Short Integration Times Research Articles

Algorithms of pulse shape analysis for Gammasphere under high count rate conditions

The implementation of digital electronics for the multi-detector Gammasphere array has provided an opportunity to perform experiments which exceed the technical capabilities of its analog counterpart. The pulse shape analysis of HPGe detectors is presented for the purpose of determining the γ-ray energy under high-counting rates and short integration times with the aim of improving the data throughput. A revised trapezoidal algorithm is delineated which is able to determine the γ-ray energies during the offline analysis without being constrained by predetermined parameters. The performance of this algorithm is discussed, and compared with that of the analog system. The measured energy resolution meets expectations for operations with high-counting rates and short integration times.

Dynamical conductance measurement of single molecular junctions with both high-speed and high-precision

Real-time and rapid monitoring of the electron transport in nanoscale structures is critical for understanding many fundamental phenomena. However, it is not possible to rapidly record the dynamical current that varied across several orders of magnitude by using a typical linear low-noise current-to-voltage converter due to its fixed gain. In addition, it faces a great challenge in carrying out a dynamical small current measurement by using a commercial source-monitor unit device with both high-precision and high-speed because a high-precision measurement normally requests long integration time, while high-speed sampling demands short integration time. To overcome these challenges, we designed a measurement system with an integrated logarithmic amplifier, which can convert the current/conductance signal (varied across eight orders of magnitude) into an output voltage signal (varied within only one order of magnitude). We successfully applied it for the dynamical conductance measurement of single molecular break junctions in which the current rapidly changed from milliampere (mA) to picoampere (pA) within tens of milliseconds under a fixed bias voltage. It is demonstrated that the intrinsic conductance can be determined accurately independent of the applied bias and the real-time dynamical conductance traces can be precisely recorded with a high-speed sampling ratio. This logarithmic amplifier design and home-made measurement system provide a way to realize a fast measurement (30 kHz) for a rapidly varied current (mA–pA), making it suitable for the characterization of single-molecule junctions during the break process, and show potential for a wide application far beyond molecule electronics.

Sensitive control of broad-area semiconductor lasers by cavity shape

The ray dynamics of optical cavities exhibits bifurcation points: special geometries at which ray trajectories switch abruptly between stable and unstable. A prominent example is the Fabry–Perot cavity with two planar mirrors, which is widely employed for broad-area semiconductor lasers. Such cavities support lasing in a relatively small number of transverse modes, and the laser is highly susceptible to filamentation and irregular pulsations. Here, we demonstrate experimentally that a slight deviation from this bifurcation point (planar cavity) dramatically changes the laser performance. In a near-planar cavity with two concave mirrors, the number of transverse lasing modes increases drastically. While the spatial coherence of the laser emission is reduced, the divergence angle of the output beam remains relatively narrow. Moreover, the spatiotemporal lasing dynamics becomes significantly more stable compared to that in a Fabry–Perot cavity. Our near-planar broad-area semiconductor laser has higher brightness, better directionality, and hence allows shorter integration times than an incandescent lamp while featuring sufficiently low speckle contrast at the same time, making it a vastly superior light source for speckle-free imaging. Furthermore, our method of controlling spatiotemporal dynamics with extreme sensitivity near a bifurcation point may be applied to other types of high-power lasers and nonlinear dynamic systems.

Highly sensitive SERS detection in a non-volatile liquid-phase system with nanocluster-patterned optical fiber SERS probes.

The use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of substances in non-volatile systems, such as edible oil and biological cells, is an important issue in the fields of food safety and biomedicine. However, traditional dry-state SERS detection with planar SERS substrates is not suitable for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems. In this paper, we take contaminant in edible oil as an example and propose an in situ SERS detection method for non-volatile complex liquid-phase systems with high-performance optical fiber SERS probes. Au-nanorod clusters are successfully prepared on optical fiber facet by a laboratory-developed laser-induced dynamic dip-coating method, and relatively high detection sensitivity (LOD of 2.4 × 10-6 mol/L for Sudan red and 3.6 × 10-7 mol/L for thiram in sunflower oil) and good reproducibility (RSD less than 10%) are achieved with a portable Raman spectrometer and short spectral integration time of 10 s even in complex edible oil systems. Additionally, the recovery rate experiment indicates the reliability and capability of this method for quantitative detection applications. This work provides a new insight for highly sensitive and rapid SERS detection in non-volatile liquid-phase systems with optical fiber SERS probes and may find important practical applications in food safety and biomedicine.

Comparison of CML Rainfall Data against Rain Gauges and Disdrometers in a Mountainous Environment.

