High Efficiency Pulse Research Articles

(Sb0.5Li0.5)TiO3-Doping Effect and Sintering Condition Tailoring in BaTiO3-Based Ceramics.

(1-x)(Ba0.75Sr0.1Bi0.1)(Ti0.9Zr0.1)O3-x(Sb0.5Li0.5)TiO3 (abbreviated as BSBiTZ-xSLT, x = 0.025, 0.05, 0.075, 0.1) ceramics were prepared via a conventional solid-state sintering method under different sintering temperatures. All BSBiTZ-xSLT ceramics have predominantly perovskite phase structures with the coexistence of tetragonal, rhombohedral and orthogonal phases, and present mainly spherical-like shaped grains relating to a liquid-phase sintering mechanism due to adding SLT and Bi2O3. By adjusting the sintering temperature, all compositions obtain the highest relative density and present densified micro-morphology, and doping SLT tends to promote the growth of grain size and the grain size distribution becomes nonuniform gradually. Due to the addition of heterovalent ions and SLT, typical relaxor ferroelectric characteristic is realized, dielectric performance stability is broadened to ~120 °C with variation less than 10%, and very long and slim hysteresis loops are obtained, which is especially beneficial for energy storage application. All samples show extremely fast discharge performance where the discharge time t0.9 (time for 90% discharge energy density) is less than 160 ns and the largest discharge current occurs at around 30 ns. The 1155 °C sintered BSBiTZ-0.025SLT ceramics exhibit rather large energy storage density, very high energy storage efficiency and excellent pulse charge-discharge performance, providing the possibility to develop novel BT-based dielectric ceramics for pulse energy storage applications.

Efficient and high-spatiotemporal-quality terawatt-class mid-infrared optical parametric amplifiers by spatially shaped pumping

We propose a method to efficiently generate terawatt (TW)-class mid-infrared (MIR) femtosecond laser pulses with high spatiotemporal quality through optical parametric chirped-pulse amplification (OPCPA). By transforming the pump-beam profile for the OPCPA from Gaussian to flat-top using a designed field mapping optics consisting of two aspherical lenses, we obtain a TW-class femtosecond laser pulse at 2 µm with a conversion efficiency of over 36% according to our simulations. Furthermore, the spatiotemporal coupling effects are greatly suppressed in our method compared to an OPCPA system that is pumped by a widely employed Gaussian profile beam. Our work provides a simple and robust method for developing OPCPA systems with high efficiency and high pulse quality.

High Efficiency and Low Complexity Dual-Reference Voltage-Based Pulse Width Modulation for Three-Phase Five-Level HANPC Inverters

High Efficiency and Low Complexity Dual-Reference Voltage-Based Pulse Width Modulation for Three-Phase Five-Level HANPC Inverters

Experimental optimization of compact double-cell stimulated Brillouin scattering pulse compressor

To optimize the output of SBS sub-nanosecond pulse compression, two kinds of compact double-cell structures are carried out and compared experimentally. The beam parameters of the compact double-cell structure are calculated theoretically, which provides the selection guidance of structural parameters such as lens focal length and SBS cell size. The dependence of lens parameters and medium parameters on SBS output parameters are experimentally studied. Results show that SBS pulse compression enters the saturation region at a low injection energy with a long focal length lens or a large gain coefficient medium. For compact double-cell setup with one lens, it is easy to obtain narrow pulses for the medium FC40 with a short phonon lifetime. While in setup with two lenses, it is easy to obtain SBS output with a high energy efficiency and narrow pulse width for HT110 medium with a large gain coefficient. The pulse width compression ratio is up to 16 times after optimization. These experimental results can provide references for the experimental design of SBS pulse compression.

