Ultrahigh Intensity Research Articles

Enhancing the bioactivity of melt electrowritten PLLA scaffold by convenient, green, and effective hydrophilic surface modification

As an emerging additive manufacturing (AM) technique, melt electrospinning writing (MEW) is used to fabricate three-dimensional (3D) submicron filament-based scaffolds with adjustable pore size and customized structure for bone regeneration. Poly(L-lactic acid) (PLLA) scaffold with excellent biodegradability and biocompatibility is first successfully manufactured using our self-assembled MEW device. However, the ultralow cell affinity and poor bioactivity severely hamper their practical applications in bone tissue engineering. These issues are caused by the severe inherent biologically inert, hydrophobicity as well as the smooth surface of the MEW PLLA filaments. In this study, a green and robust alkaline method is applied to modify the scaffold surface and to improve the bioactivity of the MEW PLLA scaffold. Without deterioration in mechanical property but robust surface hydrophilicity, the optimal MEW PLLA scaffold shows promoted surface roughness, enhanced filament tensile modulus (~ 2 folds of the as-prepared sample), and boosted crystallizability (ultrahigh WAXD intensity). Moreover, after being cultured with KUSA-A1 cells, the 0.5 M NaOH, 2 h treated MEW PLLA scaffold exhibits higher osteoinductive ability and increased immature bone tissue amounts (3 times of controlled scaffold). Thus, the flexible surface functionalization by the specific alkaline treatment was found to be an effective method for the preparation of bioactivated MEW PLLA scaffolds with promoted bone regeneration.

Ultra-high intensity lasers as tools for novel physics

Ultra-high intensity lasers as tools for novel physics

A tunable color filter using a hybrid metasurface composed of ZnO nanopillars and Ag nanoholes.

We propose the design of symmetrical and asymmetrical tunable color filters (TCFs) by using hybrid metasurface nanostructures in the visible wavelength range. They are composed of circular zinc oxide (ZnO) nanopillars and silver (Ag) nanoholes on a silica substrate. These TCFs exhibit ultrahigh transmission intensity over 90%, different tuning ranges, and polarization-dependent/independent characteristics. By changing the distance between the ZnO nanopillars and silica substrate, the resonant wavelength of TCFs could be tuned remarkably. Moreover, we also demonstrate the stability of TCFs under different disturbances and angles of incident light. Furthermore, the resonant wavelengths are red-shifted by increasing the ambient refraction index. TCFs exhibit great tunability and ultrahigh transmission intensity up to 100%. This design opens up an avenue to widespread optoelectronic applications, such as ultrahigh resolution color displays, high-efficiency biosensors, pressure sensors, and selective color filters.

Ultra-High Intensity Temporally Oscillatory Optical Kerr Effect in Carbon Disulfide Arising from Electronic and Molecular Distortions

Ultra-High Intensity Temporally Oscillatory Optical Kerr Effect in Carbon Disulfide Arising from Electronic and Molecular Distortions

Prospects for High Repetition Rate Ultrashort Pulsed Ultra-High Intensity Lasers −Development of High Repetition Rate and High Pulse Energy Laser−

Prospects for High Repetition Rate Ultrashort Pulsed Ultra-High Intensity Lasers −Development of High Repetition Rate and High Pulse Energy Laser−

QED effects on high-order harmonic generation from ultraintense laser-irradiated solid-plasmas

High-order harmonic generation (HHG) from relativistically intense laser irradiation of solid-density plasmas provides novel coherent light sources in the extreme-ultraviolet (XUV) to x-ray spectral region with attosecond duration and high intensity even toward the Schwinger limit. However, whether the HHG process and mechanism are effective at extremely high laser intensities in the QED-plasma regime remains unclear, since QED processes, such as discrete synchrotron radiation, quantum radiation reaction, and pair creation, would change the energy partition and particle dynamics. In this work, through particle-in-cell simulations, we numerically demonstrate that the HHG process with the relativistically oscillating mirror mechanism can be scaled to an ultrahigh intensity level of 1024 W/cm2. The high harmonic spectrum, attosecond pulses, and conversion efficiency are not significantly affected by the QED processes. This result is of great benefit to the generation of coherent XUV and x-ray light sources with higher intensity, higher cutoff frequency, and shorter duration.

