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Volcanic emissions are a well-known hazard that can have serious impacts on local populations and aviation operations. Whereas several remote sensing observations detect high-intensity explosive eruptions, few studies focus on low intensity and long-lasting volcanic emissions. In this work, we have managed to fully characterize those events by analyzing the volcanic plume produced on the last day of the 2018 Christmas eruption at Mt. Etna, in Italy. We combined data from a visible calibrated camera, a multi-wavelength elastic/Raman Lidar system, from SEVIRI (EUMETSAT-MSG) and MODIS (NASA-Terra/Aqua) satellites and, for the first time, data from an automatic sun-photometer of the aerosol robotic network (AERONET). Results show that the volcanic plume height, ranging between 4.5 and 6 km at the source, decreased by about 0.5 km after 25 km. Moreover, the volcanic plume was detectable by the satellites up to a distance of about 400 km and contained very fine particles with a mean effective radius of about 7 µm. In some time intervals, volcanic ash mass concentration values were around the aviation safety thresholds of 2 × 10−3 g m−3. Of note, Lidar observations show two main stratifications of about 0.25 km, which were not observed at the volcanic source. The presence of the double stratification could have important implications on satellite retrievals, which usually consider only one plume layer. This work gives new details on the main features of volcanic plumes produced during low intensity and long-lasting volcanic plume emissions.

We explain the details of the photometric operation mode of the ASTRONICAM near-IR spectrograph camera mounted on the 2.5-m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute and describe algorithms used for primary correction and overall pipeline reduction of the acquired data. We present the transformation equations from the 2MASS photometric system to the instrumental -band system. We derive color transformation coefficients between the instrumental photometric system and standard MKO-NIR (Mauna Kea Observatories Near-Infrared) system for the , , and -band filters and show that the camera system is close to the standard photometric system. We found that in the case of observations at zenith, average background brightness level, and seeing the stars with , , can be measured with a 3000-s exposure at the signal-to-noise ratio .

The Aerosol Robotic Network (AERONET) has provided highly accurate, ground-truth measurements of the aerosol optical depth (AOD) using Cimel Electronique Sun–sky radiometers for more than 25 years. In Version 2 (V2) of the AERONET database, the near-real-time AOD was semiautomatically quality controlled utilizing mainly cloud-screening methodology, while additional AOD data contaminated by clouds or affected by instrument anomalies were removed manually before attaining quality-assured status (Level 2.0). The large growth in the number of AERONET sites over the past 25 years resulted in significant burden to the manual quality control of millions of measurements in a consistent manner. The AERONET Version 3 (V3) algorithm provides fully automatic cloud screening and instrument anomaly quality controls. All of these new algorithm updates apply to near-real-time data as well as post-field-deployment processed data, and AERONET reprocessed the database in 2018. A full algorithm redevelopment provided the opportunity to improve data inputs and corrections such as unique filter-specific temperature characterizations for all visible and near-infrared wavelengths, updated gaseous and water vapor absorption coefficients, and ancillary data sets. The Level 2.0 AOD quality-assured data set is now available within a month after post-field calibration, reducing the lag time from up to several months. Near-real-time estimated uncertainty is determined using data qualified as V3 Level 2.0 AOD and considering the difference between the AOD computed with the pre-field calibration and AOD computed with pre-field and post-field calibration. This assessment provides a near-real-time uncertainty estimate for which average differences of AOD suggest a +0.02 bias and one sigma uncertainty of 0.02, spectrally, but the bias and uncertainty can be significantly larger for specific instrument deployments. Long-term monthly averages analyzed for the entire V3 and V2 databases produced average differences (V3–V2) of +0.002 with a ±0.02 SD (standard deviation), yet monthly averages calculated using time-matched observations in both databases were analyzed to compute an average difference of −0.002 with a ±0.004 SD. The high statistical agreement in multiyear monthly averaged AOD validates the advanced automatic data quality control algorithms and suggests that migrating research to the V3 database will corroborate most V2 research conclusions and likely lead to more accurate results in some cases.

