Peak Power Levels Research Articles

(Invited) Direct Ammonia Polymer Electrolyte Fuel Cell

Ammonia is a liquid fuel of high energy density and low storage pressure. These properties facilitate storage, distribution and fueling, as required for the introduction and acceptance of an alternative fuel. Distributed as liquid, ammonia cost is projected to be 30% lower than that of hydrogen distributed as compressed gas.1 The structure of direct ammonia fuel cells (DAFCs) is illustrated in Figure 1a.The hydroxide exchange membrane employed in our DAFCs work was the poly(aryl piperidinium) (PAP) membrane developed at the University of Delaware2 and at the spin-off company, W7energy LLC. Following optimization of the composition of the catalyst layers and the operation conditions, the performance of an ammonia oxygen cell at Tcell= 95 oC reached the peak power level of 580 mW cm-2 (shown in Figure 1b).A remaining significant challenge has been the DAFCs performance stability, with testing at constant current showing unstable voltage followed by the fall of the voltage to zero after only a few hours. Recognizing the origin of the instability as liquid management in the DAFCs anode, recent optimization of the anode structure improved substantially the voltage stability with the earliest test showing this improvement, which is depicted in Figure 1c. 1. Y. Zhao, B. P. Setzler, J. Wang, J. Nash, T. Wang, B. Xu, and Y. Yan, Joule, 3, 2472-2484 (2019)2. J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. B. Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu, and Y. Yan, Nature Energy, 4, 392–398 (2019) Figure 1

Multipass cells: 1D numerical model and investigation of spatio-spectral couplings at high nonlinearity

Multipass cells (MPCs) are used nowadays as nonlinear tools to perform spectral broadening and temporal manipulation of laser pulses while maintaining a good spatial quality and spatio-spectral homogeneity. However, intensive 3D nonlinear spatio-temporal simulations are required to fully capture the physics associated with pulse propagation inside these systems. In addition, the limitations of such a scheme are still under investigation. In this study, we first establish a 1D model as a useful design tool to predict the temporal and spectral properties of the output pulse for nearly Gaussian beams, in a wide range of cavity configurations and nonlinearity levels. This model allows us to drastically reduce the computation time associated with MPC design. The validity of the 1D model is first checked by comparing it to 3D simulations. The results of the 1D model are then compared with experimental data collected from a near-concentric gas-filled multipass cell presenting a high level of nonlinearity, enabling the observation of wave breaking. In a second part, we experimentally characterize the spatio-spectral profile at the output of this experimental setup, both with an imaging spectrometer and with a complete 3D characterization method known as INSIGHT. The results show that gas-filled multipass cells can be used at peak power levels close to the critical power without inducing significant spatio-spectral couplings in intensity or phase.

Q-Switched and Mode-Locked Nd/Cr:YAG Ceramic Pulse Laser

A mode-locked and Q-switched short pulse laser using the Nd3+/Cr3+:YAG ceramic has been constructed with a SESAM and Cr4+:YAG crystal optical switch based on excite state absorption (ESA). Laser oscillations of the pulse laser were observed experimentally. The Nd/Cr:YAG ceramic laser has a high conversion efficiency from white light (such as lamp light or solar light) to the laser. The Nd/Cr:YAG ceramic has a higher laser gain than the Nd:YAG laser for the same pumping power. The laser oscillation can be obtained very easily. A single-mode-locked laser pulse with fast modulation on the order of 100 ps was obtained in some pump power regimes when using the Cr4+:YAG crystal. The obtained pulse duration of the short pulse was a few hundred ps. A maximum peak power of 60 kW was obtained when using a SESAM. The same level of peak power (60 kW) was also obtained when using the Cr4+:YAG crystal.

