Normal modes and mode transformation of pure electron vortex beams

PubMed Central

Thirunavukkarasu, G.; Mousley, M.; Babiker, M.

2017-01-01

Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (TBBs) defined in the aperture plane or the Fourier transform of the transverse structure of the TBBs (FT-TBBs) in the focal plane of a lens with the said aperture. As these modes are eigenfunctions of the axial orbital angular momentum operator, they can provide a complete description of the two-dimensional transverse distribution of the wave function of any electron vortex beam in such a system, in analogy with the prominent role Laguerre–Gaussian (LG) beams played in the description of optical vortex beams. The characteristics of the normal modes of TBBs and FT-TBBs are described, including the quantized orbital angular momentum (in terms of the winding number l) and the radial index p>0. We present the experimental realization of such beams using computer-generated holograms. The mode analysis can be carried out using astigmatic transformation optics, demonstrating close analogy with the astigmatic mode transformation between LG and Hermite–Gaussian beams. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069769

Normal modes and mode transformation of pure electron vortex beams.

PubMed

Thirunavukkarasu, G; Mousley, M; Babiker, M; Yuan, J

2017-02-28

Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (TBBs) defined in the aperture plane or the Fourier transform of the transverse structure of the TBBs (FT-TBBs) in the focal plane of a lens with the said aperture. As these modes are eigenfunctions of the axial orbital angular momentum operator, they can provide a complete description of the two-dimensional transverse distribution of the wave function of any electron vortex beam in such a system, in analogy with the prominent role Laguerre-Gaussian (LG) beams played in the description of optical vortex beams. The characteristics of the normal modes of TBBs and FT-TBBs are described, including the quantized orbital angular momentum (in terms of the winding number l) and the radial index p>0. We present the experimental realization of such beams using computer-generated holograms. The mode analysis can be carried out using astigmatic transformation optics, demonstrating close analogy with the astigmatic mode transformation between LG and Hermite-Gaussian beams.This article is part of the themed issue 'Optical orbital angular momentum'. © 2017 The Author(s).

Probe measurements of the electron velocity distribution function in beams: Low-voltage beam discharge in helium

NASA Astrophysics Data System (ADS)

Sukhomlinov, V.; Mustafaev, A.; Timofeev, N.

2018-04-01

Previously developed methods based on the single-sided probe technique are altered and applied to measure the anisotropic angular spread and narrow energy distribution functions of charged particle (electron and ion) beams. The conventional method is not suitable for some configurations, such as low-voltage beam discharges, electron beams accelerated in near-wall and near-electrode layers, and vacuum electron beam sources. To determine the range of applicability of the proposed method, simple algebraic relationships between the charged particle energies and their angular distribution are obtained. The method is verified for the case of the collisionless mode of a low-voltage He beam discharge, where the traditional method for finding the electron distribution function with the help of a Legendre polynomial expansion is not applicable. This leads to the development of a physical model of the formation of the electron distribution function in a collisionless low-voltage He beam discharge. The results of a numerical calculation based on Monte Carlo simulations are in good agreement with the experimental data obtained using the new method.

Method of controlling coherent synchroton radiation-driven degradation of beam quality during bunch length compression

DOEpatents

Douglas, David R [Newport News, VA; Tennant, Christopher D [Williamsburg, VA

2012-07-10

A method of avoiding CSR induced beam quality defects in free electron laser operation by a) controlling the rate of compression and b) using a novel means of integrating the compression with the remainder of the transport system: both are accomplished by means of dispersion modulation. A large dispersion is created in the penultimate dipole magnet of the compression region leading to rapid compression; this large dispersion is demagnified and dispersion suppression performed in a final small dipole. As a result, the bunch is short for only a small angular extent of the transport, and the resulting CSR excitation is small.

Demonstration of polarization-insensitive spatial light modulation using a single polarization-sensitive spatial light modulator.

PubMed

Liu, Jun; Wang, Jian

2015-07-06

We present a simple configuration incorporating a single polarization-sensitive phase-only liquid crystal spatial light modulator (LC-SLM) to facilitate polarization-insensitive spatial light modulation. The polarization-insensitive configuration is formed by a polarization beam splitter (PBS), a polarization-sensitive phase-only LC-SLM, a half-wave plate (HWP), and a mirror in a loop structure. We experimentally demonstrate polarization-insensitive spatial light modulations for incident linearly polarized beams with different polarization states and polarization-multiplexed beams. Polarization-insensitive spatial light modulations generating orbital angular momentum (OAM) beams are demonstrated in the experiment. The designed polarization-insensitive configuration may find promising applications in spatial light modulations accommodating diverse incident polarizations.

Two-photon polymerization of a three dimensional structure using beams with orbital angular momentum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Shi-Jie; Li, Yan, E-mail: li@pku.edu.cn; Liu, Zhao-Pei

The focus of a beam with orbital angular momentum exhibits internal structure instead of an elliptical intensity distribution of a Gaussian beam, and the superposition of Gauss-Laguerre beams realized by two-dimensional phase modulation can generate a complex three-dimensional (3D) focus. By taking advantage of the flexibility of this 3D focus tailoring, we have fabricated a 3D microstructure with high resolution by two-photon polymerization with a single exposure. Furthermore, we have polymerized an array of double-helix structures that demonstrates optical chirality.

Mode-Division-Multiplexing of Multiple Bessel-Gaussian Beams Carrying Orbital-Angular-Momentum for Obstruction-Tolerant Free-Space Optical and Millimetre-Wave Communication Links.

PubMed

Ahmed, Nisar; Zhao, Zhe; Li, Long; Huang, Hao; Lavery, Martin P J; Liao, Peicheng; Yan, Yan; Wang, Zhe; Xie, Guodong; Ren, Yongxiong; Almaiman, Ahmed; Willner, Asher J; Ashrafi, Solyman; Molisch, Andreas F; Tur, Moshe; Willner, Alan E

2016-03-01

We experimentally investigate the potential of using 'self-healing' Bessel-Gaussian beams carrying orbital-angular-momentum to overcome limitations in obstructed free-space optical and 28-GHz millimetre-wave communication links. We multiplex and transmit two beams (l = +1 and +3) over 1.4 metres in both the optical and millimetre-wave domains. Each optical beam carried 50-Gbaud quadrature-phase-shift-keyed data, and each millimetre-wave beam carried 1-Gbaud 16-quadrature-amplitude-modulated data. In both types of links, opaque disks of different sizes are used to obstruct the beams at different transverse positions. We observe self-healing after the obstructions, and assess crosstalk and power penalty when data is transmitted. Moreover, we show that Bessel-Gaussian orbital-angular-momentum beams are more tolerant to obstructions than non-Bessel orbital-angular-momentum beams. For example, when obstructions that are 1 and 0.44 the size of the l = +1 beam, are placed at beam centre, optical and millimetre-wave Bessel-Gaussian beams show ~6 dB and ~8 dB reduction in crosstalk, respectively.

Mode-Division-Multiplexing of Multiple Bessel-Gaussian Beams Carrying Orbital-Angular-Momentum for Obstruction-Tolerant Free-Space Optical and Millimetre-Wave Communication Links

PubMed Central

Ahmed, Nisar; Zhao, Zhe; Li, Long; Huang, Hao; Lavery, Martin P. J.; Liao, Peicheng; Yan, Yan; Wang, Zhe; Xie, Guodong; Ren, Yongxiong; Almaiman, Ahmed; Willner, Asher J.; Ashrafi, Solyman; Molisch, Andreas F.; Tur, Moshe; Willner, Alan E.

2016-01-01

We experimentally investigate the potential of using ‘self-healing’ Bessel-Gaussian beams carrying orbital-angular-momentum to overcome limitations in obstructed free-space optical and 28-GHz millimetre-wave communication links. We multiplex and transmit two beams (l = +1 and +3) over 1.4 metres in both the optical and millimetre-wave domains. Each optical beam carried 50-Gbaud quadrature-phase-shift-keyed data, and each millimetre-wave beam carried 1-Gbaud 16-quadrature-amplitude-modulated data. In both types of links, opaque disks of different sizes are used to obstruct the beams at different transverse positions. We observe self-healing after the obstructions, and assess crosstalk and power penalty when data is transmitted. Moreover, we show that Bessel-Gaussian orbital-angular-momentum beams are more tolerant to obstructions than non-Bessel orbital-angular-momentum beams. For example, when obstructions that are 1 and 0.44 the size of the l = +1 beam, are placed at beam centre, optical and millimetre-wave Bessel-Gaussian beams show ~6 dB and ~8 dB reduction in crosstalk, respectively. PMID:26926068

Demonstration of polarization-insensitive spatial light modulation using a single polarization-sensitive spatial light modulator

PubMed Central

Liu, Jun; Wang, Jian

2015-01-01

We present a simple configuration incorporating a single polarization-sensitive phase-only liquid crystal spatial light modulator (LC-SLM) to facilitate polarization-insensitive spatial light modulation. The polarization-insensitive configuration is formed by a polarization beam splitter (PBS), a polarization-sensitive phase-only LC-SLM, a half-wave plate (HWP), and a mirror in a loop structure. We experimentally demonstrate polarization-insensitive spatial light modulations for incident linearly polarized beams with different polarization states and polarization-multiplexed beams. Polarization-insensitive spatial light modulations generating orbital angular momentum (OAM) beams are demonstrated in the experiment. The designed polarization-insensitive configuration may find promising applications in spatial light modulations accommodating diverse incident polarizations. PMID:26146032

Beam-induced electron modulations observed during TSS 1R

NASA Astrophysics Data System (ADS)

Rubin, A. G.; Burke, W. J.; Gough, M. P.; Machuzak, J. S.; Gentile, L. C.; Huang, C. Y.; Hardy, D. A.; Thompson, D. C.; Raitt, W. J.

1999-08-01

We report on modulations of electron fluxes at megahertz frequencies measured by the Shuttle Potential and Return Electron Experiment (SPREE) during fast pulsed electron gun (FPEG) beam experiments conducted after the tether break event of the Tethered Satellite System Reflight. Six intervals of sustained modulations were identified while FPEG emitted a 100 mA beam of 1 kev electrons. During five events the beam pitch angle αB was near 90° and the modulations were near even or odd half harmonics of the electron gyrofrequency fce. In the sixth event with 60°>=αB>=45°, electron modulations were near estimated values of the electron plasma frequency fpe and 2fpe. Whenever SPREE detected beam electrons modulated at a given frequency, secondary electrons were also modulated at the same frequency over a broad range of energies. Occasionally, some secondary electrons were modulated simultaneously at a second frequency. Multiple frequencies were related as ratios of low integers. In one case the beam electrons were simultaneously modulated at 0.8 MHz and 1.25 kHz. SPREE measurements suggest that the beam electrons propagate in cylindrical shells whose inner edge is marked by steep spatial gradients in fluxes at 1 keV [Hardy et al., 1995]. Inside the shell, electron distribution functions have positive slopes ∂f/∂v⊥>0 at velocities near that of the beam. Velocity space gradients act as free-energy sources to drive cavity modes that alter the instantaneous guiding centers of electrons causing SPREE to sample alternating parts of the beam cylinder's inner edge. Associated time-varying electric fields also modulated the fluxes of secondary electrons reaching SPREE. Other cavity modes may be excited through nonlinear processes [Calvert, 1982]. With αB far from 90°, electrons in the beam cylinder evolved toward bump-on-tail distributions to excite large-amplitude Langmuir modulations at fpe and its harmonics [Klimas, 1983]. Low-frequency modulations are attributed to electron interactions with ion acoustic-like waves generated as the beam moved across magnetic field lines in the ionosphere at supersonic speeds.

Angular distributions of reflected and refracted relativistic electron beams crossing a thin planar target at a small angle to its surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serov, A. V., E-mail: serov@x4u.lebedev.ru; Mamonov, I. A.; Kol’tsov, A. V., E-mail: koltsov@x4u.lebedev.ru

2015-10-15

The scattering of electrons by aluminum, copper, and lead foils, as well as by bimetallic aluminum-lead and aluminum-copper foils, has been studied experimentally. A microtron with an energy of particles of 7.4 MeV has been used as a source of electrons. The beam of particles incident on a target at small angles is split into particles reflected from the foil, which constitute a reflected beam, and particles crossing the foil, which constitute a refracted beam. The effect of the material and thickness of the foil, as well as the angle between the initial trajectory of the beam and the planemore » of the target, on the direction of motion and the angular divergence of the beam crossing the foil and the beam reflected from the foil has been analyzed. Furthermore, the effect of the sequence of metal layers in bimetallic films on the angles of refraction and reflection of the beam has been examined.« less

Topological charge algebra of optical vortices in nonlinear interactions.

PubMed

Zhdanova, Alexandra A; Shutova, Mariia; Bahari, Aysan; Zhi, Miaochan; Sokolov, Alexei V

2015-12-28

We investigate the transfer of orbital angular momentum among multiple beams involved in a coherent Raman interaction. We use a liquid crystal light modulator to shape pump and Stokes beams into optical vortices with various integer values of topological charge, and cross them in a Raman-active crystal to produce multiple Stokes and anti-Stokes sidebands. We measure the resultant vortex charges using a tilted-lens technique. We verify that in every case the generated beams' topological charges obey a simple relationship, resulting from angular momentum conservation for created and annihilated photons, or equivalently, from phase-matching considerations for multiple interacting beams.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, Daniel L.; Reginato, Louis L.

1988-01-01

An electron beam accelerator comprising an electron beam generator-injector to produce a focused beam of .gtoreq.0.1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electrons by about 0.1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially .gtoreq.0.1-1 MeV maximum energy over a time duration of .ltoreq.1 .mu.sec.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, Daniel L.; Reginato, Louis L.

1987-01-01

An electron beam accelerator comprising an electron beam generator-injector to produce a focused beam of .gtoreq.0.1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electrons by about 0.1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially 0.1-1 MeV maximum energy over a time duration of .ltoreq.1 .mu.sec.

Electron beam accelerator with magnetic pulse compression and accelerator switching

DOEpatents

Birx, D.L.; Reginato, L.L.

1984-03-22

An electron beam accelerator is described comprising an electron beam generator-injector to produce a focused beam of greater than or equal to .1 MeV energy electrons; a plurality of substantially identical, aligned accelerator modules to sequentially receive and increase the kinetic energies of the beam electron by about .1-1 MeV per module. Each accelerator module includes a pulse-forming network that delivers a voltage pulse to the module of substantially .1-1 MeV maximum energy over a time duration of less than or equal to 1 ..mu..sec.

Formation of ring-shaped light fields with orbital angular momentum using a modal type liquid crystal spatial modulator

NASA Astrophysics Data System (ADS)

Kotova, S. P.; Mayorova, A. M.; Samagin, S. A.

2018-05-01

Techniques for forming vortex light fields using a modal type liquid crystal spatial modulator were proposed. An orbital angular momentum of light passing through the modulator or reflecting from it appears as a result of the jump in the profile of phase delay by means of using special configurations of contact electrodes and predetermined values of applying voltages. The features of the generated vortex beams and capabilities for their control were simulated.

Laser Pulse Shaping for Low Emittance Photo-Injector

DTIC Science & Technology

2012-06-01

It depends on the product of the beam’s transverse size and angular divergence, , (I.2) where is the standard deviation of the electron...shows the pendulum’s phase velocity as a function of the position θp. As the pendulum oscillates back and forth, its phase, or angular , velocity and...the angular divergence and size of the optical beam. The radius of the optical beam follows the equation 24 To guarantee proper transfer

Propagation and transmission of optical vortex beams through turbid scattering wall with orbital angular momentums

NASA Astrophysics Data System (ADS)

Wang, W. B.; Gozali, Richard; Nguyen, Thien An; Alfano, R. R.

2015-03-01

Light scattering and transmission of optical Laguerre Gaussian (LG) vortex beams with different orbital angular momentum (OAM) states in turbid scattering media were investigated in comparison with Gaussian (G) beam. The scattering media used in the experiments consist of various sizes and concentrations of latex beads in water solutions. The LG beams were generated using a spatial light modulator in reflection mode. The ballistic transmissions of LG and G beams were measured with different ratios of thickness of samples (z) to scattering mean free path (ls) of the turbid media, z/ls. The results show that in the ballistic region where z/ls is small, the LG and G beams show no significant difference, while in the diffusive region where z/ls is large, LG beams show higher transmission than Gaussian beam. In the diffusive region, the LG beams with higher orbital angular momentum L values show higher transmission than the beams with lower L values. The transition points from ballistic to diffusive regions for different scattering media were studied and determined.

Production of confluent hypergeometric beam by computer-generated hologram

NASA Astrophysics Data System (ADS)

Chen, Jiannong; Wang, Gang; Xu, Qinfeng

2011-02-01

Because of their spiral wave front, phase singularity, zero-intensity center and orbital angular momentum, dark hollow vortex beams have been found many applications in the field of atom optics such as atom cooling, atom transport and atom guiding. In this paper, a method for generating confluent hypergeometric beam by computer-generated hologram displayed on the spatial light modulator is presented. The hologram is formed by interference between a single ring Laguerre-Gaussian beam and a plane wave. The far-field Fraunhofer diffraction of this optical field transmitted from the hologram is the confluent hypergeometric beam. This beam is a circular symmetric beam which has a phase singularity, spiral wave front, zero-intensity center, and intrinsic orbital angular momentum. It is a new dark hollow vortex beam.

