Mid-infrared Band Research Articles

Mid-infrared broadband metamaterial absorber based on van der Waals material

Van der Waals materials, such as α-phase molybdenum trioxide (α-MoO3), have promising prospects in modern optics technologies, such as nano-imaging, negative refraction, and infrared detection. Particularly, the natural hyperbolic properties of α-MoO3 make it an excellent candidate for perfect absorber. Here, we propose a design method for achieving broadband absorption based on van der Waals material (α-MoO3) in the mid-infrared band. The segmented cubic Hermite interpolation is used to generate various geometric structures. Numerical results show that the average spectral absorptance of the optimized structure is up to 0.993 in the wavelength range of 10.4–12.7 μm. The high absorption performance can be explained as the slow-light effect. The impact of incident angle on absorption performance is also investigated. Finally, we calculate the spectral absorptance of the proposed absorber when the crystal axes of α-MoO3 are rotated in the x-y plane. Our findings pave a novel path for designing broadband absorbers based on van der Waals materials, particularly in the mid-infrared band.

Transient nonlinear dynamics in an electrically modulated quantum cascade laser with optical injection

Based on rate equations, we mainly simulate the transient instability characteristics of an 8 µm quantum cascade laser (QCL) subject to optical injection with alternating current (AC) electrical modulation. Simulation results show that the period-one oscillation of the optical injection-locked QCL is broken by applying an AC current to the direct current (DC) bias. Combining an external optical injection and induced period current modulation can cause period-one oscillation dropouts and can display chaotic states outside the stable locking region, owing to the cooperative interplay between the AC frequency and the periodic oscillation frequency caused by the optical injection. To give a clear physical picture of the chaos under different line-width enhancement factors (LEFs), we use temporal series, Poincaré bifurcation diagrams, Fourier spectra, phase portraits, and first return maps to carefully analyze. These analytical methods are effective for the dynamical behaviors of QCLs with low LEFs, which show that the chaos of QCLs strongly rely on external modulation compared with class-B laser systems. This work paves a new way for realizing chaotic signal generation and has an important application in secure communication in the mid-infrared and terahertz frequency band.

A search for tryptophan in the gas of the IC 348 star cluster of the Perseus molecular cloud

ABSTRACT We have used spectra of the Spitzer Space Telescope to conduct a search for the aromatic amino acid tryptophan in the interstellar gas of the young star cluster IC 348. For all the strongest mid-infrared (mid-IR) laboratory bands of tryptophan, we have found counterpart emission lines in the observed spectrum which are consistent in wavelength and strength with the laboratory measurements. Assuming that the detected emission lines are due to tryptophan and using the measured fluxes, we estimate a tryptophan column density in the line of sight of the core of IC 348 in the range 109–1011 cm−2. The observed emission lines are also found in the combined spectrum of >30 interstellar locations obtained in diverse unrelated star-forming regions observed by Spitzer. This could be an indication that the molecule causing the emission is widespread in interstellar space. Future high spectral resolution mid-IR searches for proteinogenic amino acids in protostars, protoplanetary discs, and in the interstellar medium will be key to study an exogenous origin of meteoritic amino acids and to understand how the pre-biotic conditions for life were set in the early Earth.

Reconfigurable mechano-responsive soft film for adaptive visible and infrared dual-band camouflage.

Learning from nature in terms of the camouflage used by species has enabled the continuous development of camouflage technologies for the visible to mid-infrared bands to prevent objects from being detected by sophisticated multispectral detectors, thereby avoiding potential threats. However, achieving visible and infrared dual-band camouflage without destructive interference while also realizing rapidly responsive adaptivity to the varying background remains challenging for high-demand camouflage systems. Here, we report a reconfigurable mechano-responsive soft film for dual-band camouflage. Its modulation ranges for visible transmittance and longwave infrared emittance can be up to 66.3% and 21%, respectively. Rigorous optical simulations are performed to elucidate the modulation mechanism of dual-band camouflage and identify the optimal wrinkles required to achieve the goal. The broadband modulation capability (figure of merit) of the camouflage film can be as high as 2.91. Other advantages, such as simple fabrication and a fast response, make this film a potential candidate for dual-band camouflage that can adapt to diverse environments.

