors (F150W − F200W ∼ 0 mag) indicative of bimodal spectral energy distributions (SEDs) with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame UV. Moreover, all these EROs are unresolved, point-like sources in all NIRCam bands. We analyze the SEDs of eight of them with MIRI and NIRSpec observations using stellar population models and active galactic nucleus (AGN) templates. We find that dusty galaxies or obscured AGNs provide similarly good SED fits but different stellar properties: massive and dusty, logM⋆/M⊙ ∼ 10 and A V ≳ 3 mag, or low mass and obscured, logM⋆/M⊙ ∼ 7.5 and A V ∼ 0 mag, hosting an obscured quasi-stellar object (QSO). SED modeling does not favor either scenario, but their unresolved sizes are more suggestive of AGNs. If any EROs are confirmed to have logM⋆/M⊙ ≳ 10.5, it would increase the pre-JWST number density at z > 7 by up to a factor ∼60. Similarly, if they are QSOs with luminosities in the L bol > 1045–46 erg s−1 range, their number would exceed that of bright blue QSOs by more than three orders of magnitude. Additional photometry at mid-infrared wavelengths will reveal the true nature of the red continuum emission in these EROs and will place this puzzling population in the right context of galaxy evolution.

Transition from anisotropic to isotropic optical absorption in core-shell square nanowires tuned by anti-crossing engineering.

The transition from anisotropic to isotropic optical properties in nanostructures plays an important role in developing next-generation intelligent photonic devices. Currently, core-shell nanostructures, frequently accompanied by different growth rates, are typically characterized by anisotropic optical properties at mid-infrared wavelengths. This inherent anisotropy, however, poses formidable challenges in achieving optical isotropy. In this work, an electric field is employed to transform the optical anisotropy of the off-centered core-shell square nanowires into optical isotropy. Based on the finite difference method, the results show that by tuning the electric field reasonably, the anti-crossing behavior of energy levels can be induced to align the energy structures in both eccentric and concentric nanowires. Although the optical anisotropy is strongly dependent on the distance and direction of the core shift, we marks, to the best of our knowledge, the first demonstration that the restored electronic states can effectively neutralize the polarization sensitivity, achieving isotropic optical absorption with wavelengths longer than 10 μm. Our finding indicates that the anti-crossing behavior of energy levels can serve as a viable mechanism to achieve switchable optical isotropy.

On the plasmonic properties of a graphene nanoribbon and noble metal composite array

Graphene, composed of sp2 hybrid orbitals, is a hexagonal nanomaterial with a two-dimensional honeycomb lattice structure. Nowadays, thanks to its great electronic, optical, and thermal properties, there have been many promising applications based on graphene nanostructures. Under irradiations of external electromagnetic fields, the free electrons on graphene surfaces can be excited to oscillate collectively, resulting in highly localized surface plasmons. This phenomenon may provide foundations for designs of tunable plasmonic devices, therefore, graphene-based nanostructures have been widely studied so far. Besides, investigations on noble metals is another hot topic in the plasmonic community. With irradiations of incident lights, collective oscillations of free electrons on noble metals’ surfaces can also be induced, forming surface plasmons. The plasmonic characteristics can be adjusted by varying the parameters of the metals, including the geometries, thicknesses, as well as dimensions, etc. In this paper, a composite array consisting of graphene nanoribbons and noble metals is proposed, and its plasmonic properties are studied at mid-infrared wavelengths. In the structure, graphene nanoribbons are placed in between two SiO2 layers, and gold semi-cylinders and silver nanofilms are placed above the upper SiO2 layer, respectively. Using the finite difference time domain method, the light transmittance and electric field of the array are investigated, by varying the graphene’s Fermi energy and layer number, the noble metals’ sizes, as well as the period of the array, respectively. The results show that a plasmonic resonance feature is revealed in the 4–18 μm wavelength range, and the resonance characteristics can be tuned by adjusting the above parameters. The composite array structure proposed in this work may provide us with a new platform for the design of plasmonic devices in the mid-infrared regime.

