Pulse Burst Research Articles

Depth-Resolved Elemental Analysis on Moving Electrode Foils with Laser-Induced Breakdown Spectroscopy.

In this study, a new method for the inline measurement of depth profiles on a continuously moving sample with laser-induced breakdown spectroscopy is presented. The ablation profile is generated by ablating the sample with a burst of laser pulses, where the emission spectrum of each laser-induced plasma is analyzed on a spectrometer. A Q-switched Nd:YAG laser at 1064 nm with 10 mJ pulse energy, 6 ns pulse duration and 100 Hz repetition rate was used. The focusing lens for the pulsed laser and a deflection mirror are mounted on a moving stage, which is precisely aligned in height and orientation to the movement of a conveyor belt transporting the sample. The stage speed is actively synchronized to the speed of the moving sample by a wheel encoder to assure that all laser pulses hit the same position at the sample. The feasibility for depth-resolved elemental analysis on moving samples is shown for coatings of electrode foils for lithium-ion batteries. The coating homogeneity was measured at a speed up to 17 m/min. For a 100 μm coating, 10 laser pulses were needed to measure a full depth profile.

Pre-Shaped Burst-Mode Hybrid MOPA Laser System at 10 kHz Pulse Frequency

A temporal pre-shaped burst-mode hybrid fiber-bulk laser system was illustrated at a 10 kHz rate with a narrow spectral linewidth. A theoretical model was proposed to counteract the temporal profile distortion and compensate for the desired one, based on reverse process of amplification. For uniformly modulated injection, amplified shapes were recorded and investigated in series for their varied pulse duration, envelope width and amplification delay, respectively. The pre-shaped output effectively realized a uniform distribution on a time scale for both the burst envelope and pulse shape under the action of the established theoretical method. Compared with previous amplification delay methods, this model possesses the capacity to extend itself for applications in burst-mode shaping with variable parameters and characteristics. The maximum pulse energy was enlarged up to 9.68 mJ, 8.94 mJ and 6.57 mJ with a 300 ns pulse duration over envelope widths of 2 ms to 4 ms. Moreover, the time-averaged spectral bandwidths were measured and characterized with Lonrentz fits of 68.3 MHz, 67.2 MHz and 67.7 MHz when the pulse duration varied from 100 ns to 300 ns.

Ionic wind velocity and energy efficiency improvement in needle-net ionic wind generator by electrical field optimization

Ionic wind produced by high voltage discharge has been proved as a promising technique in heat dissipation, food drying, electrostatic precipitation and air propulsion. On the other hand, the low wind velocity and the low energy efficiency of the ionic wind generators limit their performance in practical industrial applications. To improve this, a single needle-net electrode structure ionic wind generator driven by positive DC voltage is constructed and the effects of the applied voltage and electrode structure on the discharge characteristics and the converting efficiency from electric energy to kinetic energy have been investigated. The results show that with the increase of the applied voltage from 4 kV to 11 kV, the discharge shows four stages, burst pulse, streamer corona, glow corona and spark discharge, and the wind velocity increases monotonously and reach 1.90 m/s at 11 kV. At the same applied voltage, the shorter needle-net distance leads to the larger wind velocity. At 15 mm needle-net distance, the needle-net electrode structure ionic wind generator shows a maximum energy efficiency value of 2.19%. A metal circular plate is attached on the needle electrode to change the spatial electric field distribution, increase the field intensity of the discharge gap, and promote the particle collision. It is found that the wind velocity and energy efficiency can be improved from 1.90 m/s to 2.35 m/s, and 1.87% to 3.14%, at same applied voltage and needle-net distance. The cooling experiment shows that the ionic wind generator with metal circular plate needle-net electrode has better heat dissipation effect.

Clinical Practice Guidelines for the Use of Electroconvulsive Therapy.

Clinical Practice Guidelines for the Use of Electroconvulsive Therapy.