Strong nonreciprocal thermal radiation based on topological edge state in one-dimensional photonic crystal with Weyl semimetal

Kirchhoff's law is the theoretical basis for characterizing thermal radiation. The construction of nonreciprocal thermal radiation needs to violate Kirchhoff's law, in which its existing methods usually utilize the magneto-optical effect with an external magnetic field. However, natural materials' relatively weak magneto-optical response in the thermal wavelength range requires a strong or moderate magnetic field. Fortunately, the unique topologically nontrivial electronic state and inherent time-reversal symmetry breaking of Weyl semimetals can exhibit highly unusual and extremely large gyrotropic optical responses in the mid-infrared band without an external magnetic field, which provides a new way to violate Kirchhoff's law. This work theoretically investigates the nonreciprocity of a multilayer structure in which a Weyl semimetal is embedded in two one-dimensional photonic crystals. The results show that the absorptivity and emissivity of the structure almost completely violate Kirchhoff's law over a broad range of angles (7° ∼ 51°) and frequencies (56.4 THz ∼ 65.3 THz) without any external magnetic field. We also discuss the effects of the incident angle, the axial vector of the Weyl semimetal, and the thickness of the Weyl semimetal on the characteristics of nonreciprocal thermal radiation. Furthermore, the electric field distribution reveals that the structurally excited topological edge states significantly enhance the local electric field in the vicinity of the Weyl semimetal, providing positive conditions for the realization of perfect strong nonreciprocal thermal radiation. We hope this work may contribute to the design of strong nonreciprocal thermal emitters.

Polychromatic full-polarization control in mid-infrared light

Objects with different shapes, materials and temperatures can emit distinct polarizations and spectral information in mid-infrared band, which provides a unique signature in the transparent window for object identification. However, the crosstalk among various polarization and wavelength channels prevents from accurate mid-infrared detections at high signal-to-noise ratio. Here, we report full-polarization metasurfaces to break the inherent eigen-polarization constraint over the wavelengths in mid-infrared. This recipe enables to select arbitrary orthogonal polarization basis at individual wavelength independently, therefore alleviating the crosstalk and efficiency degradation. A six-channel all-silicon metasurface is specifically presented to project focused mid-infrared light to distinct positions at three wavelengths, each with a pair of arbitrarily chosen orthogonal polarizations. An isolation ratio of 117 between neighboring polarization channels is experimentally recorded, exhibiting detection sensitivity one order of magnitude higher than existing infrared detectors. Remarkably, the high aspect ratio ~30 of our meta-structures manufactured by deep silicon etching technology at temperature −150 °C guarantees the large and precise phase dispersion control over a broadband from 3 to 4.5 μm. We believe our results would benefit the noise-immune mid-infrared detections in remote sensing and space-to-ground communications.

The Design, Verification, and Performance of the James Webb Space Telescope

The James Webb Space Telescope (JWST) is NASA’s flagship mission successor to the highly successful Hubble Space Telescope. It is an infrared observatory featuring a cryogenic 6.6 m aperture, deployable Optical Telescope Element (OTE) with a payload of four science instruments (SIs) assembled into an Integrated Science Instrument Module (ISIM) that provide imagery and spectroscopy in the near-infrared band between 0.6 and 5 μm and in the mid-infrared band between 5 and 28.1 μm. JWST was successfully launched on 2021 December 25 aboard an Ariane 5 launch vehicle. All 50 major deployments were successfully completed on 2022 January 8. The observatory performed all midcourse correction maneuvers and achieved its operational mission orbit around the Sun–Earth second Lagrange point (L2). All commissioning and calibration activities have been completed, and JWST has begun its science mission. This paper will provide a description of the driving requirements and their technical challenges, the engineering processes involved in the design formulation, the resulting observatory design, the verification programs that proved it to be flightworthy, and the measured on-orbit performance of the observatory. Since companion papers will describe the details of the OTE and SIs, this paper will concentrate on describing the key features of the observatory architecture that accommodates these elements, particularly those features and capabilities associated with accommodating the radiometric and image-quality performance.

High birefringence single-polarization composite structured anti-resonant fiber

We propose a highly birefringent, single-polarization composite structured anti-resonant fiber (CS-ARF). The proposed CS-ARF has an elliptical core, two symmetrically spaced arrays of elliptical air holes, and a six-tube anti-resonant structure. The birefringence and single-polarization characteristics of the proposed CS-ARF were analyzed in detail in the mid-infrared band using the finite element analysis method. The results show that the fiber can achieve birefringence up to the order of 10−2 and single-polarization transmission with a confinement loss (CL) below 10−5 dB/m in the mid-infrared band. When the refractive index of the elliptical core is set at na = 2.70, the designed CS-ARF maintains single polarization in the range of 2.5 μm to 3.197 μm with an extinction ratio of up to 1.08 × 107. In addition, we found that by setting the refractive index of the elliptical core, the CL in the y-polarization direction can be effectively adjusted.

