MW Peak Power Research Articles

兆瓦峰值功率输出的超低纤芯数值孔径大模场光子晶体光纤

兆瓦峰值功率输出的超低纤芯数值孔径大模场光子晶体光纤

Proposition of a femtosecond pulse radiolysis with terahertz probe pulses

A new concept of pulse radiolysis based on a photoinjector, which can synchronously offer femtosecond (fs) pump electron beams and intense Terahertz (THz) probe pulses, is proposed and studied in this paper. The two electron beams are generated in the radio-frequency (rf) electron gun by illuminating the photocathode with two laser pulses, then compressed and accelerated in two linear accelerators respectively. By applying the brake-applied velocity bunching bunch compression method, a few hundreds of fs electron beams with nano-Coulomb (nC) bunch charge can be obtained. The front beam can generate THz pulse with MW peak power for THz probe, and the rear beam is used to pumping the radiation induced phenomena. This new concept pulse radiolysis scheme provides a promising way for high time resolution pump-probe experiments with a novel experimental methodology.

Parametric generation in a PPLN crystal pumped by a Q-switched mode-locked Nd : YAG laser: comparison of the superluminescent and singly resonant operation regimes

The output characteristics of light in two parametric generation regimes [parametric superluminescence and parametric generation in a singly resonant optical parametric oscillator (OPO) based on a 50-mm long PPLN crystal, synchronously pumped by a 50-ps Nd : YAG laser] are compared. The total average output power at the wavelengths of signal (λ = 1475 nm) and idler (λ = 3820 nm) waves in the superluminescence regime is ∼120 mW (peak power ∼120 kW). The maximum total conversion efficiency with respect to the absorbed power in the superluminescence regime is ∼60%. The maximum conversion efficiency into the idler wave with respect to the absorbed pump power is 15% and 25% (quantum efficiencies of 54% and 90%) for the superluminescence and singly resonant OPO regimes, respectively. The maximum values of the average output power at the idler wavelength are ∼30 and ∼60 mW at degrees of pump depletion of 47% and 55% for the superluminescence and singly resonant OPO regimes, respectively.

100 MW Peak Power Picosecond Laser Based on Hybrid End-Pumped Nd:YVO4 and Side-Pumped Nd:YAG Amplifiers

A mode-locked fiber laser with pulse duration of 4.8 ps and repetition rate of 30 kHz is amplified by end-pumped Nd:YVO4 amplifiers and side-pumped Nd:YAG amplifiers. The output power is amplified up to 31.8 W, achieving a pulse peak power of more than 100 MW and a gain of 59 dB. The beam quality is well preserved with ${M^2}$ factor of 1.26, based on the method of aberration self compensation. The laser beam size in amplifiers is optimized to prevent the unwanted damage due to the high pulse peak power density by using two different types of pumping scheme. It is demonstrated to be an ideal laser source for higher harmonic generation due to high peak power and good beam quality.

Coexisting frequency combs spaced by an octave in a monolithic quantum cascade laser.

Quantum cascade lasers are proving to be instrumental in the development of compact frequency comb sources at mid-infrared and terahertz frequencies. Here we demonstrate a heterogeneous terahertz quantum cascade laser with two active regions spaced exactly by one octave. Both active regions are based on a four-quantum well laser design and they emit a combined 3 mW peak power at 15 K in pulsed mode. The two central frequencies are 2.3 THz (bandwidth 300 GHz) and 4.6 THz (bandwidth 270 GHz). The structure is engineered in a way that allows simultaneous operation of the two active regions in the comb regime, serving as a double comb source as well as a test bench structure for all waveguide internal self-referencing techniques. Narrow RF beatnotes (∼ 15 kHz) are recorded showing the simultaneous operation of the two combs, whose free-running coherence properties are investigated by means of beatnote spectroscopy performed both with an external detector and via self-mixing. Comb operation in a highly dispersive region (4.6 THz) relying only on gain bandwidth engineering shows the potential for broad spectral coverage with compact comb sources.

