Ultraviolet Band Research Articles

Ultra‐Pure Chiral Third Harmonic Generation Enabled by Mie‐Resonant Dielectric Dimer

AbstractTailoring chiroptical responses at the nanoscale is crucial for on‐chip compact polarization manipulation and enantiomer sensing. Efficient chiral second and third harmonic generation has been successfully demonstrated from bulk materials to metamaterials. Here, pronounced linear and nonlinear circular dichroisms are obtained by rotating a dielectric nanocylinder dimer. It is revealed that the giant chiroptical effects originate from multipolar Mie resonances on the dimer, especially the magnetic dipole resonance. The calculated nonlinear g‐factor can reach −1.975 in the visible regime, indicating an ultra‐pure chiral third harmonic generation in the ultraviolet band. The presented results open new horizons for enhancing and modulating the linear and nonlinear chiroptical responses of nanostructures and can find potential applications in lasing and sensing.

Nano-Micro Core-Shell Fibers for Efficient Pest Trapping.

Insect sex pheromones as an alternative to chemical pesticides hold promising prospects in pest control. However, their burst release and duration need to be optimized. Herein, pheromone-loaded core-shell fibers composed of degradable polycaprolactone and polyhydroxybutyrate were prepared by coaxial electrospinning. The results showed that this core-shell fiber had good hydrophobic performance and thermal stability, and the light transmittance in the ultraviolet band was only below 40%, which provided protection to pheromones. The core-shell structure alleviated the burst release of pheromone in the fiber and extended the release time to about 133 days. In the field, the pheromone-loaded core-shell fibers showed the same continuous and efficient trapping of Spodoptera litura as the commercial carriers. More importantly, the electrospun fibers combined with biomaterials had a degradability unmatched by commercial carriers. The structure design strategy provides ideas for the innovative design of pheromone carriers and is a potential tool for the management of agricultural pests.

Analysis of the first coronagraphic multi-band observations of a sungrazing comet

Context. Between 24 and 25 December 2021 a sungrazing comet (SOHO-4341) approached the Sun, being observed by “classical” visible light (VL) coronagraphs on board the SOHO and STEREO missions, and also by the innovative Metis coronagraph on board the ESA-NASA Solar Orbiter mission in the VL and ultraviolet (UV H I Lyman-α) band. Aims. We show how VL data acquired by the Metis coronagraph can be combined with those provided by other space-based coronagraphs to reconstruct the comet orbit, but also to provide information on the dust composition from the polarized VL emission. Moreover, we show how the UV emission can be employed to measure local plasma parameters of the ambient solar wind. Methods. By using the comet positions tracked with VL Metis images (with spatial resolution that is four times better than UV), the UV images (with a time cadence that is five times faster than VL) have been coaligned to maximize the signal-to-noise ratio in the UV band. The local electron density ne was measured from the observed exponential decay of the UV Lyman-α intensity along the tail, while the solar wind speed vwind was measured from the UV Lyman-α tail inclination with respect to the cometary orbital path deprojected in 3D. Moreover, the proton kinetic temperature Tk was also obtained by the aperture angle of the UV Lyman-α tail. Results. When the comet was at an average heliocentric distance of 14.3 R⊙, the comet had a radial speed of 155 km s−1 and a tangential speed of 59 km s−1. The comet had a UV Lyman-α tail extending in the anti-solar direction over more than 1.5 R⊙. From the analysis of the tail shape in UV we obtained the local solar wind speed (vwind = 190 km s−1), electron density (ne = 1.5 × 104 cm−3), and proton temperature (Tk = 1.2 × 106 K). Moreover, theoretical analysis of the measured UV Lyman-α intensity allowed us to estimate the radius of the cometary nucleus (Rcom = 65 m) and the water outgassing rate (QH2O = 4.8 × 1028 molec s−1). Conclusions. These results show that sungrazing comets are unique “local probes” for the ambient coronal plasma, providing measurements that are not as affected by the line-of-sight integration effects as those provided by remote sensing instruments, in regions of the Heliosphere that are not explored in situ by the ongoing space missions.

Ultra-high extinction ratio single-photon Lidar based on SiC-SPAD at solar-blind ultraviolet band

Ultra-high extinction ratio single-photon Lidar based on SiC-SPAD at solar-blind ultraviolet band

Birefringent Dispersion Optimization to Achieve Superior Nonlinear Optical Phase Matching in Deeper Solar-Blind UV Band from KH2PO4 to BeH3PO5.