Positive temperature coefficient (PTC) materials based on amorphous poly(methyl methacrylate) with ultrahigh PTC intensity, tunable switching temperature and good reproducibility

Positive temperature coefficient (PTC) materials based on amorphous polymers usually suffer from low intensity owing to their relatively small volume thermal expansion. Herein, graphene nanoplatelets (GNPs) and carbon fibers (CF) with large aspect ratios were introduced into amorphous poly(methyl methacrylate) (PMMA) via melting mixing followed by hot pressing to improve the PTC characteristics of the conductive composites. The binary PMMA/GNPs composites showed good reproducibility while the PMMA/CF composites were superior in PTC intensity and their switching temperature (positive to negative temperature coefficient) could be tuned by varying the CF concentrations. When the both binary composites were connected in series, their strengths could be fostered and their weaknesses could be circumvented. The ternary composite exhibited a superior PTC intensity of 7.17, outperforming most of the reported PTC materials. These composites have great potential for applications as temperature sensors and current limiting devices.

Kilo-Tesla axial magnetic field generation with high intensity spin and orbital angular momentum beams

Absorption of angular momentum from a high intensity laser pulse can lead to the generation of strong axial magnetic fields in plasma. The effect, known as the inverse Faraday effect, can generate kilo-Tesla strength, multipicosecond, axial magnetic fields extending over hundreds of microns in underdense plasma. In this paper we explore the effect with ultrahigh intensity circularly polarized Gaussian beams and linearly polarized orbital angular momentum beams comparing analytic expressions with three-dimensional particle-in-cell simulations. We develop a model for the transverse magnetic field profiles, introduce a model for the temporal decay, and show that while the magnetic field strength is independent of plasma density, it has a strong dependence on the laser beam waist.

General biotemplating of hierarchically ultra-vesicular microspheres for superior microwave absorption

The vesicular structure has elicited increasing interest in the field of lightweight microwave absorption (MA) materials. However, few methods exist to integrate both micro- and nanoscale vesicles within one nanoarchitecture. Herein, the high-yield and green biotemplate method is developed for the general synthesis of hierarchically ultra-vesicular microspheres (HUVMs), consisting of a hollow configuration and numerous multi-sized bubbles inside. HUVMs of metal oxides (SnO2, Co3O4, Fe2O3, and Mn2O3), their combinations, and magnetic metals (Co and CoNi) have been successfully prepared. Their synergistic multi-sized vesicles simultaneously enhance dielectric loss capacity by space charge polarization and satisfy impedance matching by large cavities, proved by electron holography. Eventually, both the SnO2 and Co HUVMs demonstrate first-rank MA performance covering almost the whole bandwidth from 2 to 18 GHz with ultrahigh absorption intensity beyond –40.0 dB. These achievements provide a new avenue for precise manipulation of ultra-porous structure and foreshadow an important direction of lightweight absorbents.

Effects of doping content and crystallite size on luminescence properties of Eu3+ doped fluorapatites obtained from natural waste

In this study, Eu 3+ doped natural fluorapatites [Ca 10 (PO 4 ) 6 F 2 :xEu 3+ (x = 0.1, 0.3 and 0.5)] were produced from a natural waste by solid-state powder synthesis, conventional sintering, and spark plasma sintering techniques. The effects of doping content and crystallite size on luminescence properties of fluorapatite were investigated by XRD, SEM, and PL analysis. The obtained results showed that luminescence emission's intensity significantly increased with doping content, but no effect was observed on the density and crystallite size. For the samples produced with different methods, emission intensity was the lowest for sintered samples by SPS (1150 °C, 10 min, 50 MPa) with the smallest crystalline size. In contrast, emission intensity was found much higher for synthesized powders with the largest crystallite size. Furthermore, upon excitation under UV radiation, the Eu doped fluorapatites demonstrated the characteristic 5 D 0 – 7 F 2 and 5 D 0 – 7 F 4 emission lines of Eu 3+ at 618 nm and 704 nm (red region) with an ultrahigh intensity that has been firstly observed in the literature. Therefore, Eu doped fluorapatites, quickly produced from a natural waste in an eco-friendly and cost-effective way, carry a potential to be used in biological applications and lightning applications.

Effects of sintering temperature and doping content on luminescence properties of rare earth (Sm+3, Eu3+, and Dy3+) doped natural fluorapatite