Enhancement of Intrinsic Temperature Reduction for Plasma Surface-Modified Nanoparticle-Doped Low-Density Polyethylene Films

The cooling performance of nanoparticle (NP)-doped radiative cooling materials depends on the dispersion of the NPs in the polymer matrix. However, it is a technical challenge to suppress agglomeration of NPs due to their high surface energy, resulting in poor dispersion of the NPs in the polymer matrix. In order to optimize the dispersion of zinc oxide (ZnO) NPs in low-density polyethylene (LDPE), NPs were treated with atmospheric pressure plasmas for 30, 60 and 90 s. The ZnO NPs were dispersed in LDPE using a xylene solution method. The dispersion of the NPs was progressively improved as the plasma-treatment time increased, likely due to the roughened and perhaps also activated NP surfaces by the plasma treatment. This made the transmittances of the films decrease in the solar-radiation band and absorptivity increased monotonically in the high-energy band as the plasma-treatment time increased, while in the mid-infrared band, the films maintained a similar high transmittance to the untreated sample. The differential scanning colorimetry analysis revealed that the crystallinities of the plasma-treated NP-doped samples were similar to those of the untreated sample. The cooling-performance tests showed that the maximum temperature reductions of the films with NP plasma-treated for 0 s, 30 s, 60 s and 90 s were 6.82, 7.90, 9.34 and 10.34 °C, respectively, corresponded to the intrinsic temperature reductions of 7.27, 8.23, 10.54, and 11.40 °C, respectively, when calculated using Cui’s Model. The results of the current study show that a simple one-step atmospheric pressure plasma treatment to the ZnO NPs can indeed improve dispersion of the NPs in LDPE and lead to the greatly improved passive-cooling performance of the film.

Graphitic carbon nitride modulated short pulse generation in an Erbium-doped fiber laser

In the present study, a few layered graphitic carbon nitrides (g-C3N4) nano-sheets were successfully manufactured by the calcination method. It demonstrates nonlinear optical (NLO) property with modulation depths of ∼4.26% at 1.5 μ m. The index-matching gel adhesion effect was used to place the g-C3N4 nano-sheets on the fiber ferrule surface to produce short-pulsed lasers. The g-C3N4 saturable absorber (SA) based Q-switched erbium-doped fiber laser (EDFL) emits at 1560.5 nm wavelength with 1.2 nm of spectral bandwidth at 3 dB. The radio frequency's signal-to-noise ratio (SNR) is 42 dB at first harmonic, demonstrating excellent pulse stability. As the pump power increases, the frequency increases from 27.2 to 108 kHz, and the pulse shortens from 14.6 to 4.2 μ s, correspondingly. The highest pulse energy, peak power, and average output power are measured to be 48.7 nJ, 11 mW, and 5.18 mW at the highest pump power of 479.1 mW. Besides, the morphology and structure of g-C3N4 were characterized by scanning electron microscopy (SEM) and X-rays powder diffraction (XRD), photoluminescence (PL) spectra, Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and UV- diffuse reflectance spectroscopy (DRS) have been also presented. Additionally, the stability of g–C3N4–SA was also measured. These findings suggest that few layered g-C3N4 nano-sheets have a substantial role as a SA in optical modulation devices and nonlinear optical properties at the near and mid-infrared band.

A Simulation-Based Study of Back-Illuminated Lateral Ge/GeSn/Ge Photodetectors on Si Platform for Mid-Infrared Image Sensing

GeSn/Ge heterojunction photodetectors (PDs) have great potential to outperform conventional mid-infrared (MIR) sensors. In this work, simulated analysis is performed to demonstrate the back-illuminated lateral double <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{Ge/}{\text{Ge}}_{\text{0.90}}{\text{Sn}}_{\text{0.10}}\text{/Ge}$</tex-math> </inline-formula> heterojunctions p-i-n PDs for MIR imaging. This lateral PDs configuration is compatible with current complementary metal–oxide–semiconductor (CMOS) technology, yielding reduced fabrication complexity and offering high resonance in optical characteristics (between 2000-and 2700-nm wavelength range), viable for high-performance operation in MIR wavelength bands. This work also investigates the effects of high-density point dislocation at GeSn/Ge heterointerface on various performance metrics, including dark current, photocurrents, detectivity, and noise-equivalent-power (NEP) of PDs. The results indicate that the defects have less impact on detectivity and NEP and have negligible impact on the collection of photogenerated carriers and thus responsivity. The device shows a maximum 3-dB optoelectrical bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 92.4 GHz, which is among the highest of other GeSn p-i-n PDs. In addition, even in the presence of defects, the device achieves high responsivity in MIR bands and its values are 0.39, 1.45, and 0.25 A/W at the operating wavelengths of 2000, 2310, and 2700 nm, respectively. Thus, the proposed work can be a major step toward GeSn-based PDs on the Si platform for MIR imaging applications.

