Electron bunch compression and acceleration in the laser wakefield

The compression and acceleration of an external electron bunch into the laser wakefield is studied using 3D modeling with the LAPLAC code and compared to analytical predictions. It is shown, for a laser propagating in a plasma channel, that the nonlinear laser pulse dynamics together with the finite laser spot size influence the electron bunch compression and acceleration due to the reduction of the laser pulse group velocity. The transverse bunch dynamics and loading effect determine the final bunch charge and density and restrict the compressed sizes of the trapped and accelerated electron bunch. The dynamics of the electron bunch are illustrated with a set of parameters where the accelerated bunch acquires an energy of the order of 2 GeV, and 1% energy spread with sub-micron sizes.     

One GeV acceleration with laser wakefield in the linear regime

We derive an expression for the maximum energy gain of an accelerated electron, in the limit that the plasma wave created by a laser wake is linear both along the longitudinal direction and in the transverse plane, and with a maximum laser power lower than the critical power for relativistic self-focusing. With an available power of 300 TW, the energy gain is of 1 GeV.     

Criteria for the optimization of parameters of a multibunch scheme of wakefield acceleration

We propose criteria for the optimization of a wakefield acceleration scheme in a dielectric-lined waveguide structure, which is aimed at increasing the efficiency of energy transfer from the driving to witness (driven) electron bunches with simultaneous increase in the accelerating field gradient. It is suggested to use a multimode acceleration structure excited by a train of short electron bunches profiled in a special manner. The proposed scheme provides for a maximum energy transformer ratio simultaneously with an increase in the wakefield as compared to the values typical of the traditional linear acceleration scheme.     

Inverse free electron lasers and laser wakefield acceleration driven by CO2 lasers

The staged electron laser acceleration (STELLA) experiment demonstrated staging between two laser-driven devices, high trapping efficiency of microbunches within the accelerating field and narrow energy spread during laser acceleration. These are important for practical laser-driven accelerators. STELLA used inverse free electron lasers, which were chosen primarily for convenience. Nevertheless, the STELLA approach can be applied to other laser acceleration methods, in particular, laser-driven plasma accelerators. STELLA is now conducting experiments on laser wakefield acceleration (LWFA). Two novel LWFA approaches are being investigated. In the first one, called pseudo-resonant LWFA, a laser pulse enters a low-density plasma where nonlinear laser/plasma interactions cause the laser pulse shape to steepen, thereby creating strong wakefields. A witness e-beam pulse probes the wakefields. The second one, called seeded self-modulated LWFA, involves sending a seed e-beam pulse into the plasma to initiate wakefield formation. These wakefields are amplified by a laser pulse following shortly after the seed pulse. A second e-beam pulse (witness) follows the seed pulse to probe the wakefields. These LWFA experiments will also be the first ones driven by a CO(2) laser beam.     

Laser Interferometer Gravitational-wave Observatories: An Overview

Abstract

The quest to detect gravitational radiation is on the threshold of a new era. Technological developments in the 1980s have led to the point where it is now possible to design an instrument based on the Michelson interferometer which should not only be able to detect gravity waves but should function as an astronomical observatory. Stimulated by the need for a southern hemisphere facility, the Australian National University in collaboration with the University of Western Australia is poised to enter this exciting field. Here, we will briefly describe the principle of operation of these giant laser interferometers and examine performance limits imposed by the Heisenberg uncertainty principle.     

Laser applications to chemical and environmental analysis: introduction to the feature issue

This issue of Applied Optics features 15 papers that describe laser techniques for measurements in chemical and environmental analysis. Many of these contributions were presented at the Optical Society of America Topical Meeting on Laser Applications to Chemical and Environmental Analysis, held in Santa Fe, New Mexico, 11-13 February 2000.     

Laser applications to chemical and environmental analysis: introduction to the feature issue

This issue of Applied Optics features 16 papers describing chemical and environmental measurements made possible by lasers. Many of these contributions were presented at the Optical Society of America Topical Meeting on Laser Applications to Chemical and Environmental Analysis, held in Orlando, Florida, 9-11 March 1998.     

Laser applications to chemical and environmental analysis: introduction to the feature issue

This issue of Applied Optics features 14 papers that describe recent advances of laser techniques, including instrumentation, application in combustion research, and detection of pollutants. Most of these contributions were presented at the Eighth Optical Society of America Topical Meeting on Laser Applications to Chemical and Environmental Analysis (8th LACEA), held in Boulder, Colorado, 7-10 February, 2002.     

Laser acceleration of particles using resonance inversions of the Cherenkov effect

The possibility of Cherenkov accelerator development for physics experiments in the 10²–10⁶ TeV range is discussed in connection with the realization of some practical schemes of Cherenkov effect inversion using both the transverse homogeneous magnetic field and several Cherenkov waves. The required fields of 10⁻²–10⁵ TV/m can be obtained by double inversion of the Cherenkov effect in conventional and artificial ionic media. Calculations of particle dynamics were made taking into account the Coulomb scattering and radiation losses. The possibility of ∼ 10⁵ T magnetic fields generation by relativistic particle beams is also discussed.     