Short review and prospective: chalcogenide glass mid-infrared fibre lasers

Rare-earth ion doped, silica glass, optical fibre amplifiers have transformed the world by enabling high speed communications and the Internet. Fibre lasers, based on rare-earth ion doped silica glass optical fibres, achieve high optical powers and are exploited in machining, sensing and medical surgery. However, the chemical structure of silica glass fibres limits the wavelength of laser operation to < 2.5 µm, which excludes the mid-infrared longer wavelength range of 3–50 µm. Rare-earth ion doping of fluoride glasses enables manufacture of fibre lasers up to a limiting 3.92 µm wavelength, but the fluoride glass chemical structure again prevents operation at longer wavelengths. Optical fibre lasers that are constructed from different rare-earth ion doped chalcogenide glass fibres will potentially operate across the 4–10 µm wavelength range, where suitable high-power lasers currently do not exist. We present a short review here of our recent work in achieving first time, continuous wave, mid-infrared fibre lasing beyond 5 μm wavelength in Ce3+-doped selenide chalcogenide fibre. We place this disruptive breakthrough into the wider fibre laser context, and also present the unprecedented advances in new cross-sector applications that will be enabled by mid-infrared fibre lasers in the 4–10 µm wavelength range. To surpass the few mW power output of the Ce3+-doped chalcogenide glass fibre lasing achieved to date, the glass quality of the doped chalcogenide fibres must now be improved, similar to the challenges originally facing the first glass fibre lasers based on silica.

Strain-tuned optical properties of bilayer silicon at midinfrared wavelengths

Optical properties of two-dimensional bilayer silicon have been explored at midinfrared wavelengths using density functional theory. In this work, progressive atomic structural deformation and the resultant variations in the optical properties of the bilayer silicon films were investigated under external in-plane strain. A phase transformation of the atomic structure has been observed at an applied in-plane tensile strain of 5.17%, at which the atomic lattice is changed from a low buckled to a buckle-free honeycomb structure. Evaluations of the optical properties were carried out by taking into account the inter- and intraband transitions. An abrupt change in the optical refraction index was observed at the phase transition. In addition, the buckle-free honeycomb structure presents a strain-resistive absorption edge pinned at 1.14 μm wavelength. Exceeding a strain threshold of 12.26% results in the development of both direct- and indirect-energy bandgap openings. The direct bandgap induced interband optical transitions, resulting in absorption peaks at midinfrared wavelengths and a drastic increase in the refraction index. Moreover, by adjusting the strain, the optical absorptions can be tuned in a wide range of wavelength at midinfrared from 1.5 to 11.5 μm.

Far-infrared Luminosity Bursts Trace Mass Accretion onto Protostars

Evidence abounds that young stellar objects undergo luminous bursts of intense accretion that are short compared to the time it takes to form a star. It remains unclear how much these events contribute to the main-sequence masses of the stars. We demonstrate the power of time-series far-infrared (far-IR) photometry to answer this question compared to similar observations at shorter and longer wavelengths. We start with model spectral energy distributions that have been fit to 86 Class 0 protostars in the Orion molecular clouds. The protostars sample a broad range of envelope densities, cavity geometries, and viewing angles. We then increase the luminosity of each model by factors of 10, 50, and 100 and assess how these luminosity increases manifest in the form of flux increases over wavelength ranges of interest. We find that the fractional change in the far-IR luminosity during a burst more closely traces the change in the accretion rate than photometric diagnostics at mid-infrared and submillimeter wavelengths. We also show that observations at far-IR and longer wavelengths reliably track accretion changes without confusion from large, variable circumstellar and interstellar extinction that plague studies at shorter wavelengths. We close by discussing the ability of a proposed far-IR surveyor for the 2030s to enable improvements in our understanding of the role of accretion bursts in mass assembly.

Potentiation of a homeopathic medicine – Thuja – using mid-infrared rays

Clinical dose reduction is achieved through potentiation, which is the process used to manufacture homeopathic medicine with varying potencies. In this study, we used 2–6 µm mid-infrared wavelength radiation to further amplify commercially available homeopathic medicines, such as thuja (Thuja occidentalis), a medication frequently used for a variety of ailments. We invented an emitter called MIRGA (mid-infrared generating atomizer) for potentiation purpose. The benefits of mid-IR potentiation include a reduction of the clinical dose, host stress, and resource and cost savings. The effects of irradiation on Thuja in chemical bond alterations and configurations are proven here by scientific instrumentations.

Simulational investigation of self-aligned bilayer linear grating enabling highly enhanced responsivity of MWIR InAs/GaSb type-II superlattice (T2SL) photodetector

Linear gratings polarizers provide remarkable potential to customize the polarization properties and tailor device functionality via dimensional tuning of configurations. Here, we extensively investigate the polarization properties of single- and double-layer linear grating, mainly focusing on self-aligned bilayer linear grating (SABLG), serving as a wire grid polarizer in the mid-wavelength infrared (MWIR) region. Computational analyses revealed the polarization properties of SABLG, highlighting enhancement in TM transmission and reduction in TE transmission compared to single-layer linear gratings (SLG) due to optical cavity effects. As a result, the extinction ratio is enhanced by approximately 2724-fold in wavelength 3–6 μm. Furthermore, integrating the specially designed SABLG with an MWIR InAs/GaSb Type-II Superlattice (T2SL) photodetector yields a significantly enhanced spectral responsivity. The TM-spectral responsivity of SABLG is enhanced by around twofold than the bare device. The simulation methodology and analytical analysis presented herein provide a versatile route for designing optimized polarimetric structures integrated into infrared imaging devices, offering superior capabilities to resolve linear polarization signatures.

