Pulse Resolution Research Articles

TES Microcalorimeters for PTOLEMY

The PTOLEMY project is devoted to directly detect the cosmic neutrino background. A key point for the project success is the development of a device which is capable of detecting electrons with an energy resolution lower than 0.05 eV. Microcalorimeters based on transition-edge sensors are among the best candidates since they already reach 0.11 eV of energy resolution for telecomm photons. To further improve the energy resolution, while maintaining a suitable saturation energy, it is necessary to reduce the transition temperature. This could be achieved by proximity effect of a normal-superconducting bilayer. To this aim, TiAu very thin films are under development to demonstrate the feasibility of reaching 0.05 eV energy resolution for light pulses of few eV. Thanks to the high electron stopping power of metals, the penetration depth of low energy incident electrons is limited to few nanometers and, with respect to visible light, we expect a high detection efficiency, while keeping similar dark counts and energy resolution.

Single-shot fourth-order autocorrelator

The temporal contrast is one of the most important parameters of an ultra-high intense laser pulse. Third-order auto-correlator or cross-correlator have been widely used to characterize the temporal contrast of an ultra-intense laser pulse in the past decades. Here, a novel and simple single-shot fourth-order auto-correlator to characterize the temporal contrast with higher time resolution and better pulse contrast fidelity in comparison to third-order correlators is proposed. The single-shot fourth-order autocorrelation consists of a frequency degenerate four-wave mixing process and a sum-frequency mixing process. The proof-of-principle experiments show that a dynamic range of approximately 10^11 compared with the noise level, a time resolution of approximately 160 fs, and a time window of 65 ps can be successfully obtained using the novel single-shot fourth-order auto-correlator, which is the highest dynamic range with simultaneous high time resolution for single-shot temporal contrast measurement so far. Furthermore, the temporal contrast of laser pulse from a PW laser system is successfully measured in single-shot with a dynamic range of about 2*10^10 and simultaneous a time resolution of 160 fs.

The ORNL Deuterated Spectroscopic Array — ODeSA

Abstract An array consisting of 12 deuterated organic liquid scintillator detectors for fast-neutron spectroscopy was designed and built at Oak Ridge National Laboratory (ORNL). This versatile array is designed for measurements with low reaction yields, such as those performed with rare isotope beams, as well as at high current DC facilities used for underground nuclear astrophysics research. Because some measurements also offer limited, or no, additional timing information, the ORNL Deuterated Spectroscopic Array (ODeSA) was optimized to utilize spectrum unfolding to extract neutron energy spectra . This array was characterized for n/ γ pulse shape discrimination, light response, resolution, and intrinsic efficiency by using the neutron time-of-flight tunnel at the Edwards Accelerator Laboratory at Ohio University. Results and future plans are discussed.

Improved Rise Approximation Method for Pulse Arrival Timing

This paper describes the deduction of pulse arrival times from digital waveforms recorded with a multichannel data-acquisition (DAQ) system. A linear rise approximation (LRA) arrival timing method provides restricted timing resolution for pulses with nonlinear rise. It reaches 1/20th of the sampling period, if the relation between signal shaping and sampling rate is optimized. We introduce a nonlinear rise approximation (nLRA), which reduces the sampling phase error (SPE) down to less than 1/100th of the sampling period. The proposed timing algorithm uses a single free parameter that can easily be adjusted for various radiation detectors. The technique permits using a rather slow pulse shaping and low sampling rates, thus strongly reducing power consumption and the costs of the system. A high-density DAQ system integrating over 2000 channels inside an OpenVPX crate is presented. A prototype has been tested in the proton beam at cooler synchrotron (COSY) at Julich Research Center (Germany).

High-resolution photoacoustic endoscope through beam self-cleaning in a graded index fiber.

