Short Wavelength Research Articles

Improved performance of land-fixed oscillating water column through dual chamber design

Improvements to the hydrodynamic efficiency of oscillating water columns (OWC) have the potential to influence commercial OWC adoption. The main goal of this study is to determine whether dual chamber OWCs with either a shared turbine or dual turbines can improve the hydrodynamic efficiency of the OWC through two-dimensional numerical simulations using computational fluid dynamics. In the numerical simulations, water depth is 0.8 m and the total length of the two chambers is 0.6 m. Numerical results show that when the non-dimensional turbine coefficient is 0.192, 1.432, and 3.070, a dual chamber dual turbine configuration can achieve between 7.6% to 26.8% greater hydrodynamic efficiency than both the single chamber single turbine and the dual chamber shared turbine configuration. Dual chamber, dual turbine configurations can increase hydrodynamic efficiency by operating over a broader range of wavelengths due to multiple resonant frequencies and are not affected by phase differences at shorter wavelengths.

Ultrashort Phase-Matching Wavelength and Strong Second-Harmonic Generation in Deep-UV-Transparent Oxyfluorides by Covalency Reduction.

The development of urgently-needed ultraviolet (UV)/deep-UV nonlinear optical (NLO) materials has been hindered by contradictory requirements of the microstructure, in particular the need for a strong second-harmonic generation (SHG) response as well as a short phase-matching (PM) wavelength. We herein employ a "de-covalency" band gap engineering strategy to adjust the optical linearity and nonlinearity. This has been achieved by assembling two types of transition-metal (TM) polyhedra ([TaO2 F4 ] and [TaF7 ]), affording the first tantalum-based deep-UV-transparent NLO materials, A5 Ta3 OF18 (A = K (KTOF), Rb (RTOF)). Experimental and theoretical studies reveal that the highly ionic bonds and strong electropositivity of tantalum in the two oxyfluorides induce record short PM wavelengths (238 (KTOF) and 240 (RTOF) nm) for d0 -TM-centered oxides, in addition to strong SHG responses (2.8 × KH2 PO4 (KTOF) and 2.6 × KH2 PO4 (RTOF)), and sufficient birefringences (0.092 (KTOF) and 0.085 (RTOF) at 546 nm). These results not only broaden the available strategies for achieving deep-UV NLO materials by exploiting the currently neglected d0 -TMs, but also push the shortest PM wavelength into the short-wavelength UV region.

Ultrashort Phase‐Matching Wavelength and Strong Second‐Harmonic Generation in Deep‐UV‐Transparent Oxyfluorides by Covalency Reduction

AbstractThe development of urgently‐needed ultraviolet (UV)/deep‐UV nonlinear optical (NLO) materials has been hindered by contradictory requirements of the microstructure, in particular the need for a strong second‐harmonic generation (SHG) response as well as a short phase‐matching (PM) wavelength. We herein employ a “de‐covalency” band gap engineering strategy to adjust the optical linearity and nonlinearity. This has been achieved by assembling two types of transition‐metal (TM) polyhedra ([TaO2F4] and [TaF7]), affording the first tantalum‐based deep‐UV‐transparent NLO materials, A5Ta3OF18 (A = K (KTOF), Rb (RTOF)). Experimental and theoretical studies reveal that the highly ionic bonds and strong electropositivity of tantalum in the two oxyfluorides induce record short PM wavelengths (238 (KTOF) and 240 (RTOF) nm) for d0‐TM‐centered oxides, in addition to strong SHG responses (2.8 × KH2PO4 (KTOF) and 2.6 × KH2PO4 (RTOF)), and sufficient birefringences (0.092 (KTOF) and 0.085 (RTOF) at 546 nm). These results not only broaden the available strategies for achieving deep‐UV NLO materials by exploiting the currently neglected d0‐TMs, but also push the shortest PM wavelength into the short‐wavelength UV region.

Structural, photoluminescence, and photocatalytic performances of Ce3+ -activated orthovanadate oxides M3 (VO4 )2 (M: Mg or Zn) synthesized by solution combustion route.