Studies of event burst phenomenon with SiPMs in liquid nitrogen

Silicon photomultiplier (SiPM) are used to collect scintillation photons in many cryogenic noble liquid detectors deployed around the world, such as DarkSide, nEXO, MEGII, ProtoDUNE and DUNE. An event burst phenomenon was observed during routine characterization on many models of SiPMs operated in liquid nitrogen. These bursts of consecutive pulses are initiated by an intense dark photoelectron pulse with an event rate much lower than the time-uncorrelated thermal dark pulse. Although the rate of these burst events is very low, it can potentially compromise some dedicated rare physics event searches which are also anticipated to be of extremely low rate. Here, we systematically studied the behavior of the event burst phenomenon and identified the probable cause of the phenomenon. This investigation is important for the selection of SiPMs for use in noble liquid detectors, high energy physics experiments, and industrial applications where SiPMs are used in cryogenic environment.

Generation of phase-stable sub-mJ ultrashort laser pulse bursts with extremely high scalable pulse number

We demonstrate generation of bursts that consist of up to 40 ultrashort pulses with 10 μJ pulse energy, 250 fs pulse duration and an ultrashort tunable spacing, from picoseconds to nanoseconds, corresponding to a terahertz intraburst repetition rate. This was achieved by the build-up of a novel thermally-stable sub-mJ Vernier Regenerative Amplifier (RA), whose round-trip detuning is similar to its master oscillator round-trip time. The RA includes two cavities pumped from a common diode, and is able to provide for either 2 bursts (one burst out of each cavity), or for one burst and a synchronous reference pulse for characterization.

Isolated attosecond pulse generation from the interaction of intense laser pulse with solid density plasma

This article gives an overview on recent progress in the generation of isolated attosecond pulse and isolated half-cycle attosecond pulse. As an isolated attosecond pulse is preferred in the pump-probe experiments for the dynamics of electrons in atom, molecule, or solid, we focus on the isolated attosecond pulses generation from the intense laser pulses interaction with solid density plasma, which have higher intensity and narrower pulse width than that generated in the interaction of laser pulse with gas target. We have firstly discussed the physical mechanism of isolated attosecond pulse generation, such as polarization gating, two-color laser pulses, attosecond light houses, and capacitor target mechanism. In the polarization gating mechanism, we have discussed the physical mechanism that the higher-order harmonic efficiency decreases with the increase of ellipticity. Both the coherent synchrotron radiation mechanism and the relativistic oscillation mechanism can control the intensity of high-order harmonic generation by controlling ellipticity of the incident laser pulse. We also discussed other mechanism to enhance the isolated attosecond pulse bursts in detail. Secondly, we focus on the isolated half-cycle attosecond pulses, which can also be generated from the intense laser pulses interaction with solid density plasma by double foil target mechanism, gas-foil target mechanism, cascaded generation mechanism, microstructured target mechanism, and three-color laser pulse mechanism. The half-cycle attosecond pulses can be useful for probing ultrafast electron dynamics in matter via asymmetric manipulation. Accordingly we discussed the physcial mechanism, experimental feasibility, calibration measurement, and application prospect of half-cycle attosecond pulse in this article. The above mechanism can directly generate ultra-intense isolated attosecond pulses in the transmission direction without requiring extra filters and gating techniques. The dense electron sheet is crucial for the generation of intense attosecond pulses in different mechanisms, such as coherent wake emission (CWE), relativistic oscillating mirror (ROM) and coherent synchrotron emission (CSE). In this article, all the mechanism for half-cycle attosecond pulses generation can ensure only one electron sheet contributing to the transmitted radiation. We discuss the theoretical model of nanobunching of the electron sheet, which shows that the relativistic oscillation is crucial for the formation of electron sheet.

Design and demonstration of a fast rising burst pulse resonance circuit

Design and demonstration of a fast rising burst pulse resonance circuit

Pulse Burst Generation and Diffraction with Spatial Light Modulators for Dynamic Ultrafast Laser Materials Processing.

