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We exhaustively investigate the temporal correlations between the ultrahigh-frequency (of the order of 1–6 GHz), very high-frequency (of the order of 10–100 MHz), and x-ray (photons with energies from 5 keV to 1 MeV) emissions together with the optical emissions in the near-infrared (within 700–1100 nm) and near-ultraviolet (within 300–400 nm) wavelength regions. The emissions are produced by a laboratory atmospheric discharge developing in an 55 cm air gap at voltages up to 1 MV. When registering various electromagnetic emissions, the discharge current and voltage are measured, as well as nanosecond imaging of the discharge evolution in its own glow is performed. The spatiotemporal localization of the discharge regions associated with the x-ray generation is carried out by employing the group of fast scintillation detectors, and the evolution of plasma structures during the x-ray generation is traced. A chronological map is constructed providing an in-depth understanding of the temporal character and correlations of various electromagnetic emissions. The map allows one to analyze fast ionization processes occurring in the gas-discharge medium and triggering the generation of the corresponding emissions. The generation mechanisms of the considered emissions in an extended high-voltage discharge are discussed. The findings can be helpful in revealing the sources of various electromagnetic emissions accompanying the formation of laboratory and atmospheric discharges. [ABSTRACT FROM AUTHOR]

An ultra-sparse, broadband programmable Active Acoustic Meta-surface (AAMS) that is demonstrated to function as a multi-functional Active Acoustic Meta-device is developed. Functionalities Acoustic Barrier (AB), Acoustic Switch (AS), and Acoustic Transmitter (AT) have been successfully explored. AB functions at a broadband frequency of 455 to 679 Hz as an approximately 100 % acoustic reflector. The functional range of the AS is 425 to 800 Hz, and similarly, the functional range of the AT is 300 to 800 Hz (the full range of the applied frequency sweep). Being a re-configurable device, the AAMS has variable thickness. On a wavelength scale, it varies from 0.10 λ to 0.99 λ for the said functionalities. Here, λ is the wavelength. [ABSTRACT FROM AUTHOR]

Despite rather extensive study of the random lasing effect in ZnO structures, the issue of the optical gain mechanisms in microstructured ZnO random lasers remains poorly understood. In this work, the radiative properties of an array of vertically aligned ZnO microrods, synthesized by a modified thermal evaporation method, were studied. The microrods exhibited lengths up to 60 μm and diameters ranging from 1 to 5 μm. Random lasing from a microrod array was observed in the near-UV range (with a laser emission peak wavelength of ∼391 nm) with a threshold down to 40 kW/cm2 under optical excitation. An analysis of the nature of optical gain in the grown structure was conducted at various temperatures. It was found that at room temperature, two-phonon-assisted exciton recombination is the main process leading to light amplification. [ABSTRACT FROM AUTHOR]

The double-ion chamber (DIC) method has been used to measure photoabsorption cross sections in the ionization region of the sample gas. In this study, we introduce a method to extend the wavelength region of the DIC measurements beyond the ionization threshold wavelength by using the photoion currents from the impurities in the sample gas. To verify this method, the photoabsorption cross sections of C2H2 (ionization threshold wavelength λth = 108.8 nm) have been measured from 105 to 137 nm. The natural impurity, acetone (λth = 127.8 nm), contained 1% in high-purity grade acetylene (C2H2) sample gas, allowing for measurements in the non-ionizing region of C2H2 up to 127.7 nm. By adding 1% benzene (λth = 134.6 nm) in the sample gas, measurements were possible even further, to 134.5 nm. This new method enables the measurement of the photoabsorption cross section by photoions that are produced from the impurities in the sample gas in a substantial amount. The current measurement methodology aligns well with the previous measurements of Suto and Lee [Suto and Lee, J. Chem. Phys. 80, 4824 (1984)]. [ABSTRACT FROM AUTHOR]

Asymmetric quantum wells (AQWs) utilizing interband transitions enhance second-order susceptibility over a wide wavelength range compared to natural crystals. The nonlinear susceptibility is further enhanced in AQWs with type-II band alignment as compared to type-I band alignment, a result of the larger interband charge shift. This enhancement is demonstrated in this work by analyzing three type-I and type-II AQW designs based on the lattice-matched InP/AlGaInAs materials systems using the envelope wavefunction approximation. The calculated interband second-order susceptibility tensor elements in type-II structures range between 20 and 1.60 × 103 pm/V for nearly resonant optical rectification and difference frequency generation applications at near-infrared and terahertz wavelengths, an improvement of nearly 1 order of magnitude over the type-I structures and 1–2 orders of magnitude over natural crystals such as LiNbO3, KTiOPO4 (KTP), or GaAs. A factor of 2–3 further enhancement of the tensor elements is achieved by optimizing the well widths and band offsets of the type-II asymmetric quantum wells. The type-II structure can be implemented in other material systems spanning the longwave infrared to visible wavelengths, enhancing nonlinear susceptibility for various applications, including photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Magic-sized nanocrystals (MSNCs) grow via jumps between very specific sizes. This discrete growth is a possible avenue toward monodisperse nanomaterials that are completely identical in size and shape. In spite of this potential, MSNCs have seen limited study and application due to their poor optical properties. Specifically, MSNCs are limited in their range of emission wavelengths and commonly exhibit poor photoluminescence quantum yields (PLQYs). Here, we report silver doping of CdSe MSNCs as a strategy to improve the optical properties of MSNCs. Silver doping leads to controllable shifts in emission wavelength and significant increases in MSNC PLQYs. These results suggest that doped MSNCs are interesting candidates for displays or luminescent solar concentrators. Finally, we demonstrate that the doping process does not affect the magic size of our MSNCs, allowing further photophysical study of this class of nanomaterial. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) film, which is the most commonly used transparent conductive film (TCF), has traditionally been believed to be transparent in the visible spectrum but to reflect infrared (IR) light beyond the plasma wavelength (λp). However, our theoretical analysis challenges this notion by demonstrating that an ultrathin ITO TCF that is thinner than the light's penetration depth can overcome the transmission barrier at λp. To validate the theoretical modeling, we have successfully fabricated ultrathin ITO films that, despite having λp ≈ 1 μm, remain transparent from 400 nm to 20 μm. This represents the broadest transparency range ever reported for any In2O3-based TCF. The 10-nm-thick ITO TCFs have high visible transmittance (91.0% at 550 nm), low resistivity (5 × 10−4 Ω cm), and good IR transmittance (averaging 60% over 1.35–18.35 μm). Their IR transparency facilitates radiative cooling of the underlying circuitry. When an operational resistor is enclosed by commercial ITO TCFs that are 140 nm thick, its temperature increases. However, using 10-nm-thick ITO TCFs instead of the commercial ones can completely avoid this temperature rise. Moreover, attaching a silver grid to a 10-nm-thick ITO TCF can reduce the effective sheet resistance to ∼10 Ω/□ at the expense of only ∼3% transmittance. This development paves the way for large-scale applications that require low sheet resistance and far-IR transparency. [ABSTRACT FROM AUTHOR]