Elliptical optical solitary waves in a finite nematic liquid crystal cell

NASA Astrophysics Data System (ADS)

Minzoni, Antonmaria A.; Sciberras, Luke W.; Smyth, Noel F.; Worthy, Annette L.

2015-05-01

The addition of orbital angular momentum has been previously shown to stabilise beams of elliptic cross-section. In this article the evolution of such elliptical beams is explored through the use of an approximate methodology based on modulation theory. An approximate method is used as the equations that govern the optical system have no known exact solitary wave solution. This study brings to light two distinct phases in the evolution of a beam carrying orbital angular momentum. The two phases are determined by the shedding of radiation in the form of mass loss and angular momentum loss. The first phase is dominated by the shedding of angular momentum loss through spiral waves. The second phase is dominated by diffractive radiation loss which drives the elliptical solitary wave to a steady state. In addition to modulation theory, the "chirp" variational method is also used to study this evolution. Due to the significant role radiation loss plays in the evolution of an elliptical solitary wave, an attempt is made to couple radiation loss to the chirp variational method. This attempt furthers understanding as to why radiation loss cannot be coupled to the chirp method. The basic reason for this is that there is no consistent manner to match the chirp trial function to the generated radiating waves which is uniformly valid in time. Finally, full numerical solutions of the governing equations are compared with solutions obtained using the various variational approximations, with the best agreement achieved with modulation theory due to its ability to include both mass and angular momentum losses to shed diffractive radiation.

Laguerre-Gaussian, Hermite-Gaussian, Bessel-Gaussian, and Finite-Energy Airy Beams Carrying Orbital Angular Momentum in Strongly Nonlocal Nonlinear Media

NASA Astrophysics Data System (ADS)

Wu, Zhenkun; Gu, Yuzong

2016-12-01

The propagation of two-dimensional beams is analytically and numerically investigated in strongly nonlocal nonlinear media (SNNM) based on the ABCD matrix. The two-dimensional beams reported in this paper are described by the product of the superposition of generalized Laguerre-Gaussian (LG), Hermite-Gaussian (HG), Bessel-Gaussian (BG), and circular Airy (CA) beams, carrying an orbital angular momentum (OAM). Owing to OAM and the modulation of SNNM, we find that the propagation of these two-dimensional beams exhibits complete rotation and periodic inversion: the spatial intensity profile first extends and then diminishes, and during the propagation the process repeats to form a breath-like phenomenon.

Effects of a modulated vortex structure on the diffraction dynamics of ring Airy Gaussian beams.

PubMed

Huang, Xianwei; Shi, Xiaohui; Deng, Zhixiang; Bai, Yanfeng; Fu, Xiquan

2017-09-01

The evolution of the ring Airy Gaussian beams with a modulated vortex in free space is numerically investigated. Compared with the unmodulated vortex, the unique property is that the beam spots first break up, and then gather. The evolution of the beams is influenced by the parameters of the vortex modulation, and the splitting phenomenon gets enhanced with multiple rings becoming light spots if the modulation depth increases. The symmetric branch pattern of the beam spots gets changed when the number of phase folds increases, and the initial modulation phase only impacts the angle of the beam spots. Moreover, a large distribution factor correlates to a hollow Gaussian vortex shape and weakens the splitting and gathering trend. By changing the initial parameters of the vortex modulation and the distribution factor, the peak intensity is greatly affected. In addition, the energy flow and the angular momentum are elucidated with the beam evolution features being confirmed.

Angular distributions of absorbed dose of Bremsstrahlung and secondary electrons induced by 18-, 28- and 38-MeV electron beams in thick targets.

PubMed

Takada, Masashi; Kosako, Kazuaki; Oishi, Koji; Nakamura, Takashi; Sato, Kouichi; Kamiyama, Takashi; Kiyanagi, Yoshiaki

2013-03-01

Angular distributions of absorbed dose of Bremsstrahlung photons and secondary electrons at a wide range of emission angles from 0 to 135°, were experimentally obtained using an ion chamber with a 0.6 cm(3) air volume covered with or without a build-up cap. The Bremsstrahlung photons and electrons were produced by 18-, 28- and 38-MeV electron beams bombarding tungsten, copper, aluminium and carbon targets. The absorbed doses were also calculated from simulated photon and electron energy spectra by multiplying simulated response functions of the ion chambers, simulated with the MCNPX code. Calculated-to-experimental (C/E) dose ratios obtained are from 0.70 to 1.57 for high-Z targets of W and Cu, from 15 to 135° and the C/E range from 0.6 to 1.4 at 0°; however, the values of C/E for low-Z targets of Al and C are from 0.5 to 1.8 from 0 to 135°. Angular distributions at the forward angles decrease with increasing angles; on the other hand, the angular distributions at the backward angles depend on the target species. The dependences of absorbed doses on electron energy and target thickness were compared between the measured and simulated results. The attenuation profiles of absorbed doses of Bremsstrahlung beams at 0, 30 and 135° were also measured.

Collision-energy-resolved angular distribution of Penning electrons for N 2-He ∗(2 3S)

NASA Astrophysics Data System (ADS)

Hanzawa, Yoshinori; Kishimoto, Naoki; Yamazaki, Masakazu; Ohno, Koichi

2006-07-01

The collision-energy-resolved angular distributions of Penning electrons for individual ionic state of N 2-He ∗(2 3S) were measured. The angular distributions showed increasing intensity in the backward (rebounding) directions with respect to initial He ∗(2 3S) beam vector because Penning ionization occurs with a collision against repulsive interaction wall followed by the electron emission from 2s orbital of He ∗. We also analyzed internal angular distribution by means of fitting parameters using classical trajectory calculations for N 2-He ∗(2 3S) on the modified interaction potential. These internal angular distributions suggested the electron emission from 2s orbital of He ∗ and they depended on collision energy and electron kinetic energy.

Feasibility study for mega-electron-volt electron beam tomography.

PubMed

Hampel, U; Bärtling, Y; Hoppe, D; Kuksanov, N; Fadeev, S; Salimov, R

2012-09-01

Electron beam tomography is a promising imaging modality for the study of fast technical processes. But for many technical objects of interest x rays of several hundreds of keV energy are required to achieve sufficient material penetration. In this article we report on a feasibility study for fast electron beam computed tomography with a 1 MeV electron beam. The experimental setup comprises an electrostatic accelerator with beam optics, transmission target, and a single x-ray detector. We employed an inverse fan-beam tomography approach with radiographic projections being generated from the linearly moving x-ray source. Angular projections were obtained by rotating the object.

Simplified Generation of High-Angular-Momentum Light Beams

NASA Technical Reports Server (NTRS)

Savchenkov, Anatoliy; Maleki, Lute; Matsko, Andrey; Strekalov, Dmitry; Grudinin, Ivan

2007-01-01

A simplified method of generating a beam of light having a relatively high value of angular momentum (see figure) involves the use of a compact apparatus consisting mainly of a laser, a whispering- gallery-mode (WGM) resonator, and optical fibers. The method also can be used to generate a Bessel beam. ( Bessel beam denotes a member of a class of non-diffracting beams, so named because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have high values of angular momentum.) High-angular-momentum light beams are used in some applications in biology and nanotechnology, wherein they are known for their ability to apply torque to make microscopic objects rotate. High-angular-momentum light beams could also be used to increase bandwidths of fiber-optic communication systems. The present simplified method of generating a high-angular-momentum light beam was conceived as an alternative to prior such methods, which are complicated and require optical setups that include, variously, holograms, modulating Fabry-Perot cavities, or special microstructures. The present simplified method exploits a combination of the complex structure of the electromagnetic field inside a WGM resonator, total internal reflection in the WGM resonator, and the electromagnetic modes supported by an optical fiber. The optical fiber used to extract light from the WGM resonator is made of fused quartz. The output end of this fiber is polished flat and perpendicular to the fiber axis. The input end of this fiber is cut on a slant and placed very close to the WGM resonator at an appropriate position and orientation. To excite the resonant whispering- gallery modes, light is introduced into the WGM resonator via another optical fiber that is part of a pigtailed fiber-optic coupler. Light extracted from the WGM resonator is transformed into a high-angular- momentum beam inside the extraction optical fiber and this beam is emitted from the polished flat output end. By adjusting the geometry of this apparatus, it is possible to generate a variety of optical beams characterized by a wide range of parameters. These beams generally have high angular momenta and can be of either Bessel or Bessel-related types.

System for obtaining smooth laser beams where intensity variations are reduced by spectral dispersion of the laser light (SSD)

DOEpatents

Skupsky, S.; Kessler, T.J.; Short, R.W.; Craxton, S.; Letzring, S.A.; Soures, J.

1991-09-10

In an SSD (smoothing by spectral dispersion) system which reduces the time-averaged spatial variations in intensity of the laser light to provide uniform illumination of a laser fusion target, an electro-optic phase modulator through which a laser beam passes produces a broadband output beam by imposing a frequency modulated bandwidth on the laser beam. A grating provides spatial and angular spectral dispersion of the beam. Due to the phase modulation, the frequencies (''colors'') cycle across the beam. The dispersed beam may be amplified and frequency converted (e.g., tripled) in a plurality of beam lines. A distributed phase plate (DPP) in each line is irradiated by the spectrally dispersed beam and the beam is focused on the target where a smooth (uniform intensity) pattern is produced. The color cycling enhances smoothing and the use of a frequency modulated laser pulse prevents the formation of high intensity spikes which could damage the laser medium in the power amplifiers. 8 figures.

System for obtaining smooth laser beams where intensity variations are reduced by spectral dispersion of the laser light (SSD)

DOEpatents

Skupsky, Stanley; Kessler, Terrance J.; Short, Robert W.; Craxton, Stephen; Letzring, Samuel A.; Soures, John

1991-01-01

In an SSD (smoothing by spectral dispersion) system which reduces the time-averaged spatial variations in intensity of the laser light to provide uniform illumination of a laser fusion target, an electro-optic phase modulator through which a laser beam passes produces a broadband output beam by imposing a frequency modulated bandwidth on the laser beam. A grating provides spatial and angular spectral dispersion of the beam. Due to the phase modulation, the frequencies ("colors") cycle across the beam. The dispersed beam may be amplified and frequency converted (e.g., tripled) in a plurality of beam lines. A distributed phase plate (DPP) in each line is irradiated by the spectrally dispersed beam and the beam is focused on the target where a smooth (uniform intensity) pattern is produced. The color cycling enhances smoothing and the use of a frequency modulated laser pulse prevents the formation of high intensity spikes which could damage the laser medium in the power amplifiers.

Electrically optical phase controlling for millimeter wave orbital angular momentum multi-modulation communication

NASA Astrophysics Data System (ADS)

Wu, Haotian; Tang, Jin; Yu, Zhenliang; Yi, Jun; Chen, Shuqing; Xiao, Jiangnan; Zhao, Chujun; Li, Ying; Chen, Lin; Wen, Shuangchun

2017-06-01

Orbital angular momentum (OAM), an emerging and fascinating degree of freedom, has highlighted an innovation in communication and optical manipulation field. The beams with different OAM state, which manifest as the phase front ;twisting; of electromagnetic waves, are mutually orthogonal, which is exactly what a new freedom applied to practical communication eagers for. Herein, we proposed a novel millimeter-wave OAM modulation technique by electrically optical phase controlling. By modulating OAM and phase of optical-millimeter-wave synchronously, the multi-modulation: quadrature orbital angular momentum modulation (QOM) communication system at W band is structured and simulated, allowing a 50 Gbit/s signal transmitting with bit-error rates less than 10-4. Our work might suggest that OAM could be compounded to more complex multi-modulation signal, and revealed a new insight into OAM based high capacity wireless and radio-over-fiber communication.

Light modulated electron beam driven radiofrequency emitter

DOEpatents

Wilson, M.T.; Tallerico, P.J.

1979-10-10

The disclosure relates to a light modulated electron beam-driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

Two-screen single-shot electron spectrometer for laser wakefield accelerated electron beams.

PubMed

Soloviev, A A; Starodubtsev, M V; Burdonov, K F; Kostyukov, I Yu; Nerush, E N; Shaykin, A A; Khazanov, E A

2011-04-01

The laser wakefield acceleration electron beams can essentially deviate from the axis of the system, which distinguishes them greatly from beams of conventional accelerators. In case of energy measurements by means of a permanent-magnet electron spectrometer, the deviation angle can affect accuracy, especially for high energies. A two-screen single-shot electron spectrometer that correctly allows for variations of the angle of entry is considered. The spectrometer design enables enhancing accuracy of measuring narrow electron beams significantly as compared to a one-screen spectrometer with analogous magnetic field, size, and angular acceptance. © 2011 American Institute of Physics

Cerenkov emissions of ion acoustic-like waves generated by electron beams emitted during TSS 1R

NASA Astrophysics Data System (ADS)

Huang, C. Y.; Burke, W. J.; Hardy, D. A.; Gough, M. P.; Olson, D. G.; Gentile, L. C.; Gilchrist, B. E.; Bonifazi, C.; Raitt, W. J.; Thompson, D. C.

During the Tethered Satellite System reflight the Spacecraft Particle Correlation Experiment detected fluxes of energetic electrons and ions that were simultaneously modulated at low frequencies during firings of both the fast pulsed electron gun (FPEG) and the electron generator assembly (EGA). The modulations have been interpreted as signatures of large-amplitude, ion acoustic-like waves excited in Cerenkov interactions between electron beams and ambient plasmas as the shuttle moved at supersonic speeds across the ionospheric magnetic field. We present examples of particle modulations observed during steady beam emissions. Measurements show that (1) most electron modulations were at frequencies of several hundred Hertz and (2) ions modulated at similar frequencies appeared at spectral energy peaks during shuttle negative charging events. Detection of modulated ion fluxes confirms the Cerenkov emission hypothesis. Observed frequency variations indicate that the EGA beam underwent more spatial spreading than the FPEG beam.

Validation of the MCNP6 electron-photon transport algorithm: multiple-scattering of 13- and 20-MeV electrons in thin foils

NASA Astrophysics Data System (ADS)

Dixon, David A.; Hughes, H. Grady

2017-09-01

This paper presents a validation test comparing angular distributions from an electron multiple-scattering experiment with those generated using the MCNP6 Monte Carlo code system. In this experiment, a 13- and 20-MeV electron pencil beam is deflected by thin foils with atomic numbers from 4 to 79. To determine the angular distribution, the fluence is measured down range of the scattering foil at various radii orthogonal to the beam line. The characteristic angle (the angle for which the max of the distribution is reduced by 1/e) is then determined from the angular distribution and compared with experiment. Multiple scattering foils tested herein include beryllium, carbon, aluminum, copper, and gold. For the default electron-photon transport settings, the calculated characteristic angle was statistically distinguishable from measurement and generally broader than the measured distributions. The average relative difference ranged from 5.8% to 12.2% over all of the foils, source energies, and physics settings tested. This validation illuminated a deficiency in the computation of the underlying angular distributions that is well understood. As a result, code enhancements were made to stabilize the angular distributions in the presence of very small substeps. However, the enhancement only marginally improved results indicating that additional algorithmic details should be studied.

Broad-band beam buncher

DOEpatents

Goldberg, D.A.; Flood, W.S.; Arthur, A.A.; Voelker, F.

1984-03-20

A broad-band beam bunther is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-

Method and system for controlling the position of a beam of light

DOEpatents

Steinkraus, Jr., Robert F.; Johnson, Gary W [Livermore, CA; Ruggiero, Anthony J [Livermore, CA

2011-08-09

An method and system for laser beam tracking and pointing is based on a conventional position sensing detector (PSD) or quadrant cell but with the use of amplitude-modulated light. A combination of logarithmic automatic gain control, filtering, and synchronous detection offers high angular precision with exceptional dynamic range and sensitivity, while maintaining wide bandwidth. Use of modulated light enables the tracking of multiple beams simultaneously through the use of different modulation frequencies. It also makes the system resistant to interfering light sources such as ambient light. Beam pointing is accomplished by feeding back errors in the measured beam position to a beam steering element, such as a steering mirror. Closed-loop tracking performance is superior to existing methods, especially under conditions of atmospheric scintillation.

Air-coupled laser vibrometry: analysis and applications.

PubMed

Solodov, Igor; Döring, Daniel; Busse, Gerd

2009-03-01

Acousto-optic interaction between a narrow laser beam and acoustic waves in air is analyzed theoretically. The photoelastic relation in air is used to derive the phase modulation of laser light in air-coupled reflection vibrometry induced by angular spatial spectral components comprising the acoustic beam. Maximum interaction was found for the zero spatial acoustic component propagating normal to the laser beam. The angular dependence of the imaging efficiency is determined for the axial and nonaxial acoustic components with the regard for the laser beam steering in the scanning mode. The sensitivity of air-coupled vibrometry is compared with conventional "Doppler" reflection vibrometry. Applications of the methodology for visualization of linear and nonlinear air-coupled fields are demonstrated.

Fiber optic inclination detector system having a weighted sphere with reference points

DOEpatents

Cwalinski, Jeffrey P.

1995-01-01

A fiber optic inclination detector system for determining the angular displacement of an object from a reference surface includes a simple mechanical transducer which requires a minimum number of parts and no electrical components. The system employs a single light beam which is split into two light beams and provided to the transducer. Each light beam is amplitude modulated upon reflecting off the transducer to detect inclination. The power values associated with each of the reflected light beams are converted by a pair of photodetectors into voltage signals, and a microprocessor manipulates the voltage signals to provide a measure of the angular displacement between the object and the reference surface.

