High-power Pulses Research Articles

Generation of optical frequency combs by Q-switching integrated multi-section semiconductor lasers.

In this work we perform a theoretical and simulation analysis of the behavior of an integrated four section distributed Bragg reflector semiconductor laser under optical injection and Q-switching operation. An electro-absorption modulator is introduced into the laser cavity to control the total losses and perform Q-switching. The simulations are done using a rate equation model. Q-switching operation produces very short and high power pulses. This, together with the use of optical injection, allows obtaining flat and broad optical frequency combs with up to 2100 optical lines within 10 dB (642 lines within 3 dB) at a repetition frequency of 100 MHz. The high chirp of the pulses is responsible for the broad spectra of these combs in comparison with gain switched combs, and the device structure allows fabrication in commercial foundries using standard building blocks.

Chirped-Pulse Amplification in an Echo-Enabled Harmonic-Generation Free-Electron Laser

The field of ultrafast science has experienced significant growth over the last decade, largely attributed to advancements in optical and laser technologies such as chirped-pulse amplification and high-harmonic generation. The distinctive characteristics of intense ultrafast free-electron lasers (FELs) have introduced novel prospects for investigating molecular dynamics, as well as providing an opportunity to gain deeper insights into nonlinear processes in materials. Therefore, high-power ultrafast FELs can be widely used for both fundamental research and practical applications. This study presents a novel approach for producing high-power femtosecond FEL pulses, utilizing chirped-pulse amplification in echo-enabled harmonic generation. Chirped seed pulses are employed to induce frequency-chirped energy modulation in the electron beam. The generated FEL pulse, which inherits the chirped frequency, can be compressed through the gratings in the off-plane mount geometry to provide ultraintense ultrafast pulses. The numerical modeling results indicate that peak power exceeding 20 GW and a pulse duration in the order of several femtoseconds can be achieved.

Design of a large-mode-area tapered fiber amplifier for amplification of ultrashort laser pulses at 1535 nm wavelength

We design a W-type large-mode-area erbium doped tapered fiber with effective mode area varying from 1770 µm2 to 840 µm2with tolerance ± 0.0005 in refractive indices of different layers of fiber. The beam quality of the pulses is ensured by effective single-mode operation. We investigate the amplification of high power femtosecond pulses in this fiber by using nonlinear Schrodinger equation including gain term. It is solved using split-step Fourier method for both up-tapered (effective mode area increasing along the length) and down tapered (effective mode area decreasing along the length) fiber configurations at centered around 1535 nm wavelength. In both configurations of fiber, input pulse parameters like peak power, pulse width, and fiber length are calculated for maximum amplification with the least amount of pulse shape distortion. In down-tapered configuration, we numerically demonstrate the amplification of 1 kW peak power, 560 fs duration pulse to 3.6 MW peak power, 12 fs amplified pulse. In up-tapered configuration, we obtain the amplification of 2 kW, 565 fs input pulse to ∼7.9 MW peak power, ∼11 fs pulse. The fiber is useful for amplifying high-power laser pulses, and the resulting pulses can be used for laser processing, spectroscopy, and remote sensing.

Kerr-lens mode-locked femtosecond Yb:CALYO oscillator with more than 20-W average power.

We report on the demonstration of a pure Kerr-lens mode-locked Yb:CALYO laser which can directly deliver sub-200 fs pulses with more than 20-W average power. With an incident pump power of 89 W, 153-fs pulses were generated with an average power of 21.5 W at a repetition rate of 77.9 MHz. The corresponding peak power and single pulse energy were 1.6 MW and 0.27 µJ, respectively. The stable operation of the mode-locking was confirmed by very small fluctuations in both spectrum and output power recorded over an hour. Second harmonic generation (SHG) was conducted with 59% conversion efficiency, which indicated that the high-power mode-locking pulses are of good quality. Stable Kerr-lens mode-locking (KLM) with 156-fs pulse duration and 27.2-W average power was also achieved with 109-W pump power. To the best of our knowledge, this is the highest average output power ever reported from a femtosecond mode-locked bulk oscillator.

Technology of experiments on non-thermal effects of powerful lectromagnetic pulses on natural and artificial environments

The features of the technology of experiments on the non-thermal effects of high-power nanosecond pulses are considered using the example of a setup used to modify biological media and other objects with heterogeneous electrophysical characteristics. An experimental setup has been created to study the non-thermal effects of high-power pulses on samples of various materials, which generates pulses with a repetition frequency of up to 500 Hz, amplitude up to 60 kV and duration 5 ns. Simulation of transient processes in the equivalent electrical circuit of the load was carried out, and a biological one was used as a load material placed in a microplate.