The nonlinear refractive index of large area monolayer molybdenum disulfide (MoS2) thin film at the 1,550 nm wavelength band is determined using time-resolved z-scan technique. MoS2 exhibits positive nonlinear phase shift with a large nonlinear refractive index, n 2 value of 1. 4 0 × 1 0 − 1 3 m 2 W − 1 . The obtained value is similar to the n 2 value of monolayer MoS2 film measured at 2.0 μ m, and is approximately five and seven orders of magnitude larger than silicon and common bulk dielectrics. The large n 2 indicates that MoS2 can be used as nonlinear refractive 2D material for photonics applications operating in the 1,550 nm optical telecommunications wavelength band. [ABSTRACT FROM AUTHOR]

The excellent anti-interference ability of near-infrared (NIR) fluorescent materials derived from long-wavelength emission has made them one of the most fascinating fluorescence probes. In this work, gold nanoclusters stabilized with glutathione (GSH-AuNCs) were prepared and exhibited excellent NIR fluorescence at 806 nm, indicating their potential as excellent fluorescence probes. It is gratifying that S2− could be sensitively and rapidly recognized through the "turn-off" strategy of NIR fluorescence of AuNCs. It is speculated that the quenching was due to the aggregation-caused quenching (ACQ) phenomenon. The combination of a longer wavelength emission of 806 nm and the strong binding ability of Au and S endowed the constructed sensing system with outstanding sensitivity and selectivity. A good linear relationship for the detection of S2− was obtained in the range of 0–23.75 μM, with a limit of detection (LOD) of 14.67 nM (S/N = 3). This NIR fluorescence probe was successfully used for the detection of S2− in real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

We develop a multilayer model to study roll waves in mudflow of Herschel–Bulkley fluids initiated by periodic and localized disturbance. Simulations are conducted of the temporal development of periodic roll waves and spatial development of wave packets due to localized disturbance. The results of the temporal development are expressed in terms of the power-law index, the relative plug-layer thickness, the Froude number, and the perturbation wavelength. Our simulation for the spatial development shows the roll waves led by a dominant front runner and followed by a quiescent tail, closely reproducing a well-known river-clogging phenomenon of the natural mudflow observed in the mountain rivers on mild slopes. The leading wave of the roll-wave packet, i.e., the front runner, grows in depth, velocity, celerity, and wavelength with distance from the localized disturbance. The front-runner wave amplitude depends on the distance from the localized disturbance, the power law index, the plug-layer thickness, and the Froude number. We calculated the front-runner's wave amplitude due to a line source of disturbance in a 1D unidirectional development and the roll waves' 2D development due to a point source. The initial nonlinear growth in the 2D front runner is a fraction of the 1D waves, but the increase in the wave amplitude with distance follows the same trend. We have also conducted a mesh refinement study to determine the convergence and accuracy. The present simulations using 64 layers have attained an accuracy within a 2% error. [ABSTRACT FROM AUTHOR]

A small-sized, circular-shaped Multiple Input Multiple Output (MIMO) antenna is investigated in this study. This antenna is suitable for wireless applications at 2.4 GHz and 5 GHz. The MIMO antenna comprises two identical, back-to-back slotted circular patch antennas with a common ground plane. The radiation direction of each antenna is oriented at 180° relative to its counterpart, providing good isolation between them. The novelty of this two-port MIMO antenna lies in its compact size of only 0.001λ ³ (where λ corresponds to the free space wavelength at 2.4 GHz) along with its dual-band 0 0 operating capability. Important parameter values of this MIMO antenna are analyzed using electromagnetic analysis software. Directivity values of 5.5 dBi (at 2.4 GHz) and 6.7 dBi (at 5 GHz), as well as reasonable bandwidths of 50 MHz (at 2.4 GHz) and 160 MHz (at 5 GHz), are obtained for this antenna. Envelope Correlation Coefficients (ECC) of 0.01 at 2.4 GHz and 0.003 at 5 GHz, along with a nearly 10 dB Diversity Gain (DG), are achieved at both frequencies for this compact antenna system. The ratio of Mean Effective Gain (MEG) between the two antennas is found to be 0.02 dB at 2.4 GHz and 0.05 dB at 5 GHz. Channel Capacity Loss (CCL) values of 0.16 bits/s/Hz and 0.089 bits/s/Hz are obtained at 2.4 GHz and 5 GHz, respectively. The characteristic parameters of this two-port circular patch antenna system are compared with those of similar antennas reported in recent literature. [ABSTRACT FROM AUTHOR]

This comparison study investigates the influence of subchannel symbol rates on the Wavelength Selective Switching (WSS) filtering penalties in elastic optical networks. Within these networks, WSS is essential for the signal filtering process. This study compares and evaluates the filtering penalty for several modulation styles and subchannel symbol rates, including variable and fixed subchannel symbol rates. This paper investigates the performance of WSS filtering and its sensitivity to these parameters through comprehensive testing and analysis. The findings enable the improvement of WSS filtering efficiency in elastic optical networks by illuminating the ideal subchannel symbol rates. This study advances effective signal processing methodologies in contemporary communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a low profile UHF-RFID reader antenna with high front-to-back ratio is presented. The antenna consists of a probe-fed U-slot rectangular patch antenna loaded with a slotted AMC reflector, formed of 2 × 2 unit cells. By incorporating the AMC reflector, a compact profile height of 0.049λ (λ is the wavelength at 910 MHz) is achieved with high gain and front-to-back ratio. The proposed reader antenna is fabricated and measured. The experimental results are similar to those predicted by electromagnetic simulation and validate the proper operation of the antenna across the entire UHF-RFID band (860–960 MHz). Moreover, the realized prototype exhibits a measured realized gain and a front-to-back ratio (F/B) greater than 5 dBi and 24 dB, respectively. The proposed design offers the advantages of low profile, high gain and F/B ratio, rendering it suitable for compact RFID readers. [ABSTRACT FROM AUTHOR]