Despite the several sources of inaccuracy, commercial microwave links (CML) have been recently exploited to estimate the average rainfall intensity along the radio path from signal attenuation. Validating these measurements against “ground truth” from conventional rainfall sensors, as rain gauges, is a challenging issue due to the different spatial sampling involved. Here, we assess the performance of a network of CML as opportunistic rainfall sensors in a challenging mountainous environment located in Northern Italy. The benchmark dataset was provided by an operational network of rain gauges and by three disdrometers. Moreover, disdrometer data were used to establish an accurate relationship between path attenuation and rainfall intensity. A new method was developed for assessing CML: time series of rainfall occurrence and rainfall depth, representative of CML radio path, were derived from the nearby rain gauges and disdrometers and compared with the same quantities gathered from the CML. It turns out that, over the very short integration times considered (10 min), CML perform well in detecting rainfall, whereas quantitative rainfall estimates may have large discrepancies.

Feed-Forward Neural Network Denoising Applied to Goldstone Solar System Radar Images

The study of Near-Earth Asteroids (NEA) is crucial for human safety. Small hazardous asteroids with small radar cross sections are not easy to detect, track, and characterize due to the small signal-to-noise ratio (SNR) of the radar echo. This manuscript describes the results obtained for the application of a feed-forward neural network (FFNN) denoising methodology to NEA data obtained from the Goldstone Solar System Radar (GSSR). We demonstrate an increase in the signal level of up to ×4 the original value—in terms of sigma above the mean noise—when applying the FFNN denoising technique to radar Z-score normalized Binary Phase Code (BPC) images. This improvement benefits better radar detection of NEAs in general. Reducing the noise background level for antennas that have lower aperture, e.g., 34 m dishes, enables the use of FFNN denoising to improve visual detections on those noisier conditions. In addition, reducing noise level benefits shorter integration times of the data to obtain adequate signal levels. When talking about detection of small bodies crossing the antenna beam, since the asteroids or debris can move across the beam quite fast, it is relevant to reduce the integration time to allow for an increased number of independent pieces of information crossing the target through the antenna beam. The increased distance between the signal level and the noise level enables a better detection of the small-bodies at shorter integration times and therefore would be very useful for the detection of objects in the cis-lunar space.

Noise behaviors of SWIR InxGa1-xAs/InP focal plane arrays as a function of lattice-mismatch degree

A quantitatively investigation on the dark noise behaviors of In0.53Ga0.47As/InP, In0.75Ga0.25As/In0.75Al0.25As/InP and In0.83Ga0.17As/In0.83Al0.17As/InP short-wavelength infrared (SWIR) focal plane arrays (FPAs) with cutoff wavelengths (λc) of 1.7, 2.2 and 2.5 μm, respectively, is presented. Theoretical FPA noise model consisting of the diode thermal noise, the dark current shot noise, the operational transimpedance amplifier (OTA) thermal noise, the 1/f noise, the sample and hold noise of the circuit, and etc. were fully taken into consideration. The results show that the dark noises are mainly composed of the OTA thermal noise of the readout circuit under short integration times (Tint) for all three FPAs. Under long Tint, the thermal noises from the photodiode arrays at 300 K is acting as the primary source for the dark noise of the lattice-matched In0.53Ga0.17As FPA, whereas noises of the lattice-mismatched 2.2 and 2.5 μm FPAs are identified to be mainly comes from the diode thermal noise, the dark current shot noise, and the 1/f noise at 150 and 180 K. In addition, an overall trend that the contribution of the 1/f noise increases significantly even if the junction impedance increases and the dark current decreases by cooling down for the extended wavelength detector, which is related to the existence of high density misfit dislocation defect-related trap states in the materials. These results suggest that lowering the junction capacitance and increasing the junction resistance are effective routes to suppress the total readout noise of the InGaAs FPAs, which essentially relies on the improvements on the material epitaxial growth and photodiode array processing recipes.Index Terms: readout noise, lattice-mismatch, focal plane array, InGaAs, noise model.

Mid-IR spectroscopy with NIR grating spectrometers.

Mid-infrared (mid-IR) spectroscopy is a crucial workhorse for a plethora of analytical applications and is suitable for diverse materials, including gases, polymers or biological tissue. However, this technologically significant wavelength regime between 2.5-10 µm suffers from technical limitations primarily related to the large noise in mid-IR detectors and the complexity and cost of bright, broadband mid-IR light sources. Here, using highly non-degenerate, broadband photon pairs from bright spontaneous parametric down-conversion (SPDC) in a nonlinear interferometer, we circumvent these limitations and realise spectroscopy in the mid-IR using only a visible (VIS) solid-state laser and an off-the-shelf, commercial near-infrared (NIR) grating spectrometer. With this proof-of-concept implementation, covering a broad range from 3.2 µm to 4.4 µm we demonstrate short integration times down to 1 s and signal-to-noise ratios above 200 at a spectral resolution from 12 cm-1 down to 1.5 cm-1 for longer integration times. Through the analysis of polymer samples and the ambient CO2 in our laboratory, we highlight the potential of this measurement technique for real-world applications.