Nonlinear-optical (NLO) crystals require birefringent phase matching (BPM), particularly in the solar-blind ultraviolet (UV) (200-280nm) and deep-UV (100-200nm) regions. Achieving BPM requires optimization of optical dispersion along with having large birefringence. This requirement is especially critical for structures with low optical anisotropy, including classical phosphate UV-NLO crystals like KH2PO4 (KDP). However, there is a scarcity of in-depth theoretical analysis and general design strategies based on structural chemistry to optimize dispersion. This study presents findings from a simplified dielectric model that uncover two vital factors to micro-optimize transparent optical dispersion: effective mass (m*) of excited states and effective number (N*) of photo-responsive states. Smoothing of dispersion occurs as m* increases and N* decreases. First-principles analysis of deep-UV KBe2BO3F2-family structures is used to confirm the conciseness and validity of the model. It further proposes substituting K+ with Be2+ to decrease N* and increase m* while enlarging bandgap. This will lead to improved dispersion and an overall enhancement of KDP's BPM capability. The existing BeH3PO5 (BDP) is predicted to improve the shortest BPM wavelength for second-harmonic generation, from 251nm in KDP to 201nm in BDP. BDP's extension into the broader UV solar-blind waveband fully supports the proposed optimization strategy.

Excellent ultraviolet band optical limiting material: 2D vanadium nanosheets

Nonlinear optics evolved gradually after the invention of laser technology and the widespread application of two-dimensional (2D) materials. Herein, using the liquid-phase exfoliation (LPE) technique, 2D Group-ⅤB vanadium (V) was effectively exfoliated (with a thickness of 5.94–6.45 nm). Under excitation of the picosecond laser, the open aperture (OA) Z-scan technique was used to examine the nonlinear absorption properties of 2D V nanosheets (NSs) at the wavelengths of 355, 532, and 1064 nm. According to the results, the 2D V NSs exhibit outstanding optical limiting (OL) behavior at 355 nm with a larger two-photon absorption (TPA) coefficient (2.41 ± 0.03 cm GW−1), low OL excitation threshold (0.71 ± 0.03 GW cm−2), and high TPA cross section (3.81 ± 0.51 × 10−45 cm4 s). That means V is expected to be used as an OL material in the ultraviolet (UV) band for such applications as laser protection, human eye protection, making optical filters, etc. Our study provides a new pathway for the use of vanadium in optics and broadens the scope of knowledge for people about transition metal elements.

Multiwavelength analysis of Fermi-LAT blazars with high-significance periodicity: detection of a long-term rising emission in PG 1553+113

ABSTRACT Blazars display variable emission across the entire electromagnetic spectrum, with time-scales that can range from a few minutes to several years. Our recent work has shown that a sample of five blazars exhibit hints of periodicity with a global significance ${\gtrsim}2\, \sigma$ at γ-ray energies, in the range of 0.1 GeV < E < 800 GeV. In this work, we study their multiwavelength emission, covering the X-ray, ultraviolet, optical, and radio bands. We show that three of these blazars present similar periodic patterns in the optical and radio bands. Additionally, fluxes in the different bands of the five blazars are correlated, suggesting a co-spatial origin. Moreover, we detect a long-term (≈10 yr) rising trend in the light curves of PG 1553+113, and we use it to infer possible constraints on the binary black hole hypothesis.

Efficient dual-wavelength metasurface for second-order differential edge detection in the ultraviolet.

Metasurfaces for edge detection through spatial analog calculations have attracted much attention due to advantages such as a flexible design and small footprint. Up until now, most studies have focused on single-wavelength operation in the near-infrared or visible regions, while little work has been done in the ultraviolet band. It is of significance to explore metasurfaces for edge detection in the ultraviolet band for their great potential in high-resolution imaging and lithography. Here, we propose a dual-wavelength H f O 2 metasurface for edge detection working at 273nm and 293nm, with 25% and 72% efficiency, respectively, controlled by the linear polarization of the incident light. The efficient dual-wavelength second-order differential calculation in the ultraviolet band of the metasurface has been confirmed by 1D signal and 2D image processing. It may find applications in the fields of computer vision and bioimaging.