In the fast‐growing field of integrated photonics, quantifying the dispersive characteristics of the optical components integrated on chip is of key importance. The short length of on‐chip components, however, makes it challenging to measure their dispersive properties. Hence, experimental data are relatively scarce, especially at wavelengths close to the zero‐dispersion wavelength (ZDW) where the dispersion‐length product becomes very small. Ideally, the dispersion should be characterized with a technique that, besides being highly sensitive, “directly” yields the dispersion value without frequency derivative calculations nor the addition of dedicated on‐chip measurement structures. To fulfill these requirements, a dispersion characterization technique is presented relying on femtosecond‐resolution time‐of‐flight measurements combined with advanced spatial light modulator (SLM) technology. With this new “direct” technique, suitable for measuring dispersion‐length products down to 5 × 10−5 ps nm−1, the dispersion of mm‐length silicon nitride waveguides is characterized, both in the weakly dispersive (close to the ZDW) and strongly dispersive regimes. Furthermore, dispersion data are presented for sub‐mm‐length trident couplers and inverted taper couplers connected to the waveguides. The resulting insights into the waveguides’ and couplers’ dispersive properties, and the wide applicability of the technique, will benefit the development of advanced photonic integrated circuits (PICs) in silicon nitride and other waveguide material platforms. [ABSTRACT FROM AUTHOR]

The blue-violet emitting phosphors is a critical aspect of achieving a high-quality full-spectrum white light-emitting diodes (WLEDs). Here, the photoluminescence characteristics of blue-violet emitting phosphors Li 6 Y(BO 3) 3 :Bi3+ and its application performances were systematically studied. The emission of the phosphors exhibits a high dependence on the excitation wavelength. Upon excitation at 372 nm, the phosphors emit blue light peaking at 407 nm. The excitation of 340 nm results in the occurrence of two peaks at 407 and 506 nm in emission spectra. A full-spectrum WLED prepared by coating a 365 nm n-UV LED and the mixture comprising the phosphors and three commercial phosphors. The WLED exhibits high color rendering index (R a = 95) and low correlated color temperature (3555 K). Consequently, Li 6 Y(BO 3) 3 :Bi3+ is a potential phosphor that can be used for full spectrum WLEDs. [ABSTRACT FROM AUTHOR]

Organisms with active camouflage ability exhibit changeable appearance with the switching of environments. However, manmade active camouflage systems heavily rely on integrating electronic devices, which encounters problems including a complex structure, poor usability, and high cost. In the current work, we report active camouflage as an intrinsic function of materials by proposing self-adaptive photochromism (SAP). The SAP materials were fabricated using donor-acceptor Stenhouse adducts (DASAs) as the negative photochromic phases and organic dyes as the fixed phases (nonphotochromic). Incident light with a specific wavelength induces linear-to-cyclic isomerization of DASAs, which generates an absorption gap at the wavelength and accordingly switches the color. The SAP materials are in the primary black state under dark and spontaneously switch to another color upon triggering by transmitted and reflected light in the background. SAP films and coatings were fabricated by incorporating polycaprolactone and are applicable to a wide variety of surfaces. [ABSTRACT FROM AUTHOR]

Designing SPADs with high sensitivity in a wide wavelength range is crucial since the applications utilizing SPAD-based sensors target different parts of the spectrum. Here, we introduce a novel technique to achieve a wider sensitivity spectrum through the insertion of a second multiplication region into the depletion region. Thanks to the proposed method, at 5.5 V excess bias voltage, the fabricated devices achieved a PDP of 78% peak at 500 nm and 25.5% at 850 nm wavelength. At the same excess bias, we measured a normalized noise of 3.7 cps/μm2 and a jitter of 165 ps at 517 nm FWHM. [ABSTRACT FROM AUTHOR]

Mechanoluminescence (ML), which generates an optical response to external mechanical stimuli, shows promise for high‐end stress sensing, flexible optoelectronic skin, dynamic mechanical visualization, and anti‐counterfeiting applications. Near‐infrared (NIR) light possesses the advantages of high tissue penetration capability and can be absorbed by certain organic molecules, thus NIR‐ML materials have potential applications in biomechanics imaging, nondestructive composition analysis, etc. However, their practical applications are limited by the emission wavelengths and bandwidths of the NIR‐ML materials. In this study, a series of double perovskites A2MSbO6:Cr3+ (A = Sr, Ba; and M = Ga, Sc) is reported with self‐recoverable NIR‐ML emissions. By modulating the composition, the ML emission coverage are tuned from NIR‐I to NIR‐II (700 nm to over 1200 nm), and adjusted the full width at half maximum of the emission to 163 nm. In addition, under ultrasonic stimulation, these A2MSbO6:Cr3+ ML materials emitted NIR light, with the NIR light from Sr2ScSbO6:Cr3+ penetrating 5 mm of beef tissue. This study expands the library of NIR‐ML light sources and the ML spectral range, thereby promoting new applications of NIR‐ML materials. [ABSTRACT FROM AUTHOR]

Nonlinear optical process is a key technology to realize optical communication. Potassium tantalate niobate (KTa1−xNbxO3, KTN) crystals with large nonlinear optical coefficients are potential functional materials for realizing χ2 nonlinear optical processes. However, to accurately modulate the nonlinear optical signals of KTN crystals, the relationship between their second harmonic generation (SHG) properties and ferroelectric domain structures needs to be further investigated. Here, we report the special SHG processes generated by self-assembled structures in KTN crystals. Multimode quasi-phase matching and broadband nonlinear Bragg diffraction are achieved with the changing of polarizations and wavelengths of the fundamental wave. The physical processes behind the multi-polarization and multi-wavelength SHG properties of the KTN crystals are revealed. Our results about the multi-polarization and multi-wavelength SHG properties of KTN crystals will provide guidance for the design and realization of multimode nonlinear optical processes. [ABSTRACT FROM AUTHOR]