Self-powered triboelectric touch sensor made of 3D printed materials

A novel approach of fabricating vertical-contact separation mode triboelectric nanogenerator employing three-dimensional (3D) printed functional layers and mechanical spring is presented with the ultimate goal of direct integration of triboelectric sensors with smart 3D objects. Commercially available elastomer TangoBlack is investigated for the first time as soft active triboelectric layer, and rigid polymers, acrylonitrile butadiene styrene (ABS) and polyamide (PA), are considered as active triboelectric layers and spring mechanism in a triboelectric touch sensor. Amongst rigid layers, the spring mechanism is prepared using 3D printed PA material since it exhibits structural rigidity along with flexibility. TangoBlack is measured to be slightly above other commercial rigid positive layers in the triboelectric series. We implement a polydimethylsiloxane (PDMS) layer printed by direct ink writing which demonstrates, when pairing with TangoBlack, ~ 300% higher average power output than nearest other pairs considered. The touch sensor behavior is evaluated for varying operational active areas, frequencies and applied forces using an automated setup, and for hand and finger tapping. For the load resistance of 273.7 MΩ, hand tapping at 2.0 ± 0.1 Hz provides peak power (PP) of 1.2 mW (peak power density of 186.4 μW/cm2), whereas finger tapping at 2.0 ± 0.1 Hz generates PP of 62.9 μW (peak power density of 48.4 μW/cm2). This work represents a major step towards the digital manufacturing of triboelectric nanogenerators which would enable their integration in 3D smart objects, notably soft wearables and robotics.

A human locomotion driven hybrid energy harvester for wrist wearable applications

In this work, a human locomotion driven hybrid energy generator has been proposed and experimentally validated for scavenging significant biomechanical energy from natural motion of arm swinging, to be used for wrist-wearable smart device applications. A proposed hybrid electromagnetic (EM) and triboelectric (TE) generator can deliver much higher output power than that of the individual harvesting device unit due to the combinational operation of EM and TE mechanisms under the same applied mechanical movements. A novel curved structural design based energy harvester is proposed from the comparative analysis of human hand swinging motion with double pendulum motion, which helps to enhance the output performance and design it fit to wear on wrist. The swinging of human arm during walking and running initiates a freely movable magnetic metal ball to oscillate inside the curved structure through both EM and TE part. The EM part consists of two coils wrapped around the curved body, one at each end and micro-structured Polydimethylsiloxane (PDMS) film is attached on the inner wall of curved body along with copper electrode for TE part. A prototype of the hybrid harvester has been fabricated and tested. The EM and TE devices are capable of delivering maximum 84.37mW peak power at 49.2Ω matching load resistance and 1.86μW peak power at 10MΩ load resistance respectively which are considerably higher than the trending state-of-the-art devices.

Design, Manufacturing, and Performance Results of a 1.2-MW Peak, 704-MHz Multibeam Inductive Output Tube

Development overview and test results of a multibeam inductive output tube that produces over 1.2 MW peak power at 704 MHz with over 65% efficiency are presented. This is a collaborative effort between Thales Electron Devices and Communications & Power Industries to design and fabricate a new RF source for the European Spallation Source. The first prototype unit has been designed and built. Initial test at CERN demonstrated output power of 1.2 MW peak, efficiency of 69.8%, and gain of 21.4 dB at 1-ms operation. When the pulselength was increased to 4 ms, instability in the RF output pulse developed as the result of a mechanical contact issue in the output window. The prototype is in the process of being repaired and the unit will be returned to CERN for full characterization and final testing in early 2018.

Self-seeded, multi-megawatt, Mamyshev oscillator.

We demonstrate a fiber oscillator that achieves 3MW peak power, is easily started, and is environmentally stable. The Mamyshev oscillator delivers 190-nJ pulses that can be compressed externally to 35fs duration. Accurate numerical modeling of the gain medium provides insight into the behavior and performance of the device.