Intravascular photoacoustic imaging can potentially improve the identification of lipid-laden atherosclerotic plaque. Most intravascular photoacoustic endoscopes use multimode fibers, which do not allow tight focusing of photons. Recent experiments on pulse propagation in multimode graded-index fibers have shown a nonlinear improvement in beam quality. Here, we harness this nonlinear phenomenon for fiber-delivery of nanosecond laser pulses. We built a photoacoustic catheter 1.4mm outer diameter, offering a lateral resolution as fine as 30μm within a depth range of 2.5mm. Such resolution is one order of magnitude better than current multimode fiber-based intravascular photoacoustic catheters. At the same time, the delivered pulse energy can reach as high as 20μJ, which is two orders of magnitude higher than that of an optical resolution photoacoustic endoscope built with a single mode fiber. These improvements are expected to promote the biomedical application of photoacoustic endoscopes which require both high resolution and high pulse energy.

MRI B0 homogeneity and geometric distortion with continuous linac gantry rotation on an Elekta Unity MR-linac

This work aimed to quantify any principal magnetic field (B0) inhomogeneity and changes in MR image geometric distortion with continuous linac gantry rotation on an Elekta Unity MR-linac. This situation occurs for around a second between treatment beams during current image guided radiotherapy treatment and would occur frequently in foreseeable real-time adaptive radiotherapy treatment.Pixel by pixel maps of B0 inhomogeneity were obtained via repeated high temporal resolution pulse sequences with the linac gantry static at 36 gantry angles spaced ten degrees apart, and in continuous rotation at both 1 and 2 rpm. Individual B0 maps were subtracted from average maps across all data and the residual peak to peak inhomogeneity was calculated for each. The bulk geometric shift and change in physical extent of a 10 cm diameter spherical flood phantom during continuous linac gantry rotation at 1 and 2 rpm was compared to the static gantry case for two pulse sequences: the real-time clinical monitoring bFFE sequence and a non-clinical EPI sequence, chosen for its susceptibility to geometric distortion.The peak to peak inhomogeneity in the deviation-from-average ppm maps, plotted against gantry angle with the gantry in continuous rotation at 1 and 2 rpm were negligibly different from equivalent data obtained with the gantry static. The real-time clinical monitoring pulse sequence was shown to give negligible geometric distortion during continuous gantry motion, whilst a non-clinical EPI sequence showed bulk shifts of the order of one pixel and gantry angle dependent changes in extent, demonstrating the sensitivity of the chosen method.MR imaging on the Elekta Unity MR-Linac with the gantry in continuous motion is negligibly different from the static gantry case with current clinical pulse sequences. Real-time tracking and treatment plan adaptation using MR images obtained with the linac gantry in motion is possible.

Energy calibration of high-resolution X-Ray TES microcalorimeters with 3 eV optical photons.

With the improving energy resolution of transitionedge sensor (TES) based microcalorimeters, performance verification and calibration of these detectors has become increasingly challenging, especially in the energy range below 1 keV where fluorescent atomic X-ray lines have linewidths that are wider than the detector energy resolution and require impractically high statistics to determine the gain and deconvolve the instrumental profile. Better behaved calibration sources such as grating monochromators are too cumbersome for space missions and are difficult to use in the lab. As an alternative, we are exploring the use of pulses of 3 eV optical photons delivered by an optical fiber to generate combs of known energies with known arrival times. Here, we discuss initial results of this technique obtained with 2 eV and 0.7 eV resolution X-ray microcalorimeters. With the 2 eV detector, we have achieved photon number resolution for pulses with mean photon number up to 133 (corresponding to 0.4 keV).

UWB Propagation Measurements and Modelling in Large Indoor Environments

In this paper, we present the results of the measurements and modeling of the propagation channel for ultra wide band (UWB) communications in large indoor environments. The selected environment is a sports center of large dimensions ($51 \times 26$ m, 7.4m height) without intermediate obstacles so that there is always direct path (DP) between TX and RX and UWB technology can be used for critical communications of sensors. On this environment, narrow band and ultra wide band measurements have been made with a high resolution pulse channel sounder (8ns) at the nominal frequency of 3.9 GHz. Narrow band measurements have been used to model path loss for the DP, while for UWB measurements, the power delay profile have been used to obtain the statistics of the multipath of the channel. Combining both models has been possible to obtain a detailed characterization of the environment. The results constitute a complete characterization of this type of indoor environments for UWB signals and can be easily extrapolated to other environments with similar characteristics, allowing the use of UWB technology for applications of critical communications for sensors and other devices.