Dual-Comb Gas Sensor Integrated with a Neural Network-Based Spectral Decoupling Algorithm of Overlapped Spectra for Gas Mixture Sensing.

Cross-interference among absorptions severely affects the ability to achieve accurate gas concentration retrieval through gas molecular specificity. In this study, a novel dual gas sensor was proposed to separate methane and water absorbance from the blended spectra of their mixture in the mid-infrared (MIR) band by employing a neural network algorithm. To address the scarcity of experimental data, the neural network was trained over a simulated data set constructed with the same distribution as the experimental ones. The system takes advantages of the broadband spectra to provide high-quality comb data and allows the neural network to establish an accurate spectral decoupling function. In addition, a feature absorption peak screening mechanism was proposed to achieve more accurate concentration retrieval, which avoids the prediction error introduced by interrogating the only peak of the separated spectra. The promising results of the systematic evaluation have demonstrated the feasibility of our methods in practical detections.

Facile "Synergistic Inner-Outer Activation" Strategy for Nano-Engineering of Nature-Skin-Derived Wearable Daytime Radiation Cooling Materials.

Natural skin-derived products, as traditional wearable materials are widely used in people's daily life due to the products' excellent origins. Herein, a versatile daytime-radiation cooling wearable natural skin (RC-skin) consisting of the collagen micro-nano fibers with the on-demand double-layer radiation cooling structure is nano-engineered through the proposed facile "synergistic inner-outer activation" strategy. The bottom layer (inner strategy) of the RC-skin is fabricated by filling the skin with the Mg11 (HPO3 )8 (OH)6 nanoparticles by soaking. The superstratum (outer strategy) is constituted by a composite coating with an irregular microporous structure. The RC-skin harvests the inherent advantages of natural building blocks including sufficient hydrophobicity, excellent mechanical properties, and friction resistance. Owing to the subtle double-layer structure design, the solar reflectance and the average emissivity in the mid-infrared band of RC-skin are ≈92.7% and ≈95%, respectively. Therefore, the RC-skin's temperature in the sub-ambient is reduced by ≈7.5°C. Various outdoor practical application experiments further substantiate that RC-skin has superior radiation cooling performances. Collectively, RC-skin has broad-application prospects for intelligent wearing, low-carbon travel, building materials, and intelligent thermoelectric power generation, and this study also provides novel strategies for developing natural-skin-derived functional materials.

Broad band solar cell absorber based on double-ring coupled disk resonator structure: from visible to mid infrared

In this paper, a broad band absorber based on a double-ring coupled disk resonator periodic structure, which can work in the visible and mid infrared range, is proposed and investigated. Results show the absorbance is large than 92.4% in the range of 300 nm–4096 nm, and the average absorption is about 97.4% from the visible to mid-infrared bands. Besides, the proposed absorber is wide angle acceptance, background refractive index (RI), and polarization state insensitive. The absorption mechanisms are analyzed and found that it mainly originated from the dielectric lossy property in short-wavelength and gap plasmonic resonances in long-wavelength. It is believed the proposed absorber can find potential applications in the fields of solar cell devices, thermal emitters, and plasmonic imaging.

A study of structural effect on the spectral property of metallic cross-hole array in mid-infrared wavelengths

Based on the earlier success in developing multichannel detection in long (8–14 μm) infrared wavelengths, this paper reports our recent progress for spectral filters in the mid-infrared band of 4–10 μm by introducing a new design with metallic cross annular hole array. The effects of structural dimensions on filtering performance were investigated by numerical simulations with the finite-difference time-domain method and experimentally verified by optical characterizations of fabricated filters made by electron beam lithography. The transmission peaks were optimized with the maximum transmittance of 62%. The existing problem of low spectral resolution of transmittances was tackled by using a thick Au film for the filter, which remains a big challenge for conventional electron beam lithography. By modeling ice lithography in amorphous solid water for constructing the filter, it was found that ice lithography certainly possesses significant advantage in replicating nanoscale features with high aspect ratio. The proposed ice lithography in this work provides an effective solution for the nanofabrication of high performance filters with dense elements in an array in the mid-infrared wavelengths.