This paper presents a research investigation into the synthesis of vanadate oxides M3 (VO4 )2 (M: Mg or Zn) using the solution combustion method and investigates their structural, photoluminescence, and photocatalytic properties after introducing cerium (Ce) as a dopant. The resulting synthesized samples all display an orthorhombic crystalline structure with crystallite sizes ranging from 71 to 110 nm. Morphological diversity among the samples is revealed through field-emission scanning electron microscopy (FESEM) imagery. Diffuse reflectance spectroscopy discloses that the introduction of Ce3+ as a dopant leads to an increase in the band gap energy. Notably, when excited at a wavelength of 340 nm, the photoluminescence emission intensity reaches its peak across all samples. This intensity undergoes enhancement due to Ce3+ doping, causing a slight shift toward shorter wavelengths attributable to the augmented band gap resulting from the dopant. Markedly, among the investigated materials, Ce3+ -activated Mg3 (VO4 )2 stands out with the most pronounced emission intensity, positioning it as a highly promising luminescent material. Additionally, the incorporation of Ce3+ has a positive effect on the photocatalytic performance of Mg3 (VO4 )2 , resulting in notable improvement.

Ni2+-doped MgTa2O6 phosphors capable of near-infrared II and III emission under blue-light excitation

Presently, Ni2+-activated near-infrared (NIR) phosphors still have disadvantages such as relatively short emission wavelength and narrow half-peak width, mismatched excitation wavelength to that of commercially available high-efficiency blue chips. Here, Ni2+-doped tetragonal MgTa2O6 NIR phosphor was successfully prepared by high-temperature solid phase method. The matrix material provided an octahedral lattice for Ni2+ to replace Ta5+ in the [TaO6] octahedron of the crystal lattice. Under the excitation of 470 nm blue light, Ni2+ was excited through 3T2(F)→3A2(F) spin-allowed transition and emitted an ultra-broadband NIR light that was 1300–2000 nm in wavelength, peaked ∼ 1620 nm, covered the NIR-II and NIR-III regions, had a full width at half maximum reached 297 nm, and a PLQY of 25.62 %. The unique ultra-broadband and long wavelength NIR emission by this phosphor was derived from Ni2+ which is situated in a weak crystal field environment due to space asymmetric distortion caused by a high charge polarization surrounding the center of the [TaO6] octahedron in a MgTa2O6 matrix. A NIR pc-LED was constructed using Ni2+-doped near-infrared phosphors packaged with a commercial high-efficiency blue LED chip (@ 470 nm), and its application prospect was demonstrated by NIR night vision monitoring and nondestructive imaging of venous in human fingers.

On the More Complex Wavelength Dependency of Airy Isostasy in Icy Shells of Ocean Worlds

AbstractThe topography of ocean worlds is often used to infer ice shell thicknesses by assuming topography is compensated by a basal root. We systematically test the stability of isostatically compensated topography in ice shells. At short horizontal wavelengths, lithospheric strength can support surface topography, while at long wavelengths, buoyancy forces can support topography at the surface and base of the ice shell over geologic time scales. These behaviors are also seen for Airy isostasy in terrestrial worlds. Contrastingly at intermediate scales, the mechanically weak lower ice shell can inhibit the transfer of buoyancy forces to the surface. Factors such as surface temperature can alter the contribution of lithospheric strength, decreasing the stability of a compensating root. This nuanced understanding of icy shell lithospheres provides crucial insights for interpreting surface features and inferring underlying ice shell thickness, with substantial relevance for upcoming space missions to the Jovian system.

600-GHz Fourier imaging based on heterodyne detection at the 2nd sub-harmonic.