Picosecond synchronously pumped diamond Raman laser

With diamond crystals as Raman media, picosecond synchronously pumped solid-state Raman laser is theoretically studied in detail for the first time. High efficient working point and effective pulse compression working point are investigated. For both 532 nm and 1064 nm pumping, high Raman conversion efficiency can be achieved for negative cavity length detuning (∆x) and diamond crystal length of 5 mm. The higher efficiency can be obtained with longer Raman crystal, longer pumping pulse width and higher pumping power. For 532 nm pumping, effective pulse width compression can be realized for ∆x = 0 nearby and diamond crystal length of 10 mm. Shorter pulse width and higher peak power of 1st Stokes laser can be achieved with longer Raman crystal, shorter pumping pulse width and higher pumping power. The findings can contribute to the design and optimization of picosecond synchronously pumped diamond Raman lasers.

Circuit analysis and modeling of a soft-switching pulse power supply based on full-bridge inverter for DBD application

PurposeHow to use a simple and classical topology to provide a high-efficiency excitation voltage for dielectric barrier discharge (DBD) loads is one of the primary problems to be solved for DBD application fields.Design/methodology/approachTo address the issue, a set of modes that can generate a high-efficiency pulse excitation voltage in a full-bridge inverter are adopted. With the set of modes, the unique equivalent circuit of DBD loads and the parasitic parameter of the step-up transformer can be fully used. Based on the set of modes, a control strategy for the full-bridge inverter is designed. To test the performance of the power supply, a simulation model is established and an experimental prototype is made with a DBD excimer lamp.FindingsThe simulation and experimental results show that not only a high-efficiency excitation voltage can be generated for the DBD load, but also the soft switching of all power switch is realized. Besides this, with the set of modes and the proposed control strategy, the inverter can operate in a high frequency. Compared with other types of power supplies, the power supply used in the paper can fully take advantage of the potential of the excimer lamp at the same input power.Originality/valueThis work considers that how to use a simple and classical topology to provide a high-efficiency excitation voltage for DBD loads is one of the primary problems to be solved for DBD application fields.

High efficiency active Q-switched laser operation with a large size rectangular core crystalline waveguide.

High efficient pulse output from a large size rectangular core crystalline waveguide actively Q-switched laser was achieved experimentally. A crystalline waveguide, with a rectangular core size of 320μm×400μm by 1.0at.% Yb:YAG (core), 600μm×600μm by 0.5at.% Er:YAG (cladding), and 7mm×7mm by 4.0at.% V:YAG (outside of the cladding) was designed and fabricated. Using a continuous diode laser as an end pump, an output pulse energy 1.75mJ@10kHz, pulse width 9.9ns (peak power 175kW), optical-optical efficiency 26%, with the beam quality of Mx2=1.15, My2=1.10, were obtained in the experiment. The design method that used to suppress amplified spontaneous emission (ASE) and parasitic oscillation by cutting off the reflection and transmission paths, can be applied for various kinds of crystalline waveguide Q-switched or mode-locked lasers.

High-Efficiency Pulse Width Modulation-Based Wireless Laser Power Transmission Step-Down System

Wireless laser power transmission is a promising technique in the far-field wireless power supply with the advantages of high-power density, and small transmitter and receiver sizes. This article proposes a high-efficiency pulse width modulation-based wireless laser power transmission step-down system based on an 808 nm laser diode and gallium arsenide photovoltaic cells. The output voltage of the proposed system is controlled with the use of pulse width modulation of the laser diode in the transmitter without switch tubes and rectifier diodes in the receiver. The model of the proposed system is built, and characteristics of the system is analyzed based on the state-space averaging method. Additionally, the steady and dynamic operations, as well as the efficiency analyses, are investigated and evaluated experimentally. With the use of the propounded system, when the load is 3 ohms and the output voltage is 1.5 V, a converter efficiency of 96.6% is obtained that is ∼10% and ∼5% higher than those of continuous wireless power transmission constant voltage systems with asynchronous and synchronous buck converters, respectively.

A Compact High Efficient Wideband Electromagnetic Pulse Radiator

A wideband electromagnetic pulse oscillation and radiation method is studied. A compact high efficient wideband electromagnetic pulse radiator is developed based on this method. Simulation analysis and experimental results show that the radiation device can obtain more than 40% equivalent voltage radiation efficiency.

