High-energy-density electron beam generation in ultra intense laser-plasma interaction

By using a two-dimensional particle-in-cell simulation,we demonstrate a scheme for highenergy-density electron beam generation by irradiating an ultra intense laser pulse onto an aluminum（Al） target.With the laser having a peak intensity of 4×10^23W cm^-2,a high quality electron beam with a maximum density of 117 nc and a kinetic energy density up to8.79×10^18J m^-3 is generated.The temperature of the electron beam can be 416 Me V,and the beam divergence is only 7.25°.As the laser peak intensity increases（e.g.,1024 W cm^-2）,both the beam energy density（3.56×10^19J m^-3） and the temperature（545 Me V） are increased,and the beam collimation is well controlled.The maximum density of the electron beam can even reach 180 nc.Such beams should have potential applications in the areas of antiparticle generation,laboratory astrophysics,etc.

Advanced Concept Ramjet Propulsion System Utilizing In-Situ Positron Antimatter Derived from Ultra-Intense Laser with Fundamental Performance Analysis

The fundamental performance analysis of an advanced concept ramjet propulsion system using antimatter is presented. Antimatter is generated by ultra-intense laser pulses incident on a gold target. The scientific foundation for the generation of antimatter by an ultra-intense laser was established in the early 1970’s and later demonstrated at Lawrence Livermore National Laboratory from 2008 to 2009. Antimatter on the scale of 2 × 1010 positrons were generated through a ~1 ps pulse from the Lawrence Livermore National Laboratory Titan laser that has an intensity of ~1020 W/cm2. The predominant mechanism is the Bethe-Heitler process, which involves high-energy bremsstrahlung photons as a result of electron-nuclei interaction. Propulsion involving lasers through chemical rather than non-chemical interaction has been previously advocated by Phipps. The major utilities of the ultra-intense laser derived antimatter ramjet are the capability to generate antimatter without a complex storage system and the ability to decouple the antimatter ramjet propulsion system from the energy source. For instance the ultra-intense laser and energy source could be terrestrial, while the ramjet could be mounted to a UAV as a propulsion system. With the extrapolation of current technologies, a sufficient number of pulses by ultra-intense lasers are eventually anticipated for the generation of antimatter to heat the propulsive flow of a ramjet. Fundamental performance analysis is provided based on an ideal ramjet derivation that is modified to address the proposed antimatter ramjet architecture.

Fundamental Architecture and Analysis of an Antimatter Ultra-Intense Laser Derived Pulsed Space Propulsion System

Antimatter has been generated in large quantities by the Lawrence Livermore National Laboratory Titan laser. The Titan laser is an ultra-intense laser system on the order of approximately 1020W/cm2 with pulse durations of roughly 1ps. With the Titan laser incident on a high atomic number target, such as gold, antimatter on the scale of 2 × 1010 positrons are generated. Roughly 90% of the generated positrons are ejected anisotropic and aft to the respective target. The mechanisms for the laser-derived positron antimatter generation involve electron interaction with the nuclei based on bremsstrahlung photons that yield electron-positron pairs as a consequence of the Bethe-Heitler process, which predominates the Trident process. Given the constraints of the current and near future technology space, a pulsed space propulsion configuration is advocated for antimatter derived space propulsion, similar in concept to pulsed radioisotope propulsion. Antimatter is generated through an ultra-intense laser on the scale of a Titan laser incident on a gold target and annihilated in a closed chamber, representative of a combustion chamber. Upon reaching a temperature threshold, the closed chamber opens, producing a pulse of thrust. The implication of the pulsed space propulsion antimatter architecture is that the energy source for the antimatter propulsion system can be decoupled from the actual spacecraft. In contrast to conventional chemical propulsion systems, which require storage of its respective propulsive chemical potential energy, the proposed antimatter propulsion architecture may have the energy source at a disparate location from the spacecraft. The ultra-intense laser could convey its laser energy over a distance to the actual spacecraft equipped with the positron antimatter pulsed space propulsion system. Hydrogen is considered as the propulsive fluid, in light of its low molecular weight. Fundamental analysis is applied to preliminarily define the performance of the positron antimatter derived pulsed space propulsion system. The fundamental performance analysis of the antimatter pulsed space propulsion system successfully reveals the architecture is viable for further evaluation.

