Viewing Angle Dependence Research Articles

Introducing emissivity directionality to the temperature-emissivity separation algorithm

Natural surfaces are mostly anisotropic emitters, contributing to the anisotropic behavior of Land Surface Temperature (LST). This characteristic of thermal infrared emissivity is well known and several studies have tried to simulate this behavior either with physical or empirical models. However, given the high heterogeneity of land surfaces, the translation of the angular dependence of emissivity as provided from measurements or models into satellite pixel scale anisotropy is generally very difficult. Here we propose a reformulation of the Mean Minimum-Maximum Difference (MMD) curve of the Temperature-Emissivity Separation (TES) algorithm to allow a correct adjustment of the TES retrievals by taking into account the emissivity angular distribution. For that purpose, the Multi-Sensor method is used to obtain directional emissivities at different sites in the Saharan and Namib desert. The data is then used to calibrate the view-angle dependence of the new MMD formulation. The TES retrievals obtained with the new formulation show a good agreement with the Multi-Sensor data. Results also suggest that the new coefficients of the MMD can be applied to other sensors with similar spectral channels. The new angle-dependent emissivities may lead to a reduction of LST bias as high as 2 K for view angles above 50o. The proposed formulation is currently only valid over barren surfaces.

Ultrabright and stable top-emitting quantum-dot light-emitting diodes with negligible angular color shift

Top emission can enhance luminance, color purity, and panel-manufacturing compatibility for emissive displays. Still, top-emitting quantum-dot light-emitting diodes (QLEDs) suffer from poor stability, low light outcoupling, and non-negligible viewing-angle dependence because, for QLEDs with non-red emission, the electrically optimum device structure is incompatible with single-mode optical microcavity. Here, we demonstrate that by improving the way of determining reflection penetration depths and creating refractive-index-lowering processes, the issues faced by green QLEDs can be overcome. This leads to advanced device performance, including a luminance exceeding 1.6 million nits, a current efficiency of 204.2 cd A−1, and a T95 operational lifetime of 15,600 hours at 1000 nits. Meanwhile, our design does not compromise light outcoupling as it offers an external quantum efficiency of 29.2% without implementing light extraction methods. Lastly, an angular color shift of Δu’v’ = 0.0052 from 0° to 60° is achieved by narrowing the emission linewidth of quantum dots.

Emulating radiative transfer with artificial neural networks

ABSTRACT Forward-modeling observables from galaxy simulations enables direct comparisons between theory and observations. To generate synthetic spectral energy distributions (SEDs) that include dust absorption, re-emission, and scattering, Monte Carlo radiative transfer is often used in post-processing on a galaxy-by-galaxy basis. However, this is computationally expensive, especially if one wants to make predictions for suites of many cosmological simulations. To alleviate this computational burden, we have developed a radiative transfer emulator using an artificial neural network (ANN), ANNgelina, that can reliably predict SEDs of simulated galaxies using a small number of integrated properties of the simulated galaxies: star formation rate, stellar and dust masses, and mass-weighted metallicities of all star particles and of only star particles with age <10 Myr. Here, we present the methodology and quantify the accuracy of the predictions. We train the ANN on SEDs computed for galaxies from the IllustrisTNG project’s TNG50 cosmological magnetohydrodynamical simulation. ANNgelina is able to predict the SEDs of TNG50 galaxies in the ultraviolet (UV) to millimetre regime with a typical median absolute error of ∼7 per cent. The prediction error is the greatest in the UV, possibly due to the viewing-angle dependence being greatest in this wavelength regime. Our results demonstrate that our ANN-based emulator is a promising computationally inexpensive alternative for forward-modeling galaxy SEDs from cosmological simulations.

84‐3: A Novel 2D Diffractive Liquid Crystal Smart Window using Single‐sided Engineered Electrode Structure

Smart window technology has been studied actively because it can simply control optical property of window by external power. Among various smart window technology, a phase grating liquid crystal (LC) device shows outstanding properties such as clear off state, high haze in on state, and no viewing angle dependence. Although it can have excellent optical performance, an LC phase grating device requires complicated pattern electrode structure on both top and bottom substrate. To make the device in cost effectiveness, it is required that simple and cost saving design of LC cell is essential.In this presentation, we will introduce our recent progress in LC phase grating smart window. Based on the optimal LC cell design, a trade‐off between performance and cost was minimized while maintaining the advantages of previously researched phase grating LC smart window.

