High-power Pulses Research Articles

Design, development and characterization of Blumlein Pulse Forming Line based pulsed power system for High Power Microwave source research

This paper describes a complete cycle of designing, developing, and characterising a Pulsed Power System (PPS) and generating microwaves using the relativistic source. For low impedance relativistic High Power Microwave (HPM) sources, Blumlein Pulse Forming Line (BPFL) based high voltage pulsed power systems are the most suited. An HPM source such as a virtual cathode oscillator (VIRCATOR) operating in nanosecond durations consists of a primary voltage source that charges a Marx pulse generator’s capacitor bank over a long time. The requirements of a diode load are met by compressing the output pulse width of a Marx generator by a BPFL. This article describes the novel design, construction and characterization of a circulating De-Ionized (DI) water insulated BPFL pulsed power system. A novel approach of insulating gas filled Marx generator of this class/rating is attempted. A pulse power system consisting of high pressure gas insulated Marx generator and circulating DI water-based BPFL was developed and experimented with the resistive load as well as HPM source. The PSPICE simulation of the Blumlein circuit for various load conditions is described. Criticalities in the design of end bushings are elaborated along with the development and testing of a compact BPFL-based pulsed power system.

High-power 100 W Kerr-lens mode-locked ring-cavity femtosecond Yb:YAG thin-disk oscillator.

High-power femtosecond pulses delivered at a high-repetition rate will aid machining throughput and improve signal-to-noise ratios for sensitive measurements. Here we demonstrate a Kerr-lens mode-locked femtosecond Yb:YAG ring-cavity thin-disk oscillator with a multi-pass scheme for the laser beam. With four passes through the thin disk, 175-fs pulses were delivered from the oscillator at an average power of 71.5 W and a repetition rate of 65.3 MHz. The corresponding intra-cavity peak power of 110 MW is ample for intra-cavity nonlinear conversion into more exotic wavelength ranges. With six passes, the average output power reached 101.3 W. To the best of our knowledge, this is the highest average output power of any mode-locked ring laser. These results confirm the viability of using multi-pass configuration on a thin-disk ring oscillator for high-throughput femtosecond applications.

Study of Active Medium Length Effect on Characteristics of Passive QSwitching and Stokes with Anti-Stokes Pulse

Objective: To study the effect of active medium length on the characteristics of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses generated by laser-Raman medium interaction in optical systems, theoretically. Methods: The optical system consists of Nd+3:YVO4, PbWO4, and Cr+4:YAG as active mediums, Raman medium, and saturable absorber materials, respectively. The rate equations model has been used in the study, and the Rung-Kutta-Fehelberg numerical method was used to solve the rate equations. Finding: The result shows that, decreasing of the active medium length leads to emit high power pulses at advanced time. It also leads to increase in initial value and the maximum value of population inversion density, and leads to increase in the energy of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses. So the decreasing of the active medium length leads to decrease in the pulses duration and the final population inversion density. To increase the power of the three generated pulses, the length of the active medium used in the system must be decreased. Novelty: The characteristics of two pulses generated by Laser-Raman interaction (passive Q-switching pulse and Stokes pulse) have been of interest in some studies. This study investigates the effect of the active medium length on the characteristics of three pulses generated (anti-Stokes pulse with Stokes pulse as well as the passive Q-switching pulses) by the optical system rather than two pulses. Keywords: Laser; Nd+3 :YVO4; passive Q-­switching pulse; Stokes and anti-­Stokes pulses 1

Ultrashort large-bandwidth X-ray free-electron laser generation with a dielectric-lined waveguide.

Large-bandwidth pulses produced by cutting-edge X-ray free-electron lasers (FELs) are of great importance in research fields like material science and biology. In this paper, a new method to generate high-power ultrashort FEL pulses with tunable spectral bandwidth with spectral coherence using a dielectric-lined waveguide without interfering operation of linacs is proposed. By exploiting the passive and dephasingless wakefield at terahertz frequency excited by the beam, stable energy modulation can be achieved in the electron beam and large-bandwidth high-intensity soft X-ray radiation can be generated. Three-dimensional start-to-end simulations have been carried out and the results show that coherent radiation pulses with duration of a few femtoseconds and bandwidths ranging from 1.01% to 2.16% can be achieved by changing the undulator taper profile.

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. These results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.

Transistor Generators of High-Power Rectangular Pulses with Submicrosecond Duration

Transistor Generators of High-Power Rectangular Pulses with Submicrosecond Duration

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review.

