High-power Nanosecond Research Articles

Вынужденное низкочастотное комбинационное рассеяние света в монокристаллическом алмазе с заглубленным графитизированным слоем

AbstractThe results of experimental observation of stimulated low-frequency Raman scattering (SLFRS) in a single-crystal diamond with a buried graphitized layer created as a result of nonlinear interaction of high-power nanosecond laser pulse with eigen oscillations of nanosized layers of diamond-graphite structures are presented. It is demonstrated that the frequency shift of the SLFRS is on the order of 10 GHz and is inversely proportional to geometrical dimensions of the nanolayers composing the structure.

Transient optical properties in fused silica measured by time-resolved high-power laser photometer

A time-resolved high-power laser photometer, which measures the real-time variations of transmission, internal reflection, and scattering simultaneously with picosecond time resolution, was developed to investigate the material response sequence during high-power nanosecond laser irradiation in thick fused silica. It was found that the transient transmission decreased sharply, accompanied by an increase in internal reflection at the rising edge of the laser pulse. The transient transmission recovered, while laser damage did not occur, but it did not recover if the scattering increased, indicating the occurrence of laser damage. The reason for the sharp decrease of transmission and the relationship between the transmission drop and laser damage were discussed.

Gasification of Coal–Water Compositions by Laser Pulses of Various Intensity

The paper analyzes the processes occurring on the interaction of high-power nanosecond laser pulses with a coal–water mixture prepared from gas-coal waste. It was found that the rate of production of a mixture of CO and H2 sharply increased at a laser radiation intensity higher than 8 J/cm2. This was expressed in a sharp increase in the concentration of the combustible components of synthesis gas (CO, up to 0.57 vol %) and in a noticeable acceleration of the growth of the mass of a gas–aerosol fuel mixture upon the absorption of laser pulses (by 40%). At low pulse energy densities, the generation of a finely dispersed (particle size, 30–70 μm) fuel aerosol was a predominant process. Gasification came into play above the effective ablation threshold when the weight ratio between synthesis gas and the sprayed aerosol reached 1 : 3. Thus, the action of laser pulses makes it possible to convert coal preparation wastes into a highly flammable gas–aerosol fuel mixture.

Высоковольтные диффузионные диоды с резким восстановлением. I. Численное моделирование

The operation of diffusion step recovery diodes (dSRD) as current interrupters in high-power nanosecond pulse generators was studied in detail by the methods of numerical computer simulation for the first time. One of the necessary conditions that minimize the loss in dSRD was specified. Dependences of pre-pulse voltage, front duration, amplitude and duration of pulse formed on the active load, and the energy of switching losses in the dSRD on the device area and the break current density are obtained. It is shown that simulation results can be described by simple analytical formulas obtained in the second part of the work, with an accuracy of 10-20% if the pulse amplitude does not exceed the avalanche breakdown voltage of the dSRD. The generalized figure of merit which can be used for optimization of dSRD parameters, a mode of its operation and comparison of efficiency of current interrupters of various types was offered.

Application of repetitive high power (high voltage) nanosecond electromagnetic pulses to improve technological properties of diamond-bearing kimberlites

In this paper we used Fourier transform infrared spectroscopy (FTIR), analytical electron microscopy, microhardness measurements and other methods to study changes in the morphological, structural defects, hydrophobicity, mechanical and technological properties of rock constituents of kimberlite igneous rocks and crystals of natural diamonds exposed to nonthermal action of the repetitive nanosecond electromagnetic pulses. The destruction of secondary mineral surface films, their removal from the diamond surfaces, the growth of crystal hydrophobicity, and an increase in the number of B2 defects were observed after 30-50 seconds of electrical pulse treatment. The obtained result indicates possibility of applying pulsed energy effects to intensify the diamond flotation and to advance efficiency of the weakening of kimberlite rock constituents without damaging the precious crystals and ensuring their preservation by the subsequent grinding of refractory ores.