Theoretical research on obtaining of picoseconds dilated pulses with a framing imaged converter tube

Variations in the temporal resolution of a pulse-dilation framing imaged converter tube (FICT) were studied. The relation between temporal resolution and dilated pulse was analyzed. The computational methods for describing pulse gradient and time-varying amplitude were derived. It explores the possibility of obtain picoseconds ultrafast pulses and the others potential application FICT from a theoretical perspective. The results show that it is higher precision to achieve the shape and amplitude of an ultrafast dilated pulse using a FICT. The relative standard deviation (RSD) range of ten thousand sample data was ± 5.8% when the time step is 50 ps, and the RSD is reduced to ± 1.9% as the time step is shortened to 10 ps. We expect that our results will expand the others potential applications of FICTs and provide that a theoretical basis for further optimizing relevant external systems of FICT.

Timing performance of organic scintillators coupled to silicon photomultipliers

This work compares the time resolution obtained from coincidence measurements using combinations of four types of silicon photomultipliers (SiPMs), five types of organic scintillators, and two timing algorithms. Organic scintillators in combination with SiPMs have shown to have equivalent or better time resolution and pulse shape discrimination (PSD) capability than with photo-multiplier tubes (PMTs). In addition, SiPMs are more compact and require low operating voltage. These factors have made them suitable for the development of compact neutron scatter cameras (NSCs) and potentially low-cost positron emission tomography (PET) systems. The following measurements analyze combinations of organic scintillators and SiPMs that could be used for these applications. Measurements and analyses assessed the time resolution of standard-output and fast-output pulses of the various scintillator and SiPM combinations. The coincidence measurements were performed using a Na-22 source to characterize time resolution where all coincident events above about a 40 keVee threshold were analyzed. Uncertainties were determined by applying bootstrapping to the acquired data sets. The full width at half maximum (FWHM) of the time difference distribution for each combination is reported as the time resolution of the system. For standard-output pulses, we found that using a digital implementation of analogue constant fraction discrimination (DIACFD) improved timing resolution greater than a single standard deviation for six of the fourteen tested combinations compared to using digital constant fraction discrimination (DCFD). Conversely, for fast-output pulses, DCFD with a moving average filter produced the best timing resolution. Among the tested non-PSD capable organic scintillators, EJ-228 coupled to a MicroFJ-SMA-60035 SensL SiPM yielded the best time resolution of 303 ± 4 ps for standard-output pulses and 227 ± 4 ps for fast-output pulses. The best time resolution found for PSD capable organic scintillators was obtained using Inrad Optics stilbene coupled to a MicroFJ-SMA-60035 SensL SiPM which yielded a time resolution of 428 ± 6 ps for standard-output pulses and 293 ± 4 ps for fast-output pulses.

Energetically wasteful wave reflections due to impedance mismatching in hypertension and their reversal with vasodilator: Time and frequency domain evaluations

BackgroundIncreased pulse wave reflections in hypertension arise due to impedance mismatching and the effective energy transmission to the vasculature is compromised. Their quantification in the time and the frequency domains are compared and the beneficial effect of vasodilator is evaluated in the study. MethodsA simple, fast time domain method for the resolution of aortic pressure and flow pulses into their forward and reflected components is presented, together with frequency domain reflection coefficient and impedance calculations. Both steady and pulsatile energy components are quantified during induced hypertension (HBP) and subsequent vasodilator (VSD, nitroprusside) treatment in experimental mongrel dogs. Corresponding power generation and usage are also analyzed. ResultsCharacteristic impedance and peripheral resistance were not statistically different between the methods (p > 0.05). Time domain reflection coefficient identified significant differences among control, HBP and VSD groups (p < 0.05) while the frequency domain method did not adequately differentiate the control and the HBP groups. Impedance calculations were similar between the two methods. Frequency domain calculations of total, mean and pulsatile power were, on average, 32.6 mW higher, 12.8 mW lower and 45.4 mW higher than their respective time domain calculations (p < 0.05). Hypertension increased energy consumption, on average, by 88.8 mJ (p < 0.05) and subsequent VSD decreased the energy consumption, on average, by 99.4 mJ (p < 0.05). ConclusionImpedance mismatching in hypertension which leads to increased wave reflections and significantly increased pulsatile work, could be effectively alleviated through vasodilator therapy. This can be quantified through the time-domain method, which is fast and equally accurate as the time-consuming frequency domain approach. The time domain method to quantify crucial parameters such as stroke work cannot be readily determined using the frequency domain methods.