Corrosion-resistant antireflective coatings on ZnS for short- to mid-wavelength IR outer window applications

Corrosion-resistant antireflective coatings on ZnS for short- to mid-wavelength IR outer window applications

Optical properties of particle dispersed coatings with gradient distribution.

Particle dispersed coatings with gradient distributions, resulting from either gravity or artificial control, are frequently encountered in practical applications. However, most current studies investigating the optical properties of coatings use the uniform model (uniform single layer assumption), overlooking the gradient distribution effects. Given the pervasiveness of gradient distributions and the widespread use of the uniform model, it is imperative to evaluate applicability conditions of the uniform model in practical applications. In this work, we comprehensively investigate the quantitative performance of the uniform model in predicting the infrared optical properties of coatings with gradient distributions of particle volume fraction using the superposition T-matrix method. The results show that the gradient distribution of particle volume fraction has a limited impact on the emissivity properties of T i O 2-PDMS coatings in the midwavelength-infrared (MWIR) and long-wavelength-infrared (LWIR) bands, which validates the uniform model for the gradient coatings with weakly scattering dielectric particles. However, the uniform model can yield significant inaccuracies in estimating the emissivity properties of Al-PDMS coatings with gradient distributions in the MWIR and LWIR bands. To accurately estimate the emissivity of such gradient coatings with the scattering metallic particles, meticulous modeling of the particle volume fraction distribution is essential.

Theoretical design of uncooled mid-infrared PbSe P+pBn+ barrier detectors

A novel uncooled mid-wavelength infrared (MWIR) P+pBn+ barrier detector based on epitaxial PbSe absorber layer on Ge substrate is theoretically investigated by finite element analysis in order to achieve optimal detection performance. The simulated results show that the P+pBn+ barrier architecture can further effectively reduce the room-temperature dark current to 4.45 mA cm−2 under −0.1 V bias, which is 12 times lower than a PbSe pBn+ unipolar barrier device in a previous study. Moreover, the P+pBn+ barrier architecture exhibits excellent responsivity and detectivity of 1.83 A W −1 and 3.23 × 1010 cm Hz1/2 W−1 at 3.8 μm, respectively. These results suggest that this P+pBn+ barrier detector based on natural MBE epitaxy technology could have potential in the emerging high-sensitivity and high-detectivity uncooled MWIR applications.

Enhanced transmission capacity through a specialty multi-channel topological optical fiber

We propose a multi-channel specialty topological fiber based on 1D periodic geometry which supports three coexisting and non-interacting topologically-protected robust light states in the mid-infrared wavelength range. Each channel comprises two topologically-distinct 1D periodic lattices that are characterized by the topological invariant, Zak phase. The interface between the trivial and the nontrivial lattices is made unconventional to provide a strong transverse confinement of the light state. Moreover, the observed multiple interface states exhibit robust simultaneous transmission of light through all the channels keeping in contact with each other with an inter-channel cross-talk of ∼−27 dB. Such highly stable, scatter-free, and robust interface states have the potential to increase the transmission capacity of the existing optical communication channels, and can eventually be utilized as an alternative platform via the space-division multiplexing schemes.

Modelling the day–night temperature variations of ultra-hot Jupiters: confronting non-grey general circulation models and observations

ABSTRACT Ultra-hot Jupiters (UHJs) are natural laboratories to study extreme physics in planetary atmospheres and their rich observational data sets are yet to be confronted with models with varying complexities at a population level. In this work, we update the general circulation model of Tan &amp; Komacek (2019) to include a non-grey radiative transfer scheme and apply it to simulate the realistic thermal structures, phase-dependent spectra, and wavelength-dependent phase curves of UHJs. We performed grids of models over a large range of equilibrium temperatures and rotation periods for varying assumptions, showing that the fractional day–night brightness temperature differences remain almost constant or slightly increase with increasing equilibrium temperature from the visible to mid-infrared wavelengths. This differs from previous work primarily due to the increasing planetary rotation rate with increasing equilibrium temperature for fixed host star type. Radiative effects of varying atmospheric compositions become more significant in dayside brightness temperature in longer wavelengths. Data-model comparisons of dayside brightness temperatures and phase-curve amplitudes as a function of equilibrium temperature are in broad agreement. Observations show a large scatter compared to models even with a range of different assumptions, indicating significantly varying intrinsic properties in the hot Jupiter population. Our cloud-free models generally struggle to match all observations for individual targets with a single set of parameter choices, indicating the need for extra processes for understanding the heat transport of UHJs.

