Tail Of Pulse Research Articles

Development of [formula omitted]/[formula omitted]/[formula omitted] discrimination with the phoswich detector using improved charge comparison method

Both pulse shape discrimination methods based on temporal difference characteristic and phoswich detectors are well-known and effective for particles discrimination, so the combination and further improvement are significant for better performance. In this paper, a phoswich detector combining YAG(Ce) and CsI(Tl) was constructed for α/β/γ discrimination using various techniques including two machine learning algorithms and an improved charge comparison method that further exploited the difference in the decay rate of pulse tail. The detector was designed with Geant4, simulating the suitable sizes of scintillators, and a high-speed digitizer was used for the collection of pulses that were from three radioactive sources. The results among the α (β) and γ rays had the figure of merit values greater than 2, simultaneously with an optimal 1.68 of the improved method that had more than twice the performance comparing the original 0.69 for α/β identification, which showed the detector is able to discriminate α, β and γ rays in mixed radiation field effectively.

Influence of pulse-tail energy of short-pulse CO2 laser in drilling of various glasses

In a short-pulse CO2 laser based on discharge excitation, there is a pulse tail that depends on the device configuration and operating conditions. The pulse tail is longer than the spike pulse and causes thermal effects such as a crack, heat-affected zones (HAZ), and so on. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Even if the same CO2 laser pulse is radiated onto glass, the processing results may differ depending on the glass material. Four types of glass, namely, crown glass, soda-lime glass, borosilicate glass, and synthetic quartz glass were irradiated with two types of short CO2 laser pulses, one with a large pulse tail and one with a small pulse tail, at a repetition rate of 200 Hz and a fluence per pulse of 22 J/cm2. As the processing characteristics, the ratios of the surface hole diameter and the HAZ diameter to the irradiation diameter, as well as the drilling depth, were investigated. The pulse-tail energy of the short CO2 laser pulses did not affect the surface hole diameter. In the glasses with small softening points of 740 °C or less, the pulse-tail energy of short CO2 laser pulses affected the HAZ with a large number of pulse irradiations with a total irradiation fluence of 2000 J/cm2 or more. The short CO2 laser pulses with a small tail produced a smaller HAZ than the short CO2 laser pulses with a large tail. In drilling with a large number of pulse irradiations, the short CO2 laser pulses with a small tail produced deeper drilling than the short CO2 laser pulses with a large tail. The glass material did not affect the surface hole diameter and the drilling depth. The glass material affected the HAZ.

X-ray timing detectors with HfO2 nanoparticle-loaded plastic scintillator and silicon avalanche photodiode

We successfully developed 20- and 40-wt% HfO2-nanoparticle-loaded plastic scintillators (Hf-PLSs), and subsequently, assembled X-ray timing scintillation detectors using the Hf-PLSs and silicon avalanche photodiodes (Si-APDs) as the photodetector. Two types of Si-APDs were examined for two different detectors. A proportional-mode APD (pAPD) exhibited a nanosecond response, but a relatively low internal gain of less than several hundred. By contrast, a Geiger-mode APD exhibited a high gain of 105−6, but its output pulse width was longer than several tens of nanoseconds; the pixelated device is called as SiPM. A pAPD (Hamamatsu Photonics S8664-4433, 3 mm in diameter) was used as the photodetector and was combined with 20 wt% Hf-PLS (∼3 mm cube) as the X-ray scintillation timing detector. A SiPM (Hamamatsu Photonics S13360-3025, 3 mm × 3 mm) was assembled with 40 wt% Hf-PLS (∼3 mm cube). The characteristics of the two types of scintillation timing detectors were evaluated using a 57.61-keV synchrotron X-ray beam to assess their applicability in nuclear resonant scattering experiments. Both the detectors were cooled down to −35 or −20 °C to reduce noise and obtain a higher APD gain. A good time resolution of (0.31 ± 0.04) ns (FWHM) was easily obtained with the SiPM detector using a large APD gain at −20 °C, although the time resolution of the pAPD detector finally reached (0.39 ± 0.04) ns (FWHM) at −35 °C owing to a small gain of 146. However, a maximum count rate of over 1.4 × 107 s−1 was observed owing to the fast response of the pAPD detector, whereas the SiPM detector exhibited a maximum count rate of 5.9 × 106 s−1 because of the long pulse tail of ∼30 ns.

