Short Wavelength Research Articles

Modal Phase-Matched Bound States in the Continuum for Enhancing Third Harmonic Generation of Deep Ultraviolet Emission.

Coherent deep ultraviolet (DUV) light sources are crucial for various applications such as nanolithography, biomedical imaging, and spectroscopy. DUV light sources can be generated by using conventional nonlinear optical crystals (NLOs). However, NLOs are limited by their bulky size, inadequate transparency at the DUV regime, and stringent phase-matching requirements for harmonic generation. Recently, dielectric metasurfaces support high Q-factor resonances and offer a promising approach for efficient harmonic generation at short wavelengths. In this study, we demonstrated a crystalline silicon (c-Si) metasurface simultaneously exciting modal phase-matched bound states in the continuum (BIC) resonance at the fundamental wavelength of 840 nm with a higher degree of freedom for precise control of the BIC resonance and a plasmonic resonance at the wavelength of 280 nm in the DUV to enhance third harmonic generation (THG). We experimentally achieved a Q-factor of ∼180 owing to the relatively large refractive index of the c-Si and the geometric symmetry breaking of the structure. We realized THG at a wavelength of 280 nm with a power of 14.5 nW by using a peak power density of 15 GW/cm2 excitation. The measured THG power is 14 times higher than the state-of-the-art THG dielectric metasurfaces using the same peak power density in the DUV regime, and the maximum obtained THG power enhancement factor is up to 48. This approach relies on the significant third-order nonlinear susceptibility of c-Si, the interband plasmonic nature of the c-Si in the DUV, and the strong field confinement of BIC resonance to boost overall nonlinear conversion efficiency to 5.2 × 10-6% in the DUV regime. Our work shows the potential of c-Si BIC metasurfaces for developing efficient and ultracompact DUV light sources using high-efficacy nonlinear optical devices.

Spectral Investigations of Fluorescence Tracers in Automotive and Aviation Fuels under Cryogenic Conditions

This study investigated spectral laser-induced fluorescence signals of dyes in fuels for automotive and aerospace applications under low temperatures and cryogenic conditions down to 183 K. For this purpose, a fluorescence chamber was developed based on cooling with liquid nitrogen. The design enabled a minimal inner chamber temperature of 153 K. Furthermore, the applicability of two-color LIF for liquid thermometry was evaluated under these conditions. The temperature determination was based on the temperature-sensitive fluorescence intensity ratio of the special dyes doped into the fuels determined in suitable spectral regions, which represented common bandpass filters. For this purpose, the fluorescence signals of the dye doped into the gasoline and jet fuel surrogate isooctane were tested as well as blends of isooctane and the ethanol biofuels E20 (comprising 80 vol.% isooctane and 20 vol.% ethanol), E40, and E100. Additionally, a realistic multi-component fuel Jet A-1 mixed with a suitable fluorescence dye was investigated. E100 was doped with Eosin-Y, and the remaining fuels were doped with Nile red. Temperature-dependent spectral LIF intensities were recorded in the range of 183 K–293 K, which simulate extreme environments for aerospace and automotive applications. Frozen fuel–dye mixtures cause significant extinction effects and prevent sufficient signal detection at low and cryogenic temperatures, defining the detection limit. A temperature decrease led to a spectral shift in the emission peaks of E100 doped with Eosin-Y toward shorter wavelengths, while the spectra of mixtures doped with Nile red were shifted toward longer wavelengths. The suggested bandpass filters produced the temperature-sensitive intensity ratio (the average over the temperature interval) of the dyes with the largest sensitivity for Jet A-1 (5.2%/K), followed by E100 (4.95%/K), E40 (4.07%/K), E20 (3.23%/K), and isooctane (3.07%/K), even at cryogenic temperatures.