Giant optical absorption of a PtSe2-on-silicon waveguide in mid-infrared wavelengths.

Low-dimensional platinum diselenide (PtSe2) is a promising candidate for high-performance optoelectronics in the short-wavelength mid-infrared band due to its high carrier mobility, excellent stability, and tunable bandgap. However, light usually interacts moderately with low-dimensional PtSe2, limiting the optoelectronic responses of PtSe2-based devices. Here we demonstrated a giant optical absorption of a PtSe2-on-silicon waveguide by integrating a ten-layer PtSe2 film on an ultra-thin silicon waveguide. The weak mode confinement in the ultra-thin waveguide dramatically increases the waveguide mode overlap with the PtSe2 film. Our experimental results show that the absorption coefficient of the PtSe2-on-silicon waveguide is in the range of 0.0648 dB μm-1 to 0.0704 dB μm-1 in a spectral region of 2200 nm to 2300 nm wavelengths. Furthermore, we also studied the optical absorption in an ultra-thin silicon microring resonator. Our study provides a promising approach to developing PtSe2-on-silicon hybrid optoelectronic integrated circuits.

Wood waste-derived dual-mode materials paving the way for year-round energy saving in buildings.

In the face of the challenges posed by global warming, traditional methods of building heating and cooling contribute significantly to electricity and coal consumption, thereby emitting considerable amounts of greenhouse gases. Here, a dual-mode thermal management structural material is created by processing sustainable cellulose and lignin derived from wood waste into gels, followed by lamination. The cellulose surface of the material exhibits the ability to scatter solar radiation backward while emitting strongly in the mid-infrared wavelengths, whereas the lignin surface absorbs visible and near-infrared light, primarily releasing energy through non-radiative transitions. Consequently, the material can achieve sub-ambient radiative cooling of 6 °C and solar heating of 27.5 °C during the daytime by simply flipping its orientation. This pioneering material showcases the potential to significantly reduce cooling energy consumption by an average of 18% and heating energy consumption by 42%. Moreover, the integration of a thermal-electric generator within the dual-layer structure optimally utilizes the temperature differential between the two layers, converting it into electrical power. Notably, the dual-mode thermal management structural material exhibits impressive mechanical strength, boasting a flexural strength of 102 MPa, surpassing that of natural wood by over 4.8 times. With its dual-mode functionality and embedded thermal-electric generator, this material represents a crucial step towards achieving both thermal comfort and energy autonomy in sustainable building practices, thereby contributing to a more environmentally friendly and efficient future.

Ultrabroadband nonlinear enhancement of mid-infrared frequency upconversion in hyperbolic metamaterials.

Metamaterials have demonstrated significant potential for enhancing nonlinear processes at the nanoscale. The presence of narrowband hot-spots and highly inhomogeneous mode-field distributions often limit the enhancement of nonlinear interactions over larger spatial scales. This has posed a formidable challenge in achieving simultaneous enhancement across a broadband spectral range, significantly constraining the potential of photonic nanostructures in enhancing nonlinear frequency conversion. Here, we propose a broadband resonant mode matching method through near-field examinations that supports the multipole modes and enables the development of an ultrabroadband-enhanced 3-5 μm mid-infrared frequency upconversion technique utilizing a hyperbolic triangular pyramidal metasurface. The gap-plasma mode of the hyperbolic metamaterial multilayer system excites narrowly high-order resonances at near-infrared pump light wavelengths, while the slow-light effect generated by the dipoles achieves ultrabroadband near-field enhancement at mid-infrared wavelengths. The symmetry breaking of the triangular structure localizes these resonant modes at the tips, enabling mode-matched modulation at different wavelengths, and thus boosting the nonlinear frequency conversion process. Our approach provides a promising platform for metasurface-based frequency conversion techniques.

Initial Results of our Spectro-photometric Monitoring of XZ Tau

We present here initial results of our spectro-photometric monitoring of XZ Tau. During our monitoring period, XZ Tau exhibited several episodes of brightness variations in timescales of months at optical wavelengths in contrast to the mid-infrared wavelengths. The color evolution of XZ Tau during this period suggests that the brightness variations are driven by changes in accretion from the disc. The mid-infrared light curve shows an overall decline in brightness by ∼ 0.5 and 0.7 magnitude respectively in WISE W1 (3.4 μm) and W2 (4.6 μm) bands. The emission profile of the hydrogen recombination lines along with that of Ca II IRT lines points towards magnetospheric accretion of XZ Tau. We have detected P Cygni profile in Hβ indicating of out-flowing winds from regions close to accretion. Forbidden transitions of oxygen are also detected, likely indicating jets originating around the central pre-main sequence star.