UV-optical Emission of AB Aur b Is Consistent with Scattered Stellar Light

The proposed protoplanet AB Aur b is a spatially concentrated emission source imaged in the millimeter-wavelength disk gap of the Herbig Ae/Be star AB Aur. Its near-infrared spectrum and absence of strong polarized light have been interpreted as evidence supporting the protoplanet interpretation. However, the complex scattered-light structures in the AB Aur disk pose challenges in resolving the emission source and interpreting the true nature of AB Aur b. We present new images of the AB Aur system obtained using the Hubble Space Telescope Wide Field Camera 3 in the ultraviolet (UV) and optical bands. AB Aur b and the known disk spirals are recovered in the F336W, F410M, and F645N bands. The spectral energy distribution of AB Aur b shows absorption in the Balmer jump, mimicking that of early-type stars. By comparing the colors of AB Aur b to those of the host star, the disk spirals, and predictions from scattered light and self-luminous models, we find that the emission from AB Aur b is inconsistent with planetary photospheric or accretion shock models. Instead, it is consistent with those measured in the circumstellar disks that trace scattered light. We conclude that the UV and visible emission from AB Aur b does not necessitate the presence of a protoplanet. We synthesize observational constraints on AB Aur b and discuss inconsistent interpretations among different data sets. Considering the significance of the AB Aur b discovery, we advocate for further observational evidence to verify its planetary nature.

Study on the Variation of Gas Radiation Characteristics of Hypersonic Reentry Vehicles

For the nonequilibrium flowfield and high-temperature gas radiation spectral characteristics of the hypersonic reentry capsule, a spectral prediction method based on quasi-steady-state assumption and line-by-line method is introduced. Meanwhile, the characteristics of the spectrum are studied to investigate the influence of viewing angles and trajectory points during reentry based on this method. We use Fire II flight test data to verify the accuracy of the gas radiation model and update the prediction values of the cumulative radiation intensity in the wavelength range of 2.2–4.1 eV by previous methods. The results show that the radiation signal is most significant at the stagnation line and gradually decreases with the deviation of the line of sight from the stagnation line. The cumulative radiation intensity of the various trajectory points exhibits a profile that increases and then decreases during reentry; it rises to its peak at 50 km. The emission spectrum of gas radiation is mainly distributed in the ultraviolet and near-infrared bands. The transition processes of atoms N and O contribute more than 90% of the total radiation intensity, and the contribution of the first negative series in the molecular spectrum is relatively considerable compared to other molecular components.

Superhydrophobic bilayer coating for passive daytime radiative cooling

Abstract Passive radiative cooling is an energy-free cooling method by exchanging thermal radiation with the cold universe through the transparent atmospheric window. Spectrum tailoring of the radiative cooler is the key to daytime radiative cooling in previously reported works. In addition, radiative coolers with large-scale fabrication and self-cleaning characteristics should be further developed to improve their industrial applicability. Herein, we propose a bilayer radiative cooling coating with the superhydrophobic property and a scalable process, by covering TiO2/acrylic resin paint with a silica/poly(vinylidene fluoride-co-hexafluoropropylene) (SiO2/P(VdF-HFP)) composite masking layer. The strong Mie scattering in TiO2/acrylic resin paint contributes to high solar reflection, while the SiO2/P(VdF-HFP) masking layer is responsible for superhydrophobicity and synergetic solar reflection in the ultraviolet band, resulting in an effective solar reflectivity of 94.0 % with an average emissivity of 97.1 % and superhydrophobicity with a water contact angle of 158.9°. Moreover, the as-fabricated coating can be cooled to nearly 5.8 °C below the temperature of commercial white paint and 2.7 °C below the local ambient temperature under average solar irradiance of over 700 W m−2. In addition, yearly energy saving of 29.0 %–55.9 % can be achieved after the coating is applied to buildings in Phoenix, Hong Kong, Singapore, Guangzhou, and Riyadh.