We describe the use of acyl imidazoles derived from aliphatic carboxylic acids for the N-heterocyclic carbene/organic photoredox co-catalyzed meta -selective functionalization of electron-rich arenes. Compared to our previous work, a change of the wavelength of the applied LED light from 440 nm to 390 nm promotes this reaction efficiently. [ABSTRACT FROM AUTHOR]

Y-branch distributed Bragg reflector (DBR) diode lasers with a stable narrowband emission in simultaneous dual-wavelength operation with spectral distances below 3.2 nm are presented. The Y-branch laser consists of two laser branches with different DBR gratings serving as wavelength-selective rear-side mirrors. Therefore, two emission wavelengths with a spectral distance defined by the DBR grating periods can be generated simultaneously. A Y-coupler combines the two ridge waveguide (RW) branches into a single straight output RW. Devices with a spectral distance of 0.6 nm and 2.0 nm emitting around 785 nm are manufactured. Selecting the operation parameters carefully, stable narrowband emission for both wavelengths is obtained. Resistors serving as heaters implemented next to the DBR gratings allow for wavelength adjustment and a tuning of the spectral distance. At an optical output power of 100 mW, the spectral distance can be shifted from 0 to 1.55 nm (0–0.76 THz) for the former device or from 1.00 to 3.15 nm (0.49–1.54 THz) for the latter device, respectively. This makes the Y-branch DBR diode laser particularly interesting for the generation of THz beat-note signals, needed to generate THz radiation via photo-mixing. [ABSTRACT FROM AUTHOR]

A dispersion-managed femtosecond optical parametric oscillator (OPO) with stable power is demonstrated in this article. The OPO, based on LiB3O5 (LBO) crystal, was synchronously pumped by a frequency-doubled, Kerr-lens mode-locked Yb: CGYA laser. The output signal had a wavelength tuning range of 680 ~ 740 nm, a maximum average power of 1.1 W, and a minimum pulse duration of 105 fs. By inserting ultraviolet fused silica (UVFS) windows into the cavity to introduce additional normal dispersion, the dual-signal-wavelength output was suppressed, and the power stability was significantly enhanced. The RMS of the one-hour power fluctuation decreased to one seventh of its original value, from 2.47% to 0.38%. This work is of particular significance for promoting the engineering application of femtosecond OPOs. [ABSTRACT FROM AUTHOR]

The enigmatic ultraviolet (UV) extinction bump at 2175  |$\, {\rm \mathring{\rm A}}$|⁠ , the strongest spectroscopic absorption feature superimposed on the interstellar extinction curve, has recently been detected at the cosmic dawn by the JWST in JADES-GS-z6-0, a distant galaxy at redshift |$z\approx 6.71$|⁠ , corresponding to a cosmic age of just 800 million years after the big bang. Although small graphite grains have historically long been suggested as the carrier of the 2175  |$\, {\rm \mathring{\rm A}}$| extinction bump and graphite grains are expected to have already been pervasive in the early Universe, in this work we demonstrate that small graphite grains are not responsible for the UV extinction bump seen at the cosmic dawn in JADES-GS-z6-0, as the extinction bump arising from small graphite grains is too broad and peaks at wavelengths that are too short to be consistent with what is seen in JADES-GS-z6-0. [ABSTRACT FROM AUTHOR]

An in situ control of a center wavelength in a 40‐pair AlInN/GaN distributed Bragg reflector (DBR) for GaN‐based vertical‐cavity surface‐emitting lasers (VCSELs) with an in situ reflectivity spectra measurement is proposed and developed. A procedure of the in situ control consists of the following three steps: 1) to grow an initial 5‐pair DBR; 2) to obtain the center wavelength value just after the initial DBR growth by the in situ reflectivity spectra measurement; and 3) to adjust growth times as a result of the obtained center wavelength value and continue the remaining 35‐pair DBR. It is experimentally demonstrated that the in situ control of the center wavelength in the 40‐pair DBRs with the ±2% thickness deviations in the initial 5‐pair DBR results in reductions of the deviation down to ±0.3%. The in situ DBR center wavelength control is a key technique for highly reproducible GaN‐based VCSELs. [ABSTRACT FROM AUTHOR]

The properties of circularly polarized light has recently been used to selectively reflect chiral metasurfaces. Here we report the more complete basic functionalities of reflectors and absorbers that display various optical phenomena under circularly polarized light at normal incidence as before. For the chiral metamirrors we designed, the circular dichroism in about 0.4 reflection is experimentally observed in visible wavelengths. The experimental results also show high reflectance for right-handed circular polarization with preserved handedness and strongly absorbed left-handed circular polarization at chiroptical resonant wavelengths. By combining a nanobrick and wire grating for our design, we find and offer a new structure to demonstrate the superposition concept of the phase in the same plane that is helpful in effectively designing chiral metamirrors, and could advance development of their ultracompact optical components. [ABSTRACT FROM AUTHOR]

Herein, the wavelength dependence of the efficiency and the lifetime of far UV‐C light‐emitting diodes (LEDs) on a single‐crystal AlN substrate is systematically analyzed from experiments and simulations. A positive relation between efficiency and emission wavelength is observed. The wall‐plug efficiency reaches 0.47, 1.0, 2.1, and 2.4% at 227, 230, 233, and 235 nm wavelengths, respectively. The simulation results show that carrier injection plays a critical role in the efficiency change in the far UV‐C region rather than in the internal quantum or light extraction efficiency. The lifetime test clearly demonstrates a trade‐off between the L70 lifetime and the emission wavelength, although the initial optical power increases with the longer wavelength. The measurement results under various wavelengths and stress currents indicate that the carriers injected in quantum wells motivate power reduction during current stress. Moreover, the internal quantum efficiency affects the degradation rate because the influence of defects becomes stronger during stress. Finally, the reliability of a 231 nm LED is investigated at a reduced current of 35 mA. The projected L70 and L50 lifetimes are 11 000 and 28 000 h, respectively, from the fitting model based on the defect generation during aging. [ABSTRACT FROM AUTHOR]