An acceleration method for the BEM-based cooling simulation of injection molding

Mold cooling process in injection molding is of great importance and most cooling analyses are based on the boundary element (BEM) approach. The BEM leads to dense influence matrices, which greatly affect the computational efficiency and scale. In this paper, an acceleration method is presented to speed up the solution procedure. In this method, the dense BEM matrix is split into a sparse dominant matrix and a dense residual matrix. The residual item is transformed from the inner iteration to the outer iteration, and the dominant item can be stored in the RAM memory so that the resulting system of equations will be solved much more quickly. Numerical experiments show that this developed approach is a cost-effective method for BEM-based simulation of injection mold cooling.     

One GeV acceleration with laser wakefield in the linear regime

We derive an expression for the maximum energy gain of an accelerated electron, in the limit that the plasma wave created by a laser wake is linear both along the longitudinal direction and in the transverse plane, and with a maximum laser power lower than the critical power for relativistic self-focusing. With an available power of 300 TW, the energy gain is of 1 GeV.     

Superhard phases of simple substances and binary compounds of the B-C-N-O system: from diamond to the latest results (a Review)

The basic known and hypothetic one- and two-element phases of the B-C-N-O system (both superhard phases having diamond and boron structures and precursors to synthesize them) are described. The attention has been given to the structure, basic mechanical properties, and methods to identify and characterize the materials. For some phases that have been recently described in the literature the synthesis conditions at high pressures and temperatures are indicated.     

激光熔化沉积成形缺陷及其控制方法综述

激光增材制造技术作为一种新型的快速成形技术,在快速精准成形的同时,还能够满足个性需求,这种成形方式完全颠覆了传统减材制造的成形理念,因而很快成为最能代表当今信息化时代的一种制造技术。常见的激光增材制造技术主要有以送粉为特征的激光熔化沉积技术(Laser melting deposition,LMD)和以粉末铺床为特征的选区激光熔化技术(Selective laser melting,SLM)。激光熔化沉积技术是采用同步送粉的方式通过大功率激光将同种或不同种的粉末熔化,然后逐行逐层地进行扫描堆积成形。利用这种方法所制备的零件不仅形状复杂,而且各项力学性能均优于铸件。相对于选区激光熔化技术,激光熔化沉积技术具有三大优势:(1)成形尺寸不受限制,可进行大尺寸的零件制造;(2)可以实现不同成分和比例的梯度材料成形;(3)可以进行零件修复与再制造。激光熔化沉积成形过程是一个涉及温度场、应力场等多物理场的耦合过程,由于材料急热、急冷的特点使得利用激光熔化沉积法制备的零件组织为非平衡态组织,过程复杂,不稳定性因素多,因此制件容易出现翘曲变形、熔合不良、尺寸精度不高、开裂等宏观缺陷,内部也容易产生气孔、夹杂、裂纹等微观缺陷,其中激光熔化沉积制备的零件中较大残余应力的存在使得裂纹对其性能的影响更为显著。当前,研究者们主要通过工艺实验及数值模拟研究了产生缺陷的原因,在一定程度上找出了产生气孔、熔合不良、裂纹等缺陷的主要影响因素,并针对这些因素进行逐步分析,在控制粉末特性,调节激光功率、扫描速度、送粉速度、搭接率等工艺参数,引入基板预热,热处理等缺陷控制方法方面取得了一定的进展。同时还利用外界先进检测、传感技术对缺陷进行了实时监测及闭环控制,为激光熔化沉积成形缺陷的控制提供了良好的辅助手段,大大提高了激光熔化沉积成形零件的性能。本文总结了近年来国内外有关激光熔化沉积成形缺陷及其控制方法的研究进展,按照缺陷的种类进行了分类归纳,分析了缺陷形成原因及影响因素,汇总了目前研究的缺陷控制方法,并探讨了当前存在的问题和未来发展前景。     

Metals and incinerators: The latest regulatory phase

Recent regulations in the United States controlling emissions of metals and halogen acid gases from boilers and industrial furnaces (BIFs) burning regu     

North American Symposium on Laser Induced Breakdown Spectroscopy (NASLIBS): introduction to feature issue

This feature issue highlights the topics of the 2011 North American Symposium on Laser Induced Breakdown Spectroscopy (NASLIBS). These include LIBS application to Security and Forensic, Biomedical and Environmental, Liquid Analysis and Fundamentals of LIBS, Instrumentation/Commercialization, Fusion with LIBS, and New Frontiers.     

Light and color in the open air: introduction to the feature issue.

This special feature of Applied Optics reports the results of new experimental and theoretical research concerning a number of naked-eye optical phenomena, including ice-crystal halo displays, mirages, rainbows, glories, optical caustics, clear-sky phenomena, cloud coronas, cloud iridescence, and the extinction of skylight.