Nanosecond Pulse Duration Research Articles

Comparison of methods for changing the spectrum of radiation of a pulse x-ray source to determine the most effective two-energy image processing

For detecting substances with similar chemical composition and density, one of the promising methods of non-destructive testing is dual-energy processing of X-ray images. In particular, dual-energy transformation algorithms can be used to search for minerals hidden within barren rock. This method is most effective when the conditions for registering X-ray images and energy levels are properly selected. This study compares the effectiveness of image processing using the dual-energy method for three cases of spectral composition variation: firstly, as a result of adjusting the voltage on the X-ray tube; secondly, by attenuating low-energy radiation through the use of a copper filter; and thirdly, by combining these two methods. Beryl particles embedded in ground muscovite are used as samples for detection. The study utilizes a pulsed X-ray radiation source that generates radiation pulses of nanosecond duration. An original high-voltage generator scheme has been implemented for the method of regulating radiation energy by changing the peak voltage on the X-ray tube. The use of X-ray sources of this type enables the acquisition of high-resolution X-ray images of moving objects.

Statistical features of the response of a superconducting hot-electron bolometer to extremely weak terahertz pulses of picosecond and nanosecond duration

We study the statistical distributions of the output signals of a superconducting hot-electron bolometer (HEB) detector exposed to weak photon pulses of 1 THz (terahertz) frequency. Pulses with variable photon numbers were generated through strongly non-degenerate parametric downconversion (PDC) in a LiNbO3 crystal at 4.8 K. Fundamental differences in histograms are found between two PDC pumping modes, with pulse widths of 28 ps and 10 ns. HEB response to a picosecond THz pulse was detected in the form of a single elementary electrical pulse (SEP), with the average amplitude proportional to radiation intensity and dispersion relative to the bolometer's dark current. HEB responses to extremely weak radiation intensities have been recorded using nanosecond pulsed illumination. We found that nanosecond histograms are asymmetrical and broaden as radiation intensity increases, indicating that the nanosecond response consists of several SEPs. Poisson–Gauss approximation of histograms indicates that not only the average number of SEPs increase but also the average amplitude of a SEP increases with increasing power of incident THz radiation.

A wireless-feeding capacitive electrode mechanism for achieving massive nanosecond parallel-discharge EDM for large-size wafer flattening

The single-crystal silicon carbide (SiC) wafer diameter is increasing beyond 8 in posing significant challenges to conventional mechanical wafer-processing methods. This study presents an innovative capacitive electrode method for electrical discharge flattening (EDF) of as-sliced large 4H-SiC wafers. The capacitive electrode can be divided into near-infinite units, which significantly reduces the working gap capacitance and enables the generation of a mass of parallel discharges with a nanosecond pulse duration (< 200 ns). This approach offers significant advantages in achieving high efficiency and surface finish simultaneously, regardless of the increase in wafer size. This novel electrode design allows wireless electricity feeding via electrostatic induction, which significantly facilitates the integration of parallel electrode units. Furthermore, a sinusoidal voltage is demonstrated for the first time to identify and promote a parallel discharge state. A model was devised to quantitatively describe the overall process. Using this model, the relationship between the gap voltage, discharge energy, and capacitive electrode properties was predicted, revealing a parallel discharge mechanism. The capacitive electrode mechanism was validated via EDF experiments on a 4H-SiC wafer. Notably, >33 parallel discharges within 6 μs were achieved in a single pulse, resulting in a minimum discharge energy of 0.312 μJ (peak current: 0.18 A, duration: 160 ns) and a surface roughness of Ra 42 nm. Moreover, a machining speed of 0.5 μm/min was achieved on a 4 in wafer, representing an improvement of an order of magnitude compared to conventional non-parallel discharge methods.

