Ultrawide Spectral Range Research Articles

Construction and photothermal properties of Ag nanoparticles modified multilevel porous CuO film with ultra-wide infrared spectrum absorption

Based on lattice vibration and energy band theory, narrow bandgap inorganic semiconductor materials have become a new type of photothermal material, but it is difficult to achieve absorption for long wavelength infrared radiation to meet the application requirements of ultra-wide spectrum (2.5–20 μm) infrared detectors. From the perspective of structural optics, this paper constructed a multilevel porous CuO film with both coral-like micro-porous and flower-like nano-porous structures based on chemical bath deposition technique, and the Ag nanoparticles were uniformly embedded in the "petal" gaps of flower-like nano-porous CuO by optimizing the dosages of PVP. Benefiting from the synergistic effect of multilevel porous structure and loaded Ag nanoparticles, the Ag nanoparticles modified multilevel porous CuO (CuO@Ag-PVP 0.05) film had an average absorption of 94.17 % over the wavelength range of 2.5–20 μm. The photothermal conversion efficiency of CuO@Ag-PVP 0.05 film can reach up to 81.12 % and 86.96 % over near-infrared and far-infrared light ranges, respectively. The various material characterizations and simulations analysis showed that the multilevel porous structure containing coral-like and flower-like multi-scale pores can form two guiding modes for light, and based on the synergistic effect of the two guiding modes, the CuO film can form a strong trapping effect for light over ultra-wide spectral range, broaden its absorption range, and enhance its absorption characteristics. The loaded Ag nanoparticles contain a large number of free electrons, which can capture light energy and convert it into heat energy through local surface plasmon resonance (LSPR) effect, further enhancing the light absorption and photothermal conversion efficiency.

Broadband Solar Absorber and Thermal Emitter Based on Single-Layer Molybdenum Disulfide.

In recent years, solar energy has become popular because of its clean and renewable properties. Meanwhile, two-dimensional materials have become a new favorite in scientific research due to their unique physicochemical properties. Among them, monolayer molybdenum disulfide (MoS2), as an outstanding representative of transition metal sulfides, is a hot research topic after graphene. Therefore, we have conducted an in-depth theoretical study and design simulation using the finite-difference method in time domain (FDTD) for a solar absorber based on the two-dimensional material MoS2. In this paper, a broadband solar absorber and thermal emitter based on a single layer of molybdenum disulfide is designed. It is shown that the broadband absorption of the absorber is mainly due to the propagating plasma resonance on the metal surface of the patterned layer and the localized surface plasma resonance excited in the adjacent patterned air cavity. The research results show that the designed structure boasts an exceptional broadband performance, achieving an ultra-wide spectral range spanning 2040 nm, with an overall absorption efficiency exceeding 90%. Notably, it maintains an average absorption rate of 94.61% across its spectrum, and in a narrow bandwidth centered at 303 nm, it demonstrates a near-unity absorption rate, surpassing 99%, underscoring its remarkable absorptive capabilities. The weighted average absorption rate of the whole wavelength range (280 nm-2500 nm) at AM1.5 is above 95.03%, and even at the extreme temperature of up to 1500 K, its heat radiation efficiency is high. Furthermore, the solar absorber in question exhibits polarization insensitivity, ensuring its performance is not influenced by the orientation of incident light. These advantages can enable our absorber to be widely used in solar thermal photovoltaics and other fields and provide new ideas for broadband absorbers based on two-dimensional materials.

Development and Fabrication of a Multi-Layer Planar Solar Light Absorber Achieving High Absorptivity and Ultra-Wideband Response from Visible Light to Infrared.

