Optical Region Research Articles

Van der Waals interfaces in multilayer junctions for ultraviolet photodetection

Developments in semiconductor science have led to the miniaturization and improvement of light detection technologies for many applications. However, traditional pn-junctions or three-dimensional device geometries for detection of ultraviolet (UV) light are still limited by the physical properties of the semiconductors used, such as the small penetration depth of UV light in silicon. Van der Waals (vdW) semiconductors and their pn-junctions can offer an alternative solution due to their optical properties and thin pn-junction region. Here, we report on a multi-layer junction that combines single layer graphene and vdW semiconductors (p-GaSe and n-In2Se3) with strong optical absorption in the UV range. The junctions have broadband spectral response (0.3-1.0 μm) and high photoresponsivity under forward and reverse bias, or without any externally applied voltage. The photoresponse differs from that of a traditional pn-junction diode as it is governed by charge transport across thin layers and light-current conversion at three vdW interfaces (e.g. the graphene/GaSe, GaSe/In2Se3 and In2Se3/graphene interfaces). The type-II band alignment at the GaSe/In2Se3 interface and electric field at the three vdW interfaces are beneficial to suppress carrier recombination for enhanced photoresponsivity (up to ~102 A/W) and detectivity (up to ~1013 Jones), beyond conventional UV-enhanced silicon detection technology.

Phase-Matching in Nonlinear Crystal-Based Monochromatic Terahertz-Wave Generation

Optically pumped nonlinear frequency down conversion is a proven approach for monochromatic terahertz (THz)-wave generation that provides superior properties such as continuous and wide tunability as well as laser-like linewidth and beam quality. Phase-matching (PM) is an important connection between the pump sources and nonlinear crystals and determines the direction of energy flow (as well as the output power). In past decades, a variety of peculiar PM configurations in the THz region have been invented and are different from the traditional ones in the optical region. We summarize the configurations that have been applied in nonlinear THz-wave generation, which mainly fall in two categories: scalar (collinear) PM and vector PM (including macroscopic noncollinear PM and microscopic vector PM). The development of this technique could relax the matching conditions in a wide range of nonlinear crystals and pump wavelengths and could finally promote the improvement of coherent THz sources.

Toward Understanding the B[e] Phenomenon. IX. Nature and Binarity of MWC645

We present the results of optical and near-IR spectroscopy and multicolor photometry of the emission-line star MWC 645, which exhibits the B[e] phenomenon. The presence of positionally variable absorption lines of a cool star detected for the first time indicates that the object is a binary system. Using a combination of the photometric and spectroscopic data as well as the Gaia EDR3 distance (D = 6.5 ± 0.9 kpc), we disentangled the components’ contributions and estimated their surface temperatures and luminosities (18, 000 ± 2000 K and 4250 ± 250 K, log L/L ⊙ = 4.0 ± 0.5 and 3.1 ± 0.3 for the hot and cool components, respectively). Quasi-cyclic short-period (months) and long-period (∼4 yr) photometric variations were detected in both optical and near-IR regions, and are most likely due to variable circumstellar extinction. Our analysis suggests that MWC 645 is a member of the FS CMa group. The object’s properties can be described by an evolutionary model of a close binary system that currently undergoes a nonconservative mass transfer between intermediate-mass stars (e.g., 7 M ⊙ + 2.8 M ⊙).

Simultaneous measurement of OH radical, H2O concentration, and temperature in a premixed CH4/air flame using TDLAS with an improved analysis method.

The OH radical concentration was measured by applying tunable diode laser absorption spectroscopy, which is an in situ optical method. An optical absorption region (P7.5ff transition at 1502.7 nm) of the OH radical was selected in the near-infrared range to measure the OH radicals quantitatively in premixed CH4/air flames. An improved direct absorption spectroscopy (DAS) method based on wavelength division multiplexing was proposed to extract the H2O absorption signal that interfered with the OH light absorption signal, and the integral intensity of OH* chemiluminescence was compared to the measured OH radical concentration based on the improved DAS method.

The Role of Spin-Flip Collisions in a Dark-Exciton Condensate

We show that a Bose-Einstein condensate consisting of dark excitons forms in GaAs coupled quantum wells at low temperatures. We find that the condensate extends over hundreds of micrometers, well beyond the optical excitation region, and is limited only by the boundaries of the mesa. We show that the condensate density is determined by spin-flipping collisions among the excitons, which convert dark excitons into bright ones. The suppression of this process at low temperature yields a density buildup, manifested as a temperature-dependent blueshift of the exciton emission line. Measurements under an in-plane magnetic field allow us to preferentially modify the bright exciton density and determine their role in the system dynamics. We find that their interaction with the condensate leads to its depletion. We present a simple rate-equations model, which well reproduces the observed temperature, power, and magnetic-field dependence of the exciton density.