The explosive demand for a wide range of data processing has sparked interest towards a new logic gate platform as the existing electronic logic gates face limitations in accurate and fast computing. Accordingly, optoelectronic logic gates (OELGs) using photodiodes are of significant interest due to their broad bandwidth and fast data transmission, but complex configuration, power consumption, and low reliability issues are still inherent in these systems. Herein, we present a novel all-in-one OELG based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) having a back-to-back p + -i-n-p-p + diode structure. Five representative logic gates (“AND”, “OR”, “NAND”, “NOR”, and “NOT”) are demonstrated with only a single SPPD via the photocurrent polarity control. For practical applications, we propose a universal OELG platform of integrated 8 × 8 SPPD pixels, demonstrating the 100% accuracy in five logic gate operations irrelevant to current variation between pixels. The authors present a novel all-in-one optoelectronic logic gates based on the bipolar spectral photo-response characteristics of self-powered perovskite photodetector. Five representative logic gates are demonstrated with only a single detector via photocurrent polarity control.

NASA's exoplanet Discovery mission Kepler was reconstituted as the K2 mission a year after the failure of the second of Kepler's four reaction wheels in 2013 May. Fine control of the spacecraft pointing is now accomplished through the use of the two remaining well-functioning reaction wheels and balancing the pressure of sunlight on the solar panels, which constrains K2 observations to fields in the ecliptic for up to approximately 80 days each. This pseudo-stable mechanism gives typical roll motion in the focal plane of 1.0 pixels peak-to-peak over 6 hr at the edges of the field, two orders of magnitude greater than typical 6 hr pointing errors in the Kepler primary mission. Despite these roll errors, the joint performance of the flight system and its modified science data processing pipeline restores much of the photometric precision of the primary mission while viewing a wide variety of targets, thus turning adversity into diversity. We define K2 performance metrics for data compression and pixel budget available in each campaign; the photometric noise on exoplanet transit and stellar activity timescales; residual correlations in corrected long-cadence light curves; and the protection of test sinusoidal signals from overfitting in the systematic error removal process. We find that data compression and noise both increase linearly with radial distance from the center of the field of view, with the data compression proportional to star count as well. At the center, where roll motion is nearly negligible, the limiting 6 hr photometric precision for a quiet 12th magnitude star can be as low as 30 ppm, only 25% higher than that of Kepler. This noise performance is achieved without sacrificing signal fidelity; test sinusoids injected into the data are attenuated by less than 10% for signals with periods upto 15 days, so that a wide range of stellar rotation and variability signatures are preserved by the K2 pipeline. At timescales relevant to asteroseismology, light curves derived from K2 archive calibrated pixels have high-frequency noise amplitude within 40% of that achieved by Kepler. The improvements in K2 operations and science data analysis resulting from 1.5 years of experience with this new mission concept, and quantified by the metrics in this paper, will support continuation of K2's already high level of scientific productivity in an extended K2 mission.

Graphene photodetectors have exhibited high bandwidth and capability of being integrated with silicon photonics (SiPh), holding promise for future optical communication devices. However, they usually suffer from a low photoresponsivity due to weak optical absorption. In this work, we have implemented SiPh-integrated twisted bilayer graphene (tBLG) detectors and reported a responsivity of 0.65 A W –1 for telecom wavelength 1,550 nm. The high responsivity enables a 3-dB bandwidth of >65 GHz and a high data stream rate of 50 Gbit s –1 . Such high responsivity is attributed to the enhanced optical absorption, which is facilitated by van Hove singularities in the band structure of high-mobility tBLG with 4.1 o twist angle. The uniform performance of the fabricated photodetector arrays demonstrates a fascinating prospect of large-area tBLG as a material candidate for heterogeneous integration with SiPh. Silicon-integrated graphene photodetectors exhibit promising bandwidths at telecom wavelengths, but their responsivity is usually limited. Here, the authors report the wafer-scale fabrication of waveguide-integrated detectors based on twisted bilayer graphene, showing responsivities up to 0.65 A/W and 3-dB bandwidths >65 GHz.