Proton Acceleration Driven by High-Intensity Ultraviolet Laser Interaction with a Gold Foil

Proton acceleration induced by a high-intensity ultraviolet laser interaction with a thin foil target was studied on an ultra-short KrF laser amplifier called LLG50 in China Institute of Atomic Energy （CIAE）. The ultraviolet laser produced pulses with a high-contrast of 109, duration of 500 fs and energy of 30 mJ. The p-polarized laser was focused on a 2.1 #m gold foil by an off-axis parabola mirror （OAP） at an incident angle of 45°. The laser intensity was 1.2× 1017 W/cm2. The divergence angle for proton energy of 265 keV or higher was 30°, which was recorded by a CR39 detector covered with 2 μm aluminum foil in the target normal direction. The maximum proton energy recorded by a CR39 detector covered with a 4 μm aluminum foil was 440 keV, and the proton energy spectrum was measured by a proton spectrometer. The ultraviolet laser acquires a relatively lower hot electron temperature, which can be ascribed to the proportional relationship of Iλ2, but a higher hot electron density because of the higher laser absorption and critical density. Higher electron density availed to strengthen the sheath electric field, and increased the proton acceleration.

Fundamental Architecture and Performance Analysis of Photofission Pulsed Space Propulsion System Using Ultra-Intense Laser

Photofission enables a unique capability for the domain of non-chemical space propulsion. An ultra-intense laser enables the capacity to induce nuclear fission through the development of bre- msstrahlung photons. A fundamental architecture and performance analysis of a photofission pulsed space propulsion system through the operation of an ultra-intense laser is presented. A historical perspective of previous conceptual nuclear fission propulsion systems is addressed. These applications use neutron derived nuclear fission;however, there is inherent complexity that has precluded further development. The background of photofission is detailed. The conceptual architecture of photofission pulsed space propulsion and fundamental performance parameters are established. The implications are the energy source and ultra-intense laser can be situated far remote from the propulsion system. Advances in supporting laser technologies are anticipated to increase the potential for photofission pulsed space propulsion. The fundamental performance analysis of the photofission pulsed space propulsion system indicates the architecture is feasible for further evaluation.

Effect of Lorentz local field correction on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (PNA) molecules

This paper investigates the effect of Lorentz local field correction （LFC） on the propagation of ultrashort laser pulses in a para-nitroaniline molecular medium under resonant and nonresonant conditions by solving numerically the full-wave Maxwell-Bloch equations beyond slowly-varying envelope approximation and rotating-wave approximation. The effect of the LFC is considerably obvious when pulses with large areas propagate in the dense molecular medium. In the case of resonance, the group velocity of the sub-pulses split from the incident pulse along propagation is severely decreased by the LFC, especially for the latest sub-pulse. However, in the case of nonresonance, the influence of the LFC on the temporal evolution of the pulse is less obvious and lacks homogeneity with an increase in incident pulse area, propagation distance and molecular density.

Project New Orion: Pulsed Nuclear Space Propulsion Using Photofission Activated by Ultra-Intense Laser

Project New Orion entails a pulsed nuclear space propulsion system that utilizes photofission through the implementation of an ultra-intense laser. The historical origins derive from the endeavors of Project Orion, which utilized thermonuclear devices to impart a considerable velocity increment on the respective spacecraft. The shear magnitude of Project Orion significantly detracts from the likelihood of progressive research development testing and evaluation. Project New Orion incorporates a more feasible pathway for the progressive research development testing and evaluation of the pulsed nuclear space propulsion system. Photofission through the application of an ultra-intense laser enables a much more controllable and scalable nuclear yield. The energy source for the ultra-intense laser is derived from a first stage liquid hydrogen and liquid oxygen chemical propulsion system. A portion of the thermal/kinetic energy of the rocket propulsive fluid is converted to electrical energy through a magneto-hydrodynamic generator with cryogenic propellant densification for facilitating the integral superconducting magnets. Fundamental analysis of Project New Orion demonstrates the capacity to impart a meaningful velocity increment through ultra-intense laser derived photofission on a small spacecraft.