Impact of spectral noise shape and correlations of laser beam jitter on acquiring optical links in space.

We investigate how the probability of acquiring an optical link between a scanning and a target spacecraft depends on the spectral shape, power, and dimensionality of the beam jitter, as well as on the choice of detector integration time, beam detection radius, and scan speed. For slow scans and long integration times, the probability of failure (Pfail) is determined by the integrated jitter power up to a critical frequency, which we verify by comparing the results of an analytical model to those of Monte Carlo simulations. Jitter above the critical frequency leads to a loss of correlation between integration windows and decreases Pfail for both 1D (radial) and 2D (radial and tangential) jitter, as long as the RMS jitter amplitude does not exceed the beam diameter. In the opposite limit of fast scans and short integration times, emergent correlations between jitter fluctuations on two adjacent scanning tracks also decrease Pfail. The analytical model is additionally used to assess the effect of multiple overlapping tracks and the impact of target drifts in the uncertainty plane.

Retracted] Research on the Model of Distance Education Resource Integration from the Perspective of Comparative Education

In order to solve the problems of high data loss rate, long time‐consuming resource integration, large amount of redundant data, and incomplete results of resource integration in traditional methods, a design method of distance education resource integration model from the perspective of comparative education is proposed. Association rules are used to mine resources and get effective resources in the context of comparative pedagogy, with the goal of increasing the impact of resource integration. Then, using a three‐tier architecture, a remote education resource integration model is created, and the mining results are combined through the application layer, resource encryption layer, and multicast communication layer to achieve distance education resource integration. Simulation results show that the method of this article has low data loss rate, short resource integration time, less redundant data, and comprehensive integration results, which provides an effective technical support for the development of education.

Highly Ordered Polymer Nanostructures via Solvent On-Film Annealing for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) has been a useful sensing technique, in which inelastic light scattering can be significantly enhanced by absorbing molecules onto rough metal surfaces or nanoparticles. Although many methods have been developed to prepare SERS substrates, it is still highly desirable and challenging to design SERS substrates, especially with highly ordered and controlled three-dimensional (3D) structures. In this work, we develop novel SERS substrates with regular volcano-shaped polymer structures using the versatile solvent on-film annealing method. Polystyrene (PS) nanospheres are first synthesized by surfactant-free emulsion polymerization and assembled on poly(methyl methacrylate) (PMMA) films. After annealing in acetic acid vapors, PMMA chains are selectively swollen and wet the surfaces of the PS nanospheres. By selectively removing the PS nanospheres using cyclohexane, volcano-shaped PMMA films can be obtained. Compared with flat PMMA films with water contact angles of ∼74°, volcano-shaped PMMA films exhibit higher water contact angles of ∼110° due to the sharp features and rough surfaces. The volcano-shaped PMMA films are then coated with gold nanoparticles (AuNPs) as SERS substrates. Using rhodamine 6G as the probe molecules, the SERS results show that the Raman signals of the volcano-shaped PMMA/AuNP hybrid substrates are much higher than those of the pristine PMMA films and PMMA films with AuNPs. For the volcano-shaped PMMA/AuNP hybrid substrates using 400 nm PS nanospheres, a high enhancement factor (EF) value of ∼1.12 × 105 with a detection limit of 10-8 M is obtained in a short integration time of 1 s. A linear calibration line with an R2 value of 0.918 is also established, demonstrating the ability to determine the concentrations of the analytes. This work offers significant insight into developing novel SERS substrates, which is crucial for improving the detection limits of analytes.

H I in and behind the Hubble Frontier Field clusters: a deep MeerKAT pilot search out to z ∼ 0.5

ABSTRACT The Hubble Frontier Fields (HFF) are a selection of well-studied galaxy clusters used to probe dense environments and distant gravitationally lensed galaxies. We explore the 21cm neutral hydrogen (H i) content of galaxies in three of the HFF clusters, Abell 2744 (z = 0.308), Abell S1063 (z = 0.346), and Abell 370 (z = 0.375), to investigate the evolution of gas in galaxies within intermediate redshift clusters. Using Early Science MeerKAT observations, we perform spectral-line stacking with H i cubes and make a 3σ stacked detection for blue galaxies in Abell S1063 ($M_\mathrm{HI} = 1.22^{+0.38}_{-0.36}\, \times 10^{10}\, \mathrm{M}_\odot$). We determine the 3σ H i mass detection limits of Abell 2744 and Abell 370 to be at the knee of the H i mass function. A final, more ambitious objective of this work is to search for gravitationally lensed H i emission behind these clusters, enabled by MeerKAT’s wide instantaneous bandwidth. We find no evidence of highly magnified H i emission at 0.33 < z < 0.58. The low thermal noise levels achieved in these pilot observations, despite short integration times, highlights the enormous potential of future MeerKAT H i observations of dense environments, and the intermediate-redshift Universe.