The objective of this study is to create a planar solar light absorber that exhibits exceptional absorption characteristics spanning from visible light to infrared across an ultra-wide spectral range. The eight layered structures of the absorber, from top to bottom, consisted of Al2O3, Ti, Al2O3, Ti, Al2O3, Ni, Al2O3, and Al. The COMSOL Multiphysics® simulation software (version 6.0) was utilized to construct the absorber model and perform simulation analyses. The first significant finding of this study is that as compared to absorbers featuring seven-layered structures (excluding the top Al2O3 layer) or using TiO2 or SiO2 layers as substituted for Al2O3 layer, the presence of the top Al2O3 layer demonstrated superior anti-reflection properties. Another noteworthy finding was that the top Al2O3 layer provided better impedance matching compared to scenarios where it was absent or replaced with TiO2 or SiO2 layers, enhancing the absorber's overall efficiency. Consequently, across the ultra-wideband spectrum spanning 350 to 1970 nm, the average absorptivity reached an impressive 96.76%. One significant novelty of this study was the utilization of various top-layer materials to assess the absorption and reflection spectra, along with the optical-impedance-matching properties of the designed absorber. Another notable contribution was the successful implementation of evaporation techniques for depositing and manufacturing this optimized absorber. A further innovation involved the use of transmission electron microscopy to observe the thickness of each deposition layer. Subsequently, the simulated and calculated absorption spectra of solar energy across the AM1.5 spectrum for both the designed and fabricated absorbers were compared, demonstrating a match between the measured and simulated results.

Fabrication and Light‐Emission Study of Ti‐δ‐Doped Quasi‐2D γ‐Alumina by Graphene‐Assisted Atomic Layer Deposition

Crystalline quasi‐2D Ti‐δ‐doped γ‐alumina (2D‐Ti:γ‐alumina) is synthesized by a facile, precursor‐alternating atomic‐layer‐deposition technique followed by a post‐growth air‐anneal at ≈800 °C. According to energy‐dispersive X‐ray spectroscopy maps, Ti atomic concentration remains uniform and approaches ≈1.5%. Subject to several UV‐light exposures, the samples are found to develop a full strength, stable emission in the ultrawide spectral range of ≈350–850 nm. The near‐infrared (NIR) emission band centered at ≈760 nm is assigned to Ti deep defect states introduced in the alumina host. According to photoluminescence excitation–emission studies, aggregate oxygen vacancies remain a primary excitation source of the NIR emission. In addition, a broad visible‐range emission band at ≈525 nm is registered in the temperature range of ≈108–348 K, but unlike the NIR band, its temperature dependence remains Arrhenius with the non‐radiative recombination activation energy of ≈73 ± 9 meV. The resultant 2D‐Ti:γ‐alumina holds promise for applications in low‐cost alumina‐based optoelectronics, photocatalytic remediation, and spectrally wide light sources.

Optical Design for Aberration Correction of Ultra-Wide Spectral Range Echelle Spectrometer

The echelle grating spectrometer, with a wide spectral range and high-resolution spectral analysis, is one of the best tools for fine spectral measurement. Nevertheless, it suffers from excessive residual aberrations and a large overall size. In this study, the design and implementation of a novel asymmetric Czerny–Turner ultra-wide spectral range achromatic echelle spectrometer are described. The echelle spectrometer has three channels, and it uses an off-axis parabolic mirror to obtain collimated light without aberrations. Three sets of gratings and dispersive prisms with different coatings are utilized as cross-dispersion elements to acquire two-dimensional images containing spectral information. Suitable detectors are selected according to the requirements of each channel, and three sets of coaxial focusing lenses are designed separately to minimize the aberration. The results of the simulation analysis by ZEMAX indicate that in the entire operating band (200–1100 nm), the root mean square radius of the dispersion spots is ≤ 2.2 μm, all of which are located within the limited range of the size of the detector, thus ensuring that the system’s spectral resolution reaches 0.02 nm at 200 nm, 0.04 nm at 650 nm, and 0.1 nm at 1100 nm.

Superachromatic polarization modulator for stable and complete polarization measurement over an ultra-wide spectral range.