Microstructure and Mechanical Properties of Aer Met 100 Ultra-high Strength Steel Joints by Laser Welding

AerMet100 ultra-high strength steel plates with a thickness of 2 mm were welded using a COz laser welding system. The influences of the welding process parameters on the morphology and microstructure of the welding joints were investigated, and the mechanical property of the welding joints was analyzed. The experimental results showed that the fusion zone of welding joint mainly consisted of columnar grains and a fine dendrite substructure grew epitaxially from the matrix. With the other conditions remaining unchanged, a finer weld microstructure was along with the scanning speed increase. The solidification microstructure gradually transformed from cellular crystal into dendrite crystal and the spaces of dendrite secondary arms rose from the fusion line to the center of the fusion zone. In the fusion zone of the weld, the rapid cooling caused the formation of martensite, which led the microhardness of the fusion zone higher than that of the matrix and the heat affected zone. The tensile strength of the welding joints was tested as 1 700 MPa, which was about 87% of the matrix. However, the tensile strength of the welding joints without defects existed was tested as 1832 MPa, which was about 94% of the matrix.

Structure Character of M-A Constituent in CGHAZ of New Ultra-Low Carbon Bainitic Steel under Laser Welding Conditions

800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.

Numerical studies on pair production in ultra-intense laser interaction with a thin solid-foil

A theoretical and numerical model of photon and electron–positron pair production in strong-field quantum electrodynamics（QED） is described. Two processes are contained in our QED theoretical model, one is photon emission in the interaction of ultra-intense laser with relativistic electron（or positron）, and the other is pair production by a gamma-ray photon interacting with the laser field.This model has been included in a PIC/MCC simulation code named BUMBLEBEE 1 D, which is used to simulate the laser plasma interaction. Using this code, the evolutions of electron–positron pair and gamma-ray photon production in ultra-intense laser interaction with aluminum foil target are simulated and analyzed. The simulation results revealed that more positrons are moved in the opposite direction to the incident direction of the laser under the charge separation field.

Effect of Foil Target Thickness in Proton Acceleration Driven by an Ultra-Short Laser

Proton acceleration experiments were carried out by a 1.2× 1018 W/cm2 ultra-short laser interaction with solid foil targets. The peak proton energy observed from an optimum target thickness of 7 μm in our experiments was 2.1 MeV. Peak proton energy and proton yield were investigated for different foil target thicknesses. It was shown that proton energy and conversion efficiency increased as the target became thinner, on one condition that the preplasma generated by the laser prepulse did not have enough shock energy and time to influence or destroy the target rear-surface. The existence of optimum foil thickness is due to the effect of the prepulse and hot electron transportation behavior on the foil target.

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4＇-bis（dimethylamino） stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.

Study on Ultra-Short Laser Pulse Ablation of Metals by Molecular Dynamics Simulation

The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of. atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5 000 m/s in Cu and 7 200 m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.

Self-Thomson Backscattering of Ultra-Intense Laser from Thin Foil Target

An electromagnetic solitary structure in attosecond regime is identified, costreaming with electron bunch. It is observed via nonlinear process of Self-Thomson backscattering of an ultra-intense laser from thin foil target. The process is termed as Self-Thomson Backscattering since the counter propagating electron sheets are generated by the drive laser itself. The radiation pressure acceleration model is considered for the interaction of a super-intense linearly polarized laser pulse with a thin foil in one-dimensional (1D) particle-in-cell (PIC) simulations.

Positron Induced Fusion Pulsed Space Propulsion through an Ultra-Intense Laser

A pulsed space propulsion system using position antimatter to induce Deuterium-Tritium fusion through an ultra-intense laser incident on a gold target is conceptually presented through fundamental performance analysis. As opposed to traditional strategies positron antimatter is considered rather than antiproton antimatter. Positron antimatter can be produced by an ultra- intense laser incident on a high atomic number target, such as gold. The ultra-intense laser production of positron antimatter mechanism greatly alleviates constraints, such as requirements for antimatter storage imperative for antiproton antimatter. Also the ultra-intense laser and associated energy source can be stationary or positioned remote while the pulsed space propulsion system using position antimatter to induce Deuterium-Tritium fusion is in flight. Various mechanisms for antimatter catalyzed fusion are considered, for which the preferred mechanism is the antiproton hotspot ignition strategy. Fundamental performance analysis is subsequently applied to derive positron antimatter generation requirements and associated propulsion performance. The characteristics of the pulsed space propulsion system using position antimatter to induce Deuterium-Tritium fusion through an ultra-intense laser incident on a gold target imply a promising non-chemical propulsion alternative for the transport of bulk cargo to support space missions.