A high-efficiency Doherty Power Amplifier for wireless base stations

ABSTRACT This paper presents a new high-efficiency two-way Doherty Power Amplifier (DPA) with a modified output matching structure for Wideband Code Division Multiple Access (W-CDMA) low-to-medium power base station applications. A blended design is proposed using the symmetrical topology of equal rated power amplifying devices with unequal output impedances for the carrier and peaking amplifier to achieve enhanced efficiency and desired linearity in 1900 MHz band. The proposed output circuit modifications encompass the usage of parasitic capacitor compensation technique for the carrier amplifier, optimum offset line along with the Doherty combiner to achieve high efficiency over 6 to 10 dB extended range of back-off operation. The measured results of the DPA demonstrate a Power Added Efficiency (PAE) of more than 49.9% at +34 dBm W-CDMA signal power, which is between 8 and 8.5 dB back-off from the peak power level of 42.2 dBm. The DPA has a large signal power gain of 13 dB at 1960 MHz. Further, the PAE is 39.5% and linearised Adjacent Channel Power Ratio (ACPR) is −46.2 dBc, both at 10 dB back-off from peak power. In these back-off power levels, this implementation provides significant efficiency improvement using symmetrical devices and with excellent linearity.

Laser-based synchrotron X-ray radiation experimental scaling.

We review the results obtained in several experimental campaigns with the INRS high-power laser system and determine the X-ray emission scaling from synchrotron radiation produced during laser wakefield acceleration (LWFA) of electrons. The physical processes affecting the generation of intense and stable X-ray beams during the propagation phase of the high-intensity ultrashort pulse in the gas jet target are discussed. We successfully produced stable propagation in the gas jet target of a relativistic laser pulse through self-guiding on length larger than the dephasing and depletion lengths, generating very intense beams of hard X-rays with up to 200 TW on target. The experimental scaling law obtained for the photon yield in the 10-40 keV range is presented and the level of X-ray emission at the 1 PW laser peak power level, now available at several laser facilities, is estimated.

Analysis and Design of Outphasing Transmitter Using Class-E Power Amplifiers With Shunt Capacitances and Shunt Filters

In this paper, a novel outphasing power amplifier (PA) based on class-E amplifiers with shunt capacitances and shunt filters is proposed. The new design provides high drain efficiency for both peak and back-off power levels. A mathematical model for the class-E power amplifier with shunt capacitance and shunt filter is presented. The proposed model enables derivation of load circuit parameters that provide optimum drain efficiency for the peak and back-off power levels using closed form mathematical expressions. Based on this model, an outphasing power amplifier is designed and subsequently implemented using microstrip transmission lines and a GaN HEMT devices. The fabricated power amplifier prototype is optimized for 2.14 GHz and provides drain efficiency of over 60% for back-off power levels up to 8.5 dB. The amplifier demonstrates a 44.3% drain efficiency for 64QAM OFDM modulated signal with 20 MHz bandwidth. Adjacent channel leakage ratio (ACLR) of −39.5 dB and error vector magnitude (EVM) of 0.9 % were achieved after the application of a memory polynomial linearization algorithm.

Nonlinear four-wave mixing with enhanced diversity and selectivity via spin and orbital angular momentum conservation

Light that can carry orbital angular momentum (OAM) has found a variety of applications in super-resolution microscopy, optical communications, and laser machining, bringing up the need for pure OAM light generation at on-demand power levels and wavelengths. Parametric four-wave mixing is a promising platform for such source generation, and while investigations of higher-order fiber modes have revealed enhanced phase-matching possibilities, the role of the angular momentum of light in this process has not yet been substantially considered. Here, with a specially designed ring-core fiber in which over 16 OAM modes can be stably guided, we demonstrate the first experiments, to our knowledge, investigating nonlinear four wave mixing between OAM modes in an optical fiber. The large modal space as well as spin and OAM conservation rules enable a high diversity of phase matching conditions while also providing high selectivity. We report parametric wavelength translations of over 438 nm and the ability to obtain kilowatt peak-power level ∼ nanosecond pulses of pure OAM beams at user defined colors.

A survey of fiber laser technology in light of laser particle accelerator

Fiber laser technology and related performance and maturity are surveyed with the perspectives of laser acceleration. Advantageous fiber attributes allow high efficiencies in energy-conversion and heat removal and superior performance in high repetition. Wide utilization in the industries has led to high reliability and cost effectiveness in fiber laser technology. With coherent combination of fiber amplifiers, average-power and peak-power levels are targeted for practical laser-driven plasma acceleration applications.