Effective catalytic and antimicrobial performance of multiple phase AgBr and polyacrylic acid doped nickel oxide nanostructures with In Silico molecular docking study

A facile co-precipitation route was adopted to synthesize NiO2 nanostructures (NSs) doped with various weight ratios (2 and 4 wt.%) of AgBr and a fixed amount of PAA. This study aimed to investigate the RhB degradation on multiple media with the antimicrobial activity of pristine and doped NiO2. The morphological, structural, elemental, and optical characterizations of prepared samples were examined. X-ray diffraction spectra (XRD) exhibited the hexagonal structure of NiO2 and confirmed the crystalline nature of the synthesized sample. The TEM images affirmed the nanoparticle and nanorod-like morphology. The UV–Vis analysis revealed that the absorption performance of synthesized samples is comprehensive in the ultraviolet region (277 nm) and band gap energy (Eg) decreased upon doping (4.1–3.36 eV). Fourier transform infrared (FTIR) has stretching and vibrational modes of Ni–O and other functional groups. NiO2 has a large band gap with a high charge recombination rate issue. The supreme performance of NiO2 can be credited to PAA and AgBr, which hinder the e−/h+ recombination process by charge separation. The catalytic activity of AgBr/PAA doped NiO2 demonstrates remarkable performance against RhB and benzoic acid, with maximum degradation in acidic medium and exhibited higher antimicrobial efficacy for Escherichia coli. Docking studies were employed to decipher the mechanism underlying the bactericidal activity of AgBr/PAA-doped NiO2 NSs and PAA-doped NiO2 NSs for β-lactamase and DNA gyrase inhibition.

An X-rays-to-radio investigation of the nuclear polarization from the radio-galaxy Centaurus A

ABSTRACT Centaurus A is one of the closest radio galaxies to Earth. Its proximity allowed us to extensively study its active galactic nucleus but the core emission mechanism remains elusive because of local strong dust and gas obscuration. The capability of polarimetry to shave-off contaminating emission has been exploited without success in the near-infrared by previous studies but the very recent measurement of the 2–8 keV polarization by the Imaging X-ray Polarimetry Explorer (IXPE) brought the question back to the fore. To determine what is the prevalent photon generation mechanism to the multiwavelength emission from the core of Centaurus A, we retrieved from the archives the panchromatic polarization measurements of the central compact component. We built the total and polarized flux spectral energy distributions of the core and demonstrated that synchrotron self-Compton models nicely fit the polarized flux from the radio to the X-ray band. The linear polarization of the synchrotron continuum is perpendicular to the jet radio axis from the optical to the radio band, and parallel to it at higher energies. The observed smooth rotation of the polarization angle in the ultraviolet band is attributed to synchrotron emission from regions that are getting closer to the particle acceleration site, where the orientation of the jet’s magnetic fields become perpendicular to the jet axis. This phenomenon support the shock acceleration mechanism for particle acceleration in Centaurus A, in line with IXPE observations of several high-synchrotron peak blazars.

Photoelectric Characteristics of n-ZnO/p-Si Heterojunction Photodetector

To solve the problems of the high experimental cost and single experimental result, the n-ZnO/p-Si heterojunction photodetector was simulated by TCAD software. Based on the established model, the photoelectric characteristics of n-ZnO/p-Si heterojunction photodetector were simulated and analyzed in terms of ZnO carrier concentration and thickness. The results show that the dark current is about 10−14 A, the photocurrent is about 10−8 A, and the photocurrent is at least three orders of magnitude larger than the dark current. The fast response time is 10−10 s. The maximum response of the device is 0.25 A/W in the ultraviolet band and the maximum response is 0.35 A/W in the visible light region. This simulated result establishes a theoretical foundation for further experimental research.

Stereolithography for manufacturing of advanced porous solids

The aim of this paper is focused on benefits of stereolithography (SLA) technology for the fabrication of the lightweight lattice structures with potential for load-bearing function and high absorption of impact energy. SLA is an additive manufacturing technology employing the principle of liquid resins curing moderated by radiation of a wavelength from ultra-violet band where resulting material parameters are tunable by setting of the curing process. The batches of samples manufactured using three different resins were subjected to quasi-static uni-axial tensile and compression tests. Acquired data were processed to derive deformation behaviour expressed as stress-strain diagrams and fundamental material properties. Based on the knowledge obtained from the mechanical tests, the setup of the fabrication parameters, the most suitable resin for manufacturing of the lattice structures and the overall suitability of SLA technology for the fabrication of advanced porous materials, were determined.

Multiplexing of bias-controlled modulation modes on a monolithic III-nitride optoelectronic chip.

III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top-down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

In vivo method for evaluating sunscreen protection against high-energy visible light.