Generation of High-Power High-Voltage Nanosecond Rectangular Pulses by Summing Quasi-Harmonic Currents

An approach to designing generators of high-power rectangular high-voltage pulses of nanosecond duration based on a Fourier representation of these pulses is considered. The design of a gigawatt-power-level generator that consists of partial-current formers, a switch, and a charging device is described. The partial-current formers are based on the use of segments of coaxial lines, the switch is manufactured in the form of a multigap gas-filled spark gap, and the charging device is a Tesla transformer that is built into one of the coaxial lines. The results of the generator tests that demonstrate the capabilities of the considered approach are presented.

Russian Physics Journal (Former Soviet Physics Journal) and its Contribution to the Development of High-Current Pulse Electronics and Electrophysics

This article assesses the impact that the journal has had on the research and development in high-current pulse electronics and electrophysics, gas electronics, physics of gas lasers, relativistic microwave electronics, plasma electronics, etc. All these fields of research involve achievements in three areas of science and technology, namely, the creation of high-power nanosecond pulse generators; fundamental studies of nanosecond high-current discharges in gases, which have led to the discovery of the phenomenon of multielectron initiation of discharges, and studies of pulsed vacuum discharges, which have resulted in the discovery of explosive electron emission. The author began his research activities in these areas in 1958 at Tomsk Polytechnic Institute and continued them at the Institute of High Current Electronics of the Siberian Branch of the USSR Academy of Sciences, which was opened in 1977. A number of articles published in the journal were devoted to priority issues such as the studies of nanosecond discharges in gases, in vacuum, and in water; the description of the properties of explosive electron emission; the invention of metal-dielectric cathodes with ferroelectrics, and the proposal of gas compression in devices based on electrically exploded cylindrical conductors.

Experimental Demonstration of a 0.34-THz Backward-Wave Oscillator With a Sinusoidally Corrugated Slow-Wave Structure

The design and experimental demonstration of a 0.34-THz backward-wave oscillator (BWO) with a sinusoidally corrugated circular waveguide is presented. The dimensions of the sinusoidally corrugated structure are at the submillimeter scale. Particle-in-cell simulations have predicted that this miniature slow-wave structure (SWS) should be capable of 0.34-THz radiation. The miniature SWS was successfully fabricated using high precision computer numerical control machining and electric discharge machining. In experimental tests, the resulting BWO produced pulse radiation with a peak RF power of ~600 kW and a pulsewidth of 1.66 ns when driven by a 100-kV, 900-A weakly relativistic electron beam. The measured frequency was in the range of 0.32–0.36 THz and the device achieved stable operation at a pulse repetition rate of 10 Hz. We describe the experimental measurement methods of pulsewidth, frequency, and power for the high-power nanosecond terahertz signal. The work is a proof-of-principle demonstration of BWO frequency extension to above 300 GHz through structure miniaturization and precision machining.

High Energy (100 mJ) and High Peak Power (8 MW) Nanosecond Pulses Delivered by Fiber Lasers and Self-Focusing Analysis Based on a Novel Mode Decomposition Method

Nanosecond (∼10 ns) laser pulses with high peak power of 8 MW and high energy of 100 mJ are reported, which are generated by a cascaded pulsed Yb-doped fiber amplifier system working at a repetition frequency of 10 Hz. The peak power that is higher than the self-focusing threshold for Gaussian beams is achieved for the first time in the fiber lasers. To analyze the self-focusing threshold for multimode lasers in fibers, a novel mode decomposition based on the beam quality measurements is introduced. Based on the mode decomposition and nonlinear laser propagation simulations, the threshold of self-focusing for our case is estimated.

High-power nanosecond pulse generation from an integrated Tm-Ho fiber MOPA over 2.1 μm.

In this paper, we report on high-power stable nanosecond pulse generation at ~2.1 μm from an integrated Tm-Ho all-fiber master oscillator power amplifier (MOPA) system. A total output power of 128.5 W is generated from the Tm-Ho hybrid MOPA, with an average power of 99.1 W from Ho emission at 2116 nm; the corresponding pulse repetition frequency and pulse width are 161 kHz and 322 ns, respectively, leading to a peak power of 1.91 kW. The Tm-Ho integrated master oscillator is designed to operate at 1980 and 2116 nm, where the former wavelength serves as the pump of the Ho-doped fiber. Stable laser pulses are generated from both the Tm and Ho oscillators owing to mutual modulation of emission from the two lasers. The prospects for further scaling in output power at ~2.1 μm using Tm-Ho integrated MOPA system are discussed.