We investigated hybrid functional transparent conductive electrodes (HFTCEs) composed of indium-tin-oxide (ITO) and silver nanowires (AgNWs) for the enhancement of output efficiency in GaN-based ultraviolet light-emitting diodes (UVLEDs). The HFTCEs demonstrated an optical transmittance of 69.5% at a wavelength of 380 nm and a sheet resistance of 16.4 Ω/sq, while the reference ITO TCE exhibited a transmittance of 76.4% and a sheet resistance of 18.7 Ω/sq. Despite the 8.9% lower optical transmittance, the UVLEDs fabricated with HFTCEs achieved a 25% increase in output efficiency compared to reference UVLEDs. This improvement is attributed to the HFTCE's twofold longer current spreading length under operating forward voltages, and more significantly, the enhanced out-coupling of localized surface plasmon (LSP) resonance with the trapped wave-guided light modes. [ABSTRACT FROM AUTHOR]

A robust method for multiplicative scatter correction (MSC) in infrared spectroscopy is presented. Using quantile regression, the outlier wavelengths (concentration‐dependent wavelengths) that are irrelevant to the regression are identified and therefore excluded from the regression model. This new MCS method, which could be implemented in its simple or extended form, is much simpler than the recently proposed methods and has only one hyperparameter (the quantile value) to be adjusted. To achieve this, a scoring function based on residual analysis can automatically determine the correct quantile value. The method is first explained using simulation data sets and then its validation is explained by analysing some experimental data sets. It was found that our new method can perform well in the presence of strong outlying variables. On the other hand, when the data sets are not associated outlying wavelengths, this method behaves similarly to the conventional MSC method. [ABSTRACT FROM AUTHOR]

The high-speed railway (HSR) operates at a high velocity, and the long-wavelength track irregularities can affect its safety and stability. The study was conducted to address control and management issues related to long-wavelength track irregularities on HSRs. It achieved this by establishing a vehicle-track dynamic analysis model based on the multi-rigid-body dynamics theory, aiming to provide recommendations for the development of standards for managing the track irregularities on HSRs. A simulation was conducted to analyze how the train speed, wavelength, and amplitude of track longitudinal irregularities affect the vehicle body's dynamic response. The variation of the vehicle body's dynamic response under different working conditions was analyzed, and the most unfavorable wavelength and sensitive wavelength ranges of the track longitudinal irregularities on HSR were studied. The control limits for track longitudinal irregularities measured by a 60 m chord were then determined. The findings indicate that the car body's vertical acceleration gradually decreased with the increase of wavelength but increased linearly with the increase of amplitude. The findings also indicate a gradual increase in the vehicle body's vertical acceleration as the train speed increases. When the train speed is 250 km/h∼350 km/h, the sensitive wavelength range of long-wavelength track irregularities is 60 m∼110 m. Based on the results, the relationships between the wavelength and the amplitude of track irregularities, train speed, and the vehicle body's vertical acceleration were acquired by the nonlinear least square method. Finally, a formula for calculating the control limits for track longitudinal irregularities measured by a 60 m chord is proposed. [ABSTRACT FROM AUTHOR]

As an advanced signal source, laser is very suitable for various photonic devices but implementing tunability of wavelength is more challenging. Herein, the study designs and synthesizes boron difluoride derivative tBuBF2, systematically studying the impact of assembly behavior on laser performance. The laser test results indicate that the emission wavelength of tBuBF2 microcrystals can be controlled by varying the length of the microcrystals, with the shorter wavelength of 0–1 vibronic lasing emission at 444 nm and the longer wavelength of 0–2 lasing emission at 468 nm. Mechanistic studies reveal that laser color change comes from an increase in optical propagation losses due to self‐absorption at the 0–1 vibronic band. Furthermore, CBP@tBuBF2 microcrystals constructed by doping with 4,4′‐bis(9‐carbazolyl)‐1,10‐biphenyl (CBP) as the guest molecule, which primarily exhibits 580 nm exciplex yellow emission while retaining weak blue emission. Moreover, it is demonstrated that the laser emission only occurred within the 0–2 vibronic band in the blue region owing to the increased self‐absorption phenomenon with 0–1 band, thus achieving controllable dual‐wavelength and exciplex emission for laser concealment. This work expands novel regulation strategy available for laser behavior control by enhancing the self‐absorption process, describing structure‐property relationships that will guide the design of advanced laser materials. [ABSTRACT FROM AUTHOR]

Decoupling of phase and polarization is significant for multidimensional light manipulation. However, this requires traditional cascaded and parallel optical elements, resulting in a bulky and complex system. Metasurfaces can potentially replace complex optical modules as novel ultrathin planar optical elements. Herein, an ultrathin single‐layer metasurface is proposed to decouple the phase and polarization based on the Pancharatnam–Berry phase. The rotation angles of the two nanofins are employed to manipulate the phase and polarization independently, significantly simplifying the design process. Diffraction‐limited focusing with a degree of linear polarization higher than 95% is achieved for wavelengths in the 405–633 nm range. Furthermore, a metasurface can arbitrarily manipulate the relative intensity between different channels. The intensity ratio is adjusted from 0.12 to 6.62. These results will pave the way for miniaturized, integrated, and multi‐channel optical elements. [ABSTRACT FROM AUTHOR]