Optical properties of Au-Hf thin films

The optical properties of thin films of intermetallic Au$_{3}$Hf were experimentally investigated for the first time, which display clear plasmonic properties in the optical and near infrared region with negative permittivity. In contrast to similar alloys, such as films of Au$_{3}$Zr, the films express more negative $\epsilon'$ values and lower $\epsilon''$ values across most of the wavelengths (370-1570 nm) investigated. The Au$_{3}$Hf films were fabricated by DC magnetron sputtering at a range of deposition temperatures, from room temperature to 415$^{o}$C, and annealed at different vacuum levels. The films mostly formed as a combination of Au$_{3}$Hf, Au$_{2}$Hf and Au$_{4}$Hf phases when deposited below 400$^{o}$C, and exclusively Au$_{3}$Hf phase at above 400$^{o}$C, indicating key conditions for isolating this phase. The films were stable when annealed at 10$^{-8}$ Torr, but when annealed again at 10$^{-6}$ Torr the films oxidised and changed into a mix of Au- Hf phases, suggesting resistance to oxidization may be an issue for un-encapsulated applications at elevated temperatures.

Extreme X-Ray Reflection in the Nucleus of the Seyfert Galaxy NGC 5033

NGC 5033 is an intriguing Seyfert galaxy because its subclassification may change with time, and because optical and submillimeter observations find that the massive black hole does not sit at the dynamical center of the galaxy, pointing to a past merger. We obtained a new optical spectrum of NGC 5033 using the 200″ Hale telescope at Palomar that clearly reveals a broad Hβ line (FWHM = 5400 ± 300 km s−1). This signals a clear view of the optical broad line region and requires Seyfert-1.5 designation. Some spectra obtained in the past suggest a Seyfert-1.9 classification, potentially signaling a variable or “changing-look” geometry. Our analysis of a 2019 Chandra spectrum of the massive black hole reveals very little obscuration, also suggesting a clean view of the central engine. However, the narrow Fe Kα emission line is measured to have an equivalent width of EW eV. This value is extremely high compared to typical values in unobscured active galactic nuclei . Indeed, the line is persistently strong in NGC 5033: the line equivalent width in a 2002 XMM-Newton snapshot is EW eV, similar to the EW eV equivalent width measured using ASCA in 1999. These results can likely be explained through a combination of an unusually high covering factor for reflection, and fluxes that are seen out of phase owing to light travel times. We examine the possibility that NGC 5033 may strengthen evidence for the X-ray Baldwin effect.

Optical Continuum Reverberation in the Dwarf Seyfert Nucleus of NGC 4395

In order to constrain the size of the optical continuum emission region in the dwarf Seyfert 1 galaxy NGC 4395 through reverberation mapping, we carried out high-cadence photometric monitoring in the griz filter bands on two consecutive nights in 2022 April using the four-channel MuSCAT3 camera on the Faulkes Telescope North at Haleakalā Observatory. Correlated variability across the griz bands is clearly detected, and the r-, i-, and z-band light curves show lags of , , and minutes with respect to the g band when measured using the full-duration light curves. When lags are measured for each night separately, the Night 2 data exhibit lower cross-correlation amplitudes and shorter lags than the Night 1 light curves. Using the full-duration lags, we find that the lag–wavelength relationship is consistent with the τ ∝ λ 4/3 dependence found for more luminous active galactic nuclei. Combining our results with continuum lags measured for other objects, the lag between g and z band scales with optical continuum luminosity as τ gz ∝ L 0.56±0.05, similar to the scaling of broad-line region size with luminosity, reinforcing recent evidence that diffuse continuum emission from the broad-line region may contribute substantially to optical continuum variability and reverberation lags.

All‐Dielectric Metasurface Empowered Optical‐Electronic Hybrid Neural Networks

AbstractOptical computing has a series of advantages over its electronic counterpart, e.g., low energy consumption, high speed, and intrinsic parallelism. Diffraction deep neural networks (D2NNs) are a prominent example capable of processing images directly without addressing the spatial locations of each element. Despite the great successes, the D2NNs typically utilize the multilayer framework and face the severe challenge of misalignment in the optical region. Herein, a single metasurface‐based optical‐electronic hybrid neural network (OENN) is proposed and experimentally demonstrated. The OENN is composed of a titanium dioxide (TiO2) metasurface and a fully‐connected electronic layer. The combination of nonlocal neural layer and nonlinear transformation has significantly expanded the neural network capacity. Consequently, the classification accuracy on handwritten digits recognition can still be as high as 98.05% without employing the architecture of cascaded metasurfaces. The OENN shall shed light on the practical applications of optical computing in the visible spectrum.