Anion Doping of Tungsten Oxide with Nitrogen: Reactive Magnetron Synthesis, Crystal Structure, Valence Composition, and Optical Properties

Anion doping of tungsten trioxide by nitrogen is used to obtain electrochrome cathode materials, the spectral transmittance of which can be controlled by the doping level. A series of samples was synthesized by reactive magnetron sputtering of a metal tungsten target in a mixture of argon, nitrogen, and oxygen gases, the flow rate of the latter was varied at a constant pressure of the gas mixture. Warm-colored tungsten oxynitride films were prepared at higher doping levels with their morphology and elemental composition characterized using scanning electron microscopy, crystal structure described using X-ray diffraction and the valence state of constituents revealed with X-ray photoelectron spectroscopy techniques. Optical properties were measured by making use of transmission spectrophotometry and spectroscopic ellipsometry. These extensive experimental studies revealed an increase in absorption towards shorter wavelengths below the wavelength of 0.5 µm with an increase in the doping level. At the same time, it was found that with an increase in the doping level, partial reduction of the tungsten occurs, and the fraction of non-stoichiometric oxygen steadily increases to half of the total oxygen content. It is a common belief that the imperfection of the doped material facilitates the intercalation of the material by electrolyte ions.

Effects of Light Color on the Growth, Feeding, Digestion, and Antioxidant Enzymes of Tripneustes gratilla (Linnaeus, 1758).

To study the effects of light color on sea urchin (Tripneustes gratilla), blue light (B, λ450nm), yellow light (Y, λ585-590nm), red light (R, λ640nm), green light (G, λ510nm), white light (W, λ400-780nm), and darkness (H) groups were established in a recirculating seawater aquaculture system. Six different LED light color treatment groups with a photoperiod of 12 L:12 D were tested for 30 days to investigate the effects of different light colors on the feeding, growth, and enzyme activities of T. gratilla (142.45 ± 4.36 g). We found that using different LED light colors caused significantly different impacts on the feeding, growth, and enzyme activity of T. gratilla. Notably, the sea urchins in group B exhibited better growth, with a weight gain rate of 39.26%, while those in group R demonstrated poorer growth, with a weight gain rate of only 26%. The feeding status differed significantly (p < 0.05) between groups B and R, with group B consuming the highest daily intake (6.03 ± 1.69 g) and group R consuming the lowest (4.54 ± 1.26 g). Throughout the three phases, there was no significant change in the viability of the α-amylase (p > 0.05). Conversely, the pepsin viability significantly increased (p < 0.05) in group B. The lipase viability consistently remained at the lowest level, with no notable differences between group W and group B. In group R, both the α-amylase and pepsin viabilities remained lower, whereas the lipase viability was noticeably greater in each phase than in group B (p < 0.05). Among the antioxidant enzymes, group R exhibited a trend of initial increase followed by decreases in catalase, superoxide dismutase, and glutathione peroxidase activities, particularly during the third stage (15-30 days), during which a significant decrease in antioxidant enzyme activity was observed (p < 0.05). Taken together, these findings suggest that blue light positively affects the growth, feeding, digestion, and antioxidant capacity of T. gratilla in comparison with those in other light environments, whereas red light had an inhibitory effect. Furthermore, T. gratilla is a benthic organism that lives on shallow sandy sea beds. Thus, as short wavelengths of blue and green light are more widely distributed on the seafloor, and long wavelengths of red light are more severely attenuated on the seafloor, shorter wavelengths of light promote the growth of bait organisms of sea urchins, which provide better habitats for T. gratilla.

Dual layer chessboard metasurface sandwiched by a spin-on-carbon for spectral modulation.

Metasurfaces, composed by metals and dielectrics in periodical order with subwavelength pitches, are of great importance for their unique ability to abruptly manipulate optical fields. So far, all the reported metasurfaces are constructed by thermally deposited metals and dielectric films, based on semiconductor processes which are expensive and time-consuming. Inspired by the outstanding dry etch property of spin-on-carbon (SOC) as the interlayer material in CMOS technology, this paper proposes to utilize the SOC as the dielectric layer in a chessboard metasurface with dual layer of gold to form an array of local surface plasmonic resonators (localized surface plasmon resonance). Finite difference and time domain (FDTD) method is used to investigate the spectral characteristics in reflectance of the metasurface in both visible and short wavelengths of infrared light. Electron beam lithography is applied to generate the nanoscale chessboard pattern on ZEP520A, followed by a conventional oxygen-based plasma etch to form high aspect ratio nanopillar arrays in SOC with the feature width under 50 nm, and ended by a thermal deposition of gold to form self-aligned dual layer local surface plasmonic resonators (LSPRs). The measured reflectance spectra agree with the simulated. A wealth of optical properties, such as coupling induced modulations of spectra by LSPRs, are revealed and analyzed. These special modes result in tunable structural colors and wavelength-selective antireflection ability. To the best of our knowledge, this is the first time that SOC is applied in the construction of metasurfaces, which has great potential for next generation nanophotonic devices.