Efficacy of a surgical cardiac ablation clamp using nanosecond pulsed electric fields: An acute porcine model

ObjectiveTo examine the effectiveness of a recently developed nonthermal technology, nanosecond pulse-field ablation (nsPFA), for surgical ablation of the atria in a beating heart porcine model. MethodsSix pigs underwent sternotomy and ablation using an nsPFA parallel clamp. The ablation electrodes (53 mm long) were embedded in the jaws of the clamp. Nine lesions per pig were created in locations chosen to be representative of the Cox-maze procedure. Four lesions were intended to electrically isolate parts of the atrium: the right atrial appendage, left atrial appendage, right pulmonary veins, and left pulmonary veins. For these lesions, exit block testing was performed both after ablation and before euthanasia; the time between the 2 tests was 3.3 ± 0.5 hours (range, 2-4 hours). Using purse string sutures, 5 more lesions were created up to the superior vena cava, down to the inferior vena cava, across the right atrial free wall, and at 2 distinct locations on the left atrial free wall. The clamp delivered a train of nanosecond duration pulses, with a total duration of 2.5 seconds, independent of tissue thickness. The heart tissue was stained with 1% triphenyltetrazolium chloride after a dwelling period of 2 hours. Subsequently, each lesion was cross sectioned at 5-mm intervals to assess the ablation depth and transmurality. In some sections, transmurality could not be established on the basis of triphenyltetrazolium chloride staining alone; for these lesions, Gomori-trichrome stains were used, and the histologic sections were evaluated for transmurality. ResultsThe ablation time was 2.5 seconds per lesion, for a total of only 22.5 seconds ablation time to create 9 lesions. A total of 53 lesions were created, resulting in 388 separate histologic sections. Transmurality was established in 386 sections (99.5%). Mean tissue thickness was 3.1 ± 1.5 mm (range, 0.2-8.6 mm). Exit block was confirmed in 23 of the 24 lesions (96%) postablation and 23 of 24 (96%) before the animals were humanely killed. Over the course of the procedure, neither pulse-induced arrhythmias nor any other complications were noted. ConclusionsThe novel nsPFA clamp device was effective in creating acute conduction block and transmural lesions in both the right and left atria in an acute porcine model. This nonthermal energy source has great potential to both shorten procedural time and enable effective ablation in the beating heart.

Electronically Controlled Dual‐Wavelength Switchable SRS Fiber Amplifier in the NIR‐II Region for Multispectral Photoacoustic Microscopy

AbstractPhotoacoustic microscopy (PAM) is a high‐resolution and non‐invasive imaging modality that provides optical absorption contrast. By employing dual‐ or multiple‐wavelength excitation, PAM extends its capabilities to offer valuable spectroscopic information. To achieve efficient multispectral PAM imaging, an essential requirement is a light source characterized by a high repetition rate and switching rate, a ≈microjoule pulse energy, and a ≈nanosecond pulse duration. However, there exists a notable deficiency in suitable light sources, particularly in the near‐infrared‐II window. In this study, a custom‐built all‐fiber‐based light source is reported that provides &gt;3 µJ, 2 ns pulses with a repetition rate of 200 kHz. Digitally addressed semiconductor seed lasers, followed by stimulated Raman scattering amplification, enabled arbitrary sequences of pulses having wavelengths of either 1168.4 or 1202.1 nm. In a switching mode of operation, a 100 kHz switching rate is used to alternate between these wavelengths in even/odd pulses. Furthermore, a high‐resolution multispectral photoacoustic microscopy of three polymer samples is demonstrated with the proposed light source.

Integrated Time Nanosecond Pulse Irreversible Electroporation (INSPIRE): Assessment of Dose, Temperature, and Voltage on Experimental and Clinical Treatment Outcomes.

This study sought to investigate a novel strategy using temperature-controlled delivery of nanosecond pulsed electric fields as an alternative to the 50-100 microsecond pulses used for irreversible electroporation. INSPIRE treatments were carried out at two temperatures in 3D tumor models using doses between 0.001 s and 0.1 s. The resulting treatment zones were quantified using viability staining and lethal electric field intensities were determined numerically. Computational modeling was then used to determine parameters necessary for INSPIRE treatments to achieve equivalent treatment zones to clinical electroporation treatments and evaluate the potential for these treatments to induce deleterious thermal damage. Lethal thresholds between 1109 and 709 V/cm were found for nominal 0.01 s treatments with pulses between 350 ns and 2000 ns at physiological temperatures. Further increases in dose resulted in significant decreases in lethal thresholds. Given these experimental results, treatment zones comparable to clinical electroporation are possible by increasing the dose and voltage used with nanosecond duration pulses. Temperature-controlled simulations indicate minimal thermal cell death while achieving equivalent treatment volumes to clinical electroporation. Nanosecond electrical pulses can achieve comparable outcomes to traditional electroporation provided sufficient electrical doses or voltages are applied. The use of temperature-controlled delivery may minimize thermal damage during treatment. Intense muscle stimulation and the need for cardiac gating have limited irreversible electroporation. Nanosecond pulses can alleviate these challenges, but traditionally have produced significantly smaller treatment zones. This study suggests that larger ablation volumes may be possible with the INSPIRE approach and that future in vivo studies are warranted.