Effect of design parameters on the exergy efficiency of a utility-scale packed bed

Abstract The optimization of a packed bed for utility-scale applications is presented herein. The paper discusses comprehensively the effects that particle size, aspect ratio and storage mass have on the exergy losses of the store throughout a complete working-cycle and seeks to provide a clear reference of what is an adequate range of aspect ratios to consider for the design of a grid-scale packed bed. A one-dimensional model that accounts for temperature-dependent properties of both, storage medium and heat transfer fluid, and self-discharge losses is used for performing the analyses. The working cycle considered for the modelling work is a 24 h long sinusoidal profile (12 h charge/12 h discharge) with a 10 MW peak power and a total energy storage requirement of 79.4 MWhth. The results show that a substantial improvement in performance can be achieved by adopting a configuration based on an aspect ratio between 0.5 and 0.8 and fine-tuning the particle size for the specific shape of the container. Furthermore, the study reveals that increasing the thermal storage mass leads to a considerable increase in efficiency. It is determined that a design with 50% additional storage mass, an aspect ratio of 0.6 and a particle size of 3.7 mm, is the optimum configuration from a techno-economic perspective, having a roundtrip exergy efficiency of 98.24%. Additionally, the paper presents a brief study on the effect of the frequency of the work-cycle, which serves as an introduction to the concept of optimizing a thermal storage system by splitting the load into multiple frequency components.

MW peak power KTP-OPO-based “eye-safe” transmitter

• 1.4 MW peak power, 28 mJ pulse energy, KTP-based optical parametric oscillator. • Detailed theoretical description of KTP Type-II choice as parametric generator. • Great potential for an “eye-safe” target illumination device. We demonstrate MW-level, single resonance optical parametric oscillator, based on KTP Type-II crystal with noncritical phase-matching. The OPO is pumped by electro-optically Q-switched Nd:YAG slab laser providing 55 mJ of pulse energy. At the output, we achieved 28 mJ of signal pulse energy at 1.57 μm with 51% conversion efficiency, corresponding to 1.4 MW of peak power.

High efficiency laser-assisted H− charge exchange for microsecond duration beams

Laser-assisted stripping is a novel approach to H- charge exchange that overcomes long-standing limitations associated with the traditional, foil-based method of producing high-intensity, time-structured beams of protons. This paper reports on the first successful demonstration of the laser stripping technique for microsecond duration beams. The experiment represents a factor of 1000 increase in the stripped pulse duration compared with the previous proof-of-principle demonstration. The central theme of the experiment is the implementation of methods to reduce the required average laser power such that high efficiency stripping can be accomplished for microsecond duration beams using conventional laser technology. The experiment was performed on the Spallation Neutron Source 1 GeV H- beam using a 1 MW peak power UV laser and resulted in ~95% stripping efficiency.

Development and performance test of a new high power RF window in S-band PLS-II LINAC

A prototype of RF window was developed in collaboration with the Pohang Accelerator Laboratory (PAL) and domestic companies. High power performance tests of the single RF window were conducted at PAL to verify the operational characteristics for its application in the Pohang Light Source-II (PLS-II) linear accelerator (Linac). The tests were performed in the in-situ facility consisting of a modulator, klystron, waveguide network, vacuum system, cooling system, and RF analyzing equipment. The test results with Stanford linear accelerator energy doubler (SLED) have shown no breakdown up to 75 MW peak power with 4.5 μs RF pulse width at a repetition rate of 10 Hz. The test results with the current operation level of PLS-II Linac confirm that the RF window well satisfies the criteria for PLS-II Linac operation.

Instrumental development of a quasi-relativistic ultrashort electron beam source for electron diffractions and spectroscopies.

A stable femtosecond electron beam system has been configured for time-resolved pump-probe experiments. The ultrafast electron diffraction (UED) system is designed with a sub-MeV photoelectron beam source pulsed by a femtosecond UV laser and nondispersive beamline components, including a bunch compressor-a pulsed S-band klystron is installed and fully commissioned with 5.5 MW peak power in a 2.5 μs pulse length. A single-cell RF photo-gun is designed to produce 1.6-16 pC electron bunches in a photoemission mode with 150 fs pulse duration at 0.5-1 MeV. The measured RF system jitters are within 1% in magnitude and 0.2° in phase, which would induce 3.4 keV and 0.25 keV of ΔE, corresponding to 80 fs and 5 fs of Δt, respectively. Our particle-in-cell simulations indicate that the designed bunch compressor reduces the time-of-arrival jitter by about an order of magnitude. The transport and focusing optics of the designed beamline with the bunch compressor enables an energy spread within 10-4 and a bunch length (electron probe) within <500 fs. In this paper, the design analysis and instrumental test results are presented along with the development of the quasi-relativistic UED system.