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Experimental study of injection seeded single-longitudinal-mode Q-switched fiber laser

--The role of injection seeding power on the operation and output characteristics of a single-longitudinal-mode (SLM) injection seeded Q-switched fiber laser is investigated. The mode coupling between seeding laser and the potential longitudinal-modes of the oscillator changes as the injection seeding power increase. So the Q-switched laser may operate at different regimes which can be distinguished by the pulse features. Only with a proper range of injection seeding power that is not too larger or too small, the operation of injection seeded Q-switched fiber laser with narrow-linewidth, high peak power and narrow pulsewidth laser pulses is possible. The Q-switched fiber laser linewidth is narrowed through inserting a dual-OCs oscillator into the laser cavity. 200-ns, 1-W peak power SLM Q-switched laser pulse with nearly transform-limited linewidth is obtained when the pump power is 300 mW.

Generation mechanism and temporal–spatial evolution of electron excitation induced by an ultrashort pulse laser in zirconia ceramic

Femtosecond lasers have been applied in the machining of zirconia (ZrO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ extrm{ZrO}}_2}$$\\end{document}) ceramics because of their ultrashort pulse duration and high peak power. However, the high-precision micromachining of zirconia remains challenging owing to an unclear understanding of the ultrafast laser–material interaction mechanisms. In this study, the transient processing phenomenon induced by a femtosecond laser pulse, namely electron excitation (filament), occurring on a picosecond to nanosecond timescale, was directly observed and quantitatively investigated inside ZrO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ extrm{ZrO}}_2}$$\\end{document}. A pump-probe imaging method comprising a focusing probe beam integrated with a high-speed camera was used. The evolution process, type variation, and related interaction mechanisms of the filament were revealed under different parameters, including laser pulse energy, sample position, and pulse duration. Finally, the generation mechanism of multiple filaments was clarified and successfully elucidated. This study reveals the ultrafast laser–material interaction mechanisms and the high-precision processing in the laser drilling of zirconia ceramics.

High repetition frequency tunability active Q-switched all-fiber laser by multi-gain sub-rings smoothing multipeak pulse and suppressing ASE self-saturation.

This paper provides a method to effectively suppress the severe ASE self-saturation when achieving high repetition frequency tunability with high output power and narrow pulse width in active Q-switched all-fiber lasers. By studying the regularity of the system's multi-stable state, we first ensured that the laser system operated in a steady state. Then output avoids uneven distribution of pulse energy or missing pulses due to period bifurcation state or chaos state. By adding multiple gain sub-rings within the cavity, the sub-ring structure itself indirectly mitigates the ASE self-saturation while smoothing the pulse. The method will avoid the severe power loss caused by traditional smoothing methods by adjusting the AOM rising edge time. It will also avoid lowering the ASE lasing threshold at high repetition frequency. Meanwhile, the intra-cavity backward ASE can be effectively absorbed by inserting the gain fiber in the sub-rings to directly mitigate the ASE self-saturation. The system's continuously adjustable repetition frequency can be as high as over 300 kHz. It ensures that output power above the watt level and a < 0.2 nm narrow bandwidth can be maintained while tuning the repetition frequency. The narrowest smoothing pulse width of 28 ns has been reached.

Commissioning of X-LAB: a very high-capacity X-band RF test stand facility at the University of Melbourne

The Compact Linear Collider (CLIC) beam-based acceleration baseline uses high-gradient travelling wave accelerating structures at a frequency of 12 GHz. In order to prove the performance of these structures at high peak power and short pulse width RF, two klystron-based test facilities will be put in operation this year. The first Southern Hemisphere X-band Laboratory for Accelerators and Beams (X-LAB) is currently being commissioned at the University of Melbourne, it will house half of the CERN X-band test stand XBOX3, which has been renamed Mel-BOX. Like XBOX3, Mel-BOX employs a novel means of combining high average power but relatively low peak power (6 MW) klystron units to direct power to two testing slots with a repetition rate of up to 400 Hz. As well as the repetition rate, peak power, pulse length and pulse shape can be customised to fit the testing requirements. This novel means of producing high power and high repetition RF pulses can eventually be used for many other applications where multiple test slots are required. This proceedings focuses on the integration and 1st commissioning of Mel-BOX with short pulses. There are also plans for it to form the basis for developing a compact accelerator for medical or university applications, such as radiotherapy and compact light sources [1].

A narrow pulse width and high peak power passively Q-switched laser based on the saturable-absorption characteristic of 2-layer TeSe2

We prepared TeSe2 saturable-absorption nanosheets. The match of band-gap energy with laser wavelength was analysed, and the TeSe2 SA was applied in solid-state lasers to obtain narrow temporal-width and high peak pulse output.

An Energy-based Analysis of High Voltage Resonant-based Pulsed Low Power Converter for Water Treatment Application

An Energy-based Analysis of High Voltage Resonant-based Pulsed Low Power Converter for Water Treatment Application

Pulsed High-Power Radio Frequency Energy Can Cause Non-Thermal Harmful Effects on the BRAIN.

High-power microwave applications are growing for both military and civil purposes, yet they can induce brain-related risks and raise important public health concerns. High-power sub-millisecond radio frequency energy pulses have been demonstrated to be able to induce neurological and neuropathological changes in the brain while being compliant with current regulatory guidelines' limits, highlighting the necessity of revising them.