Chemical-vapor deposited ultra-fast diamond detectors for temporal measurements of ion bunches.

This article reports on the development of thin diamond detectors and their characterization for their application in temporal profile measurements of subnanosecond ion bunches. Two types of diamonds were used: a 20 μm thin polycrystalline chemical vapor deposited (CVD) diamond and a membrane with a thickness of (5 ± 1) μm etched out of a single crystal (sc) CVD diamond. The combination of a small detector electrode and an impedance matched signal outlet leads to excellent time response properties with a signal pulse resolution (FWHM) of τ = (113 ± 11) ps. Such a fast diamond detector is a perfect device for the time of flight measurements of MeV ions with bunch durations in the subnanosecond regime. The scCVD diamond membrane detector was successfully implemented within the framework of the laser ion generation handling and transport project, in which ion beams are accelerated via a laser-driven source and shaped with conventional accelerator technology. The detector was used to measure subnanosecond proton bunches with an intensity of 108 protons per bunch.

Optical Partial Discharge Diagnosis in SF6 Gas-Insulated System With SiPM-Based Sensor Array

This paper aims to promote optical partial discharge (PD) detection from laboratory scale to practical application for sulfur hexafluoride (SF6)-insulated power equipment. First, a micro silicon photomultiplier (SiPM)-based PD sensor is evaluated for detecting PDs in SF6 gas and is proven to have the equivalent properties with pulse current acquisition and vacuum photomultiplier tube in terms of the signal-to-noise ratio, pulse resolution, and linearity. Then, a double-spectral PD sensor based on SiPM is first proposed and developed to realize a more specific PD diagnosis. It is demonstrated that by using the double-spectral PD sensor not only stochastic PD patterns can be obtained for PD recognition, but PD severity can be estimated as well.

Effect of Spectral Degradation and Spatio-Energy Correlation in X-Ray PCD for Imaging.

Charge sharing, scatter, and fluorescence events in a photon counting detector can result in counting of a single incident photon in multiple neighboring pixels, each at a fraction of the true energy. This causes energy distortion and correlation of data across energy bins in neighboring pixels (spatio-energy correlation), with the severity depending on the detector pixel size and detector material. If a "macro-pixel" is formed by combining the counts from multiple adjacent small pixels, it will exhibit correlations across its energy bins. Understanding these effects can be crucial for detector design and for model-based imaging applications. This paper investigates the impact of these effects in basis material and effective monoenergetic estimates using the Cramér-Rao Lower Bound. To do so, we derive a correlation model for the multi-counting events. CdTe detectors with grids of pixels with side length of $250~\mu \text{m}$ , $500~\mu \text{m}$ , and 1 mm were compared, with binning of $4\times4$ , $2\times2$ , and $1\times1$ pixels, respectively, to keep the same net 1 mm2 aperture constant. The same flux was applied to each. The mean and covariance matrix of measured photon counts were derived analytically using spatio-energy response functions precomputed from Monte Carlo simulations. Our results show that a 1 mm2 macro-pixel with $250\times 250\,\,\mu \text{m}^{\textsf {2}}$ sub-pixels shows 35% higher standard deviation than a single 1 mm2 pixel for material-specific imaging, while the penalty for effective monoenergetic imaging is <10% compared with a single 1 mm $^{\textsf {2}}$ pixel. Potential benefits of sub-pixels (higher spatial resolution and lower pulse pile-up effects) are important but were not investigated here.