High-contrast NIR fluorescent probes for selective detection of NQO1 in breast cancer

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a potential biomarker for breast cancer (BC) diagnosis and prognosis. However, existing fluorescent probes for NQO1 detection have limitations such as short emission wavelength, weak fluorescence response, or large background interference. Here, we developed two novel near-infrared (NIR) fluorescent probes, DCl-Q and DCl2-Q, that selectively detect NQO1 activity in BC cells and tissues. They consist of a trimethyl-locked quinone as the recognition group and a donor-π-acceptor structure with halogen atoms as the reporter group. They exhibit strong fluorescence emission at around 660 nm upon binding to NQO1. We demonstrated that they can distinguish BC cells with different NQO1 expression levels and image endogenous NQO1 in tumor-bearing mice. Our probes provide a convenient and highly sensitive tool for BC diagnosis and prognosis based on NQO1 detection.

Temperature dependence of optical gain in compressively strained InAsP/GaInAs based quantum well heterostructure for short wavelength infrared applications

This paper reports temperature results on InAs0.8P0.2/Ga0.3In0.7As/InP quantum well heterostructure with a type-II band alignment that causes electron and hole to have spatially separated wavefunction. Theoretical simulations of the band structure and wavefunctions are conducted using the k.p method with the Luttinger-Kohn 6 × 6 Hamiltonian. In addition, the energy dispersion curve, momentum matrix element, and optical gain are also calculated. Our results show that the proposed heterostructure is promising for fabricating 1.84 μm (short wavelength infrared region-SWIR) lasers at room temperature. The effect of an increase in temperature on energy gap, optical gain, and transition wavelength is observed. Redshift is realized as the temperature rises from 100 K to 500 K.

A DNA/Upconversion Nanoparticle Complex Enables Controlled Co-Delivery of CRISPR-Cas9 and Photodynamic Agents for Synergistic Cancer Therapy.

Photodynamic therapy (PDT) depends on the light-irradiated exciting of photosensitizer (PS) to generate reactive oxygen species (ROS), which faces challenges and limitations in hypoxia and antioxidant response of cancer cells, and limited tissue-penetration of light. Herein, a multifunctional DNA/upconversion nanoparticles (UCNPs) complex is developed which enables controlled co-delivery of CRISPR-Cas9, hemin, and protoporphyrin (PP) for synergistic PDT. An ultralong single-stranded DNA (ssDNA) is prepared via rolling circle amplification (RCA), which contains recognition sequences of single guide RNA (sgRNA) for loading Cas9 ribonucleoprotein (RNP), G-quadruplex sequences for loading hemin and PP, and linker sequences for combining UCNP. Cas9 RNP cleaves the antioxidant regulator nuclear factor E2-related factor 2 (Nrf2), improving the sensitivity of cancer cells to ROS, and enhancing the synergistic PDT effect. The G-quadruplex/hemin DNAzyme mimicks horseradish peroxidase (HRP) to catalyze the endogenous H2O2 to O2, overcoming hypoxia condition in tumors. The introduced UCNP converts NIR irradiation with deep tissue penetration to light with shorter wavelength, exciting PP to transform the abundant O2 to 1O2. The integration of gene editing and PDT allows substantial accumulation of 1O2 in cancer cells for enhanced cell apoptosis, and this synergistic PDT has shown remarkable therapeutic efficacy in a breast cancer mouse model.