Optimization of combined electron and photon beams for breast cancer

NASA Astrophysics Data System (ADS)

Xiong, W.; Li, J.; Chen, L.; Price, R. A.; Freedman, G.; Ding, M.; Qin, L.; Yang, J.; Ma, C.-M.

2004-05-01

Recently, intensity-modulated radiation therapy and modulated electron radiotherapy have gathered a growing interest for the treatment of breast and head and neck tumours. In this work, we carried out a study to combine electron and photon beams to achieve differential dose distributions for multiple target volumes simultaneously. A Monte Carlo based treatment planning system was investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. We compared breast treatment plans generated using this home-grown optimization and dose calculation software for different treatment techniques. Five different planning techniques have been developed for this study based on a standard photon beam whole breast treatment and an electron beam tumour bed cone down. Technique 1 includes two 6 MV tangential wedged photon beams followed by an anterior boost electron field. Technique 2 includes two 6 MV tangential intensity-modulated photon beams and the same boost electron field. Technique 3 optimizes two intensity-modulated photon beams based on a boost electron field. Technique 4 optimizes two intensity-modulated photon beams and the weight of the boost electron field. Technique 5 combines two intensity-modulated photon beams with an intensity-modulated electron field. Our results show that technique 2 can reduce hot spots both in the breast and the tumour bed compared to technique 1 (dose inhomogeneity is reduced from 34% to 28% for the target). Techniques 3, 4 and 5 can deliver a more homogeneous dose distribution to the target (with dose inhomogeneities for the target of 22%, 20% and 9%, respectively). In many cases techniques 3, 4 and 5 can reduce the dose to the lung and heart. It is concluded that combined photon and electron beam therapy may be advantageous for treating breast cancer compared to conventional treatment techniques using tangential wedged photon beams followed by a boost electron field.

Free electron laser with masked chicane

DOEpatents

Nguyen, Dinh C.; Carlsten, Bruce E.

1999-01-01

A free electron laser (FEL) is provided with an accelerator for outputting electron beam pulses; a buncher for modulating each one of the electron beam pulses to form each pulse into longitudinally dispersed bunches of electrons; and a wiggler for generating coherent light from the longitudinally dispersed bunches of electrons. The electron beam buncher is a chicane having a mask for physically modulating the electron beam pulses to form a series of electron beam bunches for input to the wiggler. In a preferred embodiment, the mask is located in the chicane at a position where each electron beam pulse has a maximum dispersion.

Dynamic optical modulation of an electron beam on a photocathode RF gun: Toward intensity-modulated radiation therapy (IMRT)

NASA Astrophysics Data System (ADS)

Kondoh, Takafumi; Kashima, Hiroaki; Yang, Jinfeng; Yoshida, Yoichi; Tagawa, Seiichi

2008-10-01

In intensity-modulated radiation therapy (IMRT), the aim is to deliver reduced doses of radiation to normal tissue. As a step toward IMRT, we examined dynamic optical modulation of an electron beam produced by a photocathode RF gun. Images on photomasks were transferred onto a photocathode by relay imaging. The resulting beam was controlled by a remote mirror. The modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods.

Generation of high-power, tunable terahertz radiation from laser interaction with a relativistic electron beam

DOE PAGES

Zhang, Zhen; Yan, Lixin; Du, Yingchao; ...

2017-05-01

We propose a method based on the slice energy spread modulation to generate strong subpicosecond density bunching in high-intensity relativistic electron beams. A laser pulse with periodic intensity envelope is used to modulate the slice energy spread of the electron beam, which can then be converted into density modulation after a dispersive section. It is found that the double-horn slice energy distribution of the electron beam induced by the laser modulation is very effective to increase the density bunching. Since the modulation is performed on a relativistic electron beam, the process does not suffer from strong space charge force ormore » coupling between phase spaces, so that it is straightforward to preserve the beam quality for terahertz (THz) radiation and other applications. We show in both theory and simulations that the tunable radiation from the beam can cover the frequency range of 1 - 10 THz with high power and narrow-band spectra.« less

Velocity Spread Reduction for Axis-encircling Electron Beam Generated by Single Magnetic Cusp

NASA Astrophysics Data System (ADS)

Jeon, S. G.; Baik, C. W.; Kim, D. H.; Park, G. S.; Sato, N.; Yokoo, K.

2001-10-01

Physical characteristics of an annular Pierce-type electron gun are investigated analytically. An annular electron gun is used in conjunction with a non-adiabatic magnetic reversal and an adiabatic compression to produce an axis-encircling electron beam. Velocity spread close to zero is realized with an initial canonical angular momentum spread at the cathode when the beam trajectory does not coincide with the magnetic flux line. Both the analytical calculation and the EGUN code simulation confirm this phenomenon.

Dosimetric characteristics of electron beams produced by a mobile accelerator for IORT.

PubMed

Pimpinella, M; Mihailescu, D; Guerra, A S; Laitano, R F

2007-10-21

Energy and angular distributions of electron beams with different energies were simulated by Monte Carlo calculations. These beams were generated by the NOVAC7 system (Hitesys, Italy), a mobile electron accelerator specifically dedicated to intra-operative radiation therapy (IORT). The electron beam simulations were verified by comparing the measured dose distributions with the corresponding calculated distributions. As expected, a considerable difference was observed in the energy and angular distributions between the IORT beams studied in the present work and the electron beams produced by conventional accelerators for non-IORT applications. It was also found that significant differences exist between the IORT beams used in this work and other IORT beams with different collimation systems. For example, the contribution from the scattered electrons to the total dose was found to be up to 15% higher in the NOVAC7 beams. The water-to-air stopping power ratios of the IORT beams used in this work were calculated on the basis of the beam energy distributions obtained by the Monte Carlo simulations. These calculated stopping power ratios, s(w,air), were compared with the corresponding s(w,air) values recommended by the TRS-381 and TRS-398 IAEA dosimetry protocols in order to estimate the deviations between a dosimetry based on generic parameters and a dosimetry based on parameters specifically obtained for the actual IORT beams. The deviations in the s(w,air) values were found to be as large as up to about 1%. Therefore, we recommend that a preliminary analysis should always be made when dealing with IORT beams in order to assess to what extent the possible differences in the s(w,air) values have to be accounted for or may be neglected on the basis of the specific accuracy needed in clinical dosimetry.

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications

DOE PAGES

Ren, Yongxiong; Li, Long; Wang, Zhe; ...

2016-09-12

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we show up to a 40-Gbit/s link by multiplexing and transmitting four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one atmore » 520 nm for 1-Gbit/s/beam; we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, a green laser diode is directly modulated. Lastly, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing.« less

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications

PubMed Central

Ren, Yongxiong; Li, Long; Wang, Zhe; Kamali, Seyedeh Mahsa; Arbabi, Ehsan; Arbabi, Amir; Zhao, Zhe; Xie, Guodong; Cao, Yinwen; Ahmed, Nisar; Yan, Yan; Liu, Cong; Willner, Asher J.; Ashrafi, Solyman; Tur, Moshe; Faraon, Andrei; Willner, Alan E.

2016-01-01

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we show up to a 40-Gbit/s link by multiplexing and transmitting four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for 1-Gbit/s/beam; we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, a green laser diode is directly modulated. Finally, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing. PMID:27615808

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications

NASA Astrophysics Data System (ADS)

Ren, Yongxiong; Li, Long; Wang, Zhe; Kamali, Seyedeh Mahsa; Arbabi, Ehsan; Arbabi, Amir; Zhao, Zhe; Xie, Guodong; Cao, Yinwen; Ahmed, Nisar; Yan, Yan; Liu, Cong; Willner, Asher J.; Ashrafi, Solyman; Tur, Moshe; Faraon, Andrei; Willner, Alan E.

2016-09-01

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we show up to a 40-Gbit/s link by multiplexing and transmitting four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for 1-Gbit/s/beam; we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, a green laser diode is directly modulated. Finally, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing.

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Yongxiong; Li, Long; Wang, Zhe

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we show up to a 40-Gbit/s link by multiplexing and transmitting four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one atmore » 520 nm for 1-Gbit/s/beam; we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, a green laser diode is directly modulated. Lastly, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing.« less

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications.

PubMed

Ren, Yongxiong; Li, Long; Wang, Zhe; Kamali, Seyedeh Mahsa; Arbabi, Ehsan; Arbabi, Amir; Zhao, Zhe; Xie, Guodong; Cao, Yinwen; Ahmed, Nisar; Yan, Yan; Liu, Cong; Willner, Asher J; Ashrafi, Solyman; Tur, Moshe; Faraon, Andrei; Willner, Alan E

2016-09-12

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we show up to a 40-Gbit/s link by multiplexing and transmitting four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for 1-Gbit/s/beam; we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the 40-Gbit/s link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the 4-Gbit/s link, a green laser diode is directly modulated. Finally, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing.

Two-dimensional angular transmission characterization of CPV modules.

PubMed

Herrero, R; Domínguez, C; Askins, S; Antón, I; Sala, G

2010-11-08

This paper proposes a fast method to characterize the two-dimensional angular transmission function of a concentrator photovoltaic (CPV) system. The so-called inverse method, which has been used in the past for the characterization of small optical components, has been adapted to large-area CPV modules. In the inverse method, the receiver cell is forward biased to produce a Lambertian light emission, which reveals the reverse optical path of the optics. Using a large-area collimator mirror, the light beam exiting the optics is projected on a Lambertian screen to create a spatially resolved image of the angular transmission function. An image is then obtained using a CCD camera. To validate this method, the angular transmission functions of a real CPV module have been measured by both direct illumination (flash CPV simulator and sunlight) and the inverse method, and the comparison shows good agreement.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Q.

In memory of the significant contribution of Dr. Jacques Ovadia to electron beam techniques, this session will review recent, advanced techniques which are reinvigorating the science of electron beam radiation therapy. Recent research efforts in improving both the applicability and quality of the electron beam therapy will be discussed, including modulated electron beam radiotherapy (MERT) and dynamic electron arc radiotherapy (DEAR). Learning Objectives: To learn about recent advances in electron beam therapy, including modulated electron beam therapy and dynamic electron arc therapy (DEAR). Put recent advances in the context of work that Dr. Ovadia pursued during his career in medicalmore » physics.« less

Method and apparatus for recirculation with control of synchrotron radiation

DOEpatents

Douglas, David R.; Tennant, Christopher

2016-08-02

A method for controlling beam quality degradation from ISR and CSR and stabilizing the microbunching instability (.mu.BI) in a high brightness electron beam. The method includes providing a super-periodic second order achromat line with each super period being individually linearly achromatic and isochronous, setting individual superperiod tunes to rational fractions of an integer (such as 4.sup.th or 6.sup.th integers), setting individual bend angles to be as small as practical to reduce driving terms due to dispersion and dispersive angle, and setting bend radii as large enough to suppress ISR but not negatively affect the radial dependence of CSR. The method includes setting the structure of the individual superperiods to minimize bend plane beam envelope values in the dipoles to reduce betatron response to a CSR event at a dispersed location, increasing beam angular divergence, and creating dispersion nodes in the dipoles to similarly reduce response to CSR events, and limit R.sub.56 modulation in order to mitigate .mu.BI.

Broad-band beam buncher

DOEpatents

Goldberg, David A.; Flood, William S.; Arthur, Allan A.; Voelker, Ferdinand

1986-01-01

A broad-band beam buncher is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-band response and the device as a whole designed to effect broad-band beam coupling, so as to minimize variations of the output across the response band.

Device and method for electron beam heating of a high density plasma

DOEpatents

Thode, L.E.

A device and method for relativistic electron beam heating of a high density plasma in a small localized region are described. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10/sup 17/ to 10/sup 20/.

Electra: Repetitively Pulsed Angularly Multiplexed KrF Laser System Performance

NASA Astrophysics Data System (ADS)

Wolford, Matthew; Myers, Matthew; Giuliani, John; Sethian, John; Burns, Patrick; Hegeler, Frank; Jaynes, Reginald

2008-11-01

As in a full size fusion power plant beam line, Electra is a multistage laser amplifier system. The multistage amplifier system consists of a commercial discharge laser and two doubled sided electron beam pumped amplifiers. Angular multiplexing is used in the optical layout to provide pulse length control and to maximize laser extraction from the amplifiers. Two angularly multiplexed beams have extracted 30 J of KrF laser light with an aperture 8 x 10 cm^2, which is sufficient to extract over 500 J from the main amplifier and models agree. The main amplifier of Electra in oscillator mode has demonstrated single shot and rep-rate laser energies exceeding 700 J with 100 ns pulsewidth at 248 nm with an aperture 29 x 29 cm^2. Continuous operation of the KrF electron beam pumped oscillator has lasted for more than 2.5 hours without failure at 1 Hz and 2.5 Hz. The measured intensity and pulse energy for durations greater than thousand shots are consistent at measurable rep-rates of 1 Hz, 2.5 Hz and 5 Hz.

Superplastic Aluminum Evaluation

DTIC Science & Technology

1981-06-01

Gold coated. 450 Lilt to electron beam ...................... ............... 111 16 Scanning electron micrograph of a cross section through a cavity... Gold coated. 450 tilt to electron beam ............. ...... .. ... 113 17 Typical EDAX spectra from (a) dark, angular, loose particles ((Fe,Cr)3SiAll...with atmospheric water vapor to form aluminum oxide and hydrogen. The hydrogen (already in monoatomic form) is very rapidly dissolved by the liquid

Smith-Purcell terahertz radiation from laser modulated electron beam over a metallic grating

NASA Astrophysics Data System (ADS)

Kumar, Pawan; Bhasin, Lalita; Tripathi, V. K.; Kumar, Ashok; Kumar, Manoj

2016-09-01

We propose a novel scheme of terahertz (THz) radiation generation from the beat frequency modulation of an electron beam by two co-propagating lasers and the generation of terahertz radiation by the modulated beam passing over a periodic metallic grating. The lasers cause velocity modulation of the beam by exerting a longitudinal ponderomotive force on it. In the drift space between the modulator and metallic grating, the velocity modulation translates into density and current modulation. The modulated beam, propagating over the grating of specific wave number, induces space periodic image current in the conductor that emits beat frequency Smith-Purcell radiation. With 1 μm, 4 × 1016 W/cm2 lasers, beam current modulation of the order of 50% can be achieved at optimum lengths of the modulator and drift space. Employing 10 mA, 0.5 MeV short-period electron beam, propagating at a height of 50 μ m above the grating of period 150 μm, one may obtain THz radiated power of the order of 6 mW at 10 THz.

Annular beam with segmented phase gradients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Shubo; Wu, Liang; Tao, Shaohua, E-mail: eshtao@csu.edu.cn

2016-08-15

An annular beam with a single uniform-intensity ring and multiple segments of phase gradients is proposed in this paper. Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane. The phase distribution along the circumference of the doughnut beam can be segmented with different phase gradients. Similar to a vortex beam, the annular beam can also exert torques and rotate a trapped particle owingmore » to the orbital angular momentum of the beam. As the beam possesses different phase gradients, the rotation velocity of the trapped particle can be varied along the circumference. The simulation and experimental results show that an annular beam with three segments of different phase gradients can rotate particles with controlled velocities. The beam has potential applications in optical trapping and optical information processing.« less

2 Tbit/s free-space data transmission on two orthogonal orbital-angular-momentum beams each carrying 25 WDM channels.

PubMed

Fazal, Irfan M; Ahmed, Nisar; Wang, Jian; Yang, Jeng-Yuan; Yan, Yan; Shamee, Bishara; Huang, Hao; Yue, Yang; Dolinar, Sam; Tur, Moshe; Willner, Alan E

2012-11-15

We demonstrate a 2 Tbit/s free-space data link using two orthogonal orbital angular momentum beams each carrying 25 different wavelength-division-multiplexing channels. We measure the performance for different modulation formats, including directly detected 40 Gbit/s nonreturn-to-zero (NRZ) differential phase-shift keying, 40 Gbit/s NRZ on-off keying, and coherently-detected 10 Gbaud NRZ quadrature phase-shift keying, and achieve low bit error rates with penalties less than 5 dB.

The propagation of ion-acoustic waves carrying orbital angular momentum in the electron-positron-ion plasmas

NASA Astrophysics Data System (ADS)

Mehdian, H.; Nobahar, D.; Hajisharifi, K.

2018-02-01

Ion-acoustic (IA) waves carrying orbital angular momentum (OAM) are investigated in an unmagnetized, uniform, and collisionless electron-positron-ion (e-p-i) plasma system. Employing the hydrodynamic theory, the paraxial equation in term of ion perturbed number density is derived and discussed about its Laguerre-Gaussian (LG) beam solutions. Obtaining an approximate solution for the electrostatic potential, the IA wave characteristics including helical electric field structure, energy density, and OAM density are theoretically studied. Based on the numerical analysis, the effects of positron concentration, radial and angular mode number as well as beam waist on the obtained potential profile are investigated. It is shown that the depth (height) and width of the LG potential profile wells (barriers) are considerably modify by the variation of positron concentration.