Parameter sensitivity analysis and parameter identifiability analysis of electrochemical model under wide discharge rate

The increasing demand for electric vehicles, grid stability, and high pulse power loads has driven the development of new high-power lithium-ion batteries (LIBs) that are capable of discharging at extremely high C-rates. Accurately identifying physical parameters in electrochemical models is crucial for the rational design and optimization of these new high-power LIBs. Since high-rate discharge can significantly reduce discharge time, it is essential to investigate the impact of double-layer capacitors. In this study, we present a P2D coupled double-layer capacitor model and conduct a comprehensive analysis of the sensitivity of all 32 physical parameters to terminal voltage during constant current discharge over a wide rate range of 1C to 40C. This is the first time such an analysis has been performed. We classified the parameters into three groups based on their normalized parameter sensitivity index: high sensitivity, sensitive, and insensitive, and identified 14 physical parameters that can be recognized under constant current discharge conditions. We used a genetic algorithm to identify these parameters, achieving a root mean square error below 13 mV and an average absolute error below 10 mV between the simulation results of the model and the experimental data. This work provides guidance and inspiration for the parameter identification of high-power LIBs electrochemical models.

Self-started Kerr-lens mode-locked thin-disk oscillator.

Kerr-lens mode-locking (KLM) has been widely used in thin-disk oscillators to generate high-power femtosecond pulses. Here we demonstrate a Kerr-lens mode-locked Yb:YAG thin-disk oscillator that can be self-started under two configurations. The first can deliver 13-W, 235-fs pulses at a repetition rate of 103 MHz; the second delivers 49 W at a repetition rate of 46.5 MHz, whose corresponding pulse energy of 1.05 µJ is, to the best of our knowledge, the highest energy ever obtained in self-started Kerr-lens mode-locked oscillators. A new method to initiate KLM in the form of optical perturbation in a thin-disk oscillator has also been demonstrated.

Mutual influence of intermodal and fundamental four-wave mixing of 1.0 µm and 1.5 µm nanosecond pulses in a dual-wavelength fiber laser.

We introduce the experimental and theoretical investigation of the mutual influence of two four-wave mixing (FWM) processes during the propagation of high-power nanosecond pulses at 1030 nm and 1562 nm wavelengths in the few-mode optical fiber. Both fundamental mode FWM (FM FWM) of laser pulses at these wavelengths, and intermodal FWM (IM FWM) of 1030 nm pulses, have common anti-Stokes components at 1003 nm wavelength. This leads to the mutual influence of FWM effects. As a result, the decrease of optical power of the fundamental mode is observed at both 1030 nm and 1562 nm wavelengths. The method for the suppression of such an adverse effect is proposed. It is based on the attenuation of the 1030 nm higher LP11 mode at the few-mode optical fiber input.

Physics-Based Modelling of Hybrid Cathode Li/CFx-SVO Batteries Under Pulse Discharge

Power sources of implantable cardioverter-defibrillators (ICD) require high energy density to ensure longevity and sufficient rate capability to provide high power pulses for treating abnormal heart rhythms. Such demands have led to the design of Li/CFx-SVO battery, which leverages the excellent energy density of carbon monofluoride (CFx) and power density of silver vanadium oxide (SVO) through the use of a CFx-SVO hybrid cathode. A phenomenological model based on porous electrode theory was previously developed for Li/CFx-SVO, but it overlooked phase separation in SVO, Li+ diffusion limitations in particles, and reaction heterogeneity across particles. It was thus unable to accurately predict the voltage over-recovery behavior during transitions from medium to low currents, capture relaxation behavior after high current pulses without the use of unrealistically large capacitance values, or interactions between active materials in the hybrid electrode.In this work, we present a computational model of Li/CFx-SVO battery based on Multiphase Porous Electrode Theory for hybrid electrodes (Hybrid-MPET). Hybrid-MPET framework allows us to model the phase separation during reduction of SVO, concentration gradients in SVO particles and the evolution of reaction heterogeneities across an ensemble of particles under different current rates. As a result, our Hybrid-MPET model excels at predicting voltage-capacity behavior under constant current or constant load discharge, is capable of providing physical explanation of voltage over-recovery and voltage relaxation, and captures the interactions between SVO and CFx particles during transient currents. The Hybrid-MPET models are validated against experimental data from Li/CFx-SVO batteries of different designs, and show consistent modelling capability across different electrode thickness, particle lengthscales, and discharge timescales. Our work demonstrates how physics-based models can help provide fundamental understanding of experimental phenomenon, and we further discuss how the Hybrid-MPET framework could open up new opportunities to study the performance of hybrid electrode batteries and support their engineering design in a broader range of devices. Figure 1