P‐6.4: Measurement for optical performance of flexible display based on imaging spectrometer

With the development of display technology, several new displays have attracted much attention such as OLED display, QLED display, Laser display and Mini/MicroLED display. Standard measurement methods for optical performance of flat display have been established. However, it's not easy for traditional luminance meter or colorimeter to deal with flexible display evaluation because of its viewing angle dependence which results in spectrum shift and color change. In this paper, we simulate color measurement accuracy by colorimeter and compare the results with spectrum measurement device. We analyze the influence of display's viewing angle and spectrum on the measurement accuracy. The measurement accuracy improves obviously with spectrum measurement device under different condition. In addition, we carry out spectrum and color measurement based on our imaging spectrometer which can measure multiple viewing angle at the same time. Compared with traditional spectrometer, the measurement efficiency is improved significantly without adjustment setting. The imaging spectrometer can be used for multiple viewing angle measurement and is suitable for optical performance measurement of flexible display.

Pixelating Structural Color with Cholesteric Spherical Reflectors

While structural color is a powerful means of obtaining saturated and durable pigments that minimize absorption, scattering, and negative environmental impact, appearing naturally in animals and plants as well as in carefully designed artificial composites, it is fundamentally limited to spectral colors, leaving white and other mixed colors elusive. It also normally suffers from a strong viewing angle dependence, making color definition difficult. Herein, it is demonstrated that these challenges can be overcome by using cholesteric spherical reflectors (CSRs), spheres of polymerized cholesteric liquid crystal with radial alignment of the self‐assembled helical structure. Exhibiting omnidirectional selective retroreflectivity of well‐defined color, CSRs are discrete “packages” of structural color. This allows them to be used as pixels for generating nonspectral colors, following the principle of digital displays. A method of creating densely packed monolayers of CSRs with red (R), green (G), and blue (B) retroreflection is developed. Mixing them in equal proportions gives a white surface. By embedding the CSRs in an index matching transparent medium, nonselective specular reflections and scattering are avoided. The approach can be used to create arbitrary colors, including nonspectral ones, without any absorption or nonselective scattering, opening doors to decorating surfaces as desired while minimizing light loss.

Modelling populations of kilonovae

AbstractThe 2017 detection of a kilonova coincident with gravitational-wave emission has identified neutron star mergers as the major source of the heaviest elements and dramatically constrained alternative theories of gravity. Observing a population of such sources has the potential to transform cosmology, nuclear physics, and astrophysics. However, with only one confident multi-messenger detection currently available, modelling the diversity of signals expected from such a population requires improved theoretical understanding. In particular, models that are quick to evaluate and are calibrated with more detailed multi-physics simulations are needed to design observational strategies for kilonovae detection and to obtain rapid-response interpretations of new observations. We use grey-opacity models to construct populations of kilonovae, spanning ejecta parameters predicted by numerical simulations. Our modelling focuses on wavelengths relevant for upcoming optical surveys, such as the Rubin Observatory Legacy Survey of Space and Time (LSST). In these simulations, we implement heating rates that are based on nuclear reaction network calculations. We create a Gaussian-process emulator for kilonova grey opacities, calibrated with detailed radiative transfer simulations. Using recent fits to numerical relativity simulations, we predict how the ejecta parameters from binary neutron star (BNS) mergers shape the population of kilonovae, accounting for the viewing-angle dependence. Our simulated population of BNS mergers produce peak i-band absolute magnitudes of −20 ≤ Mi ≤ −11. A comparison with detailed radiative transfer calculations indicates that further improvements are needed to accurately reproduce spectral shapes over the full light curve evolution.

Kilonovae and Optical Afterglows from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational Wave Triggers