Functional doping of acrylic PMMA with photochromic dyes

Work from Poland has studied the thermodynamic and kinetic stability of PMMA when doped with a photochromic dye molecule. Visible light absorption is induced in fabricated photochromic PMMA fibres for optoelectronic device applications. PMMA fibres doped in local regions with Bis-MSB under UV irradiation. Molecular switches are molecules that display a binary response when exposed to specific conditions or stimuli. A common example of this is a structural change in molecular switch materials when exposed to UV radiation. This means that meta-stable, higher-energy structural orientations of a molecule can appear under UV irradiation. A switching phenomenon between low- and high-energy geometries is often fully reversible making these systems suitable for use in several applications including optical switches, attenuators, holograms, optical memory, and smart textiles. The chemical structure of Photochromic Bis-MSB incorporated into PMMA fibres. PMMA, poly(methyl methacrylate), is a transparent thermoplastic material that is versatile, strong and recyclable. PMMA optical fibres offer numerous benefits, including high flexibility and numerical aperture, low production cost, and good biocompatibility. A current limitation of PMMA fibres compared to optically active silica fibres is relatively high optical absorption in the visible and near infrared region of the electromagnetic spectrum. The incorporation of photosensitive dyes introduces additional absorption bands and increases the frequencies of light that are absorbed by the material. A common photochromic dye, 1,4-bis(2-methylstyryl)benzene (Bis-MSB), displays high transmittance in the visible region of the electromagnetic spectrum. Bis-MSB also behaves as a molecular switch when exposed to light, where its geometry is changed from linear (cis) to bent (trans) configurations following bond rotation. Thus, incorporating Bis-MSB into PMMA creates a coloured material with controllable and reversible broad-range light absorption. Coloured photoresponsive materials that are transparent, such as Bis-MSB doped PMMA, are favourable polymer materials for organic electronics as they efficiently absorb light within a useful region of the electromagnetic spectrum. In this issue of Electronics Letters, Dr Piotr Miluski and colleagues at Bialystok University of Technology, Poland, fabricate Bis-MSB-doped PMMA and report the optical transmission properties and kinetic relaxation lifetimes of this unique material. Following fabrication of the Bis-MSB PMMA fibres, the samples were exposed to high-energy UV radiation with a 1 MW peak power at 355 nm laser. A colour change was immediately observed, which visibly demonstrates the molecular structural switch of Bis-MSB under UV radiation. A comparison of light transmission between the undoped fibres and the Bis-MSB-doped PMMA fibres is made in the paper. This comparison shows the frequency change of light absorption due to the presence of the dopant molecules and demonstrates that the dopant induces wideband visible light absorption between 400–670 nm. This range of wavelengths is of particular interest for solar cell applications. Thermal relaxation was shown to lead to the decolouration of the fabricated polymer fibres, which was further supported by measured relaxation times in an analysis of the kinetic properties of the system. Long relaxation times can be useful for UV indicators and optical memory systems. The “Main advantage of (Bis-MSB) doped PMMA is that it offers high transmittance of its lower energy form in the VIS spectrum range” said Miluski. The ability to harness and modulate the optical properties of a molecule and control its free-volume as it rotates from linear to bent is well demonstrated within this paper. The development of organic-based functional materials for optical fibre technology introduces some limitations, including organic breakdown at high temperatures, solvent evaporation and low thermal conductivity of polymers. Moreover, the dopant distribution and polymer host homogeneity have to be carefully controlled to ensure a continuous optical response throughout the material. Recent research developments in the field of smart organic materials offer new functional properties that do not suffer from the described disadvantages. Low-energy consumption of organic devices offers significant advantages over well-developed silicon-based electronics. In the field of photochromic polymers, one of the main challenges is the ability to modulate high-frequency optical properties. Dr Miluski predicts that photochromic PMMA fibres will be appropriate for use in real-time holograms and for optical radiation modulation in telecommunication applications. Ultra-stable cis/trans isomerisation is also strongly desired in the field of logical gates and optical memory, where the use of photo-responsive PMMA fibres could offer both lower power consumption and higher storage density.