Refractive Characteristics and Related Factors of Amblyopia after Lamellar Keratoscleroplasty in Children with Limbal Dermoids.

We examined the refractive characteristics and related factors of amblyopia in pediatric patients with limbal dermoids undergoing lamellar keratoscleroplasty. Forty-one children (mean age: 56.15 ± 22.47 months) were enrolled. Cycloplegic refraction, corneal topography, and anterior segment photography were performed. The corneal topographic and distribution characteristics of the refractive state were summarized, and the relationship between limbal dermoid invasion size and the refractive state was analyzed. The relationship between invasion size and amblyopia severity and the effect of clinical intervention at different times on amblyopia treatment were also analyzed. The spherical power distribution was −1.0–+10.75 D (average: +4.79 ± 3.09 D). The cylinder power was −1.25–−8.75 D (average: −4.19 ± 1.93 D). The axial range of astigmatism was 10–180° (average: 103.54 ± 58.16°). Equivalent spherical refraction was −3.88–+7.76 D (average: +2.70 ± 3.08 D). Twenty-five, fifteen, and one case had limboid dermoid invasion of the central circular zone (CCZ), paracentral annular zone (PCZ), and corneal limbus within 1 mm, respectively. Corneal topography of 39 patients showed flat, steep, and mean curvatures of 38.48 ± 2.12 D, 43.29 ± 1.97 D, and 40.70 ± 1.48 D, respectively. The mean astigmatism was 4.80 ± 2.93 D in the 3-mm optical region. Astigmatism was higher in CCZ than in PCZ invasion (p < 0.05). Postoperative visual acuity was positively correlated with patients’ age and amblyopia treatment duration (r = 0.392, p = 0.048; r = 0.488, p = 0.011), and was negatively correlated with astigmatism (r = −0.646, p < 0.001). High hyperopia and astigmatism are the dominant refractive errors in patients with limbal dermoids undergoing lamellar keratoscleroplasty.

Light-Shift-Free and Dead-Zone-Free Atomic-Orientation-Based Scalar Magnetometry Using a Single Amplitude-Modulated Beam

The detection dead zones and heading errors induced by light shifts are two important problems in optically pumped scalar magnetometry. We introduce an atomic-orientation-based single-beam magnetometry scheme to simultaneously solve these problems, using a polarization-reversing and path-bending Herriott cavity. Here, a reflection mirror is inserted into the cavity to bend the optical paths in the middle and divide them into two separated orthogonal regions to avoid the detection dead zone. Moreover, half-wave plates are added in the center of each optical region, so that the light polarization is flipped each time it passes the wave plates and the light-shift effects are spatially averaged out. This operation is demonstrated to eliminate the unnoticed heading errors induced by ac light shifts. The methods developed in this paper are robust to use and easy to apply other atomic devices.

Unveiling photoluminescent response of Ce-doped CaCu3Ti4O12: An experimental-theoretical approach

CaCu3Ti4O12: x% Ce (x = 0.00, 0.25, 0.50, 0.75, and 1.00) ceramic composites were prepared via solid-state reaction. Theoretical atomistic simulations were combined with experimental techniques to uncover Ce effects in the (micro)structure and photoluminescence of CaCu3Ti4O12-based ceramics. Application of perovskites ceramics in optoelectronics have been limited by their specific, narrow emission range, which compromise operational efficiency, pushing for the development of novel perovskite-emissive materials. This study results confirm that Ce ions are incorporated at Ca sites within the CaCu3Ti4O12 lattice, inducing point metal and oxygen vacancies in the optical bandgap region. Shallow-level defects (VCa′′/VO⦁⦁) were associated with broadband violet-blue photoluminescent (PL) emissions. Better color rendering may be a direct consequence of crystalline field splitting/wider PL emission. Furthermore, results demonstrate that PL on CaCu3Ti4O12: Ce system intensity can be modulated by structural defects, making it promising for applications in optoelectronics.