In the second work of this series, we explore the optimal search strategy for serendipitous and gravitational-wave-triggered target-of-opportunity (ToO) observations of kilonovae and optical short-duration gamma-ray burst (sGRB) afterglows from binary neutron star (BNS) mergers, assuming that cosmological kilonovae are AT2017gfo-like (but with viewing-angle dependence) and that the properties of afterglows are consistent with those of cosmological sGRB afterglows. A one-day cadence serendipitous search strategy with an exposure time of ∼30 s can always achieve an optimal search strategy of kilonovae and afterglows for various survey projects. We show that the optimal detection rates of the kilonovae (afterglows) are ∼0.3/0.6/1/20 yr−1 (∼50/60/100/800 yr−1) for Zwicky the Transient Facility (ZTF)/Multi-channel Photometric Survey Telescope (Mephisto)/Wide Field Survey Telescope (WFST)/Large Synoptic Survey Telescope (LSST), respectively. A better search strategy for SiTian than the current design is to increase the exposure time. In principle, a fully built SiTian can detect ∼7(2000) yr−1 kilonovae (afterglows). Population properties of electromagnetic (EM) signals detected by serendipitous observations are studied in detail. For ToO observations, we predict that one can detect ∼11 yr−1 BNS gravitational wave (GW) events during the fourth observing run (O4) by considering an exact duty cycle of the third observing run. The median GW sky localization area is expected to be ∼10 deg2 for detectable BNS GW events. For O4, we predict that ZTF/Mephisto/WFST/LSST can detect ∼5/4/3/3 kilonovae (∼1/1/1/1 afterglows) per year, respectively. The GW detection rates, GW population properties, GW sky localizations, and optimistic ToO detection rates of detectable EM counterparts for BNS GW events at the Advanced Plus, LIGO Voyager, and ET&CE eras are detailedly simulated in this paper.

P‐9.1: Highly efficient top emitting Quantum‐LED with no viewing angle dependence

P‐9.1: Highly efficient top emitting Quantum‐LED with no viewing angle dependence

The physics of Lyman-α escape from disc-like galaxies

ABSTRACT Hydrogen emission lines can provide extensive information about star-forming galaxies in both the local and high-redshift Universe. We present a detailed Lyman continuum (LyC), Lyman-α (Lyα), and Balmer line (Hα and Hβ) radiative transfer study of a high-resolution isolated Milky Way simulation using the state-of-the-art Arepo-RT radiation hydrodynamics code with the SMUGGLE galaxy formation model. The realistic framework includes stellar feedback, non-equilibrium thermochemistry accounting for molecular hydrogen, and dust grain evolution in the interstellar medium (ISM). We extend our publicly available Cosmic Lyα Transfer (COLT) code with photoionization equilibrium Monte Carlo radiative transfer and various methodology improvements for self-consistent end-to-end (non-)resonant line predictions. Accurate LyC reprocessing to recombination emission requires modelling pre-absorption by dust ($f_\text{abs} \approx 27.5\,\rm{per\,\,cent}$), helium ionization ($f_\text{He} \approx 8.7\,\rm{per\,\,cent}$), and anisotropic escape fractions ($f_\text{esc} \approx 7.9\,\rm{per\,\,cent}$), as these reduce the available budget for hydrogen line emission ($f_\text{H} \approx 55.9\,\rm{per\,\,cent}$). We investigate the role of the multiphase dusty ISM, disc geometry, gas kinematics, and star formation activity in governing the physics of emission and escape, focusing on the time variability, gas-phase structure, and spatial spectral, and viewing angle dependence of the emergent photons. Isolated disc simulations are well-suited for comprehensive observational comparisons with local Hα surveys, but would require a proper cosmological circumgalactic medium (CGM) environment as well as less dust absorption and rotational broadening to serve as analogs for high-redshift Lyα emitting galaxies. Future applications of our framework to next-generation cosmological simulations of galaxy formation including radiation-hydrodynamics that resolve ≲10 pc multiphase ISM and ≲1 kpc CGM structures will provide crucial insights and predictions for current and upcoming Lyα observations.

34‐4: Invited Student Paper: UBplus/UB‐FFS‐Premium Performance for Liquid‐Crystal TV and IT Displays

Premium displays that offer outstanding characteristics are becoming more important in liquid crystal display market. Globally, researchers are looking for ways to improve contrast, transmittance, viewing angle dependency, resolution and switching speed while keep the high reliability level of liquid crystal devices. UB (Ultra Bright)‐technology (UBplus and UBFFS) can increase panel transmittance by using negative dielectric anisotropy LC mixtures compared with traditional FFS Mode, supporting higher resolution devices. In this paper we demonstrate the advantage of UB‐LC technology for TV as well as IT applications and summarize the recent developments of such liquid crystal mixtures in terms of contrast, switching speed and reliability.