Non-iterative pulse tail extrapolation algorithms for correcting nuclear pulse pile-up

Radiation detection systems working at high count rates suffer from the overlapping of their output electric pulses, known as pulse pile-up phenomenon, resulting in spectrum distortion and degradation of the energy resolution. Pulse tail extrapolation is a pile-up correction method which tries to restore the shifted baseline of a piled-up pulse by extrapolating the overlapped part of its preceding pulse. This needs a mathematical model which is almost always nonlinear, fitted usually by a nonlinear least squares (NLS) technique. NLS is an iterative, potentially time-consuming method.The main idea of the present study is to replace the NLS technique by an integration-based non-iterative method (NIM) for pulse tail extrapolation by an exponential model. The idea of linear extrapolation, as another non-iterative method, is also investigated. Analysis of experimental data of a NaI(Tl) radiation detector shows that the proposed non-iterative method is able to provide a corrected spectrum quite similar with the NLS method, with a dramatically reduced computation time and complexity of the algorithm. The linear extrapolation approach suffers from a poor energy resolution and throughput rate in comparison with NIM and NLS techniques, but provides the shortest computation time.

Drilling of cylindrical holes in Crown glass by a short-pulse flat-top CO2 laser beam

We investigated cylindrical hole drilling in a crown glass with a high thermal expansion coefficient of 94 × 10–7 K−1 and a low melting point of 724 °C using a short-pulse CO2 laser with a flat-top beam, and also examined the drilling characteristics. The short laser pulse consisted of a pulse spike with a pulse width of 276 ns and a pulse tail with a length of 56.9 µs at a repetition rate of 200 Hz. The laser beam had a flat-top profile with an estimated M2 parameter of 13.5 and a diameter of 12.5 mm before a focusing lens. The flat-top beam was focused by the focusing lens, which had a focal length of 12.7 mm, on the glass surface at a focus offset of −0.20 mm to +0.40 mm. The incident flat-top beam produced conical holes at focus offsets of −0.20 mm to 0.00 mm and produced cylindrical holes at focus offsets of +0.20 mm to +0.40 mm. The hole depth of the cylindrical holes was 109 μm to 434 μm, the surface hole diameter was 150 μm to 366 μm, and the aspect ratio, defined as the ratio of the hole depth to the surface hole diameter, was 0.30 to 2.89. The hole depth was influenced by the focus offset and the total irradiation fluence, whereas the surface hole diameter, the taper angle and the ratio of the surface hole diameter to the irradiation diameter were influenced by the focus offset only. The ratio of the surface HAZ (Heat affected zone) diameter to the irradiation diameter was influenced by both the focus offset and the total irradiation fluence.

Tissue Ablation Using Irreversible Electrolytic Electroporation with Reduced Voltage

Thermal tissue ablation may damage surrounding healthy tissue and cause pain. In this study, tissue ablation with the sequential application of electrical energy-inducing irreversible electroporation (IRE) and electrolysis (EL) (IRE + EL = IREEL) was investigated. An IREEL device was designed to control five output pulse parameters: voltage level (VL), pulse width (PW), pulse interval (PI), pulse number (PN), and pulse tail time (PTT). IREEL experiments were conducted on vegetable tissue. The results indicated that by increasing the VL and PTT, the ablation area increased, whereas the impedance was reduced significantly. Almost no ablation area was observed when only EL or IRE at 500 V and 1000 V, respectively, were applied. The ablation area observed with IRE alone at 1500 V was defined as 100%. In the case of IREEL at 500 V and 1000 V, ablation was induced even with the use of micro-second level PTT, and ablation areas of 91% and 186% were achieved, respectively. For IREEL at a voltage of 1500 V, the ablation area expanded to 209% and the maximum temperature was 48.7 °C, whereas the temperature did not exceed 30 °C under other conditions. A change in pH was also observed in an agar-gel phantom experiment which was conducted to examine and confirm whether IREEL induced electrolysis. IREEL was able induce ablation at low voltages owing to the synergistic effect of applying IRE and EL sequentially. Moreover, the ablation areas at high voltages could be increased compared to the areas observed when IRE and EL were applied independently.