Fourier imaging is an indirect imaging method which records the diffraction pattern of the object scene coherently in the focal plane of the imaging system and reconstructs the image using computational resources. The spatial resolution, which can be reached, depends on one hand on the wavelength of the radiation, but also on the capability to measure - in the focal plane - Fourier components with high spatial wave-vectors. This leads to a conflicting situation at THz frequencies, because choosing a shorter wavelength for better resolution usually comes at the cost of less radiation power, concomitant with a loss of dynamic range, which limits the detection of higher Fourier components. Here, aiming at maintaining a high dynamic range and limiting the system costs, we adopt heterodyne detection at the 2nd sub-harmonic, working with continuous-wave (CW) radiation for object illumination at 600 GHz and local-oscillator (LO) radiation at 300 GHz. The detector is a single-pixel broad-band Si CMOS TeraFET equipped with substrate lenses on both the front- and backside for separate in-coupling of the waves. The entire scene is illuminated by the object wave, and the Fourier spectrum is recorded by raster scanning of the single-detector unit through the focal plane. With only 56 µW of power of the 600-GHz radiation, a dynamic range of 60 dB is reached, sufficient to detect the entire accessible Fourier space spectrum in the test measurements. We present a detailed comparison between plane-to-plane imaging and Fourier imaging, and show that, with both, a lateral spatial resolution of better than 0.5 mm, at the diffraction limit, is reached.

Fast Calculation on Atmospheric Rayleigh Scattering Extinction Optical Depth for Day/Night Band Radiative Transfer Model With Periodic Lunar Illumination

AbstractRayleigh scattering effect inspired by tiny atmospheric molecules generates significant extinction at relatively short wavelength, such as Day/Night Band (DNB) covering visible (VIS, 0.4–0.76 μm) and near‐infrared (NIR, 0.76–1.0 μm) wavelengths. This salient extinction effect coupled with periodic changes in lunar illumination and wide DNB will further lead to increased complexity in nocturnal fast radiative transfer model (RTM) calculation of DNB. For these reasons, this study is aimed at developing a precise and robust fast calculation method on Rayleigh scattering extinction optical depth (RayOD) for pertinent fast RTM calculation of DNB. Firstly, we coupled the lunar spectral irradiance model and the parameterized Rayleigh scattering extinction calculation module into a RTM for forward simulations. Moreover, we find that the errors in DNB‐averaged RayOD calculated from the classical fast algorithm from RTTOV (Radiative Transfer for TOVS) of training the DNB instrument coefficients (about 20% of relative error in reflectance) and the parameterization method using the central wavelength of DNB (about 5%) are too large to be tolerable in fast RTM. Finally, to address this issue, we skillfully conceptualize a new equivalent optimal central wavelength algorithm to retrieve a dynamically wavelength in DNB using observation scattering and lunar phase angles for rapidly calculating DNB‐averaged RayOD. The relative errors in simulated reflectance from coupled RTM aforementioned are subtle nuances, which are about 10−5∼10−6 order of magnitude. Besides, this robust algorithm can also correct the relative error of about 1% at dark surface caused by periodic changes in lunar illumination.

The morphology, inflorescence yield, and secondary metabolite accumulation in hemp type Cannabis sativa can be influenced by the R:FR ratio or the amount of short wavelength radiation in a spectrum

The effect of light spectra on the quality of multiple crops has been established, however, the scientific evidence related to light quality, cannabis (Cannabis sativa) morphology, and the secondary metabolite accumulation in the female inflorescences is still sparse. C. sativa inflorescences harvested for pharmaceutical purposes are primarily cultivated in controlled environments for their secondary metabolite compounds, such as cannabinoids, terpenes, and flavonoids. Indoor cultivation allows precise control over the environmental parameters, including light, which impact the inflorescence yield and quality. The effect of long (far-red) and short wavelength (blue, UV-A, UV-B) radiation on the morphology, inflorescence yield, and floral cannabinoid and terpene concentrations in a cannabidiol (CBD) dominant hemp type C. sativa genotype, FINOLA, was studied in two experiments. In the first experiment, two treatments, LOW R:FR (R:FR ratio of 1) and HIGH R:FR (R:FR ratio of 11), were compared. The second experiment included four treatments with varying blue, UV-A, and UV-B radiation content (CONTROL, BLUE, UVA, and UVB). LOW R:FR ratio treatment increased plant height and decreased inflorescence yield. HIGH R:FR ratio treatment increased CBD, tetrahydrocannabivarin acid (THCVA), and cannabigerolic acid (CBGA), and the sum of measured terpene concentrations compared with the LOW R:FR ratio treatment. Short wavelength radiation treatments did not impact inflorescence yield or plant morphology. BLUE and UVB treatments increased the cannabinoid, THCVA, concentration, but no difference in the sum of measured cannabinoid concentrations was observed between the treatments. UVB treatment increased the monoterpene, myrcene, concentration, but had no impact on the sum of measured terpenes concentration. In conclusion, the morphology, yield, and secondary metabolite accumulation in C. sativa can be influenced by altering the R:FR ratio or the amount of short wavelength radiation in a spectrum.