Assessing and Improving the Accuracy of Visible Infrared Imaging Radiometer Suite Ocean Color Products in Environments with High Solar Zenith Angles

Utilizing in situ measurement data to assess satellite-derived long-term ocean color products under different observational conditions is crucial for ensuring data quality and integrity. In this study, we conducted an extensive evaluation and analysis of Visible Infrared Imaging Radiometer Suite (VIIRS) remote sensing reflectance (Rrs) products using long-term OC-CCI in situ data from 2012 to 2021. Our research findings indicate that, well beyond its designed operational lifespan, the root mean square difference accuracy of VIIRS Rrs products across most spectral bands remains superior to 0.002 (sr−1). However, VIIRS Rrs products in shorter wavelength bands (e.g., at 412 nm) have exhibited significantly lower accuracy and a long-term bias in recent years. The annual precision of VIIRS Rrs products demonstrated a declining trend, particularly in coastal or eutrophic waters. This degradation in accuracy highlights the imperative for continuous monitoring of VIIRS performance and further advancements in the atmospheric correction algorithm, especially to address satellite records at high solar zenith angles (SZAs) and observation zenith angles (OZAs). Our analysis indicates that, in observation environments with high SZAs (greater than 70°), the accuracy of VIIRS Rrs products has declined by nearly 50% compared to typical solar zenith angle observation conditions. To address the challenge of declining accuracy under large observation geometries, we introduced the neural network atmospheric correction model (NN-V). Developed based on meticulously curated VIIRS products, the NN-V model exhibits outstanding performance in handling VIIRS data in conditions of extensive observation geometries. During the winter season in high-latitude marine regions, the NN-V model demonstrates a remarkable enhancement in ocean color product coverage, achieving an increase of nearly 20 times compared to traditional methods.

Inverting the Solvatochromism of Pyridinium-N-phenolate Dyes by the Addition of a Second Pyridinium Unit.

Three bipyridinium phenolates were synthesized, and their spectral behavior was recorded at various solvent polarities and compared to a classic pyridinium phenolate dye possessing only one pyridinium acceptor ring in its structure. The addition of a second pyridinium unit to the classic solvatochromic core results in an unexpected change in the spectral behavior from negative solvatochromism (displacement of the absorption band to shorter wavelengths) to inverted solvatochromism, characterized by the transition from negative to positive solvatochromism (displacement of the absorption band to longer wavelengths) at moderate solvent polarities.

Evaluation of Ultraviolet Radiation using the MOORA Method

Ultraviolet Radiation. Non-ionizing radiation emitting manmade sources like the sun and tanning beds includes ultraviolet (UV) radiation. Although it can help humans produce vitamin D and has other advantages, it can also be harmful to their health. The sun is a natural source of UV radiation for us. In industrial processes, as well as in medical and dental procedures, ultraviolet light is frequently used for a variety of purposes, such as the destruction of bacteria, the production of fluorescent effects, the curing of inks and resins, phototherapy, and tanning. Different UV wavelengths and intensities are employed for diverse applications. Using a UV detector is the most secure method of detecting UV radiation. Inform the class that the beads they will be using contain a unique pigment that changes color when exposed to UV radiation. UV detectors are the name of these beads. The UV light around the school can be seen using these. UV radiation is necessary to the body because it promotes the production of vitamin D. In addition to being crucial for bone development, immune system health, and blood cell production, vitamin D increases the absorption of calcium and phosphorus from meals. The three key health benefits of UV light are vitamin D production, enhanced mood, and higher energy. Moderate UV light exposure is a good source of vitamin D. This vitamin helps regulate cell division, insulin synthesis, calcium metabolism, immunity, and blood pressure. History and exploration. Due to violet being the color of the highest frequencies of visible light, the word "ultraviolet" signifies "beyond violet" (Latin ultra, "beyond"). Compared to violet light, ultraviolet has a greater frequency and a shorter wavelength. UV radiation can produce erythema, sunburn, photodamage (photoaging), photosensitivity, eye damage, changes in the skin's immune system, and chemical hypersensitivity depending on the amount and kind of radiation and the type of skin of the individual exposed. -an s-in-the-service-retailer-in-reside-in-the-retail-d-in-star-re-in-main-retail-enterprise type of place. This one. Additionally, UV radiation is produced by sunlamps and tanning beds. The multi-objective optimization by ratio analysis (MOORA) method is one of the MADM techniques. It is a group of qualities (prospective students). It is possible to calculate the worth of criteria, making this the ideal choice for decision-makers like prospective students. Hospital inpatient care, Hospital ambulatory care, Primary health care, Pharmaceuticals, Mortality, Morbidity. Cutaneous Melanoma, Basal Cell Carcinoma, Melanoma in Situ, and Actinic Keratosis. From the result, it is seen that Morbidity got the first rank whereas Primary health care is having the lowest rank.