The polarization measurement system deals with polarized light-matter interactions, and has been a kind of powerful optical metrology applied in wide fields of physics and material. In this paper, we address several general theoretical aspects related to the system model and optimization for linear polarization systems from a view of the matrix algebra. Based on these theories, we propose a new framework of superachromatic polarization modulator (PM) by combining a linear polarizer and a sequence of parallel linear retarders (LRs) for a typical kind of linear polarization system based on the rotating compensator (RC) principle. In the proposed PM, the LRs are made of quarter-wave plates and as a whole act as the RC. Compared with conventional achromatic/superachromatic composite waveplates, the LR sequence has general axis orientations and is optimized by the condition number of the instrument matrix of the PM, which thereby provide much more flexibility to achieve uniform, stable and complete polarization modulation over ultra-wide spectral range. The intrinsic mechanisms, including the working principle, optimization strategy and in-situ calibration method of the proposed PM, are presented and revealed mathematically by the matrix algebra. Results on several prototypes of the PM demonstrate the validity and capability of the proposed methods for applications in broadband polarization measurement systems. The fabricated PM is further applied to a home-made dual RC Mueller matrix ellipsometer, and the accuracy and precision in the full Mueller matrix measurement are better than 2‰ and 0.6‰ respectively over the ultra-wide spectral range of 200∼1000 nm. Compared with existing techniques, the proposed PM has advantages due to superachromatic performances over ultra-wide spectral ranges, stable and complete modulation of the polarized light, and convenience for adjustment and calibration.

Analysis of a bidirectional metamaterial perfect absorber with band-switchability for multifunctional optical applications

Metamaterial perfect absorbers (MPAs) have been widely studied due to their distinctive tunable electromagnetic properties. Conventional MPAs mostly focus on realizing perfect absorption in a single direction, which leads to their limitations for various practical applications. We propose a bidirectional MPA with the ability of switching the ultra-wideband and dual-narrowband absorption. An inversion algorithm is applied to extract the normalized impedance of the absorber for explaining the physical mechanism. Simulation results clearly manifest that the average absorptivity of 93.8% and 99.5% could be achieved both over an ultra-wide spectral range of 1200 nm and at the specific wavelengths of 589 nm and 1097 nm with polarization independence and angle insensitiveness, which are led by the multiple excitations of different resonance modes induced by the metal–insulator-metal (MIM) Fabry-Perot (F-P) cavities. Our results are desirable for the integration of multiple optical applications such as energy harvesting, thermal emission, perfect cloaking and nanoparticle detecting.

Broadband Optical Properties of Atomically Thin PtS2 and PtSe2.

Noble transition metal dichalcogenides (TMDCs) such as PtS2 and PtSe2 show significant potential in a wide range of optoelectronic and photonic applications. Noble TMDCs, unlike standard TMDCs such as MoS2 and WS2, operate in the ultrawide spectral range from ultraviolet to mid-infrared wavelengths; however, their properties remain largely unexplored. Here, we measured the broadband (245–3300 nm) optical constants of ultrathin PtS2 and PtSe2 films to eliminate this gap and provide a foundation for optoelectronic device simulation. We discovered their broadband absorption and high refractive index both theoretically and experimentally. Based on first-principle calculations, we also predicted their giant out-of-plane optical anisotropy for monocrystals. As a practical illustration of the obtained optical properties, we demonstrated surface plasmon resonance biosensors with PtS2 or PtSe2 functional layers, which dramatically improves sensor sensitivity by 60 and 30%, respectively.

Design of ultra-broadband absorption enhancement in plasmonic absorber by interaction resonance of multi-plasmon modes and Fabry-Perot mode

This paper shows a strategy to realize ultra-broadband absorption of multi-spectral coverage. A vertical cascaded plasmonic absorber constructed by multilayer helical metallic nanostructure wrapped in a pyramid-shaped dielectric jacket is presented and investigated by numerical simulations. By premeditated planning of the scale proportions of the spirals and the dimension size of the pyramid-shaped dielectric, more than 90% of absorption is realized in 189-3896 nm, an ultra-wide spectral range that basically covers the bands of near-ultraviolet, visible light, and near-infrared. The excitation mechanism of electromagnetic resonance and the formation process of light trapping are both included in the investigation through the analysis of electromagnetic field distribution. The localized surface plasmon mode in the metallic nano-spiral and the Fabry-Perot cavity mode with the gap plasmon resonance in the dielectric gap cooperatively make a significant contribution to reduce the reflection and form the ultra-broadband absorption. The simulation results show that the proposed absorber is basically insensitive to the incident angle and polarization angle, which basically keeps more than 90% absorption within the incident angle of ± 80 °. Such a specific implementation idea can also be applied to the terahertz region by modifying the geometrical size of the structure. This presented design implies new viability to develop the broadband photodetectors, solar cells, and thermal emitters.