Multi-Messenger Constraints on the Hubble Constant through Combination of Gravitational Waves, Gamma-Ray Bursts and Kilonovae from Neutron Star Mergers

The simultaneous detection of gravitational waves and light from the binary neutron star merger GW170817 led to independent measurements of distance and redshift, providing a direct estimate of the Hubble constant H0 that does not rely on a cosmic distance ladder, nor assumes a specific cosmological model. By using gravitational waves as “standard sirens”, this approach holds promise to arbitrate the existing tension between the H0 value inferred from the cosmic microwave background and those obtained from local measurements. However, the known degeneracy in the gravitational-wave analysis between distance and inclination of the source led to a H0 value from GW170817 that was not precise enough to resolve the existing tension. In this review, we summarize recent works exploiting the viewing-angle dependence of the electromagnetic signal, namely the associated short gamma-ray burst and kilonova, to constrain the system inclination and improve on H0. We outline the key ingredients of the different methods, summarize the results obtained in the aftermath of GW170817 and discuss the possible systematics introduced by each of these methods.

Modeling the view-angle dependence of the gap fraction in subtropical forests by using terrestrial laser scanning

Determining how the view angle relates to the directional gap fraction (DGF) of natural forests with varying canopy structure and terrain is beneficial for assessing the radiation transfer and understory growth. However, it remains challenging to determine how DGF depends on the view angle due to the limitation to obtain the DGF at arbitrary view angles. This study verifies a point number-based method based on terrestrial laser scanning (TLS) data to estimate the DGF at arbitrary view angles for subtropical forests on either sloped or flat terrain. We then explore how the vertical DGF in the non-nadir direction relates to that in the nadir direction, and analyze the effects of forest canopy structure and terrain on the relationship. Finally, we quantify the dependence of DGF on both view zenith angle (VZA) and view azimuthal angle (VAA). The results show that the TLS-based method captures over 67% of the variations (root mean square error≤0.12) of the optically measured DGF. The vertical DGF in the non-nadir direction is related by a power function model to that in the nadir direction. Sloped terrain weakens the dependence of DGF on the VZA especially when VZA is large than 60° in this study, and the low forest density, low average tree height, and small crown diameter strengthen the dependence of DGF on the VZA. The DGF depends on the VZA more than the VAA for forests on flat terrain. However, the VAA also plays a key role in DGF estimation for forests on sloped terrain. This study proves that TLS is a useful tool to acquire reference data of DGF which can help to understand aerial and satellite estimation analyses in subtropical forested areas.

Digital photoprogramming of liquid-crystal superstructures featuring intrinsic chiral photoswitches

Dynamic patterning of soft materials in a fully reversible and programmable manner with light enables applications in anti-counterfeiting, displays and labelling technology. However, this is a formidable challenge due to the lack of suitable chiral molecular photoswitches. Here, we report the development of a unique intrinsic chiral photoswitch with broad chirality modulation to achieve digitally controllable, selectable and extractable multiple stable reflection states. An anti-counterfeiting technique, embedded with diverse microstructures, featuring colour-tunability, erasability, reversibility, multi-stability and viewing-angle dependency of pre-recorded patterns, is established with these photoresponsive superstructures. This strategy allows dynamic helical transformation from the molecular and supramolecular to the macroscopic level using light-activated intrinsic chirality, demonstrating the practicality of photoprogramming photonics.

Fountain fringe field switching (FFFS) for wide viewing angle LCDs

To reduce or completely remove the viewing angle dependence of liquid crystal (LC) displays and devices, we have recently introduced a new electrode structure for LC displays. This electrode structure has openings (holes) in the pixel electrode (PixE) for generating fringe electric field with azimuthal degenerated distribution of the field lines around each hole, resembling a fountain. Such a field is promoting azimuthally degenerated switching of the LC molecules and thus generation of images with 360° viewing angle constant contrast when a pair of crossed circular polarisers are used. A theoretical model of the fountain fringe field, generated around a single circular hole and plurality of such holes in the PixE, is presented.

Random rubbed structure for enhanced light extraction in organic light-emitting diodes

In this study, we demonstrated a nanoscale random rubbed structure (nRRS) as an internal scattering layer for organic light-emitting diodes (OLEDs) through an innovative fabrication method. Random corrugation above the SU-8 polymer surface can be simply formed using the rubbing technique commonly employed for liquid crystal alignment. A random structure that is optimized to a nanoscale that does not deteriorate electrical stability can be engineered by controlling the rubbing process. The nRRS exhibited high transmittance (>97%) in the visible wavelength range of 380–700 nm, making it suitable for use as an internal functional layer for OLEDs. Compared to that of the reference device, the external quantum efficiency of the optimized nRRS device increased by 35.47%, and the current and power efficiencies at 3000 cd/m2 were 1.27 times higher. As the viewing angle increased from 0° to 70°, the nRRS-inserted OLED showed a negligible International Commission on Illumination 1931 coordinate shift (Δ (x, y) = (0.016, 0.022)), successfully expressing the alleviation of the viewing-angle dependency. By utilizing finite-difference time-domain simulation tool, the optical results of the device are predicted and verified. This manufacturing approach has the advantages of being applicable to large-scale production and processability at room temperature without the use of a vacuum equipment.