Free-electron interaction with nonlinear optical states in microresonators.

The short de Broglie wavelength and strong interaction empower free electrons to probe structures and excitations in materials and biomolecules. Recently, electron-photon interactions have enabled new optical manipulation schemes for electron beams. In this work, we demonstrate the interaction of electrons with nonlinear optical states inside a photonic chip-based microresonator. Optical parametric processes give rise to spatiotemporal pattern formation corresponding to coherent or incoherent optical frequency combs. We couple such "microcombs" to electron beams, demonstrate their fingerprints in the electron spectra, and achieve ultrafast temporal gating of the electron beam. Our work demonstrates the ability to access solitons inside an electron microscope and extends the use of microcombs to spatiotemporal control of electrons for imaging and spectroscopy.

SAL vibration estimation and compensation based on triangular interferometric signals.

Synthetic aperture Ladar (SAL) is an extension of synthetic aperture technology in the optical frequency band. Owing to the short wavelength of lasers, the system has high-resolution, high-data-rate, and refined imaging capabilities, which has potential in high-resolution observation fields such as ground observation and space target observation. However, the short wavelength of lasers also makes SAL severely sensitive to vibrations even on the micron order which cause azimuth defocusing and range cell migration. To address this problem, we establish a de-chirp signal model under vibration environment, and propose a vibration error estimation and compensation method using triangular interferometric signals. According to the symmetrical characteristics of triangular frequency modulated continuous wave (T-FMCW) and the time-frequency information introduced by the azimuthal vibration phase, we use a two-stage interferometry method to estimate instantaneous frequency introduced by the vibration errors that cause range cell migration. For the scenarios without obvious range cell migration, we use a one-stage interferometry method to estimate the instantaneous frequency. Subsequently, we establish a vibration compensation filter using the estimated instantaneous frequency to compensate for the vibration errors. We use two experiments to verify the effectiveness and superiority of the proposed method. The results show that the proposed method effectively eliminates range cell migration and azimuthal phase errors introduced by vibration errors, producing SAL imaging results with higher resolution than the conventional spectral correlation method.

Macular dystrophy in Kabuki syndrome due to de novo KMT2D variants: refining the phenotype with multimodal imaging and follow-up over 10 years: insight into pathophysiology

BackgroundKabuki Syndrome is a rare and genetically heterogenous condition with both ophthalmic and systemic complications and typical facial features. We detail the macular phenotype in two unrelated patients with Kabuki syndrome due to de novo nonsense variants in KMT2D, one novel. A follow-up of 10 years is reported. Pathogenicity of both de novo nonsense variants is analyzed.MethodsFour eyes of two young patients were studied by full clinical examination, kinetic perimetry, short wavelength autofluorescence, full field (ff) ERGs, and spectral-domain optical coherence tomography (SD-OCT). One patient had adaptive optic (AO) imaging. Whole exome sequencing was performed in both patients.ResultsBoth patients had de novo nonsense variants in KMTD2. One patient had c.14843C>G; p. (Ser4948ter) novel variant and the second c.11119C>T; p. (Arg3707ter). Both had a stable Snellen visual acuity of 0.2–0.3. The retinal multimodal imaging demonstrated abnormalities at the fovea in both eyes: hyperreflectivity to blue light and a well-delimited gap—disruption of ellipsoid and interdigitation layer on OCT. The dark area on AO imaging is presumed to be absent for, or with structural change to photoreceptors. The ff ERGs and kinetic visual fields were normal. The foveal findings remained stable over several years.ConclusionKabuki syndrome–related maculopathy is a distinct loss of photoreceptors at the fovea as shown by multimodal imaging including, for the first time, AO imaging. This report adds to the literature of only one case with maculopathy with two additional macular dystrophies in patients with Kabuki syndrome. Although underestimated, these cases further raise awareness of the potential impact of retinal manifestations of Kabuki syndrome not only among ophthalmologists but also other healthcare professionals involved in the care of patients with this multisystem disorder.