Polarimetric Imaging using Two Photoelastic Modulators

NASA Technical Reports Server (NTRS)

Wang, Yu; Cunningham, Thomas; Diner, David; Davis, Edgar; Sun, Chao; Hancock, Bruce; Gutt, Gary; Zan, Jason; Raouf, Nasrat

2009-01-01

A method of polarimetric imaging, now undergoing development, involves the use of two photoelastic modulators in series, driven at equal amplitude but at different frequencies. The net effect on a beam of light is to cause (1) the direction of its polarization to rotate at the average of two excitation frequencies and (2) the amplitude of its polarization to be modulated at the beat frequency (the difference between the two excitation frequencies). The resulting modulated optical light beam is made to pass through a polarizing filter and is detected at the beat frequency, which can be chosen to equal the frame rate of an electronic camera or the rate of sampling the outputs of photodetectors in an array. The method was conceived to satisfy a need to perform highly accurate polarimetric imaging, without cross-talk between polarization channels, at frame rates of the order of tens of hertz. The use of electro-optical modulators is necessitated by a need to obtain accuracy greater than that attainable by use of static polarizing filters over separate fixed detectors. For imaging, photoelastic modulators are preferable to such other electrio-optical modulators as Kerr cells and Pockels cells in that photoelastic modulators operate at lower voltages, have greater angular acceptances, and are easier to use. Prior to the conception of the present method, polarimetric imaging at frame rates of tens of hertz using photoelastic modulators was not possible because the resonance frequencies of photoelastic modulators usually lie in the range from about 20 to about 100 kHz.

Theory of free electron vortices

PubMed Central

Schattschneider, P.; Verbeeck, J.

2011-01-01

The recent creation of electron vortex beams and their first practical application motivates a better understanding of their properties. Here, we develop the theory of free electron vortices with quantized angular momentum, based on solutions of the Schrödinger equation for cylindrical boundary conditions. The principle of transformation of a plane wave into vortices with quantized angular momentum, their paraxial propagation through round magnetic lenses, and the effect of partial coherence are discussed. PMID:21930017

Single-shot coherent diffraction imaging of microbunched relativistic electron beams for free-electron laser applications.

PubMed

Marinelli, A; Dunning, M; Weathersby, S; Hemsing, E; Xiang, D; Andonian, G; O'Shea, F; Miao, Jianwei; Hast, C; Rosenzweig, J B

2013-03-01

With the advent of coherent x rays provided by the x-ray free-electron laser (FEL), strong interest has been kindled in sophisticated diffraction imaging techniques. In this Letter, we exploit such techniques for the diagnosis of the density distribution of the intense electron beams typically utilized in an x-ray FEL itself. We have implemented this method by analyzing the far-field coherent transition radiation emitted by an inverse-FEL microbunched electron beam. This analysis utilizes an oversampling phase retrieval method on the transition radiation angular spectrum to reconstruct the transverse spatial distribution of the electron beam. This application of diffraction imaging represents a significant advance in electron beam physics, having critical applications to the diagnosis of high-brightness beams, as well as the collective microbunching instabilities afflicting these systems.

Wavelength locking of single emitters and multi-emitter modules: simulation and experiments

NASA Astrophysics Data System (ADS)

Yanson, Dan; Rappaport, Noam; Peleg, Ophir; Berk, Yuri; Dahan, Nir; Klumel, Genady; Baskin, Ilya; Levy, Moshe

2016-03-01

Wavelength-stabilized high-brightness single emitters are commonly used in fiber-coupled laser diode modules for pumping Yb-doped lasers at 976 nm, and Nd-doped ones at 808 nm. We investigate the spectral behavior of single emitters under wavelength-selective feedback from a volume Bragg (or hologram) grating (VBG) in a multi-emitter module. By integrating a full VBG model as a multi-layer thin film structure with commercial raytracing software, we simulated wavelength locking conditions as a function of beam divergence and angular alignment tolerances. Good correlation between the simulated VBG feedback strength and experimentally measured locking ranges, in both VBG misalignment angle and laser temperature, is demonstrated. The challenges of assembling multi-emitter modules based on beam-stacked optical architectures are specifically addressed, where the wavelength locking conditions must be achieved simultaneously with high fiber coupling efficiency for each emitter in the module. It is shown that angular misorientation between fast and slow-axis collimating optics can have a dramatic effect on the spectral and power performance of the module. We report the development of our NEON-S wavelength-stabilized fiber laser pump module, which uses a VBG to provide wavelength-selective optical feedback in the collimated portion of the beam. Powered by our purpose-developed high-brightness single emitters, the module delivers 47 W output at 11 A from an 0.15 NA fiber and a 0.3 nm linewidth at 976 nm. Preliminary wavelength-locking results at 808 nm are also presented.

Light modulated switches and radio frequency emitters

DOEpatents

Wilson, Mahlon T.; Tallerico, Paul J.

1982-01-01

The disclosure relates to a light modulated electron beam driven radiofrequency emitter. Pulses of light impinge on a photoemissive device which generates an electron beam having the pulse characteristics of the light. The electron beam is accelerated through a radiofrequency resonator which produces radiofrequency emission in accordance with the electron, hence, the light pulses.

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

NASA Astrophysics Data System (ADS)

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

2018-01-01

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately ten meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halavanau, A.; Hyun, J.; Mihalcea, D.

A photocathode, immersed in solenoidal magnetic field, can produce canonical-angular-momentum (CAM) dominated or “magnetized” electron beams. Such beams have an application in electron cooling of hadron beams and can also be uncoupled to yield asymmetric-emittance (“flat”) beams. In the present paper we explore the possibilities of the flat beam generation at Fermilab’s Accelerator Science and Technology (FAST) facility. We present optimization of the beam flatness and four-dimensional transverse emittance and investigate the mapping and its limitations of the produced eigen-emittances to conventional emittances using a skew-quadrupole channel. Possible application of flat beams at the FAST facility are also discussed.

Optical encrypted holographic memory using triple random phase-encoded multiplexing in photorefractive LiNbO3:Fe crystal

NASA Astrophysics Data System (ADS)

Tang, Li-Chuan; Hu, Guang W.; Russell, Kendra L.; Chang, Chen S.; Chang, Chi Ching

2000-10-01

We propose a new holographic memory scheme based on random phase-encoded multiplexing in a photorefractive LiNbO3:Fe crystal. Experimental results show that rotating a diffuser placed as a random phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with angular multiplexing offers further advantages. Storage capabilities can be optimized by using a post-image random phase plate in the path of the object beam. The technique is applied to a triple phase-encoded optical security system that takes advantage of the high angular selectivity of the angular-rotational multiplexing components.

Communication using VCSEL laser array

NASA Technical Reports Server (NTRS)

Goorjian, Peter M. (Inventor)

2008-01-01

Ultrafast directional beam switching, using coupled vertical cavity surface emitting lasers (VCSELs) is combined with a light modulator to provide information transfer at bit rates of tens of GHz. This approach is demonstrated to achieve beam switching frequencies of 32-50 GHz in some embodiments and directional beam switching with angular differences of about eight degrees. This switching scheme is likely to be useful for ultrafast optical networks at frequencies much higher than achievable with other approaches. A Mach-Zehnder interferometer, a Fabry-Perot etalon, or a semiconductor-based electro-absorption transmission channel, among others, can be used as a light modulator.

Validity of the paraxial approximation for electron acceleration with radially polarized laser beams.

PubMed

Marceau, Vincent; Varin, Charles; Piché, Michel

2013-03-15

In the study of laser-driven electron acceleration, it has become customary to work within the framework of paraxial wave optics. Using an exact solution to the Helmholtz equation as well as its paraxial counterpart, we perform numerical simulations of electron acceleration with a high-power TM(01) beam. For beam waist sizes at which the paraxial approximation was previously recognized valid, we highlight significant differences in the angular divergence and energy distribution of the electron bunches produced by the exact and the paraxial solutions. Our results demonstrate that extra care has to be taken when working under the paraxial approximation in the context of electron acceleration with radially polarized laser beams.

Propagation of modulated electron and X-ray beams through matter and interactions with radio-frequency structures

NASA Astrophysics Data System (ADS)

Harris, J. R.; Miller, R. B.

2018-02-01

The generation and evolution of modulated particle beams and their interactions with resonant radiofrequency (RF) structures are of fundamental interest for both particle accelerator and vacuum electronic systems. When the constraint of propagation in a vacuum is removed, the evolution of such beams can be greatly affected by interactions with matter including scattering, absorption, generation of atmospheric plasma, and the production of multiple generations of secondary particles. Here, we study the propagation of 21 MeV and 25 MeV electron beams produced in S-band and L-band linear accelerators, and their interaction with resonant RF structures, under a number of combinations of geometry, including transmission through both air and metal. Both resonant and nonresonant interactions were observed, with the resonant interactions indicating that the RF modulation on the electron beam is at least partially preserved as the beam propagates through air and metal. When significant thicknesses of metal are placed upstream of a resonant structure, preventing any primary beam electrons from reaching the structure, RF signals could still be induced in the structures. This indicated that the RF modulation present on the electron beam was also impressed onto the x-rays generated when the primary electrons were stopped in the metal, and that this RF modulation was also present on the secondary electrons generated when the x-rays struck the resonant structures. The nature of these interactions and their sensitivities to changes in system configurations will be discussed.

Discrete monotron oscillator having one-half wavelength coaxial resonator with one-quarter wavelength gap spacing

DOEpatents

Carlsten, B.E.; Haynes, W.B.

1998-02-03

A discrete monotron oscillator for use in a high power microwave device is formed with a microwave oscillator having a half-wavelength resonant coaxial microwave cavity operating in fundamental TEM mode for microwave oscillation with an inner conductor defining a drift tube for propagating an electron beam and an outer conductor coaxial with the inner conductor. The inner conductor defines a modulating gap and an extraction gap downstream of the modulating gap. The modulating gap and the extraction gap connect the coaxial microwave cavity with the drift tube so that energy for the microwave oscillation is extracted from the electron beam at the extraction gap and modulates the electron beam at the modulating gap. For high power operation, an annular electron beam is used. 8 figs.

Discrete monotron oscillator having one-half wavelength coaxial resonator with one-quarter wavelength gap spacing

DOEpatents

Carlsten, Bruce E.; Haynes, William B.

1998-01-01

A discrete monotron oscillator for use in a high power microwave device is formed with a microwave oscillator having a half-wavelength resonant coaxial microwave cavity operating in fundamental TEM mode for microwave oscillation with an inner conductor defining a drift tube for propagating an electron beam and an outer conductor coaxial with the inner conductor. The inner conductor defines a modulating gap and an extraction gap downstream of the modulating gap. The modulating gap and the extraction gap connect the coaxial microwave cavity with the drift tube so that energy for the microwave oscillation is extracted from the electron beam at the extraction gap and modulates the electron beam at the modulating gap. For high power operation, an annular electron beam is used.

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

DOE PAGES

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

2018-01-19

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately tenmore » meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.« less

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately tenmore » meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.« less

Angular distributions and polarization fractions of helium resonance radiation (n 1P - 1 1S) in the extreme ultraviolet

NASA Technical Reports Server (NTRS)

Mumma, M. J.; Misakian, M.; Jackson, W. M.; Faris, J. L.

1973-01-01

Angular intensity distributions of helium (n 1P - 1 1S) resonance photons with respect to the exciting electron beam are presented. The angular intensity distributions were measured at selected electron impact energies from 25 eV (near threshold) to 150 eV. Polarization fractions (Pi) were obtained by analyzing the data in terms of the theoretical relation between angular intensity distribution and Pi, i.e. Iota (theta) = Iota (90) (1 - Pi sq cos theta). The experimental values for Pi are compared with recent theoretical results and with previous experimental values for the (3 1P - 2 1S) transition.

Tunable orbital angular momentum mode filter based on optical geometric transformation.

PubMed

Huang, Hao; Ren, Yongxiong; Xie, Guodong; Yan, Yan; Yue, Yang; Ahmed, Nisar; Lavery, Martin P J; Padgett, Miles J; Dolinar, Sam; Tur, Moshe; Willner, Alan E

2014-03-15

We present a tunable mode filter for spatially multiplexed laser beams carrying orbital angular momentum (OAM). The filter comprises an optical geometric transformation-based OAM mode sorter and a spatial light modulator (SLM). The programmable SLM can selectively control the passing/blocking of each input OAM beam. We experimentally demonstrate tunable filtering of one or multiple OAM modes from four multiplexed input OAM modes with vortex charge of ℓ=-9, -4, +4, and +9. The measured output power suppression ratio of the propagated modes to the blocked modes exceeds 14.5 dB.

ATTO SECOND ELECTRON BEAMS GENERATION AND CHARACTERIZATION EXPERIMENT AT THE ACCELERATOR TEST FACILITY.

DOE Office of Scientific and Technical Information (OSTI.GOV)

ZOLOTOREV, M.; ZHOLENTS, A.; WANG, X.J.

2002-02-01

We are proposing an Atto-second electron beam generation and diagnostics experiment at the Brookhaven Accelerator Test facility (ATF) using 1 {micro}m Inverse Free Electron Laser (IFEL). The proposed experiment will be carried out by an BNL/LBNL collaboration, and it will be installed at the ATF beam line II. The proposed experiment will employ a one-meter long undulator with 1.8 cm period (VISA undulator). The electron beam energy will be 63 MeV with emittance less than 2 mm-mrad and energy spread less than 0.05%. The ATF photocathode injector driving laser will be used for energy modulation by Inverse Free Electron Lasermore » (IFEL). With 10 MW laser peak power, about 2% total energy modulation is expected. The energy modulated electron beam will be further bunched through either a drift space or a three magnet chicane into atto-second electron bunches. The attosecond electron beam bunches will be analyzed using the coherent transition radiation (CTR).« less

Enhanced tunable narrow-band THz emission from laser-modulated electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiang, D.; Stupakov, G.; /SLAC

2009-06-19

We propose and analyze a scheme to generate enhanced narrow-band terahertz (THz) radiation through down-conversion of the frequency of optical lasers using laser-modulated electron beams. In the scheme the electron beam is first energy modulated by two lasers with wave numbers k{sub 1} and k2, respectively. After passing through a dispersion section, the energy modulation is converted to density modulation. Due to the nonlinear conversion process, the beam will have density modulation at wave number k = nk{sub 1} + mk{sub 2}, where n and m are positive or negative integers. By properly choosing the parameters for the lasers andmore » dispersion section, one can generate density modulation at THz frequency in the beam using optical lasers. This density-modulated beam can be used to generate powerful narrow-band THz radiation. Since the THz radiation is in tight synchronization with the lasers, it should provide a high temporal resolution for the optical-pump THz-probe experiments. The central frequency of the THz radiation can be easily tuned by varying the wavelength of the two lasers and the energy chirp of the electron beam. The proposed scheme is in principle able to generate intense narrow-band THz radiation covering the whole THz range and offers a promising way towards the tunable intense narrow-band THz sources.« less

Laser frequency modulation with electron plasma

NASA Technical Reports Server (NTRS)

Burgess, T. J.; Latorre, V. R.

1972-01-01

When laser beam passes through electron plasma its frequency shifts by amount proportional to plasma density. This density varies with modulating signal resulting in corresponding modulation of laser beam frequency. Necessary apparatus is relatively inexpensive since crystals are not required.

Measurement of minority-carrier drift mobility in solar cells using a modulated electron beam

NASA Technical Reports Server (NTRS)

Othmer, S.; Hopkins, M. A.

1980-01-01

A determination of diffusivity on solar cells is here reported which utilizes a one dimensional treatment of diffusion under sinusoidal excitation. An intensity-modulated beam of a scanning electron microscope was used as a source of excitation. The beam was injected into the rear of the cell, and the modulated component of the induced terminal current was recovered phase sensitively. A Faraday cup to measure the modulated component of beam current was mounted next to the sample, and connected to the same electronics. A step up transformer and preamplifier were mounted on the sample holder. Beam currents on the order of 400-pA were used in order to minimize effects of high injection. The beam voltage was 34-kV, and the cell bias was kept at 0-V.

Space-multiplexed optical scanner.

PubMed

Riza, Nabeel A; Yaqoob, Zahid

2004-05-01

A low-loss two-dimensional optical beam scanner that is capable of delivering large (e.g., > 10 degrees) angular scans along the elevation as well as the azimuthal direction is presented. The proposed scanner is based on a space-switched parallel-serial architecture that employs a coarse-scanner module and a fine-scanner module that produce an ultrahigh scan space-fill factor, e.g., 900 x 900 distinguishable beams in a 10 degrees (elevation) x 10 degrees (azimuth) scan space. The experimentally demonstrated one-dimensional version of the proposed scanner has a supercontinuous scan, 100 distinguishable beam spots in a 2.29 degrees total scan range, and 1.5-dB optical insertion loss.

Magnetically confined electron beam system for high resolution electron transmission-beam experiments

NASA Astrophysics Data System (ADS)

Lozano, A. I.; Oller, J. C.; Krupa, K.; Ferreira da Silva, F.; Limão-Vieira, P.; Blanco, F.; Muñoz, A.; Colmenares, R.; García, G.

2018-06-01

A novel experimental setup has been implemented to provide accurate electron scattering cross sections from molecules at low and intermediate impact energies (1-300 eV) by measuring the attenuation of a magnetically confined linear electron beam from a molecular target. High-resolution electron energy is achieved through confinement in a magnetic gas trap where electrons are cooled by successive collisions with N2. Additionally, we developed and present a method to correct systematic errors arising from energy and angular resolution limitations. The accuracy of the entire measurement procedure is validated by comparing the N2 total scattering cross section in the considered energy range with benchmark values available in the literature.