A pulse burst optical system has been developed, able to alter an energetic, ultrafast 10 ps, 5 kHz output pulse train to 323 MHz intra-burst frequency at the fundamental 5 kHz repetition rate. An optical delay line consisting of a beam-splitting polariser cube, mirrors, and waveplates transforms a high-energy pulse into a pulse burst, circulating around the delay line. Interestingly, the reflected first pulse and subsequent pulses from the delay line have orthogonal linear polarisations. This fact allows independent modulation of these pulses using two-phase-only Spatial Light Modulators (SLM) when their directors are also aligned orthogonally. With hybrid Computer Generated Holograms (CGH) addressed to the SLMs, we demonstrate simultaneous multi-spot periodic surface micro-structuring on stainless steel with orthogonal linear polarisations and cylindrical vector (CV) beams with Radial and Azimuthal polarisations. Burst processing produces a major change in resulting surface texture due to plasma absorption on the nanosecond time scale; hence the ablation rates on stainless steel with pulse bursts are always lower than 5 kHz processing. By synchronising the scan motion and CGH application, we show simultaneous independent multi-beam real-time processing with pulse bursts having orthogonal linear polarisations. This novel technique extends the flexibility of parallel beam surface micro-structuring with adaptive optics.

Schlieren imaging and spectroscopic approximation of the rotational-vibrational temperatures of a microwave discharge igniter with a resonating cavity.

A microwave discharge igniter (MDI) with a resonating cavity was developed and optimized for practical applications in an internal combustion engine. In contrast to the typical microwave ignition, the resonating cavity of the MDI induces a discharge through dielectric resonance. Its source of microwave (MW) is a 2.45GHz semiconductor oscillator that is capable of numerous oscillation patterns. To verify and demonstrate the optimum ignition performance and combustion, we varied the oscillation parameters (signal factors) of the MW to optimize the performance of the MDI using the Taguchi method. Plasma spectroscopy was used for ignition condition analysis. Two sets of microwave pulses, a first pulse followed by a second set of pulse bursts, were used to ignite a propane-air fuel. The flame kernel growth rate and O I species generation were used as the response outputs, which were obtained, respectively from Schlieren imaging and emission spectroscopy experiments. The extended pulse periods and higher MW pulse numbers of the second set of pulses improved the response outputs of the MDI. To further analyze the effect of MW oscillation patterns on plasma properties and performance, measurements were done on MW superimposed operation with the high-voltage ignition from spark plugs. The MW transmission on a typical spark plug enhanced the air plasma ignition. Higher input MW energy and more extended MW pulse widths results in increased spectral intensity and radical generation of OH, O, and N 2. An inverse relation between the temperature and spectral intensity functions of the MW pulse width was observed, which was attributed to the cutoff density of the MW-enhanced plasma.

PLUSPULS: A transcranial magnetic stimulator with extended pulse protocols

Transcranial magnetic stimulation (TMS) is increasingly applied in basic neuroscience while its field of usage for diagnosing and treating various neurological diseases broadens steadily. A TMS device generates a current pulse in the reach of several thousand ampére to produce a magnetic pulse which induces an electric field around neurons. This electric field, if high enough to depolarize the neuron membrane, generates an action potential at the neuron which travels down the neurons connected to it. The PLUSPULS TMS generates this magnetic pulse by pre-charging a pulse capacitor C with the voltage VC0 and connecting it with a stimulation coil L. The oscillation of the resonance circuit is cut off after one period and is called a biphasic pulse. PLUSPULS is a high frequency stimulator with inter stimulus intervals (ISI) down to 1ms which enables different pulse protocols as paired pulse or quadri theta burst stimulation. A GUI on PC allows a flexible control of PLUSPULS with varying amplitudes and ISI in one burst. The modular hardware and the control via GUI on PC allows for an easier adjustment on requirements to come. The article provides design considerations, hardware, firmware and software to reconstruct a modular biphasic TMS with enhanced charging network to enable extended pulse protocols.