Parametric bandwidth synthesis for active sonar

This talk presents an unconventional range processing technique applicable to linear FM pulsed and continuous active sonar. Parametric bandwidth synthesis (BWS) involves performing linear-predictive extrapolation using a low-order parametric autoregressive (AR) model to extend the bandwidth of received sonar returns. Synthetically increasing the bandwidth of echoes results in improved range resolution and greater pulse compression gain compared to standard matched filtering. It should be noted that despite the resolution improvement, BWS does not improve ranging accuracy beyond that of the transmitted signal. Using a low-order AR model for BWS enhances specular target returns and discrete scatterers, while not enhancing diffuse multipath, reverberation, and noise returns. BWS performance was verified in simulation and with sea trial data from the Littoral Continuous Active Sonar 2015 (LCAS-15) experiment. Processed results confirm that BWS improves range resolution of the echo repeater target, while suppressing multipath, diffuse reverberation, and noise. Analysis of the practical limits of BWS are also included.This talk presents an unconventional range processing technique applicable to linear FM pulsed and continuous active sonar. Parametric bandwidth synthesis (BWS) involves performing linear-predictive extrapolation using a low-order parametric autoregressive (AR) model to extend the bandwidth of received sonar returns. Synthetically increasing the bandwidth of echoes results in improved range resolution and greater pulse compression gain compared to standard matched filtering. It should be noted that despite the resolution improvement, BWS does not improve ranging accuracy beyond that of the transmitted signal. Using a low-order AR model for BWS enhances specular target returns and discrete scatterers, while not enhancing diffuse multipath, reverberation, and noise returns. BWS performance was verified in simulation and with sea trial data from the Littoral Continuous Active Sonar 2015 (LCAS-15) experiment. Processed results confirm that BWS improves range resolution of the echo repeater target, while suppr...

Position reconstruction in LUX

The (x, y) position reconstruction method used in the analysis of the complete exposure of the Large Underground Xenon (LUX) experiment is presented. The algorithm is based on a statistical test that makes use of an iterative method to recover the photomultiplier tube (PMT) light response directly from the calibration data. The light response functions make use of a two dimensional functional form to account for the photons reflected on the inner walls of the detector. To increase the resolution for small pulses, a photon counting technique was employed to describe the response of the PMTs. The reconstruction was assessed with calibration data including 83mKr (releasing a total energy of 41.5 keV) and 3H (β− with Q = 18.6 keV) decays, and a deuterium-deuterium (D-D) neutron beam (2.45 MeV) . Within the detector's fiducial volume, the reconstruction has achieved an (x, y) position uncertainty of σ = 0.82 cm and σ = 0.17 cm for events of only 200 and 4,000 detected electroluminescence photons respectively. Such signals are associated with electron recoils of energies ∼0.25 keV and ∼10 keV, respectively. The reconstructed position of the smallest events with a single electron emitted from the liquid surface (22 detected photons) has a horizontal (x, y) uncertainty of 2.13 cm.

Acetylacetone photodynamics at a seeded free-electron laser

The first steps in photochemical processes, such as photosynthesis or animal vision, involve changes in electronic and geometric structure on extremely short time scales. Time-resolved photoelectron spectroscopy is a natural way to measure such changes, but has been hindered hitherto by limitations of available pulsed light sources in the vacuum-ultraviolet and soft X-ray spectral region, which have insufficient resolution in time and energy simultaneously. The unique combination of intensity, energy resolution, and femtosecond pulse duration of the FERMI-seeded free-electron laser can now provide exceptionally detailed information on photoexcitation–deexcitation and fragmentation in pump-probe experiments on the 50-femtosecond time scale. For the prototypical system acetylacetone we report here electron spectra measured as a function of time delay with enough spectral and time resolution to follow several photoexcited species through well-characterized individual steps, interpreted using state-of-the-art static and dynamics calculations. These results open the way for investigations of photochemical processes in unprecedented detail.

Low-Cost High-Speed In-Plane Stroboscopic Micro-Motion Analyzer.