ELECTRON BEAM SHAPING AND ITS APPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halavanau, Aliaksei

Transverse and longitudinal electron beam shaping is a crucial part of high-brightness electron accelerator operations. In this dissertation, we report on the corresponding beam dynamics research conducted at Fermilab Accelerator Science and Technology facility (FAST) and Argonne Wakeeld Accelerator (AWA). We demonstrate an experimental method for spatial laser and electron beam shaping using microlens arrays (MLAs) at a photoinjector facility. Such a setup was built at AWA and resulted in transverse emittance reduction by a factor of 2. We present transverse emittance partitioning methods that were recently employed at FAST facility. A strongly coupled electron beam was generated in anmore » axial magnetic eld and accelerated in 1.3 GHz SRF cavities to 34 MeV. It was then decoupled in Round-To-Flat beam transformer and beams with emittance asymmetry ratio of 100 were generated. We introduce the new methods of measuring electron beam canonical angular momentum, beam transformer optimization and beam image analysis. We also describe a potential longitudinal space-charge amplier setup for FAST high-energy beamline. As an outcome, a broadband partially coherent radiation in the UV range could be generated.« less

Radiation source

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the relativistic electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region of the high-density plasma target.

Elastic electron differential cross sections for argon atom in the intermediate energy range from 40 eV to 300 eV

NASA Astrophysics Data System (ADS)

Ranković, Miloš Lj.; Maljković, Jelena B.; Tökési, Károly; Marinković, Bratislav P.

2018-02-01

Measurements and calculations for electron elastic differential cross sections (DCS) of argon atom in the energy range from 40 to 300 eV are presented. DCS have been measured in the crossed beam arrangement of the electron spectrometer with an energy resolution of 0.5 eV and angular resolution of 1.5∘ in the range of scattering angles from 20∘ to 126∘. Both angular behaviour and energy dependence of DCS are obtained in a separate sets of experiments, while the absolute scale is achieved via relative flow method, using helium as a reference gas. All data is corrected for the energy transmission function, changes of primary electron beam current and target pressure, and effective path length (volume correction). DCSs are calculated in relativistic framework by expressing the Mott's cross sections in partial wave expansion. Our results are compared with other available data.

Transportation of high-current ion and electron beams in the accelerator drift gap in the presence of an additional electron background

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karas’, V. I., E-mail: karas@kipt.kharkov.ua; Kornilov, E. A.; Manuilenko, O. V.

2015-12-15

The dynamics of a high-current ion beam propagating in the drift gap of a linear induction accelerator with collective focusing is studied using 3D numerical simulations in the framework of the full system of the Vlasov–Maxwell equations (code KARAT). The ion beam is neutralized by a comoving electron beam in the current density and, partially, in space charge, since the velocities of electrons and ions differ substantially. The dynamics of the high-current ion beam is investigated for different versions of additional neutralization of its space charge. It is established that, for a given configuration of the magnetic field and inmore » the presence of a specially programmed injection of additional electrons from the boundary opposite to the ion injection boundary, the angular divergence of the ion beam almost vanishes, whereas the current of the ion beam at the exit from the accelerator drift gap changes insignificantly and the beam remains almost monoenergetic.« less

Transportation of high-current ion and electron beams in the accelerator drift gap in the presence of an additional electron background

NASA Astrophysics Data System (ADS)

Karas', V. I.; Kornilov, E. A.; Manuilenko, O. V.; Tarakanov, V. P.; Fedorovskaya, O. V.

2015-12-01

The dynamics of a high-current ion beam propagating in the drift gap of a linear induction accelerator with collective focusing is studied using 3D numerical simulations in the framework of the full system of the Vlasov-Maxwell equations (code KARAT). The ion beam is neutralized by a comoving electron beam in the current density and, partially, in space charge, since the velocities of electrons and ions differ substantially. The dynamics of the high-current ion beam is investigated for different versions of additional neutralization of its space charge. It is established that, for a given configuration of the magnetic field and in the presence of a specially programmed injection of additional electrons from the boundary opposite to the ion injection boundary, the angular divergence of the ion beam almost vanishes, whereas the current of the ion beam at the exit from the accelerator drift gap changes insignificantly and the beam remains almost monoenergetic.

Spatial intensity distribution of controlled-NOT gate carrying orbital angular momentum via photonic band gap structure

NASA Astrophysics Data System (ADS)

Zhang, Yan; Wang, Xiaorui; Zhe Zhang, Yun

2018-07-01

By employing the different topological charges of a Laguerre–Gaussian beam as a qubit, we experimentally demonstrate a controlled-NOT (CNOT) gate with light beams carrying orbital angular momentum via a photonic band gap structure in a hot atomic ensemble. Through a degenerate four-wave mixing process, the spatial distribution of the CNOT gate including splitting and spatial shift can be affected by the Kerr nonlinear effect in multilevel atomic systems. Moreover, the intensity variations of the CNOT gate can be controlled by the relative phase modulation. This research can be useful for applications in quantum information processing.

Generation of a spin-polarized electron beam by multipole magnetic fields.

PubMed

Karimi, Ebrahim; Grillo, Vincenzo; Boyd, Robert W; Santamato, Enrico

2014-03-01

The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin-magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope. Copyright © 2013 Elsevier B.V. All rights reserved.

Device and method for electron beam heating of a high density plasma

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high density plasma in a small localized region. A relativistic electron beam generator produces a high voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target plasma is ionized prior to application of the electron beam by means of a laser or other preionization source. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high density target plasma causing the relativistic electron beam to efficiently deposit its energy into a small localized region within the high density plasma target.

Curved singular beams for three-dimensional particle manipulation.

PubMed

Zhao, Juanying; Chremmos, Ioannis D; Song, Daohong; Christodoulides, Demetrios N; Efremidis, Nikolaos K; Chen, Zhigang

2015-07-13

For decades, singular beams carrying angular momentum have been a topic of considerable interest. Their intriguing applications are ubiquitous in a variety of fields, ranging from optical manipulation to photon entanglement, and from microscopy and coronagraphy to free-space communications, detection of rotating black holes, and even relativistic electrons and strong-field physics. In most applications, however, singular beams travel naturally along a straight line, expanding during linear propagation or breaking up in nonlinear media. Here, we design and demonstrate diffraction-resisting singular beams that travel along arbitrary trajectories in space. These curved beams not only maintain an invariant dark "hole" in the center but also preserve their angular momentum, exhibiting combined features of optical vortex, Bessel, and Airy beams. Furthermore, we observe three-dimensional spiraling of microparticles driven by such fine-shaped dynamical beams. Our findings may open up new avenues for shaped light in various applications.

Generation of high power sub millimeter radiation using free electron laser

NASA Astrophysics Data System (ADS)

Panwar, J.; Sharma, S. C.; Malik, P.; Yadav, M.; Sharma, R.

2018-03-01

We have developed an analytical formalism to study the emission of high power radiation lying in the sub millimetre range. A relativistic electron beam (REB) is velocity modulated by the pondermotive force exerted by the laser beams. After passing through the drift space, the beam gets density modulated which further interacts with the strong field wiggler and acquires a transverse velocity that couples with the modulated density of the beam in the presence of ion channel which contribute to the non-linear current density which further leads to the emission of the radiation. The output radiation can be modified by changing the wiggler parameters and the energy of the electron beam. The power of the output radiation is found to increase with the modulation. The obtained radiation can be employed for various applications.

Space environment simulation and sensor calibration facility

NASA Astrophysics Data System (ADS)

Engelhart, Daniel P.; Patton, James; Plis, Elena; Cooper, Russell; Hoffmann, Ryan; Ferguson, Dale; Hilmer, Robert V.; McGarity, John; Holeman, Ernest

2018-02-01

The Mumbo space environment simulation chamber discussed here comprises a set of tools to calibrate a variety of low flux, low energy electron and ion detectors used in satellite-mounted particle sensors. The chamber features electron and ion beam sources, a Lyman-alpha ultraviolet lamp, a gimbal table sensor mounting system, cryogenic sample mount and chamber shroud, and beam characterization hardware and software. The design of the electron and ion sources presented here offers a number of unique capabilities for space weather sensor calibration. Both sources create particle beams with narrow, well-characterized energetic and angular distributions with beam diameters that are larger than most space sensor apertures. The electron and ion sources can produce consistently low fluxes that are representative of quiescent space conditions. The particle beams are characterized by 2D beam mapping with several co-located pinhole aperture electron multipliers to capture relative variation in beam intensity and a large aperture Faraday cup to measure absolute current density.

Space environment simulation and sensor calibration facility.

PubMed

Engelhart, Daniel P; Patton, James; Plis, Elena; Cooper, Russell; Hoffmann, Ryan; Ferguson, Dale; Hilmer, Robert V; McGarity, John; Holeman, Ernest

2018-02-01

The Mumbo space environment simulation chamber discussed here comprises a set of tools to calibrate a variety of low flux, low energy electron and ion detectors used in satellite-mounted particle sensors. The chamber features electron and ion beam sources, a Lyman-alpha ultraviolet lamp, a gimbal table sensor mounting system, cryogenic sample mount and chamber shroud, and beam characterization hardware and software. The design of the electron and ion sources presented here offers a number of unique capabilities for space weather sensor calibration. Both sources create particle beams with narrow, well-characterized energetic and angular distributions with beam diameters that are larger than most space sensor apertures. The electron and ion sources can produce consistently low fluxes that are representative of quiescent space conditions. The particle beams are characterized by 2D beam mapping with several co-located pinhole aperture electron multipliers to capture relative variation in beam intensity and a large aperture Faraday cup to measure absolute current density.

500 MHz narrowband beam position monitor electronics for electron synchrotrons

NASA Astrophysics Data System (ADS)

Mohos, I.; Dietrich, J.

1998-12-01

Narrowband beam position monitor electronics were developed in the Forschungszentrum Jülich-IKP for the orbit measurement equipment used at ELSA Bonn. The equipment uses 32 monitor chambers, each with four capacitive button electrodes. The monitor electronics, consisting of an rf signal processing module (BPM-RF) and a data acquisition and control module (BPM-DAQ), sequentially process and measure the monitor signals and deliver calculated horizontal and vertical beam position data via a serial network.

Longitudinal bunch shaping of picosecond high-charge MeV electron beams

DOE PAGES

Beaudoin, B. L.; Thangaraj, J. C. T.; Edstrom, Jr., D.; ...

2016-10-20

With ever increasing demands for intensities in modern accelerators, the understanding of space-charge effects becomes crucial. Herein are presented measurements of optically shaped picosecond-long electron beams in a superconducting L-band linac over a wide range of charges, from 0.2 nC to 3.4 nC. At low charges, the shape of the electron beam is preserved, while at higher charge densities, modulations on the beam convert to energy modulations. Here, energy profile measurements using a spectrometer and time profile measurements using a streak camera reveal the dynamics of longitudinal space-charge on MeV-scale electron beams.

Longitudinal density modulation and energy conversion in intense beams.

PubMed

Harris, J R; Neumann, J G; Tian, K; O'Shea, P G

2007-08-01

Density modulation of charged particle beams may occur as a consequence of deliberate action, or may occur inadvertently because of imperfections in the particle source or acceleration method. In the case of intense beams, where space charge and external focusing govern the beam dynamics, density modulation may, under some circumstances, be converted to velocity modulation, with a corresponding conversion of potential energy to kinetic energy. Whether this will occur depends on the properties of the beam and the initial modulation. This paper describes the evolution of discrete and continuous density modulations on intense beams and discusses three recent experiments related to the dynamics of density-modulated electron beams.

Differential cross sections for electron capture in p + H2 collisions

NASA Astrophysics Data System (ADS)

Igarashi, Akinori; Gulyás, Laszlo; Ohsaki, Akihiko

2017-11-01

Projectile angular distributions for electron capture in p + H2 collisions at 25 and 75 keV impact energies, measured by Sharma et al. [Phys. Rev. A 86, 022706 (2012)], are calculated using the CDW-EIS and eikonal approximations. Angular distributions evaluated in the CDW-EIS approximation are in good agreement with the experimental data measured for coherent projectile beams. Incoherent projectile scatterings are also considered by folding the coherent angular distributions over the transverse momentum distribution of the projectile wave-packet. Reasonable agreements with the measurements are obtained only with coherence parameters very different from those reported in the experiments.

Methods and devices for measuring orbital angular momentum states of electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

McMorran, Benjamin J.; Harvey, Tyler R.

A device for measuring electron orbital angular momentum states in an electron microscope includes the following components aligned sequentially in the following order along an electron beam axis: a phase unwrapper (U) that is a first electrostatic refractive optical element comprising an electrode and a conductive plate, where the electrode is aligned perpendicular to the conductive plate; a first electron lens system (L1); a phase corrector (C) that is a second electrostatic refractive optical element comprising an array of electrodes with alternating electrostatic bias; and a second electron lens system (L2). The phase unwrapper may be a needle electrode ormore » knife edge electrode.« less

High energy micro electron beam generation using chirped laser pulse in the presence of an axial magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akou, H., E-mail: h.akou@nit.ac.ir; Hamedi, M.

2015-10-15

In this paper, the generation of high-quality and high-energy micro electron beam in vacuum by a chirped Gaussian laser pulse in the presence of an axial magnetic field is numerically investigated. The features of energy and angular spectra, emittances, and position distribution of electron beam are compared in two cases, i.e., in the presence and absence of an external magnetic field. The electron beam is accelerated with higher energy and qualified in spatial distribution in the presence of the magnetic field. The presence of an axial magnetic field improves electron beam spatial quality as well as its gained energy throughmore » keeping the electron motion parallel to the direction of propagation for longer distances. It has been found that a 64 μm electron bunch with about MeV initial energy becomes a 20 μm electron beam with high energy of the order of GeV, after interacting with a laser pulse in the presence of an external magnetic field.« less

Electron intensity modulation for mixed-beam radiation therapy with an x-ray multi-leaf collimator

NASA Astrophysics Data System (ADS)

Weinberg, Rebecca

The current standard treatment for head and neck cancer at our institution uses intensity-modulated x-ray therapy (IMRT), which improves target coverage and sparing of critical structures by delivering complex fluence patterns from a variety of beam directions to conform dose distributions to the shape of the target volume. The standard treatment for breast patients is field-in-field forward-planned IMRT, with initial tangential fields and additional reduced-weight tangents with blocking to minimize hot spots. For these treatment sites, the addition of electrons has the potential of improving target coverage and sparing of critical structures due to rapid dose falloff with depth and reduced exit dose. In this work, the use of mixed-beam therapy (MBT), i.e., combined intensity-modulated electron and x-ray beams using the x-ray multi-leaf collimator (MLC), was explored. The hypothesis of this study was that addition of intensity-modulated electron beams to existing clinical IMRT plans would produce MBT plans that were superior to the original IMRT plans for at least 50% of selected head and neck and 50% of breast cases. Dose calculations for electron beams collimated by the MLC were performed with Monte Carlo methods. An automation system was created to facilitate communication between the dose calculation engine and the treatment planning system. Energy and intensity modulation of the electron beams was accomplished by dividing the electron beams into 2x2-cm2 beamlets, which were then beam-weight optimized along with intensity-modulated x-ray beams. Treatment plans were optimized to obtain equivalent target dose coverage, and then compared with the original treatment plans. MBT treatment plans were evaluated by participating physicians with respect to target coverage, normal structure dose, and overall plan quality in comparison with original clinical plans. The physician evaluations did not support the hypothesis for either site, with MBT selected as superior in 1 out of the 15 head and neck cases (p=1) and 6 out of 18 breast cases (p=0.95). While MBT was not shown to be superior to IMRT, reductions were observed in doses to critical structures distal to the target along the electron beam direction and to non-target tissues, at the expense of target coverage and dose homogeneity.

Energy modulation of nonrelativistic electrons with a CO2 laser using a metal microslit

NASA Astrophysics Data System (ADS)

Bae, Jongsuck; Ishikawa, Ryo; Okuyama, Sumio; Miyajima, Takashi; Akizuki, Taiji; Okamoto, Tatsuya; Mizuno, Koji

2000-04-01

A metal microslit has been used as an interaction circuit between a CO2 laser beam and nonrelativistic free electrons. Evanescent waves which are induced on the slit by illumination of the laser light modulate the energy of electrons passing close to the surface of the slit. The electron-energy change of more than ±5 eV for the 80 keV electron beam has been observed using the 7 kW laser beam at the wavelength of 10.6 μm.

Attosecond electron bunches from a nanofiber driven by Laguerre-Gaussian laser pulses.

PubMed

Hu, Li-Xiang; Yu, Tong-Pu; Sheng, Zheng-Ming; Vieira, Jorge; Zou, De-Bin; Yin, Yan; McKenna, Paul; Shao, Fu-Qiu

2018-05-08

Generation of attosecond bunches of energetic electrons offers significant potential from ultrafast physics to novel radiation sources. However, it is still a great challenge to stably produce such electron beams with lasers, since the typical subfemtosecond electron bunches from laser-plasma interactions either carry low beam charge, or propagate for only several tens of femtoseconds. Here we propose an all-optical scheme for generating dense attosecond electron bunches via the interaction of an intense Laguerre-Gaussian (LG) laser pulse with a nanofiber. The dense bunch train results from the unique field structure of a circularly polarized LG laser pulse, enabling each bunch to be phase-locked and accelerated forward with low divergence, high beam charge and large beam-angular-momentum. This paves the way for wide applications in various fields, e.g., ultrabrilliant attosecond x/γ-ray emission.