Impact of interfacial thickness on Raman intensity profiles and phonon anisotropy in short-period (AlSb)n/(GaSb)m superlattices

Comprehensive simulations of phonon dispersions ωj(q→SL) and atomic displacements are reported for short-period (AlSb)n/(GaSb)m superlattices (SLs) using a modified linear-chain model. A bond-polarizability methodology is employed for exploring the impact of meticulously included interfacial thickness Δ (≡1–3 monolayers) on the Raman intensity profiles of graded SLs in the optical phonon region. Results of ωj(q→SL) are also presented by exploiting a realistic rigid-ion-model (RIM) and considering short-range, long-range Coulomb interactions and SL symmetry. Besides the anisotropic behavior of optical phonons, the RIM provided evidence of the acoustic-mode anticrossing, minigap formation, confinement, and interface modes. Controlling the vibrational traits by altering a number of monolayers (n, m) in SLs can provide excellent opportunities for improving the electrical and thermal properties of Sb-based materials for engineering various electronic device structures.

Zeeman and laser site selective spectroscopy of C1 point group symmetry Sm3+ centres in Y2SiO5: a parametrized crystal-field analysis for the 4f 5 configuration

Parametrized crystal-field analyses are presented for both the six and seven fold coordinated, C1 symmetry Sm3+ centres in Y2SiO5, based on extensive spectroscopic data spanning the infrared to optical regions. Laser site-selective excitation and fluorescence spectroscopy as well as Zeeman absorption spectroscopy performed along multiple crystallographic directions has been utilized, in addition to previously determined g tensors for the 6H5/2Z1 and 4G5/2A1 states. The resultant analyses give good approximation to the experimental energy levels and magnetic splittings, yielding crystal-field parameters consistent with the few other lanthanide ions for which such analyses are available.

Effects of Damping Constant of Electron and Size on Quantum-Based Frequency-dependent Dielectric Function of Small Metallic Plasmonic Devices

Electron surface dissipation and quantum-limited size tend to control the material properties of exterior plasmon oscillation as the size of metal nanoparticles goes into the nanoscale domain. The need to examine this characteristic behaviour and its potential becomes imperative. This study explores the effects of the damping constant of electrons and size quantum-based frequency-dependent dielectric function (FDDF) of small metallic materials using an elementary model of electrons in a confined box. The frequency-dependent dielectric function is employed to study quantum size impacts and damping constant in the optical spectra region. The quantum amended frequency-dependent dielectric function and the absorbing spectra of silver-cube geometry for different sizes by adding damping constant and without damping constant are critically examined. The findings reveal that when the damping constant effect is absent, the multiple crests emerge for the quantum-amended frequency-dependent dielectric function and absorbing spectra of the metallic materials, highlighting the electronic discretization levels in the tiny quantum-limited structure. While the damping constant is included, the multiple summits are hidden and vanish owing to a considerable widening of the structures independently. The change in the numerical results from the quantum case to the classical case for growing widths is further illustrated for both cases. The numerical results enhance our knowledge of damping constant dissipation and quantum limited-size impact in small-scaled plasmonic devices.

Characterizing the Variable X-Ray and UV–Optical Flux Behavior of Blazars

The variability of blazars in the X-ray and optical regions both informs the physics of their emitting region and places demands on the observer if a program requires that the object be bright or faint. The extensive simultaneous X-ray and optical observation by the Neil Gehrels Swift Observatory (Swift) provides the best insight into the variable nature of these objects. This program uses Swift data for 19 X-ray-bright blazars, generally at z > 0.1, to determine their variability properties. The analysis is based on structure functions and provides insight into the nature of the variability and how it depends on time, luminosity, and redshift. We also consider strategies for observing blazars at or above average brightness, given a time delay between planning an observation and obtaining the data. This is critical to observations with orbiting X-ray telescopes, current or future. The variability in the soft X-ray band is typically three to eight times larger than at UV–optical wavelengths, at fixed time differences (i.e., 30 or 100 days). There is almost no difference in the amplitude of variation (X-ray or UV–optical) as a function of redshift (time delay of 30 days) and a modest positive correlation with luminosity. In the X-ray band, blazars that become brighter than normal typically remain bright for at least 2–3 months, although with significant flickering. One can avoid observing objects that are significantly below the average X-ray flux by scheduling the observation when F X > 0.9F X,avg, which requires monitoring observations near the time of the scheduling activity.

Ultra-broadband high-efficiency circular polarization conversion and terahertz wavefront manipulation based on an all-metallic reflective metasurface.