1 GW peak power and 100 J pulsed operation of a diode-pumped Tm:YLF laser.

We report on the generation of high energy, high power pulses in a tabletop diode-pumped Tm:YLF-based laser system, which delivers amplified pulse energies up to 108 J, as well as GW peak power performance when seeded with nanosecond duration pulses. Furthermore, the high power and efficiency capabilities of operating Tm:YLF in the multi-pulse extraction (MPE) regime were explored by seeding the experimental setup with a multi-kHz burst of pulses exhibiting a low individual pulse fluence, resulting in a 3.6 kW average power train of multi-joule-level pulses with an optical-to-optical efficiency of 19%.

Plasticity of conducting polymer dendrites to bursts of voltage spikes in phosphate buffered saline

The brain capitalizes on the complexity of both its biochemistry for neurons to encode diverse pieces of information with various neurotransmitters and its morphology at multiple scales to route different pathways for neural interconnectivity. Conducting polymer dendrites can show similar features by differentiating between cations and anions thanks to their charge accumulation profile and the asymmetry in their dendriticity that allows projecting spike signals differently. Here, we exploit such mimicry for in materio classification of bursting activity and investigate, in phosphate buffered saline, the capability of such object to sense bursts of voltage pulses of 100 mV amplitude, emitted by a local gate in the vicinity of the dendrite. The dendrite integrates the different activities with a fading memory time window that is characteristic of both the polarity of the spikes and the temporality of the burst. By this first demonstration, the ‘material-object’ definitely shows great potential to be a node halfway between the two realms of brain and electronic communication.

High-quality laser processing of fused silica with bursts of ultrafast pulses

High-quality laser processing of fused silica with bursts of ultrafast pulses

Gigahertz bursts with tunable pulse interval and pulse number based on sinusoidal saturable absorption

Optical pulse bursts are multiple pulses that arise from the balance between attractive and repulsive effects and are used for pulsed laser deposition, flow measurement, various micromachining, spectroscopic, and biomedicine. Different application fields have special requirements for the pulse burst, such as burst width, frequency, number of pulses per burst, and the pulse interval etc. Here, we propose and demonstrate the generation of GHz pulse bursts with both tunable pulse number and pulse interval in a nonlinear polarization rotation (NPR) mode-locked fiber laser for the first time. Taking advantage of the sinusoidal saturated absorption of the NPR, with the increase of pump power, only the number of pulses per burst increases one by one in a relatively low pump power range, while only the pulse interval increases gradually in a high pump power range. In addition, one pulse burst with a 22.8-GHz repetition rate is achieved, which is the highest intra-burst repetition rate directly obtained in all-fiber lasers to the best of our knowledge. The numerical results agree qualitatively well with the experiments. Our work gives an insight into the formation of pulse bursts in mode-locked fiber lasers.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.

Formation and consumption of HO2 radicals in ns pulse O2–He plasmas over a liquid water surface