The mean free path approximation and stellar collisions in star clusters: numerical exploration of the analytic rates and the role of perturbations on binary star mergers

ABSTRACTIn this paper, we compute predictions for the number of stellar collisions derived from analytic models based on the mean free path (MFP) approximation and compare them to the results of N-body simulations. Our goal is to identify the cluster conditions under which the MFP approximation remains valid. Adopting a range of particle numbers (100 ≤ N ≤ 5000) and different combinations of particle masses and radii, we explore three different channels leading to stellar collisions, all of which are expected to occur in realistic stellar environments. At high densities, binaries form from isolated three-body interactions of single stars. Hence, we consider collisions between single stars and collisions involving binary stars, after they form in our simulations. For the latter, we consider two channels for mergers, namely direct stellar collisions during chaotic single–binary interactions and perturbation-driven mergers of binaries due to random walks in eccentricity approaching unity. In the densest systems considered here, a very massive object is formed at the cluster centre, causing local stellar orbits to become increasingly Keplerian and the assumptions going into our analytic model to break down. Before reaching this limit, we obtain excellent agreement between our theoretical predictions and the simulations: The analytic rates are typically accurate to within one standard deviation for the entire parameter space considered here, but the agreement is best for short integration times. Our results have direct implications for blue straggler formation in dense star clusters, and stellar mergers in galactic nuclei hosting massive black holes.

Collaborative Low-Rank Matrix Approximation-Assisted Fast Hyperspectral Raman Imaging and Tip-Enhanced Raman Spectroscopic Imaging.

Fast acquisition of Raman images is essential for accurately characterizing the analytes' information. In this paper, we developed a collaborative low-rank matrix approximation method for fast hyperspectral Raman imaging as well as tip-enhanced Raman spectroscopy (TERS) imaging. This method combines high signal-to-noise ratio (SNR) data with the target data to perform collaborative singular value decomposition. The high-quality reference data can impose constraints on factorization, which will force its components to approximate the true signal or noise components. The simulation demonstrated that this method offers state-of-the-art signal extraction performance and, thus, can be used to accelerate data acquisition. Specifically, the results indicate that the CLRMA can largely decrease the root-mean-square error by 20.92-54.12% compared with the baseline method of our previous study. We then applied this method to the fast TERS imaging of a Au/Pd bimetallic surface and significantly decreased the integration time down to 0.1 s/pixel, which is about 10 times faster than that of conventional experiments. High-SNR TERS spectra and clear TERS images that are well consistent with scanning tunneling microscopy (STM) images can be obtained even under such a weak signal condition. We further applied this method to the fast Raman imaging of HeLa cells and obtained clear Raman images at a short integration time of 2 s/line, which is about 5 times faster than that of conventional experiments. This method offers a promising tool for TERS imaging as well as conventional Raman imaging where fast data acquisition is required.

Batch fabrication and compact integration of customized multispectral filter arrays towards snapshot imaging.

Snapshot multispectral imaging (MSI) has been widely employed in the rapid visual inspection by virtues of the non-invasive detection mode and short integration time. As the critical functional elements of snapshot MSI, narrowband, customizable, and pixel-level multispectral filter arrays (MSFAs) that are compatible with imaging sensors are difficult to be efficiently manufactured. Meanwhile, monolithically integrating MSFAs into snapshot multispectral imagers still remains challenging considering the strict alignment precision. Here, we propose a cost-efficient, wafer-level, and customized approach for fabricating transmissive MSFAs based on Fabry-Perot structures, both in the pixel-level and window-tiled configuration, by utilizing the conventional lithography combined with the deposition method. The MSFA chips own a total dimension covering the area of 4.8 mm × 3.6 mm with 4 × 4 bands, possessing the capability to maintain narrow line widths (∼25 nm) across the whole visible frequencies. After the compact integration with the imaging sensor, the MSFAs are validated to be effective in filtering and target identification. Our proposed fabrication method and imaging mode show great potentials to be an alternative to MSFAs production and MSI, by reducing both complexity and cost of manufacturing, while increasing flexibility and customization of imaging system.