Underground coal gangue sorting is a critical component of modern intelligent coal mining, holding significant importance for the preservation of natural resources and the ecological environment. Traditional methods of underground coal gangue sorting suffer from issues such as low efficiency, limited applicability, and substantial resource wastage. Addressing these challenges, this paper employs multispectral technology to gather spectral data of coal and gangue in various wavelengths. Based on the identification accuracy of coal gangue images in different wavelength bands and the correlation of spectral data, the optimal three wavelengths out of 25 are selected to construct a pseudo-RGB (Red, Green, Blue) image. Furthermore, building upon YOLOv7-tiny, an improved lightweight coal gangue recognition method is proposed. Experimental results demonstrate that the improved lightweight model has a computational load of 11.5 GFLOPs, merely 88.5% of the original model's load. The model's detection rate is 77 frames per second (fps), a 23 fps increase compared to the original model. Precision, recall, and average accuracy reach 98.7%, 97.1%, and 98.8% respectively, indicating a 1.5%, 0.2%, and 0.5% improvement over the original model. The approach effectively mitigates instances of omission, enhancing model accuracy and portability. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) have revolutionized artificial lighting, but also exposed the detrimental health effects that stem from insufficient exposure to natural light. Human-centric artificial lighting requires both visual quality and circadian lighting performance that mimics daylight's evolving spectral power distribution (SPD). Here, we present a color-tunable LED-based light source that achieves SPDs similar to various conditions of daylight and incandescent lighting over the range of visible wavelengths. This light source is comprised of a linear combination of light converter channels containing dyes exhibiting thermally activated delayed fluorescence (TADF) fabricated through additive manufacturing, photoexcited by violet-emitting LEDs (VLED). This hybrid light source establishes a new benchmark for state-of-the-art artificial lighting at approximating daylight, with Illuminating Engineering Society (IES) color gamut index Rg values within 3%, IES color fidelity index Rf values within 7% through CCT values ranging from 4277 K to 22,333 K. We propose efficiency metrics to accurately quantify similarity between light sources and the respective reference daylight spectrum encompassing visual and circadian effects, facilitating WLED benchmarking. The efficiency metrics pertaining to circadian lighting performance remain within 10% over the same CCT range. These results advance lighting science to address simultaneously the grand challenges of health and sustainability. [ABSTRACT FROM AUTHOR]

In railway transportation, the evaluation of track irregularities is an indispensable requirement to ensure the safety and comfort of railway vehicles. A promising approach is to directly use vehicle dynamic responses to assess the impact of track irregularities. However, the computational cost of obtaining the dynamic response of the vehicle body using dynamics simulation methods is large. To this end, this study proposes a physics‐informed neural operator framework for vehicle–track spatially coupled dynamics (PINO‐VTSCD) calculation, which can effectively acquire the vehicle dynamic response. The backbone structure of PINO‐VTSCD is established by the branched Fourier neural operator, which features one branch for outputting car body responses and the other branch for estimating the responses of bogie frames, wheelsets, and rails. The relative L2 loss (rLSE) of PINO‐VTSCD under the optimal hyperparameter combination is 4.96%, which is 57% lower than the convolutional neural network‐gated recurrent unit model. Evaluation cases from large‐scale simulations and real‐world track irregularities show that the proposed framework can achieve fast solution in scenarios such as different wavelength‐depth combinations and different wavelength ranges. Compared with the traditional vehicle–track coupled model, the speedup of the PINO‐VTSCD model is 32x. The improved computational efficiency of the proposed model can support many railway engineering tasks that require repetitive calculations. [ABSTRACT FROM AUTHOR]

Different track failures are proven to have different influences on train-track interactions, but their influence on pantograph-catenary interactions has not been investigated thus far. In this work, the influences of typical track failures on pantograph-catenary interaction dynamics are first investigated. A reduced train-track-pantograph-catenary interaction model is developed to study these effects. In this model, the long catenary is reduced to a small moving area around the moving pantograph, and this area is considered and modelled as the reduced catenary model based on the arbitrary Lagrangian–Eulerian method. The reduced catenary model and moving pantograph are formulated as the reduced pantograph-catenary interaction model, and it is further unidirectionally connected with the existing reduced train-track interaction model to formulate the reduced train-track-pantograph-catenary interaction model. The present reduced pantograph-catenary model is first validated by the EN50318-2018 standard, and the influences of track irregularity, track buckling, fastening failure, and track settlement on pantograph-catenary interaction dynamics are studied. The investigation results first show that the track settlement with a long wavelength has a significant influence on the pantograph-catenary interaction dynamics and can even cause contact loss with a good train-track interaction behaviour. Thus, it should be further mentioned in the maintenance of the track structure. [ABSTRACT FROM AUTHOR]

We present exponential wave integrator Fourier pseudospectral (EWI‐FP) methods and establish their error estimates of the fully discrete schemes for the Dirac equation in the massless and nonrelativistic regime. This regime involves a small dimensionless parameter where 0<ε≤1$$ 0<\varepsilon \le 1 $$, and ε$$ \varepsilon $$ is inversely proportional to the speed of light. The solution exhibits highly oscillatory behavior in time and rapid wave propagation in space in this regime. Specifically, the time oscillations have a wavelength of O(ε)$$ O\left(\varepsilon \right) $$, while the spatial oscillations have a wavelength of O(1)$$ O(1) $$, with a wave speed of O(ε−1)$$ O\left({\varepsilon}^{-1}\right) $$. We employ (symmetric) exponential wave integrators for temporal derivatives and Fourier spectral discretization for spatial derivatives. We rigorously derive the error bounds which explicitly depend on the mesh size h$$ h $$, the time step τ$$ \tau $$ and the small dimensionless parameter ε$$ \varepsilon $$. The error estimates for the EWI‐FP methods demonstrate that their meshing strategy requirement (ε$$ \varepsilon $$‐scalability) necessitates setting h=O(1)$$ h=O(1) $$ and τ=O(ε)$$ \tau =O\left(\varepsilon \right) $$ when 0<ε≪1$$ 0<\varepsilon \ll 1 $$. Finally, some numerical examples are provided to validate the error bounds. [ABSTRACT FROM AUTHOR]