Investigation of the high efficiency pulse tube refrigerator with acoustic power recovery

The efficiency of conventional pulse tube refrigerator (PTR) is bounded due to the dissipation of acoustic power at the hot end. Thus, the acoustic power recovery is of great significance for improving the efficiency of the PTR, especially in the application of middle-high temperature zone and large cooling capacity. Based on an existing inertance tube pulse tube refrigerator (ITPTR), a pneumatic piston phase shifter is designed to shift the phase difference and recover part of the acoustic power. The acoustic impedance model and dynamic model are applied to theoretically analyze the work recovery pulse tube refrigerator (WRPTR). Parametric simulation and optimization of the pneumatic piston are performed with the help of the 1-D simulation software (Sage), and the experimental system of WRPTR is successfully built. Some experiments are performed on the experimental system and the experimental results are in good agreement with the simulation results. The experimental results show that the pneumatic piston phase shifter can recover the acoustic power well with a suitable phase relationship. A relative Carnot efficiency of 20.8% is obtained at 170 K with 15 W cooling capacity. In addition, the pneumatic piston phase shifter is lighter and more compact, which is more advantageous in applications.

Development of Pulse Tube Cryocoolers at SITP for Space Application

Over the last 10 years, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, has developed very high-efficiency pulse tube cryocoolers (PTCs) for aerospace applications. These PTCs can provide cooling power from milliwatt scale to tens of watts over a range of temperatures from 30 to 170 K and can be used to cool a variety of detectors in space applications (such as quantum interference devices, radiometers and ocean color sensors) that must operate at a specific cryogenic temperature to increase the signal-to-noise ratio, sensitivity and optical resolution. This paper reviews the development of single-stage PTCs over a range of weights from 1.6 to 12 kg that offer cooling powers at the cold temperature range from 40 to 170 K. In addition, a two-stage 30 K-PTC is under development.

Design of High Efficiency Pulse Power Amplifier for Alarm Based on Floating Ground

In this paper a high efficiency pulse power amplifier for alarm based on floating ground is proposed. This pulse power amplifier, adopting inductive flyback converter, can continuously change the input voltage from 10~30V to 2.5~18V by floating ground, and then provide pulse power driver with variable operating voltage. Thus, volume adjustment can be achieved continuously. This method can help avoid the use of expensive class D amplifier, and the whole circuit is simple and stable. It has wide working voltage, which can greatly reduce the cost, narrow the product category, and make convenient its maintenance and management, so that the competitiveness of products can be improved substantially.

Electro-optically controlled divided-pulse amplification.

A novel technique for divided-pulse amplification is presented in a proof-of-principle experiment. A pulse burst, cut out of the pulse train of a mode-locked oscillator, is amplified and temporally combined into a single pulse. High combination efficiency and excellent pulse contrast are demonstrated. The system is mostly fiber-coupled, enabling a high interferometric stability. This approach provides access to the amplitude and phase of the individual pulses in the burst to be amplified, potentially allowing the compensation of gain saturation and nonlinear phase mismatches within the burst. Therefore, this technique enables the scaling of the peak power and pulse energy of pulsed laser systems beyond currently prevailing limitations.

Spectrally intense terahertz source based on triangular Selenium.

The intensity of a nonlinear terahertz (THz) source is primarily given by its spectral density. In this letter, we introduce triangular Selinium (Se) as a novel THz emitter and show numerically its superior properties to the currently used crystals for intense THz generation. The excellent phase matching enables the applicability of elongated Se crystals which results in very high spectral flatness and broad THz bandwidth (0.5–3.5 THz), high conversion efficiency and THz pulse energy.The spectral THz density produced by optical rectification in Selenium exceeds those from contemporary crystal-based THz sources.