Effect of Deuterium Plasma Irradiation on V–Ga Alloys

Indentation tests are used to investigate the effect of high-power nanosecond deuterium ion pulses (~100 keV, ~1010 W/cm2) and dense deuterium plasma (~100 eV, ~107 W/cm2) generated by a Plasma Focus machine on the mechanical properties of vanadium-based alloys such as V–5Ti–5Cr, V–5Ga–5Cr, V–5Ga, and V–5Ga–0.1Ce. It is established that the V–Ga–Cr alloys have a higher resistance to embrittlement during radiation-thermal exposure than that of V–Ti–Cr alloys. X-ray diffraction analysis shows that the structure of solid solution is retained in all investigated alloys after pulsed ion and plasma irradiation. No signs of solid solution decomposition and the precipitation of second phases are found. It is established that pulsed ion-plasma irradiation suppresses the rolling texture that is typical of the alloys in the initial state and decreases the lattice parameter of the alloys, which in the case of the V–Ga alloy can be explained by the escape of gallium from the recast surface layer. Doping with a rare earth element (cerium) increases the radiation resistance of the V–Ga alloy, which results in the stability of the mechanical properties and the lattice parameter after irradiation.

A Two-Stage DSRD-Based High-Power Nanosecond Pulse Generator

Drift step recovery diodes (DSRDs) have a special place in high-power short-pulse generation. In this paper, a cascaded configuration of two DSRD-based high-power short-pulse generators with gas discharge switches was used. The high-power pulses generated in the first stage feed the second stage in order to generate shorter pulses with higher peak powers. A prototype was implemented based on this idea. In the first stage, 1.2-kV pulses were generated from a 50-V power supply. At the output of the second stage, 2.1-kV pulses with a repetition rate of more than 50 Hz were obtained. The output peak voltage was limited by the breakdown voltage of the used DSRD. Repetitive pulses with 4-ns rise time and 1.3-kW peak power were obtained. The maximum input power was 4.1 W which showed 320 times increase in the peak power. The maximum efficiency of 20% was obtained.

Synthesis and Characterization of Quenched and Crystalline Phases: Q-Carbon, Q-BN, Diamond and Phase-Pure c-BN

We report the synthesis and characterization of quenched (Q-carbon and Q-BN) and crystalline (diamond and c-BN) phases using a non-equilibrium technique. These phases are formed as a result of the melting and subsequent quenching of amorphous carbon and nanocrystalline h-BN in a super undercooled state by using high-power nanosecond laser pulses. Pulsed laser annealing also leads to the formation of nanoneedles, microneedles and single-crystal thin films of diamond and c-BN. This formation is dependent on the nucleation and growth times, which are controlled by laser energy density and thermal conductivities of substrate and as-deposited thin film. The diamond nuclei present in the Q-carbon structure (~ 80% sp3) can also be grown to larger sizes using the equilibrium hot filament chemical vapor deposition process. The texture of diamond and c-BN crystals is 〈111〉 under epitaxial growth and 〈110〉 under rapid unseeded crystallization. Our nanosecond laser processing opens up a roadmap to the fabrication of novel phases on heat-sensitive substrates.

激光清洗用高功率纳秒脉冲掺镱光纤激光器

激光清洗用高功率纳秒脉冲掺镱光纤激光器

Remote Imaging by Nanosecond Terahertz Spectrometer with Standoff Detector

Creation and application of the remote imaging spectrometer based on high power nanosecond terahertz source with standoff detector is reported. 2D transmission images of metal objects hided in nonconductive (dielectric) materials were recorded. Reflection images of metal objects mounted on silicon wafers are recorded with simultaneous determination of the wafer parameters (thickness/material).