An ultra-wideband bandstop plasmonic filter in mid-infrared band based on metal-insulator-metal waveguide coupled with an hexagonal resonator

An ultra-wideband band-stop plasmonic filter (UWB-BSF) in mid-infrared (MIR) range based on metal–insulator–metal (MIM) waveguide coupled with a hexagonal resonator is proposed in this work. Using RSoft CAD commercial software, the designed BSF is numerically and theoretically investigated by the 2D Finite-Difference Time-Domain method. To enhance the BSFs system in mid-infrared, obtaining ultra-wide bandgap width (UWB) with the maximum passband transmission at the left and right of the bandgap and a high value of the rectangular coefficient, we increase the number of hexagonal cavities. Hence, the number of hexagonal resonators controls the range of the filtered wavelength of the BSFs system. In the case of two hexagonal-shaped resonators, the Fano resonance appears on the left and right sides of the bandgap, forming a U-shaped transmission spectrum, which is very helpful for improving the performance of the band-stop filter. Furthermore, by changing the geometric parameters of the hexagonal cavities the filtered wavelength range is shifted toward the near-infrared (NIR) band. The center wavelength of the bandgap of the proposed nano-stop-band filter is adjustable by varying the geometric parameters of the structure. This device operates in the near-infrared (NIR) and mid-infrared (MIR) wavelength ranges. With a larger bandgap width and tunable performance, this proposed nanostructure provides an advantageous application for plasmonic integrated circuits and broadband transmissions.

Tunable multi-band absorbers based on graphene metasurfaces for infrared sensing and switching

In this paper, a kind of dynamically tunable graphene metasurface which can act as a multi-band refractive index sensor or a four-state optical switch is proposed. Based on the plasmonic hybridization mechanism of a simple graphene ring array, this design exhibits dual-channel resonance modes to realize ultrahigh sensitivity for refractive index sensing, which is 4.25μm/RIU at mid-infrared band and 11.33μm/RIU at far-infrared band, respectively. The proposed design manifests an ultrabroad sensing range through tuning the Fermi level of graphene and a good insensitivity to the incident angle. In addition, we numerically demonstrate a reflective optical switch with the structure of dual-layer graphene disks which indicates that a four-state optical switch is achieved and the cut-off absorptivity is more than 98%. The concise structures are of high feasibility for fabrication and the results illustrate considerable potential in various applications including graphene optics and integrated photonic systems.

Electromagnetic radiation focusing lens based on phase transition all-dielectric microstructure

Metasurface can adjust the polarization, amplitude, phase, polarization mode, and propagation mode of electromagnetic waves flexibly and efficiently. Based on Pancharatnam–Berry phase theory, an all-medium geometric phase element structure was proposed to construct a transmission-coded metasurface metalens. In the mid-infrared band, a phase change material (GST) is used to regulate the unit structure in order to achieve the tunability of lens focus. In order to prove that the designed hyperlens has a good focusing effect, we numerically simulate the focusing electromagnetic field distribution characteristics, and the results show that the designed geometric phase hyperlens has a good focusing effect. Using the crystal and amorphous states of phase change materials, we can dynamically control the focus of the superlens.

PHANGS–JWST First Results: A Combined HST and JWST Analysis of the Nuclear Star Cluster in NGC 628

We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r eff ∼ 5 pc) and ellipticity (ϵ ∼ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r eff ∼ 12 pc, ϵ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of , as derived through B − V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

Mid-IR Observations of IRAS, AKARI, WISE/NEOWISE, and Subaru for Large Icy Asteroid (704) Interamnia: A New Perspective of Regolith Properties and Water Ice Fraction

(704) Interamnia is one of the largest asteroids located in the outer main-belt region, which may contain a large amount of water ice underneath its surface. We observe this asteroid using 8.2 m Subaru telescope at mid-infrared wave bands and utilize a thermophysical model for realistic surface layers to analyze mid-infrared data from Subaru along with those of IRAS, AKARI, and Wide-field Infrared Survey Explorer (WISE)/NEOWISE. We optimize the method to convert the WISE magnitude to thermal infrared flux with temperature-dependent color corrections, which can provide significant references for main-belt asteroids at a large heliocentric distance with low surface temperature. We derive best-fitting thermal parameters of Interamnia—a mean regolith grain size of μm, with a roughness of and rms slope of deg, thereby producing thermal inertia ranging from 9 to 92 Jm−2 s−1/2 K−1 due to seasonal temperature variation. The geometric albedo and effective diameter are evaluated to be and , respectively, being indicative of a bulk density of 1.86 ± 0.63 g cm−3. The low thermal inertia is consistent with typical B/C-type asteroids with D ≥ 100 km. The tiny regolith grain size suggests the presence of a fine regolith on the surface of Interamnia. Moreover, the seasonal and diurnal temperature distribution indicates that thermal features between the southern and northern hemispheres appear to be very different. Finally, we present an estimation of volume fraction of water ice of 9%–66% from the published grain density and porosity of carbonaceous chondrites.