Angular Patterns of Nonlinear Emission in Dye Water Droplets Stimulated by a Femtosecond Laser Pulse for LiDAR Applications

Femtosecond laser-induced fluorescence (FLIF) and femtosecond laser-induced optical breakdown spectroscopy (FIBS) are important tools for remote diagnostics of atmospheric aerosols using LiDAR (Light Identification Detection and Ranging) technology. They are based on light emission excitation in disperse media via multiphoton nonlinear processes in aerosol particles induced by high-power optical pulses. To date, the main challenge restraining the large-scale application of FLIF and FIBS in atmospheric studies is the lack of a valued theory of the stimulated light emission in liquid microparticles with a sufficiently broad range of sizes. In this paper, we fill this gap and present a theoretical model of dye water droplet emission under high intensity laser exposure that adequately simulates the processes of multiphoton excited fluorescence and optical breakdown plasma emission in microparticles and gives quantitative estimates of the angular and power characteristics of nonlinear emission. The model is based on the numerical solution to the inhomogeneous Helmholtz equations for stimulating (primary) and nonlinear (secondary) waves provided by the random nature of molecule emission in particles. We show that droplet fluorescence stimulated by multiphoton absorption generally becomes more intense with increasing particle size. Moreover, far-field plasma emission from liquid particles demonstrates a larger angular diversity when changing the droplet radius in comparison with multiphoton excited fluorescence, which is mainly due to the excitation of the internal optical field resonances in spherical particles.

Condition for Stopping the Collapse of High-Power Femtosecond Laser Pulses during Propagation through an Optical Medium

Condition for Stopping the Collapse of High-Power Femtosecond Laser Pulses during Propagation through an Optical Medium

Erosion Performance of TiAlSiN Coatings Prepared by High-Power Pulsed Magnetron Sputtering

Erosion seriously threatens the safety of high-speed rotating mechanical components in very harsh service environments, particularly for lightweight titanium alloy matrix material. In order to improve the erosion resistance of titanium alloy, TiAlSiN coatings with different phase compositions are deposited on TC6 titanium alloy using a high-power pulse magnetron sputtering discharge (HPPMS) system under various discharge voltages. The componential and microstructural evolution as well as mechanical properties of the TiAlSiN coatings are evaluated by X-ray diffraction, scanning electron microscopy, and nanoindentation, respectively. The erosion performance relative to titanium alloy is investigated by a sand blasting tester. With the increase in discharge voltage from −500 to −600 V, the peak of discharge current increases from 105 to 225 A. The prepared TiAlSiN coatings show a shift of the preferred crystallographic orientation from (220) to (200), but all of them have a dense nanocomposite structure. Their hardness (H) and elastic modulus (E) gradually increase before decreasing, arriving at maximum values of 35.34 and 360.5 GPa at −570 V. The erosion resistance of the TiAlSiN coatings dependent on the discharge voltage is consistent with the H/E ratio change. The TiAlSiN coatings prepared at −560 V exhibit the optimal erosion resistance, which is 15 times that of the TC6 substrate. The erosion behavior of the coatings is positively correlated with their hardness and toughness. Adjusting the discharge voltage of the HPPMS pulse is finally proved to be an effective way of tailoring the coating phase compositions to improve the erosion resistance of titanium alloy.

High-power xenon lamp-pumped Er:YAP pulse laser operated in free-running and acousto-optical Q-switching modes

We demonstrate a high-energy and high-power pulse laser on a xenon lamp-pumped Er:YAP crystal. The laser performance and thermal focal lengths under different working frequencies are discussed. The results show that the thermal lens effect is gradually aggravated with the increase of working frequencies, and even working at 100 Hz, a single pulse energy of 234 mJ can be achieved. A maximum average power of 41.5 W is achieved with a working frequency of 20 Hz and slope efficiency of 2.82%. This output power is much higher than other xenon lamp-pumped erbium laser devices. A Q-switched laser is demonstrated by using the TeO2 crystal, the maximum output energies of 11.5 mJ and 3.5 mJ are obtained at 50 and 100 Hz, the corresponding peak powers are 93.4 kW and 17.2 kW, respectively. The laser wavelengths and beam quality factors are also characterized in the free-running and Q-switched modes. A higher pulse energy and peak power laser could be achieved further by improving the damage threshold of TeO2 acousto-optical Q-switching. All the experimental results illustrate that the xenon lamp-pumped Er:YAP laser is a promising candidate for high-power and high-frequency mid-infrared laser devices.