Large‐Scale Multifunctional Carbon Nanotube Thin Film as Effective Mid‐Infrared Radiation Modulator with Long‐Term Stability

AbstractMid‐infrared tunable materials have attracted increasing attention for thermal radiation management in various applications ranging from infrared camouflage to radiative thermoregulation. Functional films based on graphene and carbon nanotubes by electrical gating are promising candidates because of their ultrawide spectral range from visible to terahertz and structural flexibility. However, challenges in practical applications remain, such as short cycle life, rapid performance degradation, and difficulties in the synthesis of large‐scale electrochromic films. In this paper, a scalable strategy to produce large‐scale mid‐infrared electrochromic films with long‐term stability is demonstrated, in which a sandwich‐structured thin film based on multiwalled carbon nanotubes (MWCNTs) is fabricated via a universal roll‐to‐roll process. By ionic liquid gating, the electrochromic films exhibit tunable thermal emissivity from ≈0.15–0.7 and excellent stability with 96% modulation retention over 3500 cycles. This mid‐infrared electromodulation behavior is mainly ascribed to the change in free carrier concentration of few‐walled carbon nanotubes in MWCNT films via a reversible ion‐induced doping process. The electrochromic films are found to enable effective radiative thermal regulation, dependent on tunable thermal emissivity. Moreover, applications in infrared displays for secret communication and infrared camouflage for varied environmental backgrounds are also demonstrated with 10 × 10 multipixel arrays.

On-Chip Mid-Infrared Supercontinuum Generation from 3 to 13 μm Wavelength.

Midinfrared spectroscopy is a universal way to identify chemical and biological substances. Indeed, when interacting with a light beam, most molecules are responsible for absorption at specific wavelengths in the mid-IR spectrum, allowing to detect and quantify small traces of substances. On-chip broadband light sources in the mid-infrared are thus of significant interest for compact sensing devices. In that regard, supercontinuum generation offers a mean to efficiently perform coherent light conversion over an ultrawide spectral range, in a single and compact device. This work reports the experimental demonstration of on-chip two-octave supercontinuum generation in the mid-infrared wavelength, ranging from 3 to 13 μm (that is larger than 2500 cm–1) and covering almost the full transparency window of germanium. Such an ultrawide spectrum is achieved thanks to the unique features of Ge-rich graded SiGe waveguides, which allow second-order dispersion tailoring and low propagation losses over a wide wavelength range. The influence of the pump wavelength and power on the supercontinuum spectra has been studied. A good agreement between the numerical simulations and the experimental results is reported. Furthermore, a very high coherence is predicted in the entire spectrum. These results pave the way for wideband, coherent, and compact mid-infrared light sources by using a single device and compatible with large-scale fabrication processes.

Ultrawide-bandwidth on-chip spectrometer design using band-pass filters

Here, we present the design and simulation of an ultrawide-bandwidth on-chip spectrometer that can be used in various applications, e.g. spectral tissue sensing. It covers 1200 nm wavelength range (400 nm-1600 nm) with 2 nm spectral resolution. The overall design size is only 3 × 3 cm2. The ultra-wide spectral range is made possible by using novel on-chip band-pass filters for the coarse wavelength division. The fine resolution is provided by the arrayed waveguide gratings. The band-pass filter is formed by using bend waveguides and adiabatic full-couplers. The additional loss caused by the band-pass filter is relatively small. The proposed spectrometer covers entire 400 nm-1600 nm range continuously with low crosstalk values. We envision that this design can be used in several different applications including food safety, agriculture, industrial inspection, optical imaging, and biomedical research.