In this paper, an all-metal metasurface (MS), which can achieve high-efficient reflective circular-polarization conversion and multifunctional terahertz (THz) wavefront manipulation in an ultra-broadband frequency range, is proposed and investigated theoretically. The proposed all-metal MS consists of the periodic array of a gold vertical-split-ring (VSR) structure adhered on gold substrate. Numerical simulation results indicate that the proposed MS structure can convert the incident circular-polarization (CP) wave into its orthogonal component after reflection with a conversion coefficient over 95% from 0.8 to 1.65 THz (relative bandwidth of 68.3%). The full 2π phase shift of the proposed MS in this frequency range can be obtained by changing the rotation angle of the VSR structure along the wave propagation direction. As proof of concept for the multifunctional wavefront manipulation, anomalous reflection, reflective planar focusing, and vortex beam generation are numerically demonstrated based on the Pancharatnam-Berry (PB) phase principle. Our work can provide an effective method of enhancing the performance of reflective-type all-metal MS and show endless potential in wavefront manipulation and communication applications in THz and even optical region.

A Submicrosecond-Response Ultraviolet-Visible-Near-Infrared Broadband Photodetector Based on 2D Tellurosilicate InSiTe3.

2D material (2DM) based photodetectors with broadband photoresponse are of great value for a vast number of applications such as multiwavelength photodetection, imaging, and night vision. However, compared with traditional photodetectors based on bulk material, the relatively slow speed performance of 2DM based photodetectors hinders their practical applications. Herein, a submicrosecond-response photodetector based on ternary telluride InSiTe3 with trigonal symmetry and layered structure was demonstrated in this study. The InSiTe3 based photodetectors exhibit an ultrafast photoresponse (545-576 ns) and broadband detection capabilities from the ultraviolet (UV) to the near-infrared (NIR) optical communication region (365-1310 nm). Besides, the photodetector presents an outstanding reversible and stable photoresponse in which the response performance remains consistent within 200 000 cycles of switch operation. These significant findings suggest that InSiTe3 can be a promising candidate for constructing fast response broadband 2DM based optoelectronic devices.

NIR-II phototherapy agents with aggregation-induced emission characteristics for tumor imaging and therapy

As one of the major public health concerns, malignant tumors threaten people's lives. With the increasing demand for early accurate diagnosis and the safe treatment of tumors, non-invasive optical imaging (including fluorescence imaging and photoacoustic imaging) and phototherapy (including photothermal therapy and photodynamic therapy) have received much attention. In particular, light in the near-infrared second region (NIR-II) has been attracting research interest, owing to its deep penetration, minimal tissue autofluorescence, and decreased tissue absorption and scattering. Among all biological materials, organic nanomaterials with aggregation-induced emission (AIE) properties have attracted significant attention, owing to various incomparable advantages, such as high brightness, good photostability, tunable photophysical properties, and good biosafety. To modulate the working optical region of AIE molecules to the NIR-II region, many researchers have tried a variety of methods in recent years, and the focus of this review is to summarize the three most common methods from the perspective of molecular design strategies. In addition, this article briefly reviews the recent five-year progress of NIR-II AIE luminophores in tumor imaging and phototherapy applications. The research status is also summarized and prospected, with the hope of contributing to further research.

Comparison Between L-312 Hydrophobic-Hydrophilic Acrylate and US-860 UV Hydrophilic Acrylate IOL Opacification Characteristic.

ObjectiveTo compare opacity characteristics of US-860 UV and L-312 IOL, and report the phenomenon of glistenings in hydrophobic-hydrophilic acrylic IOLs.SettingQingdao Eye Hospital.DesignExperimental study.MethodsFour medical records (4 eyes) of patients with L-312 or US-860 UV IOL opacification reporting decreased or lost vision who underwent IOL explanation between 2019 and 2021 were reviewed. Explanted IOLs were analyzed by slit-lamp examination, confocal microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) at Qingdao Eye Hospital and Qingdao university of science and technology.ResultsThe 4 explanted IOLs were represented by 2 hydrophilic acrylic designs. The preoperative mean corrected distance visual acuity changed from 1.84 ± 1.09 logarithm of the minimum angle of resolution (log MAR) to 0.20 ± 0.03 log MAR postoperatively except case 3. The mean interval of the L-312 IOL was 56.67 ± 14.19 months (range 44 to 72 months), and the interval of the US-860 UV IOL was 27 months. Morphological findings were surface, subsurface calcifications of the US-860 UV IOL material, and the optical region of L-312 IOLs are teeming with a great number of vacuoles by light microscope, scanning electron microscope and Energy Dispersive X-ray Spectral.ConclusionThe cause of US-860 UV opacification was primary calcification, and vacuoles resulted in L-312 IOL opacification.