Laser-driven quasi-static B-fields for magnetized high-energy-density experiments

We present measurements of magnetic fields generated in laser-driven coil targets irradiated by laser pulses of nanosecond duration, 1.053 μm wavelength, 500 J energy, and ∼1015 W/cm2 intensity, at the LULI2000 facility. Using two perpendicular probing axes, proton deflectometry is used to characterize the coil current and static charge at different times. Results reveal various deflection features that can be unambiguously linked to a looping quasi-steady current of well-understood polarity or to a static charging of the coil surface. Measured currents are broadly consistent with predictions from a laser-driven diode-current source and lumped circuit model, supporting the quasi-steady assessment of the discharges. Peak magnetic fields of ∼50 T at the center of 500-μm-diameter coils, obtained at the moderate laser intensity, open up the use of such laser-driven coil targets at facilities worldwide to study numerous phenomena in magnetized high-energy-density plasmas, and its potential applications.

Pulsed Field Ablation for the Treatment of Atrial Fibrillation: A Review and a Look into its Future

Pulsed field ablation (PFA) is a novel technology to treat atrial fibrillation (AF) utilizing electric fields to induce nonthermal irreversible electroporation of electrically active cardiac tissue to induce cardiac cell death. PFA offers improved safety benefits compared to traditional radiofrequency ablation (RFA) and cryoablation by specifically ablating only cardiac tissue. However, there are avenues for further optimization including neurological risk associated with microbubble formation and left atrial function post ablation. Various PFA devices with different electric pulse waveforms have been studied and tested in human trials, with the majority utilizing microsecond duration pulses. Shorter nanosecond duration pulses, or nanosecond PFA, is beginning to be studied for AF ablation. In this review we will delve into current waveforms used for PFA, areas for improvement, mechanisms behind nanosecond PFA, and its clinical impact for cardiac ablation.

Reducing switching current with Gilbert damping constant in nanomagnets with perpendicular anisotropy under Dzyaloshinskii–Moriya interaction

We report current-induced magnetization switching (j sw) with a nanosecond-duration pulse current (t p) in a perpendicularly magnetized nanomagnet under the Dzyaloshinskii–Moriya interaction (DMI) and investigate the effect of the Gilbert damping constant (α), t p, and DMI value (D) on j sw via micromagnetic simulations. When α is sufficiently small at t p = 1 ns, j sw for D = 1.0 erg cm−2 decreases by 42% compared to that for D = 0 erg cm−2. Further, j sw can be reduced under the DMI when α is small and t p is short, which is attributed to the twisted magnetization and increased initial magnetization angle.

Elucidating the role of pulse shaping on defects formation in aluminum alloys fabricated by powder bed fusion