Scalable and robust beam shaping using apodized fish-bone grating couplers.

Efficient power coupling between on-chip guided and free-space optical modes requires precision spatial mode matching with apodized grating couplers. Yet, grating apodizations are often limited by the minimum feature size of the fabrication approach. This is especially challenging when small feature sizes are required to fabricate gratings at short wavelengths or to achieve weakly scattered light for large-area gratings. Here, we demonstrate a fish-bone grating coupler for precision beam shaping and the generation of millimeter-scale beams at 461 nm wavelength. Our design decouples the minimum feature size from the minimum achievable optical scattering strength, allowing smooth turn-on and continuous control of the emission. Our approach is compatible with commercial foundry photolithography and has reduced sensitivity to both the resolution and the variability of the fabrication approach compared to subwavelength meta-gratings, which often require electron beam lithography.

Excitons in (Al,Ga)N quantum dots and quantum wells grown on (0001)-oriented AlN templates: Emission diagrams and valence band mixings

The luminescence efficiency of AlxGa1−xN quantum dots (QDs) and quantum wells (QWs), buried in AlN cladding layers and emitting in the ultraviolet range between 234 and 310 nm, has been investigated. The growth and optical properties have been done using similar aluminum composition (varying from 0.4 to 0.75) for both QDs and QWs. In order to compare as much as possible the optical properties, the QWs were fabricated with a growth time tuned such that the QW width is similar to the average height of the QDs. The photoluminescence (PL) showed emission ranging from 4 to 5.4 eV, putting into evidence differences in terms of full width at half maximum, PL intensity, and asymmetry of the line shape between QDs and QWs. The results show shorter wavelengths and a slightly narrower PL linewidth for QWs. To determine the light emission dependence with the electric field direction in the crystal, the evolutions of the emission diagrams for all samples were recorded along two orthogonal directions, namely, the “in-plane” (growth) and the “on-side” directions, from which the light emission was collected. For the whole QDs and QWs samples' series, the shapes of the emission diagram indicate emission in both in-plane and on-side directions, as evidenced by intra-valence band mixings caused by strain effects combined with the anisotropic Coulomb interactions that are particularly contributing to the polarization at wavelengths below 260 nm. Furthermore, the degree of polarization, determined for each sample, showed good agreement with results from the literature.

High-confinement alumina waveguides with sub-dB/cm propagation losses at 450 nm

Amorphous alumina is highly transparent across the visible spectrum, making it a promising candidate for low-loss waveguiding at short wavelengths. However, previous alumina waveguide demonstrations in the visible region have focused on low- to moderate-confinement waveguides, where the diffuse mode reduces the design flexibility and integration density of photonic integrated circuits. Here, we have developed a high-quality etch mask and a highly selective BCl3 plasma etch, allowing etching of amorphous alumina waveguides up to 800 nm thick. Using this process, we have fabricated waveguides using an alumina film grown by atomic layer deposition (ALD) which are the lowest-loss high-confinement waveguides for blue light to date: we achieve single-mode propagation losses of 0.8 dB/cm at a propagation wavelength of 450 nm.

Mask-less Laser Direct Imaging & Adaptive Patterning for Fan-Out Heterogeneous Integration

Mask-less Laser Direct Imaging & Adaptive Patterning for Fan-Out Heterogeneous Integration

Analysis of the optical response of reptile tissues in the visible and UV applying the KKR method.