Hydrogen-free DLC films fabricated using superimposed HiPIMS-DCMS deposition system: Bias voltage effects

Diamond-like carbon (DLC) films were grown using a superimposed high-power pulse magnetron sputtering and direct current magnetron sputtering (HiPIMS-DCMS) deposition system at various bias voltages from 0 to −350 V. The microstructure, mechanical and tribological properties of the films were studied in relation to bias voltage. The results suggested that the deposition rate of DLC films decreased gradually with the enhancement of bias voltages. The surface roughness of DLC films decreased from 2.81 nm to 0.54 nm. The values of ID/IG of DLC films decreased first and increased later with the enhancement of bias voltages, and the value of ID/IG was the minimum at −150 V. Therefore, the highest sp3 CC fraction of DLC film was obtained when deposited at −150 V. Moreover, the hardness and internal stress of DLC films also show the law of increasing first and decreasing later. DLC film obtained the maximum hardness and highest internal stress of 32.0 GPa and − 2.08 GPa at −150 V. Finally, the friction test suggested that the films had excellent tribological performance. In particular, the film deposited at −150 V had excellent tribological properties, including low friction coefficient (0.095) and low wear rate (1.36 × 10−7 mm3/N·m).

A spall and diffraction study of nanosecond pressure release across the iron ε-α phase boundary

The extreme response of polycrystalline iron at high pressures and high strain rates is revealed by means of high-power laser pulses. The compression portion of the pulse coupled with x-ray diffraction identifies the expected body-centered cubic (α) to hexagonal close packed (ε) displacive transformation. Upon release, observation shows that the complete reverse transformation takes approximately 8 ns and that the structure returns to its initial microstructural configuration, in a reversible transformation path. This is in good agreement with molecular dynamics (MD) simulations which predict an inverse dependence between transformation time and strain rate. The grain size is reduced from μm to nm range during compression and begins increasing back to the original grain size on decompression. The kinetics of the transition is dictated by heterogenous nucleation as it follows the Johnson-Mehl-Avrami-Kolmogorov equation with the appropriate time exponent of ∼1. This is confirmed by MD simulations which also identify profuse twinning and dislocation generation. The tensile pulse generated upon reflection at the free surface is captured by time-resolved free surface velocity measurements from which a peak tensile stress of 7 GPa is obtained, in stark contrast with its quasi-static value of ∼200 MPa. At these strain rates, the strength of grain interiors, which is determined by twinning and slip exceeds the strength of the boundaries, and failure initiates preferentially in the latter.

Measurement of high-power transient electromagnetic pulse field with integrated photonic electric-field sensor

To satisfy certain special requirements for high-power transient electromagnetic pulse (EMP) field measurements, such as high electric field intensity, broad bandwidth, fast rise time, and compact size, here is described an integrated electro-optic sensor. The frequency response in the range from 100 kHz to 12 GHz and the time-domain input/output characteristics of a sub-nanosecond EMP field with an intensity from 5 to 100 kV/m were experimentally characterized. The sensor was demonstrated to measure the time-domain waveform of the ultrawideband EMP field signals with a rise time of 0.35 ns and bandwidth of 1 GHz. In addition, the minimal detectable electric field strength was 16 mV/m/Hz1/2 in the frequency domain, and an intense sub-nanosecond electromagnetic pulse with a peak amplitude of 100 kV/m was observed in the time domain. The reported sensor is expected to be broadly used for intense EMP measurements.

Improved energy storage performance in rare-earth modified lead-free BNT-based relaxor ferroelectric ceramics

Dielectric ceramic capacitors with high energy storage performance are indispensable components in high-power pulse electronic systems. Herein, a collaborative optimization design is employed to achieve excellent energy storage performance in rare-earth oxides modified 0.76(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.24Sr0.7Bi0.2TiO3 (BNBT-SBT) ceramics by simultaneously enhancing the breakdown field strength (Eb) and relaxor behavior. To this end, ferroelectric domains are partially transformed into polar nanoregions by introducing relaxor ferroelectric SBT, while a smaller grain size is produced by doping rare-earth elements to improve the Eb and further disrupt the long-range order of ferroelectric polarization. It is found that the La-doped BNBT-SBT ceramic simultaneously exhibits a superior energy storage density of 4.4 J cm−3 and an ultrahigh efficiency of ∼91% under a moderate electric field of 300 kV/cm. The good temperature stability (30–120 °C), frequency endurance (1–100 Hz), electric fatigue resistance (1–106 cycles), and excellent power density (108 MW cm−3) are also obtained in the lead-free Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics. These prominent properties indicate that the La-doped BNBT-SBT ceramic is a promising candidate for applications of high-energy storage capacitors.