The Powder Bed Fusion (PBF) additive manufacturing technique, although widely studied and implemented in the industry, still presents issues of porosity and lack of fusion even when optimal processing parameters are used. The benefits and drawbacks of PBF utilizing pulsed lasers are both consequences of the transient temperature field induced by laser-matter interaction. During laser processing with nanosecond pulse durations, intense heating and cooling rates are induced, setting the melt pool dimensions, which are directly related to the occurrence of lack of fusion, and ablation of the processed material, leading to recoil pressure that induces the keyhole effect, increasing the occurrence of porosity. Consequently, controlling the transient temperature field is a major challenge in incorporating pulsed wave laser technology into PBF to minimize porosity and lack of fusion defects. In this study, to reduce porosity and lack of fusion, a smooth heating rate able to sinter powder grains is designed to facilitate heat flow through the heat affected zone, followed by a sharper heating rate that generates a fully molten region while reducing ablation at the same time. This work represents the first attempt to control the transient temperature field, by shaping a nanosecond laser pulse in the time domain, thereby affecting the formation of defects. The effects of the pulse shape on build quality quantified by lack of fusion and high-energy spherical pores were investigated using X-ray microtomography, molecular dynamics (MD), X-ray diffraction (XRD), Electron Backscatter Diffraction (EBSD), and finite element simulations. The variation of porosity and lack of fusion within manufactured samples were revealed by the high-resolution 3D X-ray micro computed tomography. The differences in the transient temperature field, resulting residual stresses, and microstructure are attributed to the differences in the energy delivery rates within the time domain shaped laser pulses. Laser pulse shaping is an additional parameter that plays an important role in optimizing the PBF as-processed part's production opening a new research niche.

Нетепловое воздействие мощных микроволновых электромагнитных импульсов на насекомых-вредителей зерна

Experimental results on the non-thermal effect of powerful electromagnetic pulses of nanosecond duration on grain pests are presented. The possibility of the death of most insects is shown.

ETAM: Next Generation Event Timer for Picosecond-Precision Time and Amplitude Measurements.

Riga Event Timers have the ability to measure the interval between events with high resolution, on the order of picoseconds. However, they have several drawbacks, such as sensitivity to environmental temperature changes and an inability to capture the amplitude of the events. In this work, we present the ETAM: a next generation Event Timer. Its innovative features include adaptive correction of measurement errors based on an internal temperature sensor, and integrated peak-detector circuit to determine the amplitude of nanosecond-duration pulses. Evaluation shows that the ETAM has high thermal stability with a root mean square error (RMSE) of <3 ps in a temperature range between 0 and +40 °C, and accurate event amplitude measurement capability, with <2.3 mV RMSE in the 100-1000 mV range. These improvements allow the ETAM to be used in satellite laser ranging, optical time-domain reflectometry, and other field applications that require temperature- and amplitude-based time correction in addition to high robustness, performance, and stability.

Pulse-on-Demand Operation for Precise High-Speed UV Laser Microstructuring

Laser microstructuring has been studied extensively in the last decades due to its versatile, contactless processing and outstanding precision and structure quality on a wide range of materials. A limitation of the approach has been identified in the utilization of high average laser powers, with scanner movement fundamentally limited by laws of inertia. In this work, we apply a nanosecond UV laser working in an intrinsic pulse-on-demand mode, ensuring maximal utilization of the fastest commercially available galvanometric scanners at scanning speeds from 0 to 20 m/s. The effects of high-frequency pulse-on-demand operation were analyzed in terms of processing speeds, ablation efficiency, resulting surface quality, repeatability, and precision of the approach. Additionally, laser pulse duration was varied in single-digit nanosecond pulse durations and applied to high throughput microstructuring. We studied the effects of scanning speed on pulse-on-demand operation, single- and multipass laser percussion drilling performance, surface structuring of sensitive materials, and ablation efficiency for pulse durations in the range of 1–4 ns. We confirmed the pulse-on-demand operation suitability for microstructuring for a range of frequencies from below 1 kHz to 1.0 MHz with 5 ns timing precision and identified the scanners as the limiting factor even at full utilization. The ablation efficiency was improved with longer pulse durations, but structure quality degraded.

Detailed look into the unstable S-N border during propagation of the N-zone into the thin YBaCuO film

The focus is on the initial processes which change the shape of the bending S-N border during pulsed electrical S-N switching of thin YBaCuO films. These processes were noted on the SEM images of damaged films. The YBaCuO strip samples of high critical current densities were damaged by overcritical current pulses of nanosecond duration. The processes obtain different properties depending on the effective penetration length that the films have. During the N-zone propagation by the channel, led by the top unstable S-N border, an iterative transformation of the S-N border shape takes place. Two sets of the processes at the single transformation step, demonstrating weak and strong coherent jets action, are visualized and described. The origin of coherent jet formation, which is the driving force of the processes, is discussed. A peculiar interpretation of the moving top of the N-zone as a band in the state of Richtmayer-Meshkov instability is also proposed. It appears that devices with elements of the micro-scale dimensions should manifest the ultra-high speed of the S-N switching.