Doppler Influence on Waveform Orthogonality in 79 GHz MIMO Phase-Coded Automotive Radar

Utilization of phase-coded waveforms in automotive MIMO radars for short to medium range applications is studied. Performances of three most-promising binary code families (Gold, APAS and ZCZ sequences) are compared. Design trade-offs of practical implementation of phased-coded waveforms for MIMO radar are analyzed for the first time for a possible future System on Chip implementation. Orthogonality of the waveforms in case of moving targets is analyzed. The implications of the code properties for the Range-Doppler map, as well as the Range-Angular map, are pointed out. Doppler frequency shift impact on such performance indicators as the target peak power and range sidelobe levels in the range-Doppler plane, as well as the range and azimuth sidelobe behavior, and the angular error in the azimuthal plane have been comprehensively studied for the first time. It is shown that the time-staggered transmit scheme with autocorrelation properties only (while introducing azimuthal errors) results in improved performance compared to code division multiplexing with auto- and cross-correlation properties.

A 4–32 GHz SiGe Multi-Octave Power Amplifier With 20 dBm Peak Power, 18.6 dB Peak Gain and 156% Power Fractional Bandwidth

This letter presents the design and characterization results of a multi-octave power amplifier (MOPA) fabricated in a 0.13- $\mu \text{m}$ SiGe-BiCMOS technology. The single-stage power amplifier is implemented as the stack of a cascode amplifier combining broadband input matching network with resistive feedback, and a common-base amplifier with base capacitive feedback. Measurement results show that the design delivers a peak saturated output power level of 20.2 dBm, with output of 1 dB compression at 19.4 dBm. The measured 3-dB power bandwidth is from 4 to 32 GHz, covering three octaves. The corresponding power fractional bandwidth (PFBW) is 156%. The measured peak power added efficiency is 20.6%, and peak small-signal gain is 18.6 dB. The fabricated integrated circuit occupies an area of 0.71 mm2. To compare state-of-the-art MOPAs, the power amplifier figure of merit defined by the international technology roadmap for semiconductors (ITRS) is modified to include PFBW and area. To the best of authors’ knowledge, the presented design achieves the highest figure of merit among multi-octave PAs in a silicon-based integrated circuit technology reported in the literature.

Comparison of performance-related physical fitness and anaerobic power between Korean wheelchair badminton national and backup players.

The purpose of this study was to compare performance-related physical fitness factors and anaerobic power between national and backup players to enhance the performance of wheelchair badminton players and to discover and foster new athletes. This study included 12 wheel-chair badminton players divided into two groups: national players (n=7) and backup players (n=5). Collected data included cardiorespiratory endurance, muscle endurance, muscle strength, power, agility, and anaerobic power. Results indicated that the national players achieved a significantly higher level of muscle endurance, peak power, and mean power than the backup players. Although none of the parameters showed statistically significant differences, the performance levels of the national players were higher than those of the backup players. Because the physical fitness aspects of wheelchair players vary according to their ability and are essential factors, individualized training programs for enhancing performance and preventing injuries among wheelchair badminton players should be developed.

Deep reinforcement learning for coherent beam combining applications.

Coherent beam combining is a method to scale the peak and average power levels of laser systems beyond the limit of a single emitter system. This is achieved by stabilizing the relative optical phase of multiple lasers and combining them. We investigated the use of reinforcement learning (RL) and neural networks (NN) in this domain. Starting from a randomly initialized neural network, the system converged to a phase stabilization policy, which was comparable to a software implemented proportional-integral-derivative (PID) controller. Furthermore, we demonstrate the capability of neural networks to predict relative phase noise, which is one potential advantage of this method.