Free-space coupling, essential for various communication applications, often faces significant signal loss and interference from ambient light. Traditional methods rely on integrating complex optical and electronic systems, leading to bulkier and costlier communication equipment. Here, we show an asymmetric 2D–3D–2D perovskite structure device to achieve a frequency-selective photoresponse in a single device. By combining two electromotive forces of equal magnitude in the opposite directions, the device output is attenuated to zero under constant light illumination. Because these reverse photodiodes have different response speeds, the device only responds near a certain frequency, which can be tuned by manipulating the 2D perovskite components. The target device achieves an ultrafast response of 19.7/18.3 ns in the frequency-selective photoresponse range 0.8–9.7 MHz. This anti-interference photodetector can accurately transmit character and video data under strong light interference with a source intensity of up to 454 mW cm −2 . Signal transmission without the interference from ambient light is prerequisite for optical communications. Min et al. design an asymmetric 2D-3D-2D perovskite photodetector with frequency-selective photoresponse for real-time high fidelity optical communications under strong light interference.

Computational imaging enables retrieval of the spatial information of an object with the use of single-pixel detectors. By projecting a series of known random patterns and measuring the backscattered intensity, it is possible to reconstruct a two-dimensional (2D) image. We used several single-pixel detectors in different locations to capture the 3D form of an object. From each detector we derived a 2D image that appeared to be illuminated from a different direction, even though only a single digital projector was used for illumination. From the shading of the images, the surface gradients could be derived and the 3D object reconstructed. We compare our result to that obtained from a stereophotogrammetric system using multiple cameras. Our simplified approach to 3D imaging can readily be extended to nonvisible wavebands.

We report the detection of gravity modes in RR Lyrae stars. Thanks to Photometer AntarctIca eXtinction (PAIX), the first Antarctic polar photometer. Unprecedented and uninterrupted UBVRI time-series photometric ground-based data are collected during 150 days from the highest plateau of Antarctica. PAIX light-curve analyses reveal an even richer power spectrum with mixed modes in RR Lyrae stars. The nonlinear nature of several dominant peaks, showing lower and higher frequencies, occurs around the dominant fundamental radial pressure mode. These lower frequencies and harmonics linearly interact with the dominant fundamental radial pressure mode and its second and third overtone pressure modes, as well. Half-integer frequencies are also detected, likewise side-peak structures, demonstrating that HH Puppis is a bona-fide Blazhko star. Fourier correlations are used to derive underlying physical characteristics for HH Puppis. The most striking finding is the direct detection of gravity waves. We interpret the excitation mechanism of gravity waves in RR Lyrae stars by the penetrative convection-driving mechanism. We demonstrate that RR Lyrae stars’ pulsation is excited by several distinct mechanisms, and hence RR Lyrae stars are simultaneously g-mode and p-mode pulsators. Our discoveries make RR Lyrae stars very challenging stellar objects, and provide their potential to undergo at the same time g and p modes toward an advancement of the theory of stellar evolution and a better understanding of the universe.

Graphene-based photodetectors have attracted strong interest for their exceptional physical properties, which include an ultrafast response 1 , 2 , 3 across a broad spectrum 4 , a strong electron–electron interaction 5 and photocarrier multiplication 6 , 7 , 8 . However, the weak optical absorption of graphene 2 , 3 limits its photoresponsivity. To address this, graphene has been integrated into nanocavities 9 , microcavities 10 and plasmon resonators 11 , 12 , but these approaches restrict photodetection to narrow bands. Hybrid graphene–quantum dot architectures can greatly improve responsivity 13 , but at the cost of response speed. Here, we demonstrate a waveguide-integrated graphene photodetector that simultaneously exhibits high responsivity, high speed and broad spectral bandwidth. Using a metal-doped graphene junction coupled evanescently to the waveguide, the detector achieves a photoresponsivity exceeding 0.1 A W −1 together with a nearly uniform response between 1,450 and 1,590 nm. Under zero-bias operation, we demonstrate response rates exceeding 20 GHz and an instrumentation-limited 12 Gbit s −1 optical data link. A chip-integrated graphene photodetector with a high responsivity of over 0.1 A W −1 , high speed and broad spectral bandwidth is realized through enhanced absorption due to near-field coupling. Under zero-bias operation, response rates above 20 GHz and an instrumentation-limited 12 Gbit s −1 optical data link are demonstrated.