Understanding photochemical pathways of laser-induced metal ion reduction through byproduct analysis.

Laser-induced reduction of metal ions is attracting increasing attention as a sustainable route to ligand-free metal nanoparticles. In this work, we investigate the photochemical reactions involved in reduction of Ag+ and [AuCl4]- upon interaction with lasers with nanosecond and femtosecond pulse duration, using strong-field ionization mass spectrometry and spectroscopic assays to identify stable molecular byproducts. Whereas Ag+ in aqueous isopropyl alcohol (IPA) is reduced through plasma-mediated mechanisms upon femtosecond laser excitation, low-fluence nanosecond laser excitation induces electron transfer from IPA to Ag+. Both nanosecond and femtosecond laser excitation of aqueous [AuCl4]- produce reactive chlorine species by Au-Cl bond homolysis. Formation of numerous volatile products by IPA decomposition during both femtosecond and nanosecond laser excitation of [AuCl4]- is attributed to enhanced optical breakdown by the Au nanoparticle products of [AuCl4]- reduction. These mechanistic insights can inform the design of laser synthesis procedures to improve control over metal nanoparticle properties and enhance byproduct yields.

Self-Mode-Locking Regime in a K-Band Gyro-TWT With External Reflections

For the first time, self-mode-locking regime in a continuous-wave (CW) K-band helical waveguide gyro-TWT with strong external reflections was obtained experimentally. We have registered correlated sequences of nanosecond-duration pulses with a peak intensity of more than seven times larger than the mean intensity of the output radiation.

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%.

Enhanced resolution optoacoustic microscopy using a picosecond high repetition rate Q-switched microchip laser.

Conventional optoacoustic microscopy (OAM) instruments have at their core a nanosecond pulse duration laser. If lasers with a shorter pulse duration are used, broader, higher frequency ultrasound waves are expected to be generated and as a result, the axial resolution of the instrument is improved. Here, we exploit the advantage offered by a picosecond duration pulse laser to enhance the axial resolution of an OAM instrument. In comparison to an instrument equipped with a 2-ns pulse duration laser, an improvement in the axial resolution of 50% is experimentally demonstrated by using excitation pulses of only 85ps. To illustrate the capability of the instrument to generate high-quality optoacoustic images, en-face, in-vivo images of the brain of Xenopus laevis tadpole are presented with a lateral resolution of throughout the entire axial imaging range.

Experimental Investigation on Flow Characteristics and Ignition Performance of Plasma-Actuated Flame Holder

Improving the performance of flame holders has been a key focus of research on ramjet combustors. The plasma actuator has the potential to improve the ignition performance by manipulating the flow field of the flame holder. In this study, a plasma-actuated flame holder was designed. The aim of this study is to improve the performance of ramjet combustor by applying plasma discharge to the flame holder. The aerodynamic effects and ignition performance of the flame holder were investigated. The results demonstrated that the induced jet direction of the surface arc discharge was perpendicular to the actuator. The induced jet dissipated faster at lower pressures. The aerodynamic actuation intensity and jet area increased with the number of channels of surface arc discharges. Increasing discharge frequencies can increase the discharge times and jet height. The aerodynamic effects under a microsecond pulse duration were better than those under a nanosecond pulse duration. Actuators installed on the inside surface showed better performance than those installed outside. Under different total flow temperature conditions, the plasma-actuated flame holder significantly extended the ignition pressure limit and increased the combustion efficiency by 9.12% and 4.3% on average, respectively.

Hot phonon effects and Auger recombination on 3 μm room temperature lasing in HgTe-based multiple quantum well diodes

We propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. A model for accounting for hot phonons is developed for calculating the nonequilibrium temperature of electrons and holes. Using a comprehensive model accounting for carrier drift and diffusion, Auger recombination, and hot-phonon effects, we predict of lasing at λ∼3 μm at room temperature in the 2.1 nm HgTe/Cd0.85Hg0.15Te quantum well heterostructure. The output power in the pulse can reach up to 600 mW for 100 nanosecond-duration pulses.