All-in-one wearable electronics design: Smart electrochromic liquid-crystal-clad fibers without external electrodes

Smart textiles and wearable sensors based on liquid crystal materials with highly tunable and controllable discoloration are attracting attention due to their promising functionality. However, products previously reported almost relies on the extra transparent conductive electrode to provide a stable electric field and resulting in complexity and inconvenience. Besides, practical applications remain limited by the lack of continuously processed long electrochromic fibers suitable for industrial weaving. This work presents smart electrochromic liquid-crystal-clad (ECLCC) fibers with multi-environmental stability and long-range controllability that are prepared continuously using simple tailormade instruments. By introducing a variety of electrochromic materials (CLCs) and a distinctive device design (coaxial dual-counter-electrode sandwich structure), multiple rapid and uniform color changes can be achieved over a long duration. The monofilament conductive core provides ECLCC fiber with enhanced color effects without viewing angle dependence, as well as good flexibility and stretchability. The fiberized coaxial electrode structure realizes the flexible electrochromic of textiles compared to the previously parallel sandwich structure of the traditional liquid crystal display. Thus, complex textiles can be easily knitted from fibers that respond to different external electro stimuli, showed the potential applications in intelligent clothing that sense and report the healthy condition of the wearer or the situation of the surrounding environment.

26.5: View Angle Characteristics of LCD/OLED/miniLED/microLED Panels

The view angle characteristics refer to the changes in the luminance that occur with varying view directions which is defined as the luminance's view angle dependence (LVAD) in this paper. Recently the LVAD of OLED/LCD/miniLED/microLED panels attracts more attention. In this paper, the LVAD of OLED/LCD/mini LED/micro LED were measured and compared. For each panel, the LVAD of three gray levels and three colors at nine positions and four azimuth angles has been measured. The gray levels are 255/128/32, the colors are red (R), green (G), blue (B) and the azimuth angles are 0/90/180/270 degrees. It was found that the LVAD of OLED/miniLED/microLED changes a lot with colors except LCD panels. And the LVAD of all panels changes with the measurement azimuth angles. Gray levels will also affect the LVAD if different gray levels are with different spectra. Besides, OLED/LCD/miniLED panels exhibit the same LVAD at different positions.

Validation of Sentinel-3 SLSTR Land Surface Temperature Retrieved by the Operational Product and Comparison with Explicitly Emissivity-Dependent Algorithms

Land surface temperature (LST) is an essential climate variable (ECV) for monitoring the Earth climate system. To ensure accurate retrieval from satellite data, it is important to validate satellite derived LSTs and ensure that they are within the required accuracy and precision thresholds. An emissivity-dependent split-window algorithm with viewing angle dependence and two dual-angle algorithms are proposed for the Sentinel-3 SLSTR sensor. Furthermore, these algorithms are validated together with the Sentinel-3 SLSTR operational LST product as well as several emissivity-dependent split-window algorithms with in-situ data from a rice paddy site. The LST retrieval algorithms were validated over three different land covers: flooded soil, bare soil, and full vegetation cover. Ground measurements were performed with a wide band thermal infrared radiometer at a permanent station. The coefficients of the proposed split-window algorithm were estimated using the Cloudless Land Atmosphere Radiosounding (CLAR) database: for the three surface types an overall systematic uncertainty (median) of −0.4 K and a precision (robust standard deviation) 1.1 K were obtained. For the Sentinel-3A SLSTR operational LST product, a systematic uncertainty of 1.3 K and a precision of 1.3 K were obtained. A first evaluation of the Sentinel-3B SLSTR operational LST product was also performed: systematic uncertainty was 1.5 K and precision 1.2 K. The results obtained over the three land covers found at the rice paddy site show that the emissivity-dependent split-window algorithms, i.e., the ones proposed here as well as previously proposed algorithms without angular dependence, provide more accurate and precise LSTs than the current version of the operational SLSTR product.

Axisymmetric Radiative Transfer Models of Kilonovae

Abstract The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g., in total r-process mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations around the peak brightness are uncertain by at least an order of magnitude. Mixed two-component models with lanthanide-rich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide “curtaining,” which persists even if the relative mass of lanthanide-rich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometry-dependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the r-process abundances.