Photon Beaming in External Compton models

NASA Astrophysics Data System (ADS)

Hutter, Anne; Spanier, Felix

In attempt to model blazar emission spectra, External Compton models have been employed to fit the observed data. In these models photons from the accretion disk or the CMB are upscat-tered via the Compton effect by the electrons and contribute to the emission. In previous works the resulting scattered photon angular distribution has been calculated for ultrarelativistic elec-trons. This work aims to extend the result to the case of mildly relativistic electrons. Hence, the beaming pattern produced by a relativistic moving blob consisting of isotropic distributed electrons, which scatter photons of an isotropic external radiation is calculated numerically. The isotropic photon density distribution in the blob frame is Lorentz-transformed into the rest frame of the electron and results in an anisotropic distribution with a preferred direction where it is upscattered by the electrons. The photon density distribution is determined and transformed back into the blob frame. As the photons in the rest frame of the electrons are dis-tributed anisotropically the scattering does not reproduce this anisotropic distribution. When transforming back into the blob frame the resulting photon distribution won't be isotropic. Approximations have shown that the resulting photon distribution is boosted more strongly than a distribution assumed to be isotropic in the rest frame of the electrons. Hence, in order to obtain the beaming caused by external Compton it is of particular interest to derive a more exact approximation of the resulting photon angular distribution.

RHEED-TRAXS as a tool for in-situ stoichiometry control.

NASA Astrophysics Data System (ADS)

Chandril, Sandeep; Keenan, Cameron; Myers, Thomas; Lederman, David

2008-03-01

RHEED-total reflection x-ray spectroscopy (-TRAXS) is an in-situ chemical and structural characterization technique which is highly surface sensitive. This consists of a grazing-angle electron beam from which characteristic x-rays from the sample are measured also at grazing angles. We have demonstrated that monolayer sensitivity in Y and Mn films on GaN can be achieved. We have also developed a theoretical model for the angular dependence of the x-ray Kα peaks for the thin films, based on Parratt's formalism for x-ray reflectivity and the electron trajectory simulation software CASINO, to correct for grazing angle electron beam as a source for x-rays. As the angular dependence is highly dependent upon the film thickness and the smoothness of the film, it can be used to determine the deposition rate of individual elements as well as the interface chemical roughness

Soft X-ray spectrometer design for warm dense plasma measurements on DARHT Axis-I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramey, Nicholas Bryan; Perry, John Oliver; Coleman, Joshua Eugene

2017-07-11

A preliminary design study is being performed on a soft X-ray spectrometer to measure K-shell spectra emitted by a warm dense plasma generated on Axis-I of the Dual-Axis Radiographic Hydrodynamic Testing (DARHT) facility at Los Alamos National Laboratory. The 100-ns-long intense, relativistic electron pulse with a beam current of 1.7 kA and energy of 19.8 MeV deposits energy into a thin metal foil heating it to a warm dense plasma. The collisional ionization of the target by the electron beam produces an anisotropic angular distribution of K-shell radiation and a continuum of both scattered electrons and Bremsstrahlung up to themore » beam energy of 19.8 MeV. The principal goal of this project is to characterize these angular distributions to determine the optimal location to deploy the soft X-ray spectrometer. In addition, a proof-of-principle design will be presented. The ultimate goal of the spectrometer is to obtain measurements of the plasma temperature and density to benchmark equation-of-state models of the warm dense matter regime.« less

A spin-modulated telescope for measurement of cosmic microwave background anisotropy

NASA Astrophysics Data System (ADS)

Staren, John William

The measurement of anisotropy in the Cosmic Microwave Background (CMB) advances our knowledge of the early Universe from which the radiation originated. The angular power spectrum of CMB anisotropy at sub-degree scales depends heavily on comsological parameters such as Ob, O 0 and H0. In pursuit of critical power spectrum measurements over a range of angular scales, a spin-modulated telescope with a single cryogenic amplifier used in a total power radiometer is designed, built and tested. The new technique of spin-modulation with a spinning flat mirror canted 2.5° relative to its spin axis modulates the beam in a 10° oval pattern on the sky at 2.5 Hz. This rapid two-dimensional modulation of the beam is tested at balloon altitudes to minimize the atmospheric offset and determine the efficacy of the scan and telescope design. Maps of over 600 and 400 square degrees are made of regions observed using the spin-modulation and a 20° azimuth scan. These maps yield a 95% confidence level flat band power upper limit of DeltaTℓ = Tcmb(ℓ(ℓ + 1)Cℓ/2pi)0.5 < 77 muK at ℓ = 38 and are free of systematics effects and striping due to long-term drifts in our amplifier to the levels tested here. Planning for the next telescope, with multiple amplifiers, is performed to ensure its success.

Toward single mode, atomic size electron vortex beams.

PubMed

Krivanek, Ondrej L; Rusz, Jan; Idrobo, Juan-Carlos; Lovejoy, Tracy J; Dellby, Niklas

2014-06-01

We propose a practical method of producing a single mode electron vortex beam suitable for use in a scanning transmission electron microscope (STEM). The method involves using a holographic "fork" aperture to produce a row of beams of different orbital angular momenta, as is now well established, magnifying the row so that neighboring beams are separated by about 1 µm, selecting the desired beam with a narrow slit, and demagnifying the selected beam down to 1-2 Å in size. We show that the method can be implemented by adding two condenser lenses plus a selection slit to a straight-column cold-field emission STEM. It can also be carried out in an existing instrument, the monochromated Nion high-energy-resolution monochromated electron energy-loss spectroscopy-STEM, by using its monochromator in a novel way. We estimate that atom-sized vortex beams with ≥ 20 pA of current should be attainable at 100-200 keV in either instrument.

Electron beam cooling in intense focussed laser pulses

NASA Astrophysics Data System (ADS)

Yoffe, Samuel R.; Noble, Adam; Macleod, Alexander J.; Jaroszynski, Dino A.

2017-05-01

In the coming years, a new generation of high-power laser facilities (such as the Extreme Light Infrastructure) will become operational, for which it is important to understand how the interaction with intense laser pulses affects the bulk properties of relativistic electron bunches. At such high field intensities, we expect both radiation reaction and quantum effects to have a dominant role to play in determining the dynamics. The reduction in relative energy spread (beam cooling) at the expense of mean beam energy predicted by classical theories of radiation reaction has been shown to occur equally in the longitudinal and transverse directions, whereas this symmetry is broken when the theory is extended to approximate certain quantum effects. The reduction in longitudinal cooling suggests that the effects of radiation reaction could be better observed in measurements of the transverse distribution, which for real-world laser pulses motivates the investigation of the angular dependence of the interaction. Using a stochastic single-photon emission model with a (Gaussian beam) focussed pulse, we find strong angular dependence of the stochastic heating.

Focusing properties of cylindrical vector vortex beams

NASA Astrophysics Data System (ADS)

Xiaoqiang, Zhang; Ruishan, Chen; Anting, Wang

2018-05-01

In this paper, following Richards and Wolf vectorial diffraction theory, the focusing properties of cylindrical vector vortex beams (CVVB) are investigated, and a diffractive optical element (DOE) is designed to spatially modulate the amplitude of the CVVB. Simulated results show that the CVVB focused by an objective also carry orbital angular momentum (OAM), and the optical fields near the focal region can be modulated by changing the topological charge of the CVVB. We numerically simulate the focus properties of radially and azimuthally polarized beams with topological charge equal to 0, 1, 2 and 10 respectively. As a result, a dark channel with a length about 20 λ can be obtained. These new properties have the potential applications such as particle acceleration, optical trapping and material processing.

Light-driven phase shifter

DOEpatents

Early, James W.

1990-01-01

A light-driven phase shifter is provided for modulating a transmission light beam. A gaseous medium such as argon is provided with electron energy states excited to populate a metastable state. A tunable dye laser is selected with a wavelength effective to deplete the metastable electron state and may be intensity modulated. The dye laser is directed through the gaseous medium to define a first optical path having an index of refraction determined by the gaseous medium having a depleted metastable electron state. A transmission laser beam is also directed through the gaseous medium to define a second optical path at least partially coincident with the first optical path. The intensity of the dye laser beam may then be varied to phase modulate the transmission laser beam.

Self-consistent analysis of radiation and relativistic electron beam dynamics in a helical wiggler using Lienard-Wiechert fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tecimer, M.; Elias, L.R.

1995-12-31

Lienard-Wiechert (LW) fields, which are exact solutions of the Wave Equation for a point charge in free space, are employed to formulate a self-consistent treatment of the electron beam dynamics and the evolution of the generated radiation in long undulators. In a relativistic electron beam the internal forces leading to the interaction of the electrons with each other can be computed by means of retarded LW fields. The resulting electron beam dynamics enables us to obtain three dimensional radiation fields starting from an initial incoherent spontaneous emission, without introducing a seed wave at start-up. Based on the formalism employed here,more » both the evolution of the multi-bucket electron phase space dynamics in the beam body as well as edges and the relative slippage of the radiation with respect to the electrons in the considered short bunch are naturally embedded into the simulation model. In this paper, we present electromagnetic radiation studies, including multi-bucket electron phase dynamics and angular distribution of radiation in the time and frequency domain produced by a relativistic short electron beam bunch interacting with a circularly polarized magnetic undulator.« less

Energy modulation of nonrelativistic electrons in an optical near field on a metal microslit

NASA Astrophysics Data System (ADS)

Ishikawa, R.; Bae, J.; Mizuno, K.

2001-04-01

Energy modulation of nonrelativistic electrons with a laser beam using a metal microslit as an interaction circuit has been investigated. An optical near field is induced in the proximity of the microslit by illumination of the laser beam. The electrons passing close to the slit are accelerated or decelerated by an evanescent wave contained in the near field whose phase velocity is equal to the velocity of the electrons. The electron-evanescent wave interaction in the microslit has been analyzed theoretically and experimentally. The theory has predicted that electron energy can be modulated at optical frequencies. Experiments performed in the infrared region have verified theoretical predictions. The electron-energy changes of more than ±5 eV with a 10 kW CO2 laser pulse at the wavelength of 10.6 μm has been successfully observed for an electron beam with an energy of less than 80 keV.

Adaptive electron beam shaping using a photoemission gun and spatial light modulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.

The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam imagemore » to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.« less

Adaptive electron beam shaping using a photoemission gun and spatial light modulator

NASA Astrophysics Data System (ADS)

Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.; Kiefer, Jacob; Bazarov, Ivan

2015-02-01

The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.

Adaptive electron beam shaping using a photoemission gun and spatial light modulator

DOE PAGES

Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.; ...

2015-02-01

The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam imagemore » to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.« less

Flat-Lens Focusing of Electron Beams in Graphene

PubMed Central

Tang, Yang; Cao, Xiyuan; Guo, Ran; Zhang, Yanyan; Che, Zhiyuan; Yannick, Fouodji T.; Zhang, Weiping; Du, Junjie

2016-01-01

Coupling electron beams carrying information into electronic units is fundamental in microelectronics. This requires precision manipulation of electron beams through a coupler with a good focusing ability. In graphene, the focusing of wide electron beams has been successfully demonstrated by a circular p-n junction. However, it is not favorable for information coupling since the focal length is so small that the focal spot locates inside the circular gated region, rather than in the background region. Here, we demonstrate that an array of gate-defined quantum dots, which has gradually changing lattice spacing in the direction transverse to propagation, can focus electrons outside itself, providing a possibility to make a coupler in graphene. The focusing effect can be understood as due to the gradient change of effective refractive indices, which are defined by the local energy band in a periodic potential. The strong focusing can be achieved by suitably choosing the lattice gradient and the layer number in the incident direction, offering an effective solution to precision manipulation of electron beams with wide electron energy range and high angular tolerance. PMID:27628099

Continuous Beam Steering From a Segmented Liquid Crystal Optical Phased Array

NASA Technical Reports Server (NTRS)

Titus, Charles M.; Pouch, John; Nguyen, Hung; Miranda, Felix; Bos, Philip J.

2002-01-01

Optical communications to and from deep space probes will require beams possessing divergence on the order of a microradian, and must be steered with sub-microradian precision. Segmented liquid crystal spatial phase modulators, a type of optical phased array, are considered for this ultra-high resolution beam steering. It is shown here that in an ideal device of this type, there are ultimately no restrictions on the angular resolution. Computer simulations are used to obtain that result, and to analyze the influence of beam truncation and substrate flatness on the performance of this type of device.

Continuous Beam Steering From A Segmented Liquid Crystal Optical Phased Array

NASA Technical Reports Server (NTRS)

Pouch, John; Nguyen, Hung; Miranda, Felix; Titus, Charles M.; Bos, Philip J.

2002-01-01

Optical communications to and from deep space probes will require beams possessing divergence on the order of a microradian, and must be steered with sub-microradian precision. Segmented liquid crystal spatial phase modulators, a type of optical phased array, are considered for this ultra-high resolution beam steering. It is shown here that in an ideal device of this type, there are ultimately no restrictions on the angular resolution. Computer simulations are used to obtain that result, and to analyze the influence of beam truncation and substrate flatness on the performance of this type of device.

Near-field collimation of light carrying orbital angular momentum with bull's-eye-assisted plasmonic coaxial waveguides.

PubMed

Pu, Mingbo; Ma, Xiaoliang; Zhao, Zeyu; Li, Xiong; Wang, Yanqin; Gao, Hui; Hu, Chenggang; Gao, Ping; Wang, Changtao; Luo, Xiangang

2015-07-10

The orbital angular momentum (OAM) of light, as an emerging hotspot in optics and photonics, introduces many degrees of freedom for applications ranging from optical communication and quantum processing to micromanipulation. To achieve a high degree of integration, optical circuits for OAM light are essential, which are, however, challenging in the optical regime owing to the lack of well-developed theory. Here we provide a scheme to guide and collimate the OAM beam at the micro- and nano-levels. The coaxial plasmonic slit was exploited as a naturally occurring waveguide for light carrying OAM. Concentric grooves etched on the output surface of the coaxial waveguide were utilized as a plasmonic metasurface to couple the OAM beam to free space with greatly increased beam directivity. Experimental results at λ = 532 nm validated the novel transportation and collimating effect of the OAM beam. Furthermore, dynamic tuning of the topological charges was demonstrated by using a liquid crystal spatial light modulator (SLM).

Near-field collimation of light carrying orbital angular momentum with bull’s-eye-assisted plasmonic coaxial waveguides

NASA Astrophysics Data System (ADS)

Pu, Mingbo; Ma, Xiaoliang; Zhao, Zeyu; Li, Xiong; Wang, Yanqin; Gao, Hui; Hu, Chenggang; Gao, Ping; Wang, Changtao; Luo, Xiangang

2015-07-01

The orbital angular momentum (OAM) of light, as an emerging hotspot in optics and photonics, introduces many degrees of freedom for applications ranging from optical communication and quantum processing to micromanipulation. To achieve a high degree of integration, optical circuits for OAM light are essential, which are, however, challenging in the optical regime owing to the lack of well-developed theory. Here we provide a scheme to guide and collimate the OAM beam at the micro- and nano-levels. The coaxial plasmonic slit was exploited as a naturally occurring waveguide for light carrying OAM. Concentric grooves etched on the output surface of the coaxial waveguide were utilized as a plasmonic metasurface to couple the OAM beam to free space with greatly increased beam directivity. Experimental results at λ = 532 nm validated the novel transportation and collimating effect of the OAM beam. Furthermore, dynamic tuning of the topological charges was demonstrated by using a liquid crystal spatial light modulator (SLM).

Near-field collimation of light carrying orbital angular momentum with bull’s-eye-assisted plasmonic coaxial waveguides

PubMed Central

Pu, Mingbo; Ma, Xiaoliang; Zhao, Zeyu; Li, Xiong; Wang, Yanqin; Gao, Hui; Hu, Chenggang; Gao, Ping; Wang, Changtao; Luo, Xiangang

2015-01-01

The orbital angular momentum (OAM) of light, as an emerging hotspot in optics and photonics, introduces many degrees of freedom for applications ranging from optical communication and quantum processing to micromanipulation. To achieve a high degree of integration, optical circuits for OAM light are essential, which are, however, challenging in the optical regime owing to the lack of well-developed theory. Here we provide a scheme to guide and collimate the OAM beam at the micro- and nano-levels. The coaxial plasmonic slit was exploited as a naturally occurring waveguide for light carrying OAM. Concentric grooves etched on the output surface of the coaxial waveguide were utilized as a plasmonic metasurface to couple the OAM beam to free space with greatly increased beam directivity. Experimental results at λ = 532 nm validated the novel transportation and collimating effect of the OAM beam. Furthermore, dynamic tuning of the topological charges was demonstrated by using a liquid crystal spatial light modulator (SLM). PMID:26159423

Compact beam transport system for free-electron lasers driven by a laser plasma accelerator

DOE PAGES

Liu, Tao; Zhang, Tong; Wang, Dong; ...