Velocity mismatch effect on the dynamic MTF of a TDI image sensor

By analyzing the process of time delay integration dynamic imaging, we establish a model of velocity mismatch. Based on this model, we analyze the influence of different factors on the dynamic imaging process, and a modulation transfer function (MTF) is used to evaluate imaging quality. According to the simulation, the velocity mismatch and scan stage are the main factors for image quality. The MTF of the image sensor decreases with the velocity mismatch, and the scan stage increases. In addition, an image with higher contrast can be obtained in a short integration time. However, a shorter integration time leads to insufficient sampling. Furthermore, we establish a dynamic MTF testing system, and evaluate the experiment at different imaging modes. Through data comparison, the experimental data are consistent with theoretical data.

Focus on analytical equipment, spectroscopy, and spectrometry

Focus on analytical equipment, spectroscopy, and spectrometry

MERGHERS pilot: MeerKAT discovery of diffuse emission in nine massive Sunyaev–Zel’dovich-selected galaxy clusters from ACT

ABSTRACT The MeerKAT Exploration of Relics, Giant Halos, and Extragalactic Radio Sources (MERGHERS) survey is a planned project to study a large statistical sample of galaxy clusters with the MeerKAT observatory. Here we present the results of a 16-h pilot project, observed in response to the 2019 MeerKAT Shared Risk proposal call, to test the feasibility of using MeerKAT for a large cluster study using short (0.2–2.1 h) integration times. The pilot focuses on 1.28-GHz observations of 13 massive, low-to-intermediate redshift (0.22 < z < 0.65) clusters from the Sunyaev–Zel’dovich-selected Atacama Cosmology Telescope (ACT) DR5 catalogue that show multiwavelength indications of dynamical disturbance. With a 70 per cent detection rate (9/13 clusters), this pilot study validates our proposed MERGHERS observing strategy and provides twelve detections of diffuse emission, eleven of them new, indicating the strength of MeerKAT for such types of studies. The detections (signal-to-noise ratio ≳ 6) are summarized as follows: two systems host both relic(s) and a giant radio halo, five systems host radio haloes, and two have candidate radio haloes. Power values, k-corrected to 1.4 GHz, assuming a fiducial spectral index of α = −1.3 ± 0.4, are consistent with known radio halo and relic scaling relations.

A Reanalysis of the October 2016 “Meteotsunami” in British Columbia With Help of High-Frequency Radars and Autoregressive Modeling

On October 14, 2016, the coastal high-frequency radar system in Tofino (British Columbia, Canada) triggered an automatic tsunami warning based on the identification of abnormal surface current patterns. This occurred in the absence of any reported seismic event but coincided with a strong atmospheric perturbation, which qualified the event as meteotsunami. We reanalyze this case in the light of a new radar signal processing method, which was designed recently for inverting fast-varying sea surface currents from the complex voltage time series received on the antennas. This method, based on autoregressive modeling combined with a maximum entropy method, yields a dramatic improvement in both the signal-to-noise ratio and the quality of the surface current estimation for very short integration time. This makes it possible to evidence the propagation of a sharp wavefront of surface current during the event and to map its magnitude and arrival time over the radar coverage. We show that the amplitude and speed of the inferred residual current do not comply with a Proudman resonance mechanism but are consistent with the propagation of a low-pressure atmospheric front. This supports the hypothesis of a storm surge rather than a true meteotsunami to explain this event. Beyond this specific case, another outcome of the analysis is the promising use of HF radars as proxy’s for the characterization of atmospheric fronts.

High-Frequency Radar Ocean Current Mapping at Rapid Scale With Autoregressive Modeling

In this article, we use an autoregressive (AR) approach combined with a maximum entropy method (MEM) to estimate radial surface currents from coastal high-frequency radar (HFR) complex voltage time-series. The performances of this combined AR-MEM model are investigated with synthetic HFR data and compared with the classical Doppler spectrum approach. It is shown that AR-MEM drastically improves the quality and the rate of success of the surface current estimation for short integration time. To confirm these numerical results, the same analysis is conducted with an experimental data set acquired with a 16.15-MHz HFR in Toulon. It is found that the AR-MEM technique is able to provide high-quality and high-coverage maps of surface currents even with very short integration time (about 1 min) where the classical spectral approach can only fulfill the quality tests on a sparse coverage. Further useful application of the technique is found in the tracking of surface current at high-temporal resolution. Rapid variations of the surface current at the time scale of the minute are unveiled and shown consistent with an f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5/3</sup> decay of turbulent spectra.