Fluorapatite (FAP), thermally and chemically stable, has a suitable host structure for rare earth elements (REE). Rare-earth elements doped hydroxyapatite and fluorapatite have been known for a long time and have been studied extensively in industry and literature. In this study, REE doped natural fluorapatites (Ca10(PO4)6F2:xLn3+ (where x ​= ​0.5 ​mol for 1-mol FAP and Ln3+: Sm+3, Eu3+, and Dy3+) sintered at 1150 ​°C for 1 ​h. In addition, Ca10(PO4)6F2:xEu3+ (x ​= ​0.1, 0.5 and 1 ​mol for 1-mol FAP) was also conventionally sintered at 1100 ​°C, 1150 ​°C and 1200 ​°C. XRD, FTIR, SEM, and PL analysis investigated the phase evolution, microstructural development, and luminescence properties of the RE-doped FAP structure. No significant change in XRD and FTIR analysis results was observed with the addition of different rare-earth elements to natural fluorapatite compared to undoped natural fluorapatite. The emission spectra of Sm doped FAP, Eu doped FAP, and Dy doped FAP were recorded with an excitation wavelength of 407 ​nm, 281 ​nm, and 389 ​nm, and the strongest emissions were observed at 608 ​nm, 614 ​nm, and 578 ​nm, respectively. The emission intensity of Eu-doped fluorapatites increases with increasing sintering temperature. On the other hand, the emission intensity does not directly increase with the increasing doping content. The highest luminescent intensity was observed for Ca10(PO4)6F2:1Eu3+ sintered at 1200 ​°C in the red region upon excitation under UV radiation. In this study, ultra-high intensity luminescent materials that emit green and orange light were produced by doping Dy3+ and Sm3+ ions, respectively, for the first time to natural fluorapatite. The luminescent FAPs, produced from waste in an eco-friendly way, can be used in LED and bioimaging applications.

Experimental study of knock combustion and direct injection on knock suppression in a high compression ratio methanol engine

Methanol is a competitive low-carbon fuel for spark ignition engines. Though it has higher knock resistance than gasoline fuel, knocking combustion is still an obstacle for the application of methanol in spark ignition engines with relatively higher compression ratios. In this work, experimental investigations into knocking combustion and suppression were conducted on a single-cylinder, naturally aspirated, SI engine with a compression ratio of 15. Firstly, the knocking characteristics of the methanol engine with stoichiometric mixture under port fuel injection mode were evaluated. Results showed that knocking combustion occurred under medium and high loads. Especially, under the condition of indicated mean effective pressure (IMEP) = 0.7 MPa, some random heavy knock cycles with ultra-high knock intensity were observed. The frequency of heavy knock was 2.5% and the highest maximum amplitude of pressure oscillations reached 2.39 MPa. This heavy knock was similar to the super-knock phenomenon in boosted direct injection gasoline engines, and it can not be eliminated by retarding spark timing or adopting fuel-lean combustion. Then, the mechanism of the heavy knock was studied by thermodynamic condition analysis. Results showed that the heavy knock was triggered by pre-ignition which was induced by some hot spots in the combustion chamber. Finally, to make the best use of the charge cooling effect, the methanol direct injection strategy was applied to suppress the knocking combustion. When the engine worked with full opening throttle and adopt a single injection, the maximum knock intensity decreased to 0.43 MPa×°CA at −350 °CA ATDC start of injection which was 5.1% of the maximum value during port fuel injection mode. With the co-optimization of the start of injection and spark timing, the engine with a stoichiometric mixture could operate within the knock intensity limit at full load. Under this operating condition, the crank angle of 50% mass fraction burned located at 12 °CA ATDC and IMEP = 1.05 MPa was achieved. What’s more, adopting the optimal split injection instead of a single injection, the knock intensity was further reduced by 14.3% with a slight reduction of 0.02 MPa in IMEP.

Quantum Electrodynamics vacuum polarization solver

The self-consistent modeling of vacuum polarization due to virtual electron-positron fluctuations is of relevance for many near term experiments associated with high intensity radiation sources and represents a milestone in describing scenarios of extreme energy density. We present a generalized finite-difference time-domain solver that can incorporate the modifications to Maxwell’s equations due to vacuum polarization. Our multidimensional solver reproduced in one-dimensional configurations the results for which an analytic treatment is possible, yielding vacuum harmonic generation and birefringence. The solver has also been tested for two-dimensional scenarios where finite laser beam spot sizes must be taken into account. We employ this solver to explore different types of laser configurations that can be relevant for future planned experiments aiming to detect quantum vacuum dynamics at ultra-high electromagnetic field intensities.

Strong interplay between superluminosity and radiation friction during direct laser acceleration

Using a test-particle model, we examine direct laser acceleration of electrons within a magnetic filament that has been shown to form inside a laser-irradiated plasma. We focus on ultra-high intensity interactions where the force of radiation friction caused by electron emission of electromagnetic radiation must be taken into account. It is shown that even relatively weak superluminosity of laser wave fronts—the feature that has been previously neglected—qualitatively changes the electron dynamics, leading to a so-called attractor effect. As a result of this effect, electrons with various initial energies reach roughly the same maximum energy and emit roughly the same power in the form of x-rays and gamma-rays. Our analysis implies that the primary cause of the superluminosity is the laser-heated plasma. The discovered strong interplay between superluminosity and radiation friction is of direct relevance to laser-plasma interactions at high-intensity multi-PW laser facilities.