2017-02-01

Utilizing laser-driven plasma accelerators (LPAs) as a high-quality electron beam source is a promising approach to significantly downsize the x-ray free-electron laser (XFEL) facility. A multi-GeV LPA beam can be generated in several-centimeter acceleration distance, with a high peak current and a low transverse emittance, which will considerably benefit a compact FEL design. However, the large initial angular divergence and energy spread make it challenging to transport the beam and realize FEL radiation. In this paper, a novel design of beam transport system is proposed to maintain the superior features of the LPA beam and a transverse gradient undulator (TGU)more » is also adopted as an effective energy spread compensator to generate high-brilliance FEL radiation. As a result, theoretical analysis and numerical simulations are presented based on a demonstration experiment with an electron energy of 380 MeV and a radiation wavelength of 30 nm.« less

High-speed femtosecond laser beam shaping based on binary holography using a digital micromirror device.

PubMed

Cheng, Jiyi; Gu, Chenglin; Zhang, Dapeng; Chen, Shih-Chi

2015-11-01

In this Letter, we present a digital micromirror device (DMD)-based ultrafast beam shaper, i.e., DUBS. To our knowledge, the DUBS is the first binary laser beam shaper that can generate high-resolution (1140×912 pixels) arbitrary beam modes for femtosecond lasers at a rate of 4.2 kHz; the resolution and pattern rate are limited by the DMD. In the DUBS, the spectrum of the input pulsed laser is first angularly dispersed by a transmission grating and subsequently imaged to a DMD with beam modulation patterns; the transmission grating and a high-reflectivity mirror together compensate the angular dispersion introduced by the DMD. The mode of the output beam is monitored by a CCD camera. In the experiments, the DUBS is programmed to generate four different beam modes, including an Airy beam, Bessel beam, Laguerre-Gaussian (LG) beam, and a custom-designed "peace-dove" beam via the principle of binary holography. To verify the high shaping rate, the Airy beam and LG beam are generated alternately at 4.2 kHz, i.e., the maximum pattern rate of our DMD. The overall efficiency of the DUBS is measured to be 4.7%. With the high-speed and high-resolution beam-shaping capability, the DUBS may find important applications in nonlinear microscopy, optical manipulation, and microscale/nanoscale laser machining, etc.

Free-space wavelength-multiplexed optical scanner demonstration.

PubMed

Yaqoob, Zahid; Riza, Nabeel A

2002-09-10

Experimental demonstration of a no-moving-parts free-space wavelength-multiplexed optical scanner (W-MOS) is presented. With fast tunable lasers or optical filters and planar wavelength dispersive elements such as diffraction gratings, this microsecond-speed scanner enables large several-centimeter apertures for subdegree angular scans. The proposed W-MOS design incorporates a unique optical amplifier and variable optical attenuator combination that enables the calibration and modulation of the scanner response, leading to any desired scanned laser beam power shaping. The experimental setup uses a tunable laser centered at 1560 nm and a 600-grooves/mm blazed reflection grating to accomplish an angular scan of 12.92 degrees as the source is tuned over an 80-nm bandwidth. The values for calculated maximum optical beam divergance, required wavelength resolution, beam-pointing accuracy, and measured scanner insertion loss are 1.076 mrad, 0.172 nm, 0.06 mrad, and 4.88 dB, respectively.

Attosecond time-energy structure of X-ray free-electron laser pulses

NASA Astrophysics Data System (ADS)

Hartmann, N.; Hartmann, G.; Heider, R.; Wagner, M. S.; Ilchen, M.; Buck, J.; Lindahl, A. O.; Benko, C.; Grünert, J.; Krzywinski, J.; Liu, J.; Lutman, A. A.; Marinelli, A.; Maxwell, T.; Miahnahri, A. A.; Moeller, S. P.; Planas, M.; Robinson, J.; Kazansky, A. K.; Kabachnik, N. M.; Viefhaus, J.; Feurer, T.; Kienberger, R.; Coffee, R. N.; Helml, W.

2018-04-01

The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

Absorptive pinhole collimators for ballistic Dirac fermions in graphene

PubMed Central

Barnard, Arthur W.; Hughes, Alex; Sharpe, Aaron L.; Watanabe, Kenji; Taniguchi, Takashi; Goldhaber-Gordon, David

2017-01-01

Ballistic electrons in solids can have mean free paths far larger than the smallest features patterned by lithography. This has allowed development and study of solid-state electron-optical devices such as beam splitters and quantum point contacts, which have informed our understanding of electron flow and interactions. Recently, high-mobility graphene has emerged as an ideal two-dimensional semimetal that hosts unique chiral electron-optical effects due to its honeycomb crystalline lattice. However, this chiral transport prevents the simple use of electrostatic gates to define electron-optical devices in graphene. Here we present a method of creating highly collimated electron beams in graphene based on collinear pairs of slits, with absorptive sidewalls between the slits. By this method, we achieve beams with angular width 18° or narrower, and transmission matching classical ballistic predictions. PMID:28504264

Attainment of Electron Beam Suitable for Medium Energy Electron Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seletskiy, Sergei M.

Electron cooling of charged particle beams is a well-established technique at electron energies of up to 300 keV. However, up to the present time the advance of electron cooling to the MeV-range energies has remained a purely theoretical possibility. The electron cooling project at Fermilab has recently demonstrated the ¯rst cooling of 8.9 GeV/c antiprotons in the Recycler ring, and therefore, has proved the validity of the idea of relativistic electron cool- ing. The Recycler Electron Cooler (REC) is the key component of the Teva- tron Run II luminosity upgrade project. Its performance depends critically on the quality of electronmore » beam. A stable electron beam of 4.3 MeV car- rying 0.5 A of DC current is required. The beam suitable for the Recycler Electron Cooler must have an angular spread not exceeding 200 ¹rad. The full-scale prototype of the REC was designed, built and tested at Fermilab in the Wideband laboratory to study the feasibility of attaining the high-quality electron beam. In this thesis I describe various aspects of development of the Fermilab electron cooling system, and the techniques used to obtain the electron beam suitable for the cooling process. In particular I emphasize those aspects of the work for which I was principally responsible.« less

Plasma based optical guiding of an amplitude-modulated electromagnetic beam

NASA Astrophysics Data System (ADS)

Singh, Mamta; Gupta, D. N.

2015-06-01

We propose the stronger optical guiding of an electromagnetic beam in a plasma by considering the amplitude modulation of the fundamental beam. With the advent of high power source of electromagnetic radiation, the electron velocity in a plasma may become quite large (comparable to the light velocity in free space). Thus, the effect of relativistic mass variation must be taken into account. The relativistic effect of the laser propagation in a plasma leads to self-focusing because of the dielectric constant of a plasma being an increasing function of the intensity. The ponderomotive force of the laser beam pushes the electrons out of the region of high intensity, which reduces the local electron density and increases the plasma dielectric function further, leading to even more selffocusing of the laser. In this work, we consider a short pulse laser of finite spot size as an amplitude modulation in time. Our findings show an efficient optical guiding mechanism based on amplitude modulation signal propagation in plasmas. Medium nonlinearity becomes stronger if an amplitude modulated beam is introduced, which contributes significantly in laser guiding in plasmas. Furthermore, the rate of laser self-focusing is increased with modulation index due the fact of stronger Kerr effect. The study related to amplitude modulated optical signal may be useful for communication technology.

There are many ways to spin a photon: Half-quantization of a total optical angular momentum

PubMed Central

Ballantine, Kyle E.; Donegan, John F.; Eastham, Paul R.

2016-01-01

The angular momentum of light plays an important role in many areas, from optical trapping to quantum information. In the usual three-dimensional setting, the angular momentum quantum numbers of the photon are integers, in units of the Planck constant ħ. We show that, in reduced dimensions, photons can have a half-integer total angular momentum. We identify a new form of total angular momentum, carried by beams of light, comprising an unequal mixture of spin and orbital contributions. We demonstrate the half-integer quantization of this total angular momentum using noise measurements. We conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization. PMID:28861467

Coherent infrared radiation from the ALS generated via femtosecond laser modulation of the electron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byrd, J.M.; Hao, Z.; Martin, M.C.

2004-07-01

Interaction of an electron beam with a femtosecond laser pulse co-propagating through a wiggler at the ALS produces large modulation of the electron energies within a short {approx}100 fs slice of the electron bunch. Propagating around the storage ring, this bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories. The length of the perturbation evolves with a distance from the wiggler but is much shorter than the electron bunch length. This perturbation causes the electron bunch to emit short pulses of temporally and spatially coherent infrared light which are automatically synchronized to the modulating laser. Themore » intensity and spectra of the infrared light were measured in two storage ring locations for a nominal ALS lattice and for an experimental lattice with the higher momentum compaction factor. The onset of instability stimulated by laser e-beam interaction had been discovered. The infrared signal is now routinely used as a sensitive monitor for a fine tuning of the laser beam alignment during data accumulation in the experiments with femtosecond x-ray pulses.« less

Twisting Neutron Waves

NASA Astrophysics Data System (ADS)

Pushin, Dmitry

Most waves encountered in nature can be given a ``twist'', so that their phase winds around an axis parallel to the direction of wave propagation. Such waves are said to possess orbital angular momentum (OAM). For quantum particles such as photons, atoms, and electrons, this corresponds to the particle wavefunction having angular momentum of Lℏ along its propagation axis. Controlled generation and detection of OAM states of photons began in the 1990s, sparking considerable interest in applications of OAM in light and matter waves. OAM states of photons have found diverse applications such as broadband data multiplexing, massive quantum entanglement, optical trapping, microscopy, quantum state determination and teleportation, and interferometry. OAM states of electron beams have been used to rotate nanoparticles, determine the chirality of crystals and for magnetic microscopy. Here I discuss the first demonstration of OAM control of neutrons. Using neutron interferometry with a spatially incoherent input beam, we show the addition and conservation of quantum angular momenta, entanglement between quantum path and OAM degrees of freedom. Neutron-based quantum information science heretofore limited to spin, path, and energy degrees of freedom, now has access to another quantized variable, and OAM modalities of light, x-ray, and electron beams are extended to a massive, penetrating neutral particle. The methods of neutron phase imprinting demonstrated here expand the toolbox available for development of phase-sensitive techniques of neutron imaging. Financial support provided by the NSERC Create and Discovery programs, CERC and the NIST Quantum Information Program is acknowledged.

Observation of the Self-Modulation Instability via Time-Resolved Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gross, M.; Engel, J.; Good, J.

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximatelymore » $$200\\text{ }\\text{ }\\mathrm{keV}/c$$ amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.« less

Observation of the Self-Modulation Instability via Time-Resolved Measurements

DOE PAGES

Gross, M.; Engel, J.; Good, J.; ...

2018-04-06

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximatelymore » $$200\\text{ }\\text{ }\\mathrm{keV}/c$$ amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.« less

Device and method for relativistic electron beam heating of a high-density plasma to drive fast liners

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner which is generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner.

High current nonlinear transmission line based electron beam driver

NASA Astrophysics Data System (ADS)

Hoff, B. W.; French, D. M.; Simon, D. S.; Lepell, P. D.; Montoya, T.; Heidger, S. L.

2017-10-01

A gigawatt-class nonlinear transmission line based electron beam driver is experimentally demonstrated. Four experimental series, each with a different Marx bank charge voltage (15, 20, 25, and 30 kV), were completed. Within each experimental series, shots at peak frequencies ranging from 950 MHz to 1.45 GHz were performed. Peak amplitude modulations of the NLTL output voltage signal were found to range between 18% and 35% for the lowest frequency shots and between 5% and 20% for the highest frequency shots (higher modulation at higher Marx charge voltage). Peak amplitude modulations of the electron beam current were found to range between 10% and 20% for the lowest frequency shots and between 2% and 7% for the highest frequency shots (higher modulation at higher Marx charge voltage).

A Model of Relation between Fluctuation of Double Differential Total Ionospheric Electron Content and Angular Distance of the Two Satellites Observed by Same-beam VLBI

NASA Astrophysics Data System (ADS)

Xiao, Yao; Qing-hui, Liu

2018-01-01

Time delay and phase fluctuation are produced when the signals of a spacecraft are transmitted through the ionosphere of the earth, which give rise to a great influence on the measurement precision of VLBI (Very Long Baseline Interferometry). Using the 1-year same-beam VLBI data of 2 satellites (Rstar and Vstar) in the Japanese lunar exploration project SELENE, we obtained a model of the relation between the fluctuation of double differential total electron content in the ionosphere and the angular distance of the two satellites. For the 6 baselines, the root mean square r of fluctuation (in units of TECU) and the angular distance of the two satellites θ (in units of ∘) has a relation of r = 0.773θ + 0.562, and for the 4 VLBI stations, the relation is r = 0.554θ + 0.399 from the baselines inversion. The results can serve as a reference for the derivation of differential phase delay and for the occultation observation and study of planetary ionospheres.

Compensation for the phase-type spatial periodic modulation of the near-field beam at 1053 nm

NASA Astrophysics Data System (ADS)

Gao, Yaru; Liu, Dean; Yang, Aihua; Tang, Ruyu; Zhu, Jianqiang

2017-10-01

A phase-only spatial light modulator is used to provide and compensate for the spatial periodic modulation (SPM) of the near-field beam at the near infrared at 1053nm wavelength with an improved iterative weight-based method. The transmission characteristics of the incident beam has been changed by a spatial light modulator (SLM) to shape the spatial intensity of the output beam. The propagation and reverse propagation of the light in free space are two important processes in the iterative process. The based theory is the beam angular spectrum transmit formula (ASTF) and the principle of the iterative weight-based method. We have made two improvements to the originally proposed iterative weight-based method. We select the appropriate parameter by choosing the minimum value of the output beam contrast degree and use the MATLAB built-in angle function to acquire the corresponding phase of the light wave function. The required phase that compensates for the intensity distribution of the incident SPM beam is iterated by this algorithm, which can decrease the magnitude of the SPM of the intensity on the observation plane. The experimental results show that the phase-type SPM of the near-field beam is subject to a certain restriction. We have also analyzed some factors that make the results imperfect. The experiment results verifies the possible applicability of this iterative weight-based method to compensate for the SPM of the near-field beam.

Robust and adjustable C-shaped electron vortex beams

NASA Astrophysics Data System (ADS)

Mousley, M.; Thirunavukkarasu, G.; Babiker, M.; Yuan, J.

2017-06-01

Wavefront engineering is an important quantum technology, often applied to the production of states carrying orbital angular momentum (OAM). Here, we demonstrate the design and production of robust C-shaped beam states carrying OAM, in which the usual doughnut-shaped transverse intensity structure of the vortex beam contains an adjustable gap. We find that the presence of the vortex lines in the core of the beam is crucial for maintaining the stability of the C-shape structure during beam propagation. The topological charge of the vortex core controls mainly the size of the C-shape, while its opening angle is related to the presence of vortex-anti-vortex loops. We demonstrate the generation and characterisation of C-shaped electron vortex beams, although the result is equally applicable to other quantum waves. C-shaped electron vortex beams have potential applications in nanoscale fabrication of planar split-ring structures and three-dimensional chiral structures as well as depth sensing and magnetic field determination through rotation of the gap in the C-shape.

Elastic electron scattering from formamide

NASA Astrophysics Data System (ADS)

Buk, M. V.; Bardela, F. P.; da Silva, L. A.; Iga, I.; Homem, M. G. P.

2018-05-01

Differential cross sections for elastic electron scattering by formamide (NH2CHO) were measured in the 30–800 eV and 10°–120° ranges. The angular distribution of scattered electrons was obtained using a crossed electron beam-molecular beam geometry. The relative flow technique was applied to normalize our data. Integral and momentum-transfer cross sections were derived from the measured differential cross sections. Theoretical results in the framework of the independent-atom model at the static-exchange-polarization plus absorption level of approximation are also given. The present measured and calculated results are compared with those available in the literature showing a generally good agreement.

THE ANGULAR DISTRIBUTION OF POSITRONS IN $pi$$sup +$-$mu$$sup +$-e$sup +$ DECAY IN PROPANE (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alikhanyan, A.I.; Kirillov-Ugryumov, V.G.; Kotenko, L.P.

1958-01-01

In consideration of the wide use of propane bubble cameras, investigations were made of the angular distribution of electrons from pi /sup +/ -- mu /sup +/--e/sup +/ decay in propane to determine the possibility of using propane in angular correlation measurements of processes simlar to mu --e decay. The scheme of the experiment made with a bubble chamber of (7.2 x 6.5 x 16)cm/ dmensions bombarded by a 175-Mev pi -meson beam from a phasotron is described. (R.V.J.)

Bright attosecond γ-ray pulses from nonlinear Compton scattering with laser-illuminated compound targets

NASA Astrophysics Data System (ADS)

Zhu, Xing-Long; Chen, Min; Yu, Tong-Pu; Weng, Su-Ming; Hu, Li-Xiang; McKenna, Paul; Sheng, Zheng-Ming

2018-04-01

Attosecond light sources have the potential to open up totally unexplored research avenues in ultrafast science. However, the photon energies achievable using existing generation schemes are limited to the keV range. Here, we propose and numerically demonstrate an all-optical mechanism for the generation of bright MeV attosecond γ-photon beams with desirable angular momentum. Using a circularly polarized Laguerre-Gaussian laser pulse focused onto a cone-foil target, dense attosecond bunches ( ≲ 170 as ) of electrons are produced. The electrons interact with the laser pulse which is reflected by a plasma mirror, producing ultra-brilliant (˜1023 photons/s/mm2/mrad2/0.1%BW) multi-MeV (Eγ,max > 30 MeV) isolated attosecond ( ≲ 260 as ) γ-ray pulse trains. Moreover, the angular momentum is transferred to γ-photon beams via nonlinear Compton scattering of ultra-intense tightly focused laser pulse by energetic electrons. Such a brilliant attosecond γ-photon source would provide the possibilities in attosecond nuclear science.