High verticality vapor-liquid-solid growth of GaAs0.99Bi0.01 nanowires using Ga-Bi assisted catalytic droplets.

GaAsBi nanowires (NWs) are promising for optoelectronic applications in the near- and mid-infrared wavelengths due to the optical properties of the Bi-containing compound and the nanowire structure benefits. In general, synthesizing the GaAsBi NWs results in uncontrollable metamorphic structures and spontaneous Bi-containing droplets. Here, we explore the potential of using the droplets as catalysts to form GaAsBi nanowires (hence, the vapor-liquid-solid growth mechanism) on GaAs (111) substrates by molecular beam epitaxy. The GaAsBi NWs experience a two-step growth: Bi droplet deposition and GaAsBi nanowire growth. The optimal droplet deposition temperature (250 °C) is defined based on the droplet morphologies. The gradation of growth temperatures of GaAsBi NWs to 250 °C, 300 °C, and 350 °C results in high-aspect-ratio NWs, tilted NWs, and low-aspect-ratio NWs, respectively. Structural investigation shows that the optimal (low-aspect-ratio) NW has the composition of GaAs0.99Bi0.01 with the catalytic droplet of Ga0.99Bi0.01 decorated on its tip. Detailed structural analyses show that the Bi content progressively increases from the NW stem to the wire-substrate interface. The satisfying GaAsBi NW morphology does not warrant the expected superior optical results. Photoluminescence study suggests that the NW has a strong carrier thermalization from the NW stem to the wire-substrate interface influenced by the graded NW growth temperature profile.

Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

Nebular-phase observations of peculiar Type Ia supernovae (SNe Ia) provide important constraints on progenitor scenarios and explosion dynamics for both these rare SNe and the more common, cosmologically useful SNe Ia. We present observations from an extensive ground- and space-based follow-up campaign to characterize SN 2022pul, a super-Chandrasekhar mass SN Ia (alternatively “03fg-like” SN), from before peak brightness to well into the nebular phase across optical to mid-infrared (MIR) wavelengths. The early rise of the light curve is atypical, exhibiting two distinct components, consistent with SN Ia ejecta interacting with dense carbon–oxygen (C/O)-rich circumstellar material (CSM). In the optical, SN 2022pul is most similar to SN 2012dn, having a low estimated peak luminosity (M B = −18.9 mag) and high photospheric velocity relative to other 03fg-like SNe. In the nebular phase, SN 2022pul adds to the increasing diversity of the 03fg-like subclass. From 168 to 336 days after peak B-band brightness, SN 2022pul exhibits asymmetric and narrow emission from [O i] λ λ6300, 6364 (FWHM ≈ 2000 km s−1), strong, broad emission from [Ca ii] λ λ7291, 7323 (FWHM ≈ 7300 km s−1), and a rapid Fe iii to Fe ii ionization change. Finally, we present the first ever optical-to-MIR nebular spectrum of an 03fg-like SN Ia using data from JWST. In the MIR, strong lines of neon and argon, weak emission from stable nickel, and strong thermal dust emission (with T ≈ 500 K), combined with prominent [O i] in the optical, suggest that SN 2022pul was produced by a white dwarf merger within C/O-rich CSM.

High-resolution, Mid-infrared Color Temperature Mapping of the Central 10″ of the Galaxy

The neighborhood of the Galactic black hole boasts a plethora of extended interstellar gas and dust features, as well as populations of compact (unresolved or marginally resolved) features such as the G objects. Most are well manifested in the infrared. To disentangle and characterize the infrared structure of the extended features and identify compact sources, we used 3.8 μm (L′ filter) data from the NIRC2 imager at the Keck Observatory and 8.6 μm (PAH1 filter) data from the VISIR imager at the Very Large Telescope to produce the highest-resolution mid-IR color temperature map of the inner half-parsec of the Galactic center to date. From this map, we compile a catalog of features that stand out from their background. In particular, we identify 33 compact sources that stand out against the local background temperature, 11 of which are newly identified and candidates for being members of the G object population. Additionally, we resolve and newly characterize the morphology of several known extended features. These results prepare the way for ongoing and future JWST studies that have access to a greater range of mid-infrared wavelengths and thus will allow for refined estimation of the trends of dust temperatures.