A design of debris mitigation system for high-repetition-rate petawatt laser experiments

The shooting of high-power laser pulses on solid targets will generate a large amount of debris which can damage the expensive optical elements and impair the laser focusing quality. The existing and upcoming high-repetition-rate petawatt lasers which are able to deliver hundreds of shots in minutes would face more serious debris problems. In this work, we propose a high-speed-spinning multi-disc debris mitigation system. An optimization method based on Bayesian Optimization is developed to acquire the optimal parameters of the system.

Enhanced energy-storage density in (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 antiferroelectric ceramics

Antiferroelectric ceramics with unique characteristics of electric-field-induced antiferroelectric to ferroelectric phase transitions and ultra-fast charging-discharging rate, which are demanded in high pulse power devices. In this work, (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 (PLZSH) antiferroelectric ceramics with x = 0∼0.20 were prepared via a conventional solid-state reaction approach. Incommensurate modulation structure with a 1/n<110> superlattice was observed in AFE at room temperature, which was associated with the unique domain boundaries, contributing the obvious declined AFE-FE phase transition electric field as well as the enhanced energy storage density. It was also observed that the maximum recoverable energy storage density (Wrec) increases from 2.93 J/cm3 (x = 0) to 5.72 J/cm3 (x = 0.15), and the corresponding energy-storage efficiency uprises from 82.4 % to 87.8 % with the increasing x at 280 kV/cm. The superior energy density and efficiency indicate that the obtained PLZSH antiferroelectric ceramics are promising for practical applications in pulse power devices.

Correction: Li et al. Dry Friction Performances of MoNx Coatings Deposited by High–Power Pulsed Magnetron Sputtering. Magnetochemistry 2023, 9, 60

In the original publication [...]

High-power long-picosecond pulse fiber laser at 2 μm with a narrow spectral width

Herein, stable mode-locked pulse trains with an ultra-narrow linewidth at the 2 μm region were obtained in a compact all polarization-maintaining fiber oscillator, which can directly deliver nearly transform-limited pulse with a duration of ∼105.6 ps and a spectral width of ∼86 pm. Relying on the multistage Tm-doped fiber amplifier chains, the output power of ∼19.42 W with a narrow linewidth and the maximum output power of ∼100.7 W were obtained, respectively. The narrow linewidth pulse laser may have the promising potential applications in mid-infrared spectroscopy and polymer processing.

The Transient Cooling Performance of a Compact Thin-Film Thermoelectric Cooler with Horizontal Structure

Thermoelectric cooling is an ideal solution for chip heat dissipation due to its characteristics of no refrigerant, no vibration, no moving parts, and easy integration. Compared with a traditional thermoelectric device, a thin-film thermoelectric device significantly improves the cooling density and has tremendous advantages in the temperature control of electronic devices with high-power pulses. In this paper, the transient cooling performance of a compact thin-film thermoelectric cooler with a horizontal structure was studied. A 3D multi-physics field numerical model with the Thomson effect considered was established. And the effects of impulse current, thermoelectric leg length, pulse current imposition time, and the size of the contact thermal resistance on the cooling performance of the device were comprehensively investigated. The results showed that the model achieved an active cooling temperature difference of 25.85 K when an impulse current of 0.26 A was imposed. The longer the length of the thermoelectric leg was, the more unfavorable it was to the chip heat dissipation. Due to the small contact area between different sections of the device, the effect of contact thermal resistance on the cooling performance of the device was moderate.

Ultrahigh Energy Storage in Tungsten Bronze Dielectric Ceramics Through a Weakly Coupled Relaxor Design.

Dielectric energy-storage capacitors, known for their ultrafast discharge time and high-power density, find widespread applications in high-power pulse devices. However, ceramics featuring a tetragonal tungsten bronze structure (TTBs) have received limited attention due to their lower energy-storage capacity compared to perovskite counterparts. Herein, a TTBs relaxor ferroelectric ceramic based on the Gd0.03 Ba0.47 Sr0.485-1.5 x Smx Nb2 O6 composition, exhibiting an ultrahigh recoverable energy density of 9 J cm-3 and an efficiency of 84% under an electric field of 660kV cm-1 is reported. Notably, the energy storage performance of this ceramic shows remarkable stability against frequency, temperature, and cycling electric field. The introduction of Sm3+ doping is found to create weakly coupled polar nanoregions in the Gd0.03 Ba0.47 Sr0.485 Nb2 O6 ceramic. Structural characterizations reveal that the incommensurability parameter increases with higher Sm3+ content, indicative of a highly disordered A-site structure. Simultaneously, the breakdown strength is also enhanced by raising the conduction activation energy, widening the bandgap, and reducing the electric field-induced strain. This work presents a significant improvement on the energy storage capabilities of TTBs-based capacitors, expanding the material choice for high-power pulse device applications.