Controllable multi-stable-state operation in an AOM actively Q-switched all-fiber laser system.

This paper presents a comprehensive experimental study of multi-stable-state output characteristics in an all-fiber laser with an acoustic-optical modulator (AOM) as the Q-switcher. For the first time, in this structure, the partitioning of the pulsed output characteristics is explored, dividing the operating status of the laser system into four zones. The output characteristics, the application prospects, and the parameter setting rules for working in stable zones are presented. In the second stable zone, a peak power of 4.68 kW with 24 ns was obtained at 10 kHz. This is the narrowest pulse duration achieved with an AOM actively Q-switched all-fiber linear structure. The pulse narrowing is attributed to the rapid release of signal power and pulse tail truncated by AOM shutdown.

Resolving the Emission Regions of the Crab Pulsar’s Giant Pulses. II. Evidence for Relativistic Motion

The Crab Pulsar is the prime example of an emitter of giant pulses. These short, very bright pulses are thought to originate near the light cylinder, at ∼1600 km from the pulsar. The pulsar’s location inside the Crab Nebula offers an unusual opportunity to resolve the emission regions, using the nebula, which scatters radio waves, as a lens. We attempt to do this using a sample of 61,998 giant pulses found in coherently combined European VLBI network observations at 18 cm. These were taken at times of relatively strong scattering and hence good effective resolution. From correlations between pulse spectra, we show that the giant pulse emission regions are indeed resolved. We infer apparent diameters of ∼2000 and ∼2400 km for the main and interpulse components, respectively, and show that with these sizes the correlation amplitudes and decorrelation timescales and bandwidths can be understood quantitatively, both in our observations and in previous ones. Using pulse-spectra statistics and correlations between polarizations, we also show that the nebula resolves the nanoshots that comprise individual giant pulses. The implied diameters of ∼1100 km far exceed light-travel-time estimates, suggesting the emitting plasma is moving relativistically, with γ ≃ 104, as inferred previously from drifting bands during the scattering tail of a giant pulse. If so, the emission happens over a region extended along the line of sight by ∼107 km. We conclude that relativistic motion likely is important for producing giant pulses, and may be similarly for other sources of short, bright radio emission, such as fast radio bursts.

The role of multi-photon dissociation of high pressure SF6 gas in TEA CO2 lasers pulse shaping

High pressure SF6 gas has been irradiated by intense TEA CO2 laser pulses with different wavelengths around 10.6μm and then, temporal variations of the transmitted laser pulses have been characterized at different energy fluences and gas pressures. It has been shown that for every fluence above the multi-photon dissociation threshold of SF6 molecules, there is a certain cut-off pressure at which the pulse spike is completely quenched. While, the pulse tail escapes with an appreciable fraction of its initial energy. FTIR spectra of the irradiated gases together with other experimental evidences have clearly revealed the occurrence of laser induced multi-photon dissociation of SF6 molecules, that should be considered as the main responsible for the observed pulse shaping effects.