Controlled Fusion Strategy Using Ultra-Intense Laser Derived Positron Generation for Initiation

A controllable strategy for eliciting nuclear fusion is presented through ultra-intenselaser derived positron generation by a conceptual first physics perspective. The capability to generate positrons on demand in a controlled manner through an ultra-intense laser incident on a high atomic number target, such as gold, is the intrinsic core to the foundation of controllable nuclear fusion. Positron antimatter generated from the periphery of the fusion fuel pellet provides the basis for initiating the fusion reaction, which is regulated by controlling the operation of the ultra-intense laser. A dual pulsed Fast Ignition mechanism is selected to achieve the fusion reaction. Based on first physics performance analysis the controllable strategy for eliciting nuclear fusion through ultra-intenselaser derived positron generation offers a realizable means for achieving regulated nuclear fusion. A future perspective of the controllable fusion strategy addresses the opportunities and concerns of a pathway toward regulated nuclear fusion.

Mirror Mapping of Laser Interferometer Measurement System on Ultra-precise Movement Stage

The accuracy and repeatability of the laser interferometer measurement system （LIMS） are often limited by the mirror surface error that comes from the mirror surface shape and distortion. This paper describes a new method to calibrate mirror map on ultraprecise movement stage （UPMS） with nanopositioning and to make a real-time compensation for the mirror surface error by using mirror map data tables with the software algorithm. Based on the mirror map test model, the factors affecting mirror map are analyzed through geometric method on the UPMS with six digrees of freedom. Dam processing methods including spline interpolation and spline offsets are used to process the raw sampling data to build mirror map tables. The linear interpolation as compensation method to make a real-time correction on the stage mirror unflatness is adopted and the correction formulas are illuminated. In this way, the measurement accuracy of the system is obviously improved from 40 nm to 5 nm.

Accuracy design of ultra-low residual reflection coatings for laser optics

Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity（the degree of inhomogeneous is between -0.2 and 0.2） is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is-0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and -0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.

Ultra Q:YAG与传统Nd:YAG激光玻璃体消融术治疗飞蚊症的疗效比较

目的:通过观察Ultra Q∶YAG玻璃体消融术治疗飞蚊症的长期效果,评价Ultra Q:YAG较传统Nd∶YAG激光的治疗优势。方法:回顾性分析2018-05/2020-01于我院确诊为玻璃体混浊并接受激光玻璃体消融术治疗的112例130眼患者的临床资料。所有患者均接受了激光玻璃体消融术治疗,根据不同治疗方法分为A、B两组,A组(60例70眼)接受Ultra Q∶YAG玻璃体消融术治疗;B组(52例60眼)接受传统Nd∶YAG激光治疗。根据患者玻璃体混浊的形态将A、B组各分为两亚组:其中A1组45例52眼和B1组30例38眼,玻璃体混浊形态多为Weiss环、絮状、致密膜状;A2组15例18眼和B2组22例22眼,玻璃体混浊形态多为细点状、丝状、网状。比较治疗前后的BCVA,治疗次数差异及主觉症状改善情况。结果:BCVA:治疗前A1组和A2组、B1组和B2组、A组和B组均无差异(P>0.05);A组和B组在治疗后2wk,1mo时均有差异(P<0.001),A1组和A2组在治疗后1、6、12mo均有差异(P=0.019、0.042、<0.001)。A组患者治疗后的主觉症状改善程度优于B组(P=0.006)。A1组治疗后的主觉症状改善程度优于A2组(P<0.001)。Ultra Q∶YAG比传统Nd∶YAG激光所需的激光治疗次数少(P<0.001)。同一种激光方法,不同玻璃体混浊形态,治疗次数无差异(P>0.05)。结论:Ultra Q∶YAG较传统Nd∶YAG激光进行玻璃体消融治疗飞蚊症,更易于操作、更安全、具有更好的主觉症状改善,尤其是对于伴有Weiss环、絮状、致密膜状混浊物的患者。

超脉冲(UltraPulse)点阵王治疗面部凹陷性瘢痕疗效观察

目的:观察超脉冲点阵王激光治疗面部凹陷性瘢痕的临床疗效。方法:将116例面部凹陷性瘢痕患者随机分为实验组与对照组,实验组:58例,采用超脉冲点阵王激光去除面部瘢痕;对照组:58例,采用微晶磨削术治疗面部瘢痕,比较两组的临床效果。结果:实验组治疗后的疗效优于对照组,差异有统计学意义;术后实验组的疼痛评分、水肿评分低于对照组,红肿持续时间、结痂时间少于对照组。结论:面部凹陷性瘢痕采用超脉冲点阵王激光治疗,具有效果好、不良反应小的特点。