Overexposure to sunlight can have many harmful biological effects on the skin, leading to skin cancer and photoaging. As ultraviolet (UV) radiation has been identified as a cause of DNA damage and oxidative stress in the skin, the photoprotection provided by sunscreens is evaluated through their ability to filter UV light, using the sun protection factor (SPF). However, recent data have shown that high-energy visible (HEV) light can also cause biological skin damage. To develop a new in vivo method for evaluating the protection provided by sunscreens across a broad range of wavelengths, including the HEV band, based on multispectral image analysis. This study evaluated the absorption properties of six commercially available sunscreens (five SPF 50+ products containing organic UV filters, and one product containing the wide spectrum filter, phenylene bis-diphenyltriazine [TriAsorB™]) and of a control product containing no filter. Multispectral images were acquired from the skin on the forearms of healthy volunteers, before and after application of the test products. Images taken with LEDs emitting light at wavelengths ranging from UV to infrared were used to generate light reflectance maps for each product. The levels of absorbance of light in the UV and visible bands were then calculated. The product containing the wide spectrum filter exhibited significantly higher absorbance over the HEV band (380-450 nm) than the control product and the other commercial sunscreens. All the sunscreens tested showed the same level of absorbance at 365 nm (UVA). Multispectral imaging provides a simple and reliable in vivo method for assessing the real-world protection provided by sunscreens against all forms of photo-induced skin damage, including that induced by HEV radiation.

Analysis of Aerosol Optical Depth and Forward Scattering in an Ultraviolet Band Based on Sky Radiometer Measurements

The sky-radiometer/sun-photometer is the most widely used instrument for obtaining aerosol optical depth (AOD) or aerosol optical properties worldwide. Due to the existence of field of view (FOV, 1°), the radiation received by the sky-radiometer includes the forward scattering in addition to direct solar irradiance. This leads to more diffuse light errors of retrieved AODs, especially for shorter wavelength and heavily polluted weather conditions. Using simulation data of three typical aerosol particles (dust, soot, water-soluble), we first verified the accuracy of the Monte Carlo method for calculating the forward scattering effect. Based on the sky-radiometer data collected in Xi’an (2015–2020) where heavy pollution weather is common, the relative errors and correction factors of the AOD were obtained under different conditions, including various short wavelengths (≤400 nm), solar zenith angles (SZAs) and AODs. Our analysis indicates the close dependence of AOD correction factors on wavelength, SZA, AOD and the optical properties of aerosol particles. The mean relative error in Xi’an increases with the decrease of wavelength (~16.1% at 315 nm) and decreases first and then increases with the increase of the SZA. The relative errors caused by forward scattering can exceed 10% when the AOD is greater than 1 and 25% when the AOD is larger than 2 in the ultraviolet (UV) band. The errors with a wavelength greater than 400 nm and an AOD below 1.0 can be within 5%, which can be ignored. The correlation coefficients of AODs before and after a correction from 315 nm to 400 nm are greater than 0.96, which basically increase with the increase of the wavelength. This indicates that the significance of the forward scattering effect in the Xi’an area with heavy pollution cannot be ignored for short wavelengths. However, such effect is negligible at the longer wavelengths and lower AODs (<1.0) of a sky-radiometer.

Hollow-core pear-shaped conjoined-tube fiber with low loss in the ultraviolet band

PCTF (pear-shaped conjoined-tube fiber) is presented as a new ultraviolet (UV) guiding fiber with low loss. Results indicate that two PCTFs have better properties than that of previous studies in the UV band. The total loss of two PCTFs is less than 1 dB/km, and its bandwidth exceeds 150 nm between 0.2 and 0.4 μm. Furthermore, PCTF's single-mode performance is very promising, as evidenced by the higher-order mode extinction ratio (HOMER) over 103. The fabrication tolerance is discussed in this paper and results show that the tolerance is good enough to fabricate by normal fiber drawing process. This fiber is promising in applications for nonlinear optics, ultrafast optics, high power laser, and quantum optics.

Multiwavelength Observations of the Blazar PKS 0735+178 in Spatial and Temporal Coincidence with an Astrophysical Neutrino Candidate IceCube-211208A

Abstract We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.°2 away from the best-fit position of the IceCube neutrino event IceCube-211208A detected on 2021 December 8. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV γ-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution (SED), and the γ-ray data from Fermi-LAT, VERITAS, and H.E.S.S. require a spectral cutoff near 100 GeV. Both the X-ray and γ-ray measurements provide strong constraints on the leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed SED. The existence of an external photon field in the source would instead explain the observed γ-ray spectral cutoff in both the leptonic and lepto-hadronic models and allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. We show a numerical lepto-hadronic model with external target photons that reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power.