Phase transition of potassium sodium niobate under high pressures

As a piezoelectric material, K0.5Na0.5NbO3 (KNN) has broad application prospects in ultrasonic transducers, sensors, and biomedicine areas. Its structure information under high pressures is of great significance for guiding device design. In this study, the high-pressure structural evolution of KNN has been studied. Two structural phase transitions were revealed by high-pressure Raman spectrum. The phase transition boundary was found by Raman vibration mode analysis, with transformation ranges of 2.5–4.6 and 6.8–9.4 GPa. The phase structures were determined by in situ neutron diffraction, with a phase transformation path of orthogonal Amm2 (O) → tetragonal P4mm (T) → cubic Pm3¯m (C) structure at high pressures. Synchrotron x-ray diffraction further confirmed the phase transformation path. During the processes of phase transitions, the path of Nb atom was clearly described as moving toward [1¯01] and then [100] direction. An output power density of KNN ceramic devices was comparable to that of commercially available PZT 95/5. The density of KNN ceramic is approximately half that of PZT 95/5, which means a significant advantage in terms of weight reduction and miniaturization of equipment in global demand. The phase transition of ferroelectric materials under high pressures provides scientific guidance for the development of high-power pulse power devices.

Efficiency of Conversion of the Magnetic Energy into Z-Pinch Radiation of Nested Arrays of Mixed Composition at the Angara-5-1 Facility

The results of experiments on the study of the generation of high-power pulsed soft X-ray (SXR) emission with a photon energy higher than 100 eV (in the spectral range with wavelengths λ shorter than 120 Å) during the plasma implosion of nested arrays of mixed composition with different ratios of array radii carried out on a pulse power facility Angara-5-1 with a discharge current level of up to 3.5 MA are presented. The outer array consisted of fibers of a substance with a low atomic number (plastic), and the inner array consisted of a substance with a high atomic number (tungsten, W). In the case of nested arrays of this design, a significant increase in the peak SXR power was obtained compared to single tungsten arrays with the same parameters as for the tungsten array in the inner array. By optimizing the linear mass of the outer array and the ratio of array radii, powerful SXR pulses were prepared with a high pulse power up to 18 TW, pulse energy of ~140 kJ and short pulse duration of ~5 ns. It is shown that by optimizing the linear mass of the outer array (fiber array) it is possible to achieve ~90% conversion of the electromagnetic energy pumped into the vicinity of the array into X-ray emission pinch energy. In this case, the fraction of the kinetic energy of the plasma implosion into the emission energy is not higher than 30%. In shots optimal over the output SXR power, an increase in the fraction of the X-ray emission energy in the spectral range of λ ∈ (30, 40) Å was recorded that is 30–100% than that in single tungsten arrays with similar parameters.

Ion current density on the substrate during short-pulse HiPIMS

A probe method for measuring the ion current density and theoretical calculations of the dynamics of neutral and charged plasma particles using the ionization region model (IRM) is used to study short and ultra-short pulse high-power impulse magnetron sputtering (HiPIMS). This paper studies reasons for the increase in the average ion current density on the substrate at shorter pulses, when the average discharge power does not change. HiPIMS pulses are applied to the copper target at constant values of average discharge power (1000 W) and peak current (150 А), respectively, while the pulse time of the discharge voltage ranges from 4 to 50 µs. A power supply with low output inductance is designed to generate ultra-short pulses. It is shown that shorter discharge pulses lead to a multiple growth (from 2 to 7 mA cm−2) in the average ion current density on the substrate and a growth in the peak intensity of Ar+, Cu+ and Cu2+ recorded by optical emission spectroscopy. A theoretical model of this effect is based on the spatially averaged IRM, which considers afterglow effects. According to theoretical calculations, the increase in the average ion current density on the substrate is determined by the plasma dissipation in the ionized region after the pulse ends. Also, a decrease in the copper deposition rate from 180 to 60 nm min−1 with decreasing pulse time from 40 to 4 µs is explored. A comparison of experimental data with those obtained earlier shows that the suggested dependences of the ion current density and deposition rate on the HiPIMS pulse time are typical for discharge systems with different cathode materials and configurations, i.e., for single- and dual-magnetron systems. This indicates a common nature of the phenomena observed and additionally confirms the results obtained.