Structural colors in nature are frequently produced by the ordered arrangement of nanoparticles. Interesting examples include reptiles and birds utilizing lattice-like formation of nanoparticles to produce a variety of colors. A famous example is the panther chameleon which is even able to change its color by actively varying the distance between guanine nanocrystals in its skin. Here, we demonstrate that the application of rigorous electromagnetic methods is important to determine the actual optical response of such biological systems. By applying the Korringa-Kohn-Rostoker (KKR) method we calculate the efficiencies of the reflected diffraction orders that can be viewed from directions other than the specular. Our results reveal that important characteristics of the reflectance spectra, especially within the ultraviolet (UV) and short visible wavelengths region, cannot be predicted by approximate models like the often-applied Maxwell-Garnett approach. Additionally, we show that the KKR method can be employed for the design of multi-layer structures with a desired optical response in the UV regime.

Artificial light at night alters predation on colour-polymorphic camouflaged prey

Artificial light at night (ALAN) disrupts biological processes across taxa and at all levels of organisation. Despite growing interest in this globally pervasive sensory pollutant, its impact on colour-guided processes remains largely unexplored. This is especially concerning given the rapid transition in recent years away from narrow-spectrum lighting and towards broad-spectrum options such as white LEDs, which are rich in the short wavelengths of light to which many taxa are particularly sensitive. Camouflage is particularly likely to be disrupted by broader spectra of ALAN due to changes in conspicuousness in background matching prey, which may alter prey recognition in visually guided predators. We simulated natural intensities of moonlight with and without ALAN, using both broad-spectrum (‘white’) ALAN and ALAN filtered to remove the characteristic short (blue) wavelength peak of broad-spectrum LEDs to test whether filtering might mitigate their effects. We tested how exposure to these light treatments impacted predator-prey interactions, using the intertidal crab Carcinus maenas and contrasting colour morphs of the colour-polymorphic snail Littorina obtusata as a model system. Exposure to broad-spectrum ALAN reduced overall predation and reversed the pattern of colour-based prey selection observed under control conditions. Snails were 55 % less likely to be attacked under broad-spectrum ALAN than in control conditions, with likelihood decreasing over 70 % for yellow snails. Yellow snails were over 26 % more likely to be attacked than brown ones under control conditions, but brown snails were over 40 % more likely to be attacked than yellow ones under broad-spectrum ALAN. Exposure to filtered ALAN removed any significant colour-based difference in prey recognition. Our results demonstrate that spectral composition is a crucial aspect of ALAN as a sensory pollutant, capable of instigating profound changes in predator-prey interactions that could drive changes in population demography and increase morphological homogeneity in species that depend on colour polymorphism for camouflage.

Harnessing Short-Range Surface Plasmons in Planar Silver Films via Disorder-Engineered Metasurfaces.

Short-range surface plasmon polaritons (SR-SPPs) can arise due to the hybridization of surface plasmon polaritons propagating along the two interfaces of a thin metal slab. In optics, they have gained particular interest for imaging and sensing applications because of their short wavelengths at optical frequencies along with strong field enhancement. However, mediating the interaction of SR-SPPs with photons in planar films is difficult because of the large momentum mismatch. For efficient coupling, nanostructuring such thin films (∼20 nm thickness), or placing metallic nanostructures in close proximity to the planar film, is technologically challenging and can strongly influence the SR-SPP properties. In this article, harnessing SR-SPPs in planar silver films is demonstrated using disorder-engineered metasurfaces. Disorder-engineering is realized by the light-controlled growth of silver nanoparticles. The dispersion of the hybrid modes with the silver thickness is measured and compared with simulations. We anticipate these results to introduce a facile method for harnessing SR-SPPs in planar optical systems and make use of their promising properties for imaging, sensing, and nonlinear optics.