Instrumentation for high-speed imaging and laser vibrometry is essential for the understanding and analysis of microstructure dynamics, but commercial instruments are largely unaffordable for most microelectromechanical systems (MEMS) laboratories. We present the implementation of a very low cost in-plane micro motion stroboscopic analyzer that can be directly attached to a conventional probe station. The low-cost analyzer has been used to characterize the harmonic motion of 52.1 kHz resonating comb drive microactuators using ~50 ns pulsed light-emitting diode (LED) stroboscope exposure times, producing sharp and high resolution (~0.5 μm) device images at resonance, which rivals those of several orders of magnitude more expensive systems. This paper details the development of the high-speed stroboscopic imaging system and presents experimental results of motion analysis of example microstructures and a discussion of its operating limits. The system is shown to produce stable stroboscopic LED illumination to freeze device images up to 11 MHz.

Towards Optical Partial Discharge Detection with Micro Silicon Photomultipliers.

Optical detection is reliable in intrinsically characterizing partial discharges (PDs). Because of the great volume and high-level power supply of the optical devices that can satisfy the requirements in photosensitivity, optical PD detection can merely be used in laboratory studies. To promote the practical application of the optical approach in an actual power apparatus, a silicon photomultiplier (SiPM)-based PD sensor is introduced in this paper, and its basic properties, which include the sensitivity, pulse resolution, correlation with PD severity, and electromagnetic (EM) interference immunity, are experimentally evaluated. The stochastic phase-resolved PD pattern (PRPD) for three typical insulation defects are obtained by SiPM PD detector and are compared with those obtained using a high-frequency current transformer (HFCT) and a vacuum photomultiplier tube (PMT). Because of its good performances in the above aspects and its additional advantages, such as the small size, low power supply, and low cost, SiPM offers great potential in practical optical PD monitoring.

Enhanced Molecular Sensitivity of Cisplatin Imaging by Time-of-Flight X-ray Fluorescence CT for Simultaneous Chemoradiation Therapy

Image guidance in radiation therapy is established in modern treatment systems. Potential on-board molecular imaging devices are tempting as they would allow among others chemotherapy monitoring of cisplatin based drugs. In this contribution, the principle of time-of-flight (ToF) detection in combination with the molecular imaging modality x-ray fluorescence CT (XFCT) is studied. The addition of ToF information allows to reduce the scatter component in human examinations to levels comparable to those achieved in preclinical studies. The benefits of additional ToF information to standard XFCT is studied on the basis of Monte-Carlo simulations where the fluorescent Kβ photons of cisplatin with emission energies of 75.7 and 77.9 keV are examined. The detector geometry is set up in a scatter reduced back-orientation, given by a spherical detector with an acceptance angle of 120° in regard to the iso-center. The performance is compared for two different detector systems. One time with a 2 cm thick Si detector with an energy resolution of 400 eV FWHM and the other time with a 2 mm thick CdTe detector with a resolution of 1 keV. The molecular sensitivities for the described setup for XFCT imaging with and without ToF information are investigated for phantom diameters of 16, 26, and 36 cm. Each phantom contains six one centimeter diameter cylindrical target regions in the center of the phantom. The ToF precision of the pulsed x-ray source and the time resolution of the detector are both varied between 30 and 500 ps. The scatter reduction capability is analyzed by comparing the amount of reconstructed background photons in the central 5x5 cm2field of view. Image reconstruction with ToF kernels matching to the pulse length of the beam and the detector time resolution are utilized within a MLEM reconstruction framework. The additional time of flight information is able to substantially lower the scatter content in the reconstructed images where a scatter reduction of 94, 78, and 5% for the time resolution and beam pulse length of 30, 100, and 500 ps, respectively. The molecular sensitivity accessible in the center of the field of view is 60, 75, and 80 pM/L for the Si detector and 140, 150, and 165 pM/L for the CdTe detector for a time resolution of 30 ps and a target dose of 50 mGy. The incorporation of ToF information in XFCT imaging shows promising results for the imaging of high atomic number probes in human sized objects. Especially cisplatin imaging is interesting, for a combined radio-chemo therapy as existing on-board imaging systems could be upgraded with this new technology. It was shown that the majority of the scattered photons originate within the vicinity of the phantom surface and which makes the inclusion of ToF information extreme alluring for lesions in deep tissue and the concept achieves clinically relevant molecular sensitivities.