Underwater images are often subject to color deviation and a loss of detail due to the absorption and scattering of light. The challenge of enhancing underwater images is compounded by variations in wavelength and distance attenuation, as well as color deviation that exist across different scales and layers, resulting in different degrees of color deviation, attenuation, and blurring. To address these issues, we propose a novel multi-scale and multi-layer lattice transformer (MMLattFormer) to effectively eliminate artifacts and color deviation, prevent over-enhancement, and preserve details across various scales and layers, thereby achieving more accurate and natural results in underwater image enhancement. The proposed MMLattFormer model integrates the advantage of LattFormer to enhance global perception with the advantage of "multi-scale and multi-layer" configuration to leverages the differences and complementarities between features of various scales and layers to boost local perception. The proposed MMLattFormer model is comprised of multi-scale and multi-layer LattFormers. Each LattFormer primarily encompasses two modules: Multi-head Transposed-attention Residual Network (MTRN) and Gated-attention Residual Network (GRN). The MTRN module enables cross-pixel interaction and pixel-level aggregation in an efficient manner to extract more significant and distinguishable features, whereas the GRN module can effectively suppress under-informed or redundant features and retain only useful information, enabling excellent image restoration exploiting the local and global structures of the images. Moreover, to better capture local details, we introduce depthwise convolution in these two modules before generating global attention maps and decomposing images into different features to better capture the local context in image features. The qualitative and quantitative results indicate that the proposed method outperforms state-of-the-art approaches in delivering more natural results. This is evident in its superior detail preservation, effective prevention of over-enhancement, and successful removal of artifacts and color deviation on several public datasets. [ABSTRACT FROM AUTHOR]

Herein, an integrated electro‐optically tunable narrow‐linewidth III–V laser with an output power of 738.8 μW and an intrinsic linewidth of 45.55 kHz at the C band is demonstrated. The laser cavity is constructed using a fiber Bragg grating (FBG) and a tunable Sagnac loop reflector (TSLR) fabricated on thin‐film lithium niobate. The combination of the FBG and the electro‐optically tunable TSLR offers the advantages of single spatial mode, single frequency, narrow linewidth, and wide wavelength tunability for the electrically pumped hybrid integrated laser, which features a frequency tuning range of 20 GHz and a tuning efficiency of 0.8 GHz V−1. [ABSTRACT FROM AUTHOR]

Dark modes are defined by their lack of radiative coupling to the far field. However, the modes can be made to couple to far field radiation by symmetry breaking. For a resonant dimer, obliquely incident waves can create a phase difference in the currents between the elements, resulting in symmetry breaking. This work reduces symmetry breaking effects by minimizing the size of a dimer of dipolar elements with respect to its resonant wavelength. We obtain a mode that can experimentally be excited from the near field but has negligible excitation in the far field for obliquely incident waves. Such a mode could have use in wireless security applications. [ABSTRACT FROM AUTHOR]

The evolution of the cathodoluminescence spectra from commercially available nanodiamonds with high density of nitrogen‐vacancy defects has been studied in a large wavelength range, from 200 to 800 nm, and temperatures from 5 to 300 K, in order to achieve a temperature probe with high spatial resolution. The full width at half maximum of the peak associated to the neutral charge state of the NV center has been found to evolve with temperature in a predictable way, although its value may vary from sample to sample. We have attributed this shift to the differences in the nanodiamonds surface chemistry. [ABSTRACT FROM AUTHOR]

Uniaxial materials have achieved new prominence in photonics because they can have hyperbolic spectral regions with metallic (ε<0) and dielectric (ε>0) permittivities along different crystal axes. In the lossless case, this results in an open hyperboloid dispersion relation, allowing materials to support highly confined modes with extremely large wavevectors. However, even small losses change the character of the hyperbolic dispersion from open hyperboloids to closed surfaces with finite maximum k, significantly limiting the extent to which highly-confined modes can be achieved. Here, we derive a simple analytic formula for the dispersion relation in the presence of loss and show that for some typical materials the maximum wavevector in hyperbolic materials is roughly ten times the free-space. The scaling of the maximum wavevector is derived, and it is shown that there is a universal scaling relation between the propagation length and the wavelength, which implies that the shortest wavelengths in any hyperbolic material are strongly attenuated. [ABSTRACT FROM AUTHOR]

Self‐protective carbonized polymer dots (CPDs) with advantageous crosslinked nano‐structures have attracted considerable attention in metal‐free room temperature phosphorescence (RTP) materials, whereas their RTP emissions are still limited to short wavelength. Expanding their RTP emissions to Near‐Infrared (NIR) range is attractive but suffers from the difficulties in constructing narrow energy levels and inhibiting intense non‐radiative decay. Herein, a crosslink‐enhanced emission (CEE)‐dominated construction strategy was proposed, achieving desired NIR RTP (710 nm) in self‐protective CPDs for the first time. Structural factors, i.e. crosslinking (covalent‐bond CEE), conjugation (conjugated amine with bridging N−H and C=C group), and steric hindrance (confined‐domain CEE), were confirmed indispensable for triggering NIR RTP emission in CPDs. Contrast experiments and theoretical calculations further revealed the rationality of the design strategy originating from CEE in terms of promoting the narrow energy level emission of triplet excitons and inhibiting the non‐radiative quenching. This work not only firstly achieves NIR RTP in self‐protective CPDs but also helps understand the origin of NIR RTP to further guide the synthesis of diverse CPDs with efficient long‐wavelength RTP emission. [ABSTRACT FROM AUTHOR]

The development of metasurfaces necessitates the rapid fabrication of nanoarrays on diverse substrates at large scales, the preparation of patterned nanoarrays on both planar and curved surfaces, and even the creation of nanoarrays on prefabricated structures to form multiscale metastructures. However, conventional fabrication methods fall short of these rigorous requirements. In this work, a novel self‐assembly hybrid manufacturing (SAHM) method is introduced for the rapid and scalable fabrication of shape‐controllable nanoarrays on various rigid and flexible substrates. This method can be easily integrated with other fabrication techniques, such as lithography and screen printing, to produce patterned nanoarrays on both planar and non‐developable surfaces. Utilizing the SAHM method, nanoarrays are fabricated on prefabricated micropillars to create multiscale pillar‐nanoarray metastructures. Measurements indicate that these multiscale metastructures can manipulate electromagnetic waves across a range of wavelengths. Therefore, the SAHM method demonstrates the potential of multiscale structures as a new paradigm for the design and fabrication of metasurfaces. [ABSTRACT FROM AUTHOR]