Ultra-wide spectral range (0.4–8 μm) transparent conductive ZnO bulk single crystals: a leading runner for mid-infrared optoelectronics

Transparent conductive oxides have been widely applied to solar cells, liquid crystal displays, and other optoelectronic devices because of their excellent transparent conductive properties in the visible-near-infrared (Vis-NIR) region. At present, the transparent conductive oxide films (TCOFs) such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), and aluminum-doped zinc oxide (AZO) are widely noticed and used. However, a high carrier concentration (≥1020 cm−3) of these TCOFs leads to a result that their transparency will be affected by the plasmons effect, and thus their transparent range will generally end around 2–3 μm. As such, they are more applicable in the Vis-NIR region but unable to meet the requirements of mid-infrared (MIR) optoelectronic devices. Faced with this situation, herein, we reported the native ZnO bulk single crystals with low background carrier concentration (1015–1016 cm−3) and high carrier mobility (μ > 300 cm2 V−1 s−1). These single crystals boast excellent transparent conductive properties (IR cutoff edge: 6–8 μm, Rsheet: 3.7–28.5 Ω/sq) with an advantage that they can be massively produced by a hydrothermal method at a low cost. Based on these merits, the native ZnO bulk single crystals bring a new possibility of breaking the bottleneck of MIR transparent conductivity.

Tunable broadband multiresonance graphene terahertz sensor

We proposed a tunable multiresonance graphene sensor consisting of a graphene disk and three non-overlapping graphene rings on a dielectric substrate. Compared to the previous reports, our proposed graphene sensor acts in an ultrawide spectral range from mid-to far-infrared ranges. The resonance of the graphene disk is in the mid-infrared range, while the resonance of graphene rings is in the far-infrared range. The multiple plasmonic resonance of the proposed structure is highly sensitive to the change of the substrate permittivity such that the frequency sensitivity of the graphene disk, ring 1, ring 2, and ring 3 are 2.72, 0.878, 0.582, and 0.529 THz (THz) per substrate permittivity unit (THz/SPU), respectively. Interestingly, by increasing the radii of each graphene subarray ring a red-shift of the transmission resonance dips toward the THz frequencies can be observed. It is found that by changing the Fermi energy of graphene, each resonance dip of the proposed structure can be flexibly controlled without re-manufacturing the structure. The performance of our proposed structure makes it a powerful tool for using in the optical devices with operating in the mid-to far-infrared range.

长焦距无热化星敏感器光学系统设计

Optical system is the core component of autonomous navigation star sensor to realize the collection of star light and high-precision attitude measurement. In this paper, the optical system of high precision star sensor was taken as the research object, the influence mechanism of the accuracy of optical system for detecting different color temperature stars were studied and analyzed. It is difficult to suppress the centroid drift caused by the changes of star color temperature and ambient temperature through later calibration, which needs to be controlled under the stage of optical design. The calculation model and allocation method of optical system design wavelength weight were established, and the performance evaluation was carried out. In addition to the conventional energy concentration, distortion and asymmetric aberrations, the centroid drift of star color temperature and ambient temperature change were proposed as the main index of accuracy evaluation. According to the application requirements, a long focal star sensor optical system based on space satellite platform was designed, with the focal length of 95 mm, the relative aperture of f 2.4, the field view of 8°× 8°, the spectrum range of 450-1 000 nm, and the energy concentration of more than 85% in 3×3 pixels. Based on the regular glass materials, the lateral color aberration of the optical system was corrected under ultra-wide spectral range and long focal. The lateral color aberration of the full field was less than 0.9 μm; The results of accuracy analysis show that the accuracy of centroid position is less than 0.36 μm in the range of 2 600-9800 K, and the change of focal length is less than 2.7 μm in the range of 0-40℃, and the accuracy of centroid position caused by temperature is less than 0.45 μm.