XLi 2MnO 3·(1 − x)LiMO 2 blended with LiFePO 4 to achieve high energy density and pulse power capability

A lithium-ion positive electrode is proposed that contains both high energy density and efficient pulse power capability, even at low state-of-charge (SOC). The pulse power capability at low SOC is attractive for applications, such as plug-in hybrid electric vehicles (PHEVs), which require pulse power operation over the entire useable SOC window. A lithium- and manganese-rich transition-metal layered-oxide (LMR-NMC), also classified as a layered–layered oxide material, is blended with a lithium iron phosphate (LFP) to achieve a potentially low-cost, high-performance electrode. The LMR-NMC material provides high energy by delivering cathode material gravimetric energy densities greater than 890 Wh kg −1. The pulse power capability of this material at low SOC is greatly improved by incorporating a modest quantity of LFP. The LFP serves as an internal redox couple to charge and discharge the more rate-limited LMR-NMC material at moderate to low SOCs.

Two-level DC current power-exchange system based on structures with switched capacitors for autonomous power systems

A new method of constructing single- and multicycle power-exchange systems of autonomous DC current sources based on bilateral resonant-type DC voltage capacitor converters with high efficiency and low conductive pulse noise is considered. The specific features of the operation of exchange systems are studied and expressions for calculating their energy factors and the parameters of elements of the power circuit are obtained.

New Materials for Short-Pulse Amplifiers

Laser amplifiers seek high power, efficiency, and short pulse durations. Research laboratories in this field have focused their investigations toward new laser materials that can be efficiently diode pumped, sustain high-power pumping, and have broad emission bandwidth to achieve ultrashort pulse amplification. This is why, for more than ten years now, new Yb-doped materials have been intensively investigated. In the actual state of the art, they represent the more promising and successful materials for these kinds of applications. In this paper, we will do a short review of the last and more impacting discoveries and demonstrations in this field over the last few years.

Conductively-cooled, high-energy, single-frequency diode pumped slab laser for space applications

A laser-diode-pumped high efficiency, high pulse energy and single-frequency oscillator and amplifier for potential space environment applications have been developed and demonstrated using conductively-cooled heat removal. A diode-pumped injection seeded single-frequency oscillator was achieved by using the resonance-detection technique in Q-Switching operation, and Nd: YAG zigzag slabs based on “pump on bounce” are used in power amplifier stage for high-efficiency pulse energy extraction. Output pulse energy of 800 mJ with 11 ns pulse duration is obtained at a repetition rate of 100 Hz, with a near 3× diffraction-limit beam and an optical-to-optical efficiency of 18%. The experimental result shows that the laser has compact structure, high efficiency, reliability, conductive cooling and can be used for space environments.

Design and analysis of broadband high-efficiency pulse compression gratings

We report on two effective methods, multiparameter optimization and local optimization combined with the diffraction bandwidth merit function, to design a broadband pulse compression grating (PCG), and we present broadband, high-efficiency PCGs based on both the multilayer dielectric grating (MDG) and metal-multilayer dielectric grating (MMDG) models. For MDG, the average diffraction efficiency is higher than 97.5% for TE polarization light over the 100 nm bandwidth centered at 800 nm. Moreover, a novel multilayer structure, which comprises higher index material in the high-reflectivity mirror and relatively lower index material on top, is first proposed to yield higher average efficiency, broader bandwidth, and excellent fabrication tolerance. For MMDG, it exhibits an ultrabroadband top-hat diffraction spectrum with average efficiency exceeding 97% over the 200 nm wavelength wide centered at 1053 nm. In addition, the MMDG structure, which has the best tolerance for grating fabrication, is determined by investigating characteristics of MMDGs with different thin-film structures.

High efficiency pulse compression in tapered microstructure fibers in anomalous dispersion region

A kind of linerly tapered microstructure fiber has been proposed in this paper. The central wavelength, which is located in the anomalous dispersion region, is 1550 nm. We use an adaptive split-step Fourier method to numerically study the propagation of 1 ps laser pulse in this microstructure optical fiber. For the tapered fiber under consideration, a compression factor of 56.9 and a quality factor of 27 can be achieved in a fiber 1 m long. With the pulse shape evolution in the fiber, we find that in anomalous dispersion region, the pulse can be highly efficiently compressed by the increasing of nonlinearity coefficient and the decreasing of dispersion coefficient. Compared with the normal photonic crystal fibers, the thicker end of the tapered fiber is apt to be coupled to the laser pulse which has a larger effective mode area.