Hydroperoxyl (HO2) radicals are an important precursor in the formation of hydrogen peroxide (H2O2), a key species in plasma-liquid interactions, such that their formation and consumption pathways need to be understood. In this work, the generation and decay of HO2 have been studied in a controlled environment, in ns pulse discharge O2–He plasmas in contact with a liquid water surface. For this, time-resolved, absolute number densities of HO2 in O2–He mixtures excited by a repetitive ns pulse discharge are measured in situ by cavity ring down spectroscopy (CRDS). The discharge cell with external electrodes to generate the plasma and a water reservoir are integrated into the CRDS cavity. The high-reflectivity cavity mirrors are purged with helium to protect them from water vapor condensation. The experimental results are obtained at near room temperature, both during the discharge pulse burst and in the afterglow. The HO2 number density is inferred from the CRDS data using a spectral model exhibiting good agreement with previous measurements of absolute HO2 absorption cross sections. HO2 is generated during the discharge burst and decays in the afterglow between the bursts. The HO2 number density is also measured vs. the O2 fraction in the mixture. Comparison with the kinetic modeling predictions demonstrates good agreement with the data and identifies the dominant HO2 generation and decay processes. HO2 in the plasma is formed predominantly by the recombination of H atoms, generated by the electron impact dissociation of water vapor, with O2 molecules. Reactions with O atoms and hydroxyl (OH) radicals are among the main HO2 decay processes in the afterglow. HO2 is also detected when O2 is not present in the mixture. In this case, it is generated primarily by the recombination of OH radicals, via the formation of H2O2. The results demonstrate that CRDS can also be used for HO2 and other plasma chemical reaction product measurements in atmospheric pressure plasma jets impinging on a liquid water surface in ambient air.

Hints of a universal width–energy relation for classified fast radio bursts

The total available sample of fast radio bursts (FRBs) has been growing steadily in recent years, facilitating the study of FRBs from a statistical point of view. At the same time, the classification of FRBs is currently an imperative issue. We propose that the brightness temperature of bursts can serve as an ideal criterion for classification. In this work, we gather the available data for all localized FRBs and we find a positive relation between the intrinsic pulse width and burst energy, Ti ∝ Eν0.25, for three repeating FRBs that is similar to that of our previous work using FRB 20121102A data alone. The critical line TB, cri is found to vary for different FRBs, which may reflect the differences in source properties. This relation can put strong constraints on mainstream radiation mechanisms. It is evident that neither the coherent curvature radiation or synchrotron maser radiation have the capability to reach the high brightness temperature required to reproduce this relation.

Porcine skin ablation using mid-infrared picosecond pulse burst

We present the porcine skin ablation using a mid-infrared high-repetition-rate picosecond pulse burst laser. A burst-mode pulse with a repetition rate of 16.32 MHz was generated from a home-built difference frequency generation (DFG) system operating at 3 μm. Within each burst, there were 16 equally spaced 8.5 ps sub-pulses at an intra-burst repetition rate of ∼3.3 GHz. To study the laser-tissue interaction, laser powers of 1 to 2 W, and scanning times from 1 to 10 with spot size of ∼50 μm were applied to irradiate the fresh porcine skin. The results demonstrate that the burst-mode pulse with modest peak power density of MW/cm2 is efficient for tissue ablation. The optimized ablation depth increased with the average power and scanning times, reaching a maximal incision depth of 150 μm. Thanks to the high repetition rate of intra-burst pulse and high absorption of radiation, the ablation width and thermal effect width kept within 50 μm and 25 μm in all control groups. It is believed that as the first demonstration, such mid-infrared burst-mode laser radiation with modest power intensity is of great potential to realize micron penetration depth and low thermal effect in high-precision surgery applications.

Satellite laser ranging at ultra-high PRF of hundreds of kilohertz all day

Satellite laser ranging (SLR) had been operated at a pulse repetition frequency (PRF) from ∼10 Hz to 10 kHz; the ultra-high PRF of SLR (UH-SLR) is a trend of development. In this study, an alternate working mode of laser firing and gated pulse bursts is proposed to solve the problem of laser echo interference by laser backscattering. Through an ultra-high PRF of 200-kHz picosecond green laser with single-pulse energy of 80 μJ and a pulse width of 10 ps and a ranging gate device, UH-SLR has been built by an aperture of the 60-cm SLR system in the Shanghai Astronomical Observatory. By this UH-SLR, low-orbit to high-orbit and geostationary orbit satellites are measured night and day and also for low-orbit and medium-orbit satellites in the daytime. The normal point (NP) accuracy is ∼30 μm for low-orbit satellites and ∼100 μm for high-orbit satellites, which provides an effective method for the development of ultra-high PRF and high-precision space target laser ranging.