An analytical method to determine the complex refractive index of an ultra-thin film by ellipsometry

We proposed a completely analytical method to determine the complex refractive index of an ultra-thin film on an arbitrary substrate by ellipsometry. The method is based on directly solving the polynomial equation derived from the 2nd-order Taylor expansion of ellipsometric functions without any prior knowledge about electronic transitions of the material. Numerical simulations demonstrate that the proposed method can be applied to deal with ultra-thin films with a wide thickness range from a single atomic layer to 5 nm over an ultra-broad spectral range from deep ultraviolet to infrared regions. With the proposed method, complex refractive indices of typical two-dimensional (2D) materials, including the monolayer graphene and 1–3 layer WSe2, were experimentally investigated over an ultra-wide spectral range (193–1690 nm). The proposed method shows great potential in the accurate determination of complex refractive indices of ultra-thin films especially the emerging 2D materials.

Complex Optical Conductivity of Two-Dimensional MoS2: A Striking Layer Dependency.

The complex optical conductivities of two-dimensaionl (2D) materials are fundamental for extended applications of related optoelectronic devices. Here, we systematically investigate the layer-dependent evolutions in the complex optical conductivities of 1-6 layer 2D MoS2 over an ultrawide spectral range (0.73-6.42 eV) by spectroscopic ellipsometry. We identify five feature peaks (A-E) in the optical conductivity spectra, which present interesting layer dependencies due to the scaling effect. Results suggest that the center energies of peaks A and B are nearly layer-independent, while those of peaks C and D exhibit redshifts as the layer increases. We interpret these layer-dependent evolutions as the competition between the decreasing exciton effect and the prominent band shrinkage with the increasing layer number. Additionally, the applicability of the classical slab model and the surface current model in evaluating the optical conductivities of 2D MoS2 with different layers is discussed from an experimental perspective.

On the anomalous optical conductivity dispersion of electrically conducting polymers: ultra-wide spectral range ellipsometry combined with a Drude–Lorentz model

Ultra-wide range spectral range ellipsometry sheds light on the anomalous optical conductivity of conducting polymers.

Comprehensive characterization of a general composite waveplate by spectroscopic Mueller matrix polarimetry.

Composite waveplates (CWs) consisting of multiple single waveplates are basic polarization elements and widely used to manipulate the polarized light in optical systems, and their performances affect the final accuracy and precision significantly. This research proposes a method for the comprehensive characterization of an arbitrary CW based on spectroscopic Mueller matrix polarimetry. An analytical model is established to describe a general CW by extending Jones' equivalent theorem with Mueller matrix calculus. In this model, an arbitrary CW is optically equivalent to a cascaded system consisting of a linear retarder with slight diattenuation followed by an optical rotator, and its polarization properties are completely described by four polarization parameters, including the retardance, the fast axis azimuth, the rotation angle, and the diattenuation angle. Analytical relations between the polarization properties, the structure, and the Mueller matrix of the CW are then derived from the established model. By the proposed method, the polarization parameters of an arbitrary CW can be comprehensively characterized over an ultra-wide spectral range via only one measurement. Moreover, the actual structure of the CW, including the thicknesses and fast axis azimuths of the single waveplates, as well as the axis alignment errors, can be completely reconstructed from the polarization spectra. Experiments performed with a house-developed broadband Mueller matrix polarimeter on three typical CWs including a compound zero-order waveplate, an achromatic waveplate and a specially designed biplate have demonstrated the capability of the proposed method.

Ultrabroadband and Flattened Dispersion in Aluminum Nitride Slot Waveguides

Aluminum nitride (AlN) is an emerging platform for a wide range of on-chip applications. One promising feature is that both the second- and third-order nonlinearities are available in crystalline AlN waveguides. We design an AlN slot waveguide with a flat and low dispersion over an ultrawide spectral range from near-infrared to mid-infrared. A dual-slot structure is designed and the flattened group velocity dispersion within -13 and +11 ps/(nm·km) over 2000-nm-wide bandwidth with three zero dispersion wavelengths is achieved. The impacts of the structural parameters are analyzed in detail and the phase-matching condition in four-wave mixing process is investigated as well. A 3-dB conversion bandwidth of 1200 nm and -28-dB conversion efficiency are predicted in a 1-cm-long horizontal dual-slot AlN waveguide with the pump power of 2 W.