Electromagnetic TE- and TM-waves propagation in a plane waveguide covered with graphene characterized by nonlinear conductivity

Background. Guiding properties of waveguiding structures with graphene are of great importance for various applications and have been studied in many papers. In all such studies, graphene was characterized, as a rule, by linear surface conductivity. However, if the intensity of an electromagnetic wave is large enough, the interaction of graphene with the electromagnetic wave becomes nonlinear; in this case, it is more correct to describe graphene by nonlinear conductivity.&#x0D; Aim. This work is aimed at studying the influence of cubic nonlinearity of graphene, corresponding to the so-called self-action effects (not affecting the frequency of the incident wave), on the propagation of TE- and TM-polarized waves in the structure, which is a plain dielectric layer covered on one side by graphene.&#x0D; Methods. In this study, the guiding properties of the waveguide are studied using primarily an analytical approach. Thus, from Maxwell's equations, material equations and boundary conditions, a couple of dispersion equations for TE-and TM-polarized waves is derived and then its solvability is studied. In addition, some numerical experiments are carried out in the study.&#x0D; Results. The dispersion equations of the studied waveguiding structure for TE- and TM-polarized waves are derived in explicit form. Studying analytically obtained equations, conditions for waveguide parameters are found, providing the existence of a given number of waveguide modes. In addition, some numerical results are obtained in the paper, which give an idea of the influence of nonlinear effects on the electromagnetic waves propagating in the structure.&#x0D; Conclusion. The results obtained in this paper reveal two effects related to the cubic nonlinearity of graphene. Firstly, in a plain dielectric layer with graphene coating in the strong nonlinear regime TE-waves with longer wavelength and TM-waves with shorter wavelength propagate compared to electromagnetic waves that propagate in the same structure in the linear regime. Secondly, the strong cubic nonlinearity leads to a greater localization of the electromagnetic wave within the waveguiding structure.

Near-mid infrared spectroscopy of carbonaceous chondrites: Insights into spectral variation due to aqueous alteration and thermal metamorphism in asteroids

Carbonaceous chondrites (CCs) are windows into the early Solar System and the histories of their parent bodies. Their infrared spectral signatures are powerful proxies for deciphering their composition and evolution history, but still present formidable challenges in relation to determining the degree of secondary processing such as aqueous alteration and thermal metamorphism via comprehensive data and mid-infrared feature. In our study, we delved into the infrared spectra spanning 1–25 μm of 17 CCs, with distinct petrological characteristics and varying degrees of alteration. Through this investigation, we uncovered distinct spectral patterns that shed light on the processes of alteration and metamorphism. As aqueous alteration intensifies, two key spectral features, the 3 μm-region absorption feature associated with OH-bearing minerals and water, and the 6 μm band indicative of water molecules, both grow in intensity. Simultaneously, their band centers shift towards shorter wavelengths. Moreover, as alteration progresses, a distinctive absorption feature emerges near 2.72 μm, resembling the OH absorption feature found in serpentine and saponite minerals. Comparison of aqueous alteration to laboratory-heated CCs suggests that the 3 μm region OH/H2O absorption feature differs between CC heated to less than or more than ∼300 °C. Further insights are gained by examining the vibrational features of silicate minerals, notably influencing the 10 μm and 20 μm regions. The 12.4 μm /11.4 μm reflectance ratio diminishes, and the reflectance peak in the 9–14 μm range shifts towards shorter wavelengths. These changes are attributed to the transformation of anhydrous silicates into phyllosilicates. In the 15–25 μm region, the influence of thermal metamorphism becomes evident and results in the appearance of more spectral features, the single reflectance peak at 22.1 μm undergoes a transformation into two distinct peaks at 19 μm and 25 μm, which is primarily attributed to the increased presence of anhydrous silicates and olivine recrystallization. These findings offer novel insights into the volatile-rich compositions of C-complex asteroids and the thermal evolution histories of their parent bodies.