Key parameters for surface plasma wave excitation in the ultra-high intensity regime

Ultra-short high-power lasers can deliver extreme light intensities (≥1020 W/cm2 and ≤30 fs) and drive large amplitude Surface Plasma Wave (SPW) at over-dense plasma surface. The resulting current of energetic electron has great interest for applications, potentially scaling with the laser amplitude, provided that the laser–plasma transfer to the accelerated particles mediated by SPW is still efficient at ultra-high intensity. By means of particle-in-cell simulations, we identify the best condition for SPW excitation and show a strong correlation between the optimum surface plasma wave excitation angle and the laser's angle of incidence that optimize the electron acceleration along the plasma surface. We also discuss how plasma density and plasma surface shape can be adjusted in order to push to higher laser intensity the limit of surface plasma wave excitation. Our results open the way to new experiments on forthcoming multi-petawatt laser systems.

A Self-Diffraction Temporal Filter for Contrast Enhancement in Femtosecond Ultra-High Intensity LaserSupported by the National Natural Science Foundation of China (Grant Nos. 11774410 and 91850209), and the Strategic Priority Research Program of CAS (Grant No. XDB16030200).

We demonstrated a nonlinear temporal filter based on the self-diffraction (SD) process. Temporal contrast enhancement, angular dispersion and spectrum broadening properties of the SD process are investigated in experiment and simulation. Driven by spectral phase well compensated laser pulses with bandwidth of 28 nm, the filter produced clean pulses with a temporal contrast higher than 1010 and excellent spatial profile, the spectrum of which was smoothed and broadened to 64 nm. After implementing this filter into a home-made 30 TW Ti:sapphire amplifier, temporal contrast of the amplified pulses was enhanced to 1010 within the time scale of –400 ps.

Fabrication of ZnO-nanowire-coated thin-foil targets for ultra-high intensity laser interaction experiments

The coupling of ultra-intense, ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum–solid interface and is usually quite low. However, laser absorption can be enhanced via micro or nanopatterning of the target surface. Depending on the laser features and target geometry, conditions can be optimized for the generation of hot dense matter, which can be used to produce high-brightness radiation sources or even to accelerate particles to relativistic energies. In this context, ZnO nanowires were grown on metallic, thin-foil targets. The use of a thin-foil substrate was dictated by the need to achieve proton acceleration via target normal sheath acceleration at the rear side. The chemical process parameters were studied in-depth to provide control over the nanowire size, shape, and distribution. Moreover, the manufacturing process was optimized to provide accurate reproducibility of key parameters in the widest possible range and good homogeneity across the entire foil area.

Proposal and design of an 81.25 MHz interdigital H-mode dual-beam drift tube linac

A novel type dual-beam drift tube linac (DB-DTL) was proposed at the Institute of Modern Physics for ultra-high intensity heavy-ion acceleration. With two identical beam apertures located in the vertical direction with the same off-set from the cavity axis, two beams could be accelerated simultaneously by the DB-DTL and then be merged to one, thus double the current beam intensity limit, which is of great significance for ultra-high intensity heavy-ion acceleration. An 81.25 MHz proof-of-principle cavity was developed to demonstrate this new concept. Designed and optimized with the alternative phase focusing (APF) scheme, this prototype cavity was supposed to accelerate 10 mA protons beam from 0.56 MeV to 2.5 MeV in one meter with transmission efficiency more than 90%. Inter-digital H-mode (IH) structure was adopted by this DB-DTL, thus high shunt impedance could be achieved which significantly reduce the power loss. With efficient cooling, this cavity was capable to work at the pulsed mode with a maximum duty cycle of 10%. Beam dynamics simulations, electromagnetic design and optimization of the prototype cavity, and multi-physics analyses of this DB-DTL will be presented in this paper.

Single-shot spatiotemporal characterization of a multi-PW laser using a multispectral wavefront sensing method.

The single-shot spatiotemporal characterization of an ultrahigh intensity laser pulse was performed using a multispectral wavefront sensor. For the measurement of the spatio-spectral electric field, a femtosecond laser pulse was spectrally modulated and separated by a Fabry-Perot etalon coupled with a grating pair, and its spatio-spectral electric field was measured with a wavefront sensor. The spatiotemporal electric field was reconstructed from the measured spatio-spectral electric field of a multi-PW laser pulse. We found that the spatiotemporal distortion could reduce the focused laser intensity by 15%, compared to the case of a diffraction-limited and transform-limited laser pulse.

Super-Heavy Ions Acceleration Driven by Ultrashort Laser Pulses at Ultrahigh Intensity

Laser ion acceleration driven by the utmost intense laser pulses pushes superheavy gold ions to unprecedented energies, key for applications ranging from nuclear physics to next-generation accelerators.