XUV Sources Based on Intra-Oscillator High Harmonic Generation With Thin-Disk Lasers: Current Status and Prospects

Ultrafast thin-disk laser (TDL) oscillators provide higher intracavity pulse energy, average power, and peak power levels than any other femtosecond laser oscillator technology. They are suitable for driving extreme nonlinear interactions directly inside the laser oscillator. High harmonic generation (HHG) driven inside ultrafast TDL oscillators is a very recent approach for the generation of coherent extreme ultraviolet (XUV) light at multi-megahertz repetition rates. In this paper, we review the current state of the development, discuss the technological potential, and give an outlook toward the future developments. We compare the current performance to established technologies and evaluate possible limitations. We discuss future improvements, such as reduction of the driving pulse duration and increase of the intracavity peak power, efficient extraction of the XUV light from the cavity, and carrier-envelope offset frequency stabilization of the generated XUV light. Due to the power scalability of the TDL concept and the possibility to operate in a spectrally broadened regime with pulse durations below the gain bandwidth limitation, intra-oscillator HHG with TDLs has a high potential for powerful table-top multi-megahertz coherent XUV light sources for science and applications.

Impedance Matrix and Parameters Measurement Research for Long Primary Double-Sided Linear Induction Motor

Static longitudinal end effect caused by truncated iron and coil windings is the inherent characteristic of linear motors. For multisegment long primary double-sided linear induction motors (DLIMs), subsection power supply mode results in longer iron than excited coil windings, which aggravates the static longitudinal end effect. First, the characteristics of the DLIM impedance matrix are researched through experiments. The impedance matrix is calculated by the measured amplitude and phase of the three-phase voltage and current. Unlike the traditional rotating induction motor, the matrix of DLIM is not a traditional cyclic symmetric matrix. Positive-sequence impedance, which is defined and obtained based on the impedance matrix, could be used to measure parameters by open-circuit and short-circuit experiments. The parameters measurement method is validated more accurate than the traditional average phase impedance. The research results, which are validated by test data from the long primary DLIM system capable of producing 400 kN of force, operating at the 100-MW peak power level, could be the reference for accurate description of the dynamics motor model and parameter measurement.

High-energy pulse self-compression and ultraviolet generation through soliton dynamics in hollow capillary fibres

Optical soliton dynamics can cause the extreme alteration of the temporal and spectral shape of a propagating light pulse. They occur at up to kilowatt peak powers in glass-core optical fibres and the gigawatt level in gas-filled microstructured hollow-core fibres. Here we demonstrate optical soliton dynamics in large-core hollow capillary fibres. This enables scaling of soliton effects by several orders of magnitude to the multi-mJ energy and terawatt peak power level. We experimentally demonstrate two key soliton effects. First, we observe self-compression to sub-cycle pulses and infer the creation of sub-femtosecond field waveforms - a route to high-power optical attosecond pulse generation. Second, we efficiently generate continuously tunable high-energy (1 to 16 $\mu$J) pulses in the vacuum and deep ultraviolet (110 nm to 400 nm) through resonant dispersive-wave emission.These results promise to be the foundation of a new generation of table-top light sources for ultrafast strong-field physics and advanced spectroscopy.

Numerical modelling and optimization of actively Q-switched waveguide lasers based on liquid crystal transducers.

We have recently experimentally demonstrated that a novel liquid crystal-based photonic transducer for sensing systems could be utilized as an active Q-switch in a miniaturised and integrated waveguide laser system. In this paper, we now present a comprehensive numerical modelling study of this novel laser architecture by deriving a set of equations that accurately describe the temporal optical response of the liquid crystal cell as a function of applied voltage and by combining this theoretical model with laser-rate equations. We validate the accuracy of this model by comparing the results with previously obtained data and find them in excellent agreement. This enables us to predict that under realistic conditions and moderate pump power levels of 500 mW, the laser system should be capable of generating peak power levels in excess of 1.1 kW with pulse widths of about 20 ns, corresponding to pulse energies > 20 μJ. We believe that such a low-cost and ultra-compact laser source could find applications ranging from trace gas sensing and LIDAR to material processing.

Vortex laser from anti-resonant ring coupled cavities.