MW peak power Er/Yb-doped fiber femtosecond laser amplifier at 1.5 µm center wavelength

An erbium (Er)/ytterbium (Yb) co-doped double-clad fiber is configured to amplify single-mode pulses with a high average power of 10 W at a 1.5 µm center wavelength. The pulse duration at the exit of the Er/Yb fiber amplifier is measured to be ~440 fs after grating-based compression. The whole single-mode operation of the amplifier system permits the M2-value of the output beam quality to be evaluated better than 1.05. By tuning the repetition rate from 100 MHz down to 600 kHz, the pulse peak power is scaled up to 19.1 MW to be the highest ever reported using an Er/Yb single-mode fiber. The proposed amplifier system is well suited for strong-power applications such as free-space LIDAR, non-thermal machining and medical surgery.

A low-power reversible alkali atom source

An electrically controllable, solid-state, reversible device for sourcing and sinking alkali vapor is presented. When placed inside an alkali vapor cell, both an increase and decrease in the rubidium vapor density by a factor of two are demonstrated through laser absorption spectroscopy on 10–15 s time scales. The device requires low voltage (5 V), low power (&amp;lt;3.4 mW peak power), and low energy (&amp;lt;10.7 mJ per 10 s pulse). The absence of oxygen emission during operation is shown through residual gas analysis, indicating that Rb is not lost through chemical reaction but rather by ion transport through the designed channel. This device is of interest for atomic physics experiments and, in particular, for portable cold-atom systems where dynamic control of alkali vapor density can enable advances in science and technology.

1.56 µm sub-microjoule femtosecond pulse delivery through low-loss microstructured revolver hollow-core fiber

We report for the first time, to the best of our knowledge, on ~1 MW peak power femtosecond pulse delivery through ≈10 m-long air-filled microstructured revolver hollow-core fiber (RHCF) in the telecom spectral band near 1.56 µm wavelength. We have developed a high-power all-fiber master oscillator power amplifier source based on the novel large-mode area erbium-doped double-clad fiber with 980 nm multi-mode diode pumping that emits up to 530 nJ pulses shorter than 400 fs with 1.42 W maximum average power. These pulses have been further launched into low-loss (<30 dB km−1) RHCF with eight non-touched cylindrical capillaries-based cladding and 61 µm core size with more than 80% efficiency. Owing to low dispersion and nonlinearity of the RHCF developed, the output pulse characteristics (spectral and temporal) are close to the input ones for low and moderate pulse energies. However, we have observed significant nonlinear spectral filtering together with pulse shortening (down to 353 fs) at the maximum output average power of 0.94 W. We believe that the system developed may be highly promising for high-precision material processing and other high-energy and high-power laser applications.

3.4 MW峰值功率皮秒光纤激光系统的光谱特性

3.4 MW峰值功率皮秒光纤激光系统的光谱特性

1.57 MW peak power pulses generated by a diode-pumped Q-switched Nd:LuAG ceramic laser

The pulse characteristics of a laser diode dual-end-pumped electro-optic Q-switched Nd:LuAG ceramic laser at various repetition rates are presented. The largest output pulse energy of 11 mJ is realized at the repetition rate of 100 Hz with pump energy of 84.3 mJ, and the slope efficiency in respect to pump pulse energy is 18.6%. The single pulse peak power reaches up to 1.57 MW. Using Nd:LuAG ceramic as the amplification medium seeded by an Nd:YAG laser of 5.2 mJ, a 10.3 mJ amplified pulse is obtained with pump pulse energy of 42.8 mJ, corresponding to an extraction efficiency of 11.9%.