1 kHz Oscillation of short-pulse CO2 laser pumped by longitudinal discharge without pre-ionization

Commonly, a gas laser pumped by a pulsed discharge requires a pre-ionization system to form a uniform discharge at a high repetition rate like 1 kHz. In this paper, however, a longitudinally excited CO2 laser without any pre-ionization system operated at a repetition rate of 1 kHz. The discharge tube was made of an alumina ceramic tube with an inner diameter of 8 mm, an outer diameter of 16 mm and a length of 80 cm, and two metallic electrodes attached to the two ends of the tube, and did not have a pre-ionization system or a fast gas flow system. The CO2 laser produced short pulses with a spike pulse width of 200 ns, a pulse tail length of 150 μs, a spike pulse to pulse tail energy ratio of 1:112, a laser energy of 35.2 mJ, and a circular Gaussian-like beam at a repetition rate of 1 kHz, a CO2/N2/He gas mixing ratio of 1:1:5, a gas pressure of 4.6 kPa and an input energy of 738 mJ to the circuit generating fast, high-voltage pulses. The dependence of the laser energy on the repetition rate, the CO2/N2/He gas mixing ratio, and the input energy was investigated.

Deterioration of ion beam neutralization caused by reflection of electrostatic solitary waves within pulsed ion beam

The neutralization of an ion beam pulse directly by electron injection excites the two-stream instability of neutralizing electrons and gives rise to an electrostatic solitary wave (ESW) in the long time limit. The ESW propagates stably and reflects back and forth in the potential well of the ion beam pulse. Through a two-dimensional particle-in-cell code, we numerically simulated the whole neutralization process of the ion beam pulse as well as the excitation and propagation of the ESW. It is found that the reflections of the ESW at the edges of the ion beam pulse cause a lot of neutralizing electrons to be thrown out, forming escaping electrons released in a pulsed manner. Each reflection of the ESW accelerates the reduction of the neutralization degree and brings a small disturbance to the ESW. The accumulative effect of multiple reflections results in rapid collapse of the ESW at the end. The reflections of the ESW at the head and tail of the beam pulse cause the ion beam to lose more neutralizing electrons than the slow attenuation of the ESW inside the ion beam.

Some experimental studies on the UV spark pin-array pre-ionization in TEA CO2 laser

The output characteristics of a UV pin array pre-ionized transversely excited atmospheric CO2 laser have been experimentally studied in detail. The effects of the applied voltage and capacitance of the main capacitors on the laser performance was investigated. By increasing the voltage at a constant capacitance, not only the laser output energy increases, but also the pulse build-up time, width and tail length decrease. Also, the stability conditions of the discharge were investigated and the cross section of the laser output beam at different input energies was compared.

Development of a dielectric corona pre-ionized TEA CO2 laser with CO2-rich gas mixture suitable for second harmonic generation

A simple dielectric corona pre-ionized TEA CO2 laser, which is suitable for SHG applications, has been developed with the help of high concentration of carbon dioxide. The intense, very uniform UV pre-ionization and low-inductance discharge circuit permit the best laser performance with a gas mixture rich in CO2. In order to achieve the most acceptable combination of the peak power, output energy and pulse duration, not only N2:CO2 ratio varies in favor of CO2 but also helium concentration is significantly reduced. When CO2 concentration varied from 20 to 53% in the experiment, a more symmetrical, shorter output pulse (a FWHM of ∼60 ns) with a significantly lower tail and a lower energy (∼700 mJ) was obtained with a rich gas mixture of CO2:N2:He = 10:1:8 than a lean gas mixture of 1:1:3 while the peak output power was virtually kept constant (∼5.8 MW). The effect of the laser gas mixture on optimizing the energy and time parameters of SH waveform has been studied numerically. The calculations show that for the rich gas mixture the residual tail of the SH pulse is completely eliminated by the nonlinear conversion and the corresponding waveform has a lower total duration (∼600 ns). Moreover, the energy conversion efficiency can be increased by 29% with the rich mixture compared to the lean mixture.