Optical vortex Laguerre-Gaussian (LG0l) modes have wide-ranging applications due to their annular spatial form and orbital angular momentum. Their direct generation from a laser is attractive, due to the pure and high-power modes possible; however, previous demonstrations have had limited ranges of applicability. Here, we propose and implement direct LG0l vortex mode generation with an anti-resonant ring (ARR) coupled laser cavity geometry, where the gain medium inside the ARR is shared between two laser cavities. This generation uses standard wavelength-insensitive optical components, is suitable for high peak and average power levels, and could be applied to any bulk gain medium in pulsed or continuous wave regimes. This work demonstrates the technique with a diode end-pumped Nd:YVO4 gain medium. From 24 W of pump power, 8.9 W LG01 and 4.3 W LG02 modes were generated, all with high mode purity and pure handedness. The LG01 mode handedness was controlled with a new technique.

Sub-picosecond pulsed THz FET detector characterization in plasmonic detection regime based on autocorrelation technique

Many THz applications require detection of sub-picosecond THz pulses. Electronic detectors, in particular, can address this challenge. We report on the detection of sub-picosecond THz pulses generated by a large-area interdigitated photoconductive antenna using a AlGaN/GaN high electron mobility transistor with integrated bow-tie antenna. We demonstrate that the detector’s photoresponse is linear in a wide range of gate bias voltages regarding the available THz radiation power with peak power levels of a few hundreds of milliwatts. We apply an autocorrelation technique to investigate the spectral response of our detector within a bandwidth exceeding 1 THz. We observe an unexpected frequency roll-off of responsivity, which can not be predicted using a framework of standard distributed transmission line theory. However, we show that the data can be understood if one accounts for only partial plasmon screening by the gate electrode, so that the results adhere simply to the distributed resistive mixing approximation, whereby the device suffers from the observed roll-off. This indicates, that for novel detectors and radiation sources, which intend to utilize plasma waves, it is important to ensure efficient screening by the gate electrode.

MULTI® - rope-less elevator demonstrator at test tower Rottweil

Background: The world’s first linear motor driven passenger elevator system MULTI® started test operation at test tower Rottweil, Germany. A full scale showcase has been installed, the commissioning is finished and extensive testing activities are performed. The new test tower in Rottweil provides the perfect test and certification environment to get this ground-breaking product onto the market.
 The propulsion of the cars is based on an ironless long-stator linear motor with distributed active drive, motor and sensor elements. This technology allows cars to move individually in the same elevator shaft without any ropes. The same type of linear motor will also be used to exchange cars horizontally from one shaft to another. Herewith a movement of the cars in a loop or any vertical and horizontal travel path can be realized. The testing procedures to characterize the operation of the MULTI® include measurements of electrical, mechanical and thermal quantities.
 Smart energy management feeds power of descending cars for rising cars. To overcome the high power demand for acceleration cars, an energy buffering system is installed.
 Aim: This paper focuses on the power and energy management of the MULTI® demonstrator. The benefit of intelligent buffering strategy is depicted.
 Methods: Full scale prototype, numerical simulation, testing and measurement. 
 Results: This paper presents first measurement results of the MULTI® demonstrator mainly focusing on the power and energy characteristics of the propulsion system.
 Conclusion: Using an energy buffering system, the peak input power of the MULTI® can be reduced to 50% of the peak power level without energy buffer. The power from downward moving cars is recuperated and used for upward driving cars, balanced by the energy buffer without stressing the grid.

A Spread Spectrum Clock Generator With Nested Modulation Profile for a High-Resolution Display System

A spread-spectrum clock generator is implemented using a nested modulation profile to reduce the peak power levels of radiated electro-magnetic emissions in display products. The display data interface is a potential source of interference, and the spread spectrum technique has been extensively used for display interfaces. The proposed nested profile can further reduce electro-magnetic interference without any degradation in the other characteristics. A test chip was fabricated using a 55-nm CMOS process, and the test results indicate a 41-dB reduction. The sensitivity of a wireless receiver to interference is tested, and the EVM results for the proposed nested profile exhibits an improvement of 1.4 dB compared to those of the triangular profile.