A Small Dynistor Generator of High-Power Nanosecond Pulses

A generator of high-power nanosecond current pulses on the basis of a dynistor, which is switched on within 1 ns, is described. Its dimensions are 70 × 80 × 25 mm; at a power voltage of 2.2 kV, the generator switches weakly damped alternating bell-shaped current pulses with an amplitude of 5 kA and a duration of 400 ns.

Target alignment in the Shen-Guang II Upgrade laser facility

The Shen-Guang II Upgrade (SG-II-U) laser facility consists of eight high-power nanosecond laser beams and one short-pulse picosecond petawatt laser. It is designed for the study of inertial confinement fusion (ICF), especially for conducting fast ignition (FI) research in China and other basic science experiments. To perform FI successfully with hohlraum targets containing a golden cone, the long-pulse beam and cylindrical hohlraum as well as the short-pulse beam and cone target alignment must satisfy tight specifications (30 and $20~\unicode[STIX]{x03BC}\text{m}$ rms for each case). To explore new ICF ignition targets with six laser entrance holes (LEHs), a rotation sensor was adapted to meet the requirements of a three-dimensional target and correct beam alignment. In this paper, the strategy for aligning the nanosecond beam based on target alignment sensor (TAS) is introduced and improved to meet requirements of the picosecond lasers and the new six LEHs hohlraum targets in the SG-II-U facility. The expected performance of the alignment system is presented, and the alignment error is also discussed.

Effect of high-power nanosecond electromagnetic pulses on the structural, chemical, and technological properties of natural dielectric minerals

We studied the mechanism of the structural surface modification, and the subsequent changes of microhardness, physical chemical and technological properties of calcium-bearing minerals (calcite, scheelite, and fluorite) and rock-forming minerals of diamond-bearing kimberlites (olivine and serpentine) under the non-thermal effect of high-voltage nanosecond pulses. X-ray photoelectron spectroscopy (XPS), infrared Fourier spectroscopy (FTIR), analytical scanning electron microscopy (SEM–EDX), atomic force microscopy, microhardness measurements (Vickers hardness test, HV), electrophoretic light scattering experiments (ζ-potential), and other methods were employed to examine the structural, chemical, electrical, mechanical and physicochemical changes in the surface properties of natural dielectric minerals as a result of pulsed energy impacts. According to XPS, DRIFTS, SEM-EDX and microhardness testing data, the effect of high-voltage nanosecond pulses leads to damage the surface microstructure of geomaterials with the subsequent formation of traces of surface breakdowns and microcracks, softening of Ca-bearing minerals and rock-forming minerals of kimberlites, and reducing their microhardness by 40–67% overall. Using the adsorption of Hammett indicators from aqueous media, it has been an established fact that the acceptor properties of calcite and scheelite surfaces grow and the electron donor ability of fluorite increases as a result of pulsed electric field treatment during the first 30 s. Preliminary electromagnetic pulse treatment generally enhances Ca-bearing mineral flotation activity by 5–12%.

Analysis and Design of Coherent Combining of two Q-Switched Fiber Laser in Mach-Zehnder Type Cavity

Abstract In this work, we have developed an analytical model of an actively Q-switched Ytterbium-doped fiber laser by using two coupled cavities with amplifying fibers in Mach–Zehnder interferometer configuration. This oscillator system provides high peak power and high energy nanosecond pulse. The pulse energy is almost twice the energy of an individual fiber laser with a combining efficiency goes up 99%. This concept brings some novel perspectives for scaling the high energy and high peak power of nanosecond pulse fiber laser.

A generator of high-power nanosecond pulses based on a modular two-level summator

A modular approach to designing generators of high-power high-voltage nanosecond pulses on the basis of a two-level wave summator and transistor formers of partial pulses is considered. The design and parameters of the modules that are oriented at the development of generators of voltage pulses of up to 300 kV at a current of up to 4 kA are described. The capabilities of these modules are demonstrated based on the example of a pulse generator with a power of 10 MW, a varied pulse duration of 50–150 ns, and a pulse repetition rate of up to 2 kHz.