Crown Glass Drilling by Short-Pulse CO2 Laser with Tunable Pulse Tail

Crown Glass Drilling by Short-Pulse CO2 Laser with Tunable Pulse Tail

Longitudinally excited short-pulse CO2 laser with large discharge tube without preionization

A longitudinally excited CO2 laser with a large discharge tube having an inner diameter of 16 mm and a length of 80 cm produced short laser pulses with an energy of 38.1 mJ at a repetition rate of 700 Hz. The CO2 laser did not have a preionization system or a fast gas flow system. The dependence of the laser output and discharge voltage on the repetition rate, the gas pressure and the structure of the discharge tube in 1:1:4 and 1:1:2 mixtures of CO2/N2/He gas was investigated. At a repetition rate of 300 Hz or more, the laser energy decreased as the repetition rate increased. The 1:1:4 mixture of CO2/N2/He gas produced a higher laser energy than the 1:1:2 mixture of CO2/N2/He gas. At a repetition rate of 300 Hz or less, the laser beam profile was doughnut-shaped. At a repetition rate of 400 Hz or more, the center of the laser profile had a high energy. At a high repetition rate, the fast discharge may have collected in the center of the discharge tube. Moreover, an increase in the repetition rate decreased the discharge formation time and the energy of a pulse tail part of the laser pulse waveform.

Solitons near avoided mode crossings in χ(2) nanowaveguides

We present a model for ${\ensuremath{\chi}}^{(2)}$ waveguides accounting for three modes, two of which make an avoided crossing at the second harmonic wavelength. We introduce two linearly coupled pure modes and adjust the coupling to replicate the waveguide dispersion near the avoided crossing. Analysis of the nonlinear system reveals continuous wave (CW) solutions across much of the parameter space and prevalence of its modulational instability. We also predict the existence of the avoided-crossing solitons, and study peculiarities of their dynamics and spectral properties, which include formation of a pedestal in the pulse tails and associated pronounced spectral peaks. Mapping these solitons onto the linear dispersion diagrams, we make connections between their existence and CW existence and stability. We also simulate the two-color soliton generation from a single-frequency pump pulse to back up its formation and stability properties.

Spectral index-flux relation for investigating the origins of steep decay in \u03b3-ray bursts

γ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (1051 − 1053 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

AbstractIn this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr−1) and peak (~2.6 km yr−1) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre‐pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later.The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment‐transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process‐factors largely independent of high flow.In contrast, persistent changes occurred to out‐of‐channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service‐indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period.This study captured a two‐signal response from the sediment pulse: (1) short‐ to medium‐term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer‐term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales.

Relativistic slingshot: A source for single circularly polarized attosecond x-ray pulses.

We propose a mechanism to generate a single intense circularly polarized attosecond x-ray pulse from the interaction of a circularly polarized relativistic few-cycle laser pulse with an ultrathin foil at normal incidence. Analytical modeling and particle-in-cell simulation demonstrate that a huge charge-separation field can be produced when all the electrons are displaced from the target by the incident laser, resulting in a high-quality relativistic electron mirror that propagates against the tail of the laser pulse. The latter is efficiently reflected as well as compressed into an attosecond pulse that is also circularly polarized.

Experimental and extraction procedure for the electrical characterisation of silicon photomultiplier detectors

Silicon photomultipliers (SiPMs), owing to their low-level photon counting capabilities, have increased in popularity in the field of high energy astrophysics, particle physics and medical imaging. It is crucial to accurately characterise SiPMs so they can be optimised for a particular application such as the Compact High Energy Camera (CHEC-S) for Imaging Atmospheric Cherenkov Telescopes (IACT). Extraction techniques, applied to SiPMs, can quantify opto-electrical parameters such as gain, quenching resistance, junction, parasitic and grid capacitance, rise time constant and slow and fast fall time constants. Various authors have applied and compared different extraction techniques to SiPMs, usually based on the Laplace Transform in the s-domain of the equivalent circuit model. These techniques typically utilise the pulse tail, and therefore only parameterise the recharge phase of the pulse. We will improve upon existing methods by utilising the discharge phase of an SiPM pulse in our transfer function model. In this paper, we have also applied this method to present the electrical characterisation of a novel SiPM detector: Hamamatsu LVR3 S14520-6075. The paper also details a method by which an accurate, average pulse shape, uncontaminated by after-pulsing or dark noise, can be obtained. This is a prerequisite for our analysis method, which fits the pulse shape derived from the transfer function of the SiPM model to the experimental data.