Ultra-broadband solar absorber based on TiN metamaterial from visible light to mid-infrared

We study and design an ultra-broadband absorber based on TiN metamaterial. The proposed structure consists of a rectangle pillar, two rectangle rings, an Al2O3 substrate, and a TiN substrate. The average absorption in the range of 300–4962 nm is 97.02%. The physical mechanism is illustrated by electric-field and magnetic-field distributions, including the dielectric lossy property of TiN itself in shorter wavelengths, Fabry–Perot resonance, and local surface plasmon resonance in longer wavelengths. The result indicates that the energy absorption spectrum can be well matched with the standard solar spectrum under AM 1.5 over the full range of 300–5000 nm, and then we compare the solar absorption spectrum of different structures. In the end, the influence of different materials and geometrical parameters on absorption is investigated. The absorber can achieve ultra-broadband perfect absorption, and has a simple structure that is easy to manufacture. The result of this work can be applied in many potential fields, for example, thermal photovoltaic power generation, infrared imaging, solar cells, and other optoelectronic devices.

Mitochondria-targeted NO donor enables synergistic NO and photodynamic therapies for effective inhibition of cancer cell proliferation and migration

Previously reported light-controlled nitric oxide donors are usually activated by blue or green light. The insufficient ability of short wavelength light to penetrate tissues and its potential phototoxicity to living organisms greatly restricted in vivo applications. This study presents the development of a novel mitochondria-targeted nitric oxide donor, R–NO, capable of controlled nitric oxide and photosensitizer release under white light irradiation in mitochondria. R–NO is capable of generating nitric oxide and R–NH, a novel photosensitizer that can produce O2•- upon irradiation with a single light source. In addition, the highly toxic ONOO− can be produced by the rapid reaction of nitric oxide and O2•-. Harnessing the synergistic effects of PDT, nitric oxide therapy and highly toxic ONOO−, the proliferation and migration of cancer cells can be significantly inhibited upon light irradiation with R–NO. Futhermore, our MTT experiments demonstrated that simultaneous producing of O2•- and nitric oxide in the same region is crucial for efficient cancer cell inhibition. These interesting findings underscore the enhanced synergistic effect achieved by combining PDT and NO therapy in a single molecule for cancer cell treatment.

An adaptive approach to remove tensile instability in SPH for weakly compressible fluids

Smoothed Particle Hydrodynamics (SPH) is plagued by the phenomenon of tensile instability, which is the occurrence of short wavelength zero energy modes resulting in unphysical clustering of particles. The root cause of the instability is the shape of derivative of the compactly supported kernel function which may yield negative stiffness in the particle interaction under certain circumstances. In this work, an adaptive algorithm is developed to remove tensile instability in SPH for weakly compressible fluids. Herein, a B-spline function is used as the SPH kernel and the knots of the B-spline are adapted to change the shape of the kernel, thereby satisfying the condition associated with stability. The knot-shifting criterion is based on the particle movement within the influence domain. This enables the prevention of instability in fluid problems where excessive rearrangement of particle positions occurs. A 1D dispersion analysis of an Oldroyd B fluid material model is performed to show how the algorithm prevents instabilities for short wavelengths but ensures accuracy at large wavelengths. The efficacy of the approach is demonstrated through a few benchmark fluid dynamics simulations where a visco-elastic Oldroyd B material model and a non-viscous Eulerian fluid material model are considered.

The Stability of Shear Flow of Viscous Electrically Conducting Fluid in the Presence of Velocity and Magnetic Shears

Abstract 
 The linear stability of shear flow of an incompressible, viscous electrically conducting fluid permeated by sheared magnetic field is investigated. An unbounded two layer model consisting of different viscosity and magnetic diffusivity fluids with different velocity shear and magnetic shears is examined for the two dimensional disturbances. An analytical study using the short wavelength approximation shows that the configuration is always unstable for different diffusivities and for different shears. When the magnetic field does not vanish on the interface it may be stabilizing or destabilizing the system depending on the values of certain parameters.
 Key words: Stability, shear flow, electrically conducting fluid, unbounded two layer model magnetic shear, short wavelength approximation