Infrared polarization detection has attracted wide applications in military and civilian fields by demonstrating more accurate target detection and identification capabilities due to more dimensional target information. A multifocal metalens for simultaneous detection of the polarization state of incident light at dual wavelengths is proposed based on the independent control of orthogonally polarized light. When light is incident at different wavelengths, the metalens array splits and focuses the light on three different polarization bases to form six focal points with various positions. When the incident light with varying states of polarization of dual wavelengths to be detected passes through the substrate and reaches the metalens array, the incident light detected in each wavelength forms six focal points at different positions of the focal plane of the metalens. The Stokes parameters are calculated based on the intensities of the six polarization components in the same focal plane to determine the polarization data of the azimuthal and elliptic angles of the incident light detected in each wavelength. In addition, the theoretical Stokes parameters of incident light with different polarization states at two wavelengths are compared with the reconstructed Stokes parameters, proving our method's validity. The device can directly examine the polarization state of the incident light in mid-wave infrared and long-wave infrared, significantly simplifying the polarization detection system. [ABSTRACT FROM AUTHOR]

We demonstrated high-performance 8.9 μ m cutoff wavelength nBn InAs/InAsSb type-II strained-layer superlattice (T2SL). These detectors exhibit a long minority carrier (hole) lifetime of 1.2 μ s at 80 K, high quantum efficiency of 40% for back-side illuminated devices without antireflection coating, and low dark current density of 4.6 × 10−6 A/cm2 at 80 K. We measured absorption, minority carrier (hole) lifetime, quantum efficiency, and spectral response as a function of the temperature and applied bias. We investigated the temperature dependence of the hole diffusion length and mobility and found that their values increase with temperature from 1.3 μ m and 6.5 cm2/Vs at 30 K to 6.5 μ m and 36 cm2/Vs at T = 90 K. We compared the measured diffusion length and mobility of holes in long-wavelength infrared (LWIR) T2SL with these parameters of a high-performance mid-wavelength infrared (MWIR) T2SL. Unexpectedly, hole mobility in LWIR T2SL was found to be higher than in MWIR that is contrary to the theoretical predictions. [ABSTRACT FROM AUTHOR]

All-optical nonlinear activation functions (NAFs) are crucial for enabling rapid optical neural networks (ONNs). As linear matrix computation advances in integrated ONNs, on-chip all-optical NAFs face challenges such as limited integration, high latency, substantial power consumption, and a high activation threshold. In this work, we develop an integrated nonlinear optical activator based on the butt-coupling integration of two-dimensional (2D) MoTe2 and optical waveguides (OWGs). The activator exhibits an ultra-broadband response from visible to near-infrared wavelength, a low activation threshold of 0.94 μW, a small device size (~50 µm2), an ultra-fast response rate (2.08 THz), and high-density integration. The excellent nonlinear effects and broadband response of 2D materials have been utilized to create all-optical NAFs. These activators were applied to simulate MNIST handwritten digit recognition, achieving an accuracy of 97.6%. The results underscore the potential application of this approach in ONNs. Moreover, the classification of more intricate CIFAR-10 images demonstrated a generalizable accuracy of 94.6%. The present nonlinear activator promises a general platform for three-dimensional (3D) ultra-broadband ONNs with dense integration and low activation thresholds by integrating a variety of strong nonlinear optical (NLO) materials (e.g., 2D materials) and OWGs in glass. Nonlinear activation function (NAF) devices are important for the implementation of optical neural networks. Here, the authors report the integration of 2D MoTe2 with optical waveguides to fabricate broadband all-optical NAF devices exhibiting activation thresholds down to 0.94 μW, a device size of ~50 μm2, and response rates up to 2.08 THz. [ABSTRACT FROM AUTHOR]

In chromatic confocal line sensors, calibration is usually divided into peak extraction and wavelength calibration. In previous research, the focus was mainly on peak extraction. In this paper, a kernel-based algorithm is proposed to deal with wavelength calibration, which corresponds to the mapping relationship between peaks (i.e., the wavelengths) in image space and profiles in physical space. The primary component of the mapping function is depicted using polynomial basis functions, which are distinguished along various dispersion axes. Considering the unknown distortions resulting from field curvature, sensor fabrication and assembly, and even the inherent complexity of dispersion, a typical kernel trick-based nonparametric function element is introduced here, predicated on the notion that similar processes conducted on the same sensor yield comparable distortions.To ascertain the performance with and without the kernel trick, we carried out wavelength calibration and groove fitting on a standard groove sample processed via glass grinding and with a reference depth of 66.14 μm. The experimental results show that depths calculated by the kernel-based calibration algorithm have higher accuracy and lower uncertainty than those ascertained using the conventional polynomial algorithm. As such, this indicates that the proposed algorithm provides effective improvements. [ABSTRACT FROM AUTHOR]

Macrocyclic Cu(I)–pyrazolate tetramers (Cu4pz4) can fold into compact structures with luminescent Cu4 cores whose emission wavelengths are sensitive to steric effects along the periphery of the macrocycle. Introducing CF3 at the C4 position of 3,5-di-tBu-pyrazolate increases steric crowding that modifies the conformational behavior of the Cu4pz4 complex, highlighted by a low-temperature martensitic transition. Variable-temperature analysis of solid-state luminescence reveal an unexpected blueshifting of emission with rising temperature. [ABSTRACT FROM AUTHOR]

Understanding the lattice thermal conductivity (κl) of β-Ga2O3 is very intriguing owing to its advantages in high-voltage and high-temperature applications. Despite several attempts, the underlying mechanism and causes of the notable discrepancies found in the κl values of β-Ga2O3 along [100] and [001] directions calculated using first principles remained unresolved. We demonstrate that the understanding of the nature of chemical bonding is crucial to overcome the inconsistency in theoretically reported κl values. In low-symmetry structures such as β-Ga2O3, the nature of the interactions is primarily long-range; therefore, a sufficiently large supercell inclusive of various bonding characteristics is required to capture relevant phonon wavelengths. Bonding nature-aware structure modeling allows precise estimation of acoustic and optical mode contributions towards κl. Additionally, phonon mean free path analysis confirms that considering only third-order interaction terms is adequate to determine the κl of β-Ga2O3. The calculated κl values are in excellent agreement with experimentally reported values in all three directions. Our results establish that the bonding nature and its influence on phonon scattering are essential to consider in calculating κl accurately. [ABSTRACT FROM AUTHOR]