Analysis of the short wavelength range of QSOs

In this work we try to classify objects using the MgII 2798 Å line from optical spectra. For that, we use BZQ type objects from BZCAT catalogue. From SDSS catalogues we have 618 BZQ objects which have optical spectra and only in 139 objects there are MgII and Hβ lines simultaneously (z=0.3345-1.0915). By the shape of MgII lines, we grouped these spectra into 3 categories: Broad &amp; Narrow, Broad+Narrow, and Broad.

Sun-as-a-star variability of Hα and Ca II 854.2 nm lines

Studies of stellar magnetic fields mostly rely on proxies derived from chromospheric lines, typically forming in the UV and shorter wavelengths and therefore accessible only from space based observatories. Even Ca II K or H observations, forming in regions accessible from the ground, are not always available. As a result, there is a crucial need to explore alternative activity proxies to overcome the limitations posed by observational constraints. Using sun-as-a-star observations acquired with the ISS at SOLIS we investigated the correlation between the Ca II K emission index and indices derived from the Hα 656.3 nm and Ca II 854.2 nm lines, which are well known chromospheric diagnostics. We found that both the core intensities and widths of the two lines are positively correlated with the Ca II K emission index (ρ ≳ 0.8), indicating their suitability as reliable indicators of magnetic activity, the width of the Hα line showing the highest correlation (ρ = 0.9). We also found that such correlations vary with the activity cycle. Specifically, during the analyzed cycle 24, the correlations with the Ca II K index varied 14% for the Hα width, 33% for the Hα core intensity, and doubled for the two Ca II 854.2 nm line indices. These results suggest that, among the investigated indices, the Hα width best traces magnetic activity. Results are discussed at the light of current knowledge of the formation heights of the two lines, and of spatially resolved solar observations.

Generation of superposed orbital angular momentum beams using a free-electron laser oscillator.

With wavelength tunability, free-electron lasers (FELs) are well-suited for generating orbital angular momentum (OAM) beams in a wide photon energy range. We report here the first experimental demonstration of OAM beam generation using an oscillator FEL with the tens of picosecond pulse duration. Lasing around 458 nm, we have produced the four lowest orders of superposed Laguerre-Gaussian beams using a very long FEL resonator of 53.73 m. The produced beams have good beam quality, excellent stability, and substantial average power. We have also developed a pulsed operation mode for these beams with a highly reproducible temporal structure for a range of repetition rate of 1-30 Hz. This development can be extended to short wavelengths, for example to x-rays using a future x-ray FEL oscillator. The OAM operation of such a storage-ring FEL also paves the way for the generation of OAM gamma-ray beams via inverse Compton scattering.

Discriminating early-stage diabetic retinopathy with subjective and objective perimetry.

To prevent progression of early-stage diabetic retinopathy, we need functional tests that can distinguish multiple levels of neural damage before classical vasculopathy. To that end, we compared multifocal pupillographic objective perimetry (mfPOP), and two types of subjective automated perimetry (SAP), in persons with type 2 diabetes (PwT2D) with either no retinopathy (noDR) or mild to-moderate non-proliferative retinopathy (mmDR). Both eyes were assessed by two mfPOP test methods that present stimuli within either the central ±15° (OFA15) or ±30° (OFA30), each producing per-region sensitivities and response delays. The SAP tests were 24-2 Short Wavelength Automated Perimetry and 24-2 Matrix perimetry. Five of eight mfPOP global indices were significantly different between noDR and mmDR eyes, but none of the equivalent measures differed for SAP. Per-region mfPOP identified significant hypersensitivity and longer delays in the peripheral visual field, verifying earlier findings. Diagnostic power for discrimination of noDR vs. mmDR, and normal controls vs. PwT2D, was much higher for mfPOP than SAP. The mfPOP per-region delays provided the best discrimination. The presence of localized rather than global changes in delay ruled out iris neuropathy as a major factor. mfPOP response delays may provide new surrogate endpoints for studies of interventions for early-stage diabetic eye damage.