Silicon pore optics for the international x-ray observatory

NASA Astrophysics Data System (ADS)

Wille, E.; Wallace, K.; Bavdaz, M.; Collon, M. J.; Günther, R.; Ackermann, M.; Beijersbergen, M. W.; Riekerink, M. O.; Blom, M.; Lansdorp, B.; de Vreede, L.

2017-11-01

Lightweight X-ray Wolter optics with a high angular resolution will enable the next generation of X-ray telescopes in space. The International X-ray Observatory (IXO) requires a mirror assembly of 3 m2 effective area (at 1.5 keV) and an angular resolution of 5 arcsec. These specifications can only be achieved with a novel technology like Silicon Pore Optics, which is developed by ESA together with a consortium of European industry. Silicon Pore Optics are made of commercial Si wafers using process technology adapted from the semiconductor industry. We present the manufacturing process ranging from single mirror plates towards complete focusing mirror modules mounted in flight configuration. The performance of the mirror modules is tested using X-ray pencil beams or full X-ray illumination. In 2009, an angular resolution of 9 arcsec was achieved, demonstrating the improvement of the technology compared to 17 arcsec in 2007. Further development activities of Silicon Pore Optics concentrate on ruggedizing the mounting system and performing environmental tests, integrating baffles into the mirror modules and assessing the mass production.

Conceptual Design of a 50--100 MW Electron Beam Accelerator System for the National Hypersonic Wind Tunnel Program

DOE Office of Scientific and Technical Information (OSTI.GOV)

SCHNEIDER,LARRY X.

2000-06-01

The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1--2 MeV at a beam power level of 50--100 MW. Direct-current electron accelerator technology can readily generate high average power beams to approximately 5 MeV at output efficiencies greater than 90%. However, due to the nature of research and industrial applications, there has never been a requirement for a single module with an output power exceeding approximately 500 kW. Although a 50--100 MW module is a two-order extrapolation from demonstrated power levels, the scaling of accelerator components appears reasonable. This paper presents an evaluation of componentmore » and system issues involved in the design of a 50--100 MW electron beam accelerator system with precision beam transport into a high pressure flowing air environment.« less

Extraction of space-charge-dominated ion beams from an ECR ion source: Theory and simulation

NASA Astrophysics Data System (ADS)

Alton, G. D.; Bilheux, H.

2004-05-01

Extraction of high quality space-charge-dominated ion beams from plasma ion sources constitutes an optimization problem centered about finding an optimal concave plasma emission boundary that minimizes half-angular divergence for a given charge state, independent of the presence or lack thereof of a magnetic field in the extraction region. The curvature of the emission boundary acts to converge/diverge the low velocity beam during extraction. Beams of highest quality are extracted whenever the half-angular divergence, ω, is minimized. Under minimum half-angular divergence conditions, the plasma emission boundary has an optimum curvature and the perveance, P, current density, j+ext, and extraction gap, d, have optimum values for a given charge state, q. Optimum values for each of the independent variables (P, j+ext and d) are found to be in close agreement with those derived from elementary analytical theory for extraction with a simple two-electrode extraction system, independent of the presence of a magnetic field. The magnetic field only increases the emittances of beams through additional aberrational effects caused by increased angular divergences through coupling of the longitudinal to the transverse velocity components of particles as they pass though the mirror region of the electron cyclotron resonance (ECR) ion source. This article reviews the underlying theory of elementary extraction optics and presents results derived from simulation studies of extraction of space-charge dominated heavy-ion beams of varying mass, charge state, and intensity from an ECR ion source with emphasis on magnetic field induced effects.

Comparison of film measurements and Monte Carlo simulations of dose delivered with very high-energy electron beams in a polystyrene phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazalova-Carter, Magdalena; Liu, Michael; Palma, Bianey

2015-04-15

Purpose: To measure radiation dose in a water-equivalent medium from very high-energy electron (VHEE) beams and make comparisons to Monte Carlo (MC) simulation results. Methods: Dose in a polystyrene phantom delivered by an experimental VHEE beam line was measured with Gafchromic films for three 50 MeV and two 70 MeV Gaussian beams of 4.0–6.9 mm FWHM and compared to corresponding MC-simulated dose distributions. MC dose in the polystyrene phantom was calculated with the EGSnrc/BEAMnrc and DOSXYZnrc codes based on the experimental setup. Additionally, the effect of 2% beam energy measurement uncertainty and possible non-zero beam angular spread on MC dosemore » distributions was evaluated. Results: MC simulated percentage depth dose (PDD) curves agreed with measurements within 4% for all beam sizes at both 50 and 70 MeV VHEE beams. Central axis PDD at 8 cm depth ranged from 14% to 19% for the 5.4–6.9 mm 50 MeV beams and it ranged from 14% to 18% for the 4.0–4.5 mm 70 MeV beams. MC simulated relative beam profiles of regularly shaped Gaussian beams evaluated at depths of 0.64 to 7.46 cm agreed with measurements to within 5%. A 2% beam energy uncertainty and 0.286° beam angular spread corresponded to a maximum 3.0% and 3.8% difference in depth dose curves of the 50 and 70 MeV electron beams, respectively. Absolute dose differences between MC simulations and film measurements of regularly shaped Gaussian beams were between 10% and 42%. Conclusions: The authors demonstrate that relative dose distributions for VHEE beams of 50–70 MeV can be measured with Gafchromic films and modeled with Monte Carlo simulations to an accuracy of 5%. The reported absolute dose differences likely caused by imperfect beam steering and subsequent charge loss revealed the importance of accurate VHEE beam control and diagnostics.« less

Adaptive free-space optical communications through turbulence using self-healing Bessel beams

PubMed Central

Li, Shuhui; Wang, Jian

2017-01-01

We present a scheme to realize obstruction- and turbulence-tolerant free-space orbital angular momentum (OAM) multiplexing link by using self-healing Bessel beams accompanied by adaptive compensation techniques. Compensation of multiple 16-ary quadrature amplitude modulation (16-QAM) data carrying Bessel beams through emulated atmospheric turbulence and obstructions is demonstrated. The obtained experimental results indicate that the compensation scheme can effectively reduce the inter-channel crosstalk, improve the bit-error rate (BER) performance, and recuperate the nondiffracting property of Bessel beams. The proposed scheme might be used in future high-capacity OAM links which are affected by atmospheric turbulence and obstructions. PMID:28230076

Measuring the orbital angular momentum spectrum of an electron beam

PubMed Central

Grillo, Vincenzo; Tavabi, Amir H.; Venturi, Federico; Larocque, Hugo; Balboni, Roberto; Gazzadi, Gian Carlo; Frabboni, Stefano; Lu, Peng-Han; Mafakheri, Erfan; Bouchard, Frédéric; Dunin-Borkowski, Rafal E.; Boyd, Robert W.; Lavery, Martin P. J.; Padgett, Miles J.; Karimi, Ebrahim

2017-01-01

Electron waves that carry orbital angular momentum (OAM) are characterized by a quantized and unbounded magnetic dipole moment parallel to their propagation direction. When interacting with magnetic materials, the wavefunctions of such electrons are inherently modified. Such variations therefore motivate the need to analyse electron wavefunctions, especially their wavefronts, to obtain information regarding the material's structure. Here, we propose, design and demonstrate the performance of a device based on nanoscale holograms for measuring an electron's OAM components by spatially separating them. We sort pure and superposed OAM states of electrons with OAM values of between −10 and 10. We employ the device to analyse the OAM spectrum of electrons that have been affected by a micron-scale magnetic dipole, thus establishing that our sorter can be an instrument for nanoscale magnetic spectroscopy. PMID:28537248

Concept of a tunable source of coherent THz radiation driven by a plasma modulated electron beam

NASA Astrophysics Data System (ADS)

Zhang, H.; Konoplev, I. V.; Doucas, G.; Smith, J.

2018-04-01

We have carried out numerical studies which consider the modulation of a picosecond long relativistic electron beam in a plasma channel and the generation of a micro-bunched train. The subsequent propagation of the micro-bunched beam in the vacuum area was also investigated. The same numerical model was then used to simulate the radiation arising from the interaction of the micro-bunched beam with a metallic grating. The dependence of the radiation spectrum on the parameters of the micro-bunched beam has been studied and the tunability of the radiation by the variation of the micro-bunch spacing has been demonstrated. The micro-bunch spacing can be changed easily by altering the plasma density without changing the beam energy or current. Using the results of these studies, we develop a conceptual design of a tunable source of coherent terahertz (THz) radiation driven by a plasma modulated beam. Such a source would be a potential and useful alternative to conventional vacuum THz tubes and THz free-electron laser sources.

Longitudinal dynamics of an intense electron beam

NASA Astrophysics Data System (ADS)

Harris, John Richardson

2005-11-01

The dynamics of charged particle beams are governed by the particles' thermal velocities, external focusing forces, and Coulomb forces. Beams in which Coulomb forces play the dominant role are known as space charge dominated, or intense. Intense beams are of great interest for heavy ion fusion, spallation neutron sources, free-electron lasers, and other applications. In addition, all beams of interest are dominated by space charge forces when they are first created, so an understanding of space charge effects is critical to explain the later evolution of any beam. Historically, more attention has been paid to the transverse dynamics of beams. However, many interesting and important effects in beams occur along their length. These longitudinal effects can be limiting factors in many systems. For example, modulation or structure applied to the beam at low energy will evolve under space charge forces. Depending on the intended use of the beam and the nature of the modulation, this may result in improved or degraded performance. To study longitudinal dynamics in intense beams, experiments were conducted using the University of Maryland Electron Ring, a 10 keV, 100 mA electron transport system. These experiments concentrated on space charge driven changes in beam length in parabolic and rectangular beams, beam density and velocity modulation, and space charge wave propagation. Coupling between the transverse and longitudinal dynamics was also investigated. These experiments involved operating the UMER gun in space charge limited, temperature limited, triode amplification, photon limited, and hybrid modes. Results of these experiments are presented here, along with a theoretical framework for understanding the longitudinal dynamics of intense beams.

Device and method for imploding a microsphere with a fast liner

DOEpatents

Thode, Lester E.

1981-01-01

A device and method for relativistic electron beam heating of a high-density plasma in a small localized region. A relativistic electron beam generator or accelerator produces a high-voltage electron beam which propagates along a vacuum drift tube and is modulated to initiate electron bunching within the beam. The beam is then directed through a low-density gas chamber which provides isolation between the vacuum modulator and the relativistic electron beam target. The relativistic beam is then applied to a high-density target plasma which typically comprises DT, DD, hydrogen boron or similar thermonuclear gas at a density of 10.sup.17 to 10.sup.20 electrons per cubic centimeter. The target gas is ionized prior to application of the electron beam by means of a laser or other preionization source to form a plasma. Utilizing a relativistic electron beam with an individual particle energy exceeding 3 MeV, classical scattering by relativistic electrons passing through isolation foils is negligible. As a result, relativistic streaming instabilities are initiated within the high-density target plasma causing the relativistic electron beam to efficiently deposit its energy and momentum into a small localized region of the high-density plasma target. Fast liners disposed in the high-density target plasma are explosively or ablatively driven to implosion by a heated annular plasma surrounding the fast liner generated by an annular relativistic electron beam. An azimuthal magnetic field produced by axial current flow in the annular plasma, causes the energy in the heated annular plasma to converge on the fast liner to drive the fast liner to implode a microsphere.

Laser modulator for LISA pathfinder

NASA Astrophysics Data System (ADS)

Voland, C.; Lund, G.; Coppoolse, W.; Crosby, P.; Stadler, M.; Kudielka, K.; Özkan, C.

2017-11-01

LISA Pathfinder is an ESA experiment to demonstrate the key technologies needed for the LISA mission to detect gravitational waves in space. The LISA Pathfinder spacecraft represents one arm of the LISA interferometer, containing an optical metrology system and two proof masses as inertial references for the drag-free control system. The LISA Pathfinder payload consists of two drag-free floating test masses located in the inertial sensors with their control electronics and an optical metrology subsystem. The optical metrology subsystem monitors the movement of both test masses relative to each other and to the spacecraft with very high sensitivity and resolution. This is achieved with a heterodyne Mach- Zehnder interferometer. This interferometer requires as input two coherent laser beams with a heterodyne frequency difference of a few kHz. To generate the two laser beams with a heterodyne frequency difference a Nd:YAG laser is used together with the Laser Modulator. The Nd:YAG laser generates a single coherent laser signal at a wavelength of 1064nm which is fibre coupled to the Laser Modulator. The Laser Modulator then generates the two optical beams with the required heterodyne frequency offset. In addition, the Laser Modulator is required to perform laser amplitude stabilization and optical path difference control for the two optical signals. The Laser Modulator consists of an optical unit - the LMU - and RF synthesiser, power amplification and control electronics. These electronics are all housed in the Laser Modulator Electronics (LME). The LMU has four primary functions: • Splitting of the input laser beam into two paths for later superposition in the interferometer. • Applying different frequency shifts to each of the beams. • Providing amplitude modulation control to each of the beams. • Providing active control of the optical path length difference between the two optical paths. The present paper describes the design and performance of the LMU together with a summary of the results of the Laser Modulator engineering model test campaign.

Plasma phenomena at magnetic neutral points

NASA Technical Reports Server (NTRS)

Sturrock, P. A.

1975-01-01

A model of the plasma focus is considered, in which large axial electric fields are induced by the imploding current sheet during the final few nanoseconds of the collapse phase. This field provides a mechanism for creation of a beam of electrons of highly suprathermal energies. For this beam, the bremsstrahlung radiation is calculated, which is expected either from electron-deuteron collisions in the focused plasma itself or from the beam as it reaches the walls of the device. Comparison with experimental results indicates that the walls are the more likely source of these hard X-rays and also find qualitative agreement of the expected angular distribution of X-rays with experiment.

Dosimetry for electron Intra-Operative RadioTherapy: Comparison of output factors obtained through alanine/EPR pellets, ionization chamber and Monte Carlo-GEANT4 simulations for IORT mobile dedicate accelerator

NASA Astrophysics Data System (ADS)

Marrale, Maurizio; Longo, Anna; Russo, Giorgio; Casarino, Carlo; Candiano, Giuliana; Gallo, Salvatore; Carlino, Antonio; Brai, Maria

2015-09-01

In this work a comparison between the response of alanine and Markus ionization chamber was carried out for measurements of the output factors (OF) of electron beams produced by a linear accelerator used for Intra-Operative Radiation Therapy (IORT). Output factors (OF) for conventional high-energy electron beams are normally measured using ionization chamber according to international dosimetry protocols. However, the electron beams used in IORT have characteristics of dose per pulse, energy spectrum and angular distribution quite different from beams usually used in external radiotherapy, so the direct application of international dosimetry protocols may introduce additional uncertainties in dosimetric determinations. The high dose per pulse could lead to an inaccuracy in dose measurements with ionization chamber, due to overestimation of ks recombination factor. Furthermore, the electron fields obtained with IORT-dedicated applicators have a wider energy spectrum and a wider angular distribution than the conventional fields, due to the presence of electrons scattered by the applicator's wall. For this reason, a dosimetry system should be characterized by a minimum dependence from the beam energy and from angle of incidence of electrons. This become particularly critical for small and bevelled applicators. All of these reasons lead to investigate the use of detectors different from the ionization chamber for measuring the OFs. Furthermore, the complete characterization of the radiation field could be accomplished also by the use of Monte Carlo simulations which allows to obtain detailed information on dose distributions. In this work we compare the output factors obtained by means of alanine dosimeters and Markus ionization chamber. The comparison is completed by the Monte Carlo calculations of OFs determined through the use of the Geant4 application "iort _ therapy" . The results are characterized by a good agreement of response of alanine pellets and Markus ionization chamber and Monte Carlo results (within about 3%) for both flat and bevelled applicators.

High-speed electronic beam steering using injection locking of a laser-diode array

NASA Astrophysics Data System (ADS)

Swanson, E. A.; Abbas, G. L.; Yang, S.; Chan, V. W. S.; Fujimoto, J. G.

1987-01-01

High-speed electronic steering of the output beam of a 10-stripe laser-diode array is reported. The array was injection locked to a single-frequency laser diode. High-speed steering of the locked 0.5-deg-wide far-field lobe is demonstrated either by modulating the injection current of the array or by modulating the frequency of the master laser. Closed-loop tracking bandwidths of 70 kHz and 3 MHz, respectively, were obtained. The beam-steering bandwidths are limited by the FM responses of the modulated devices for both techniques.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tuve, C.; Albergo, S.; Boemi, D.

Neutrons produced in the {sup 40}Ca+H reaction at E{sub lab}=357A and 565A MeV have been detected using a three-module version of the multifunctional neutron spectrometer MUFFINS. The detector covered a narrow angular range around the beam in the forward direction (0{degree}{minus}3.2{degree}). Semi-inclusive neutron production cross sections, at the two energies, are reported together with neutron energy spectra, angular, rapidity, and transverse momentum distributions. Comparison with a Boltzmann-Nordheim-Vlasov approach + phase space coalescence model is discussed. {copyright} {ital 1997} {ital The American Physical Society}

Correction of measured Gamma-Knife output factors for angular dependence of diode detectors and PinPoint ionization chamber.

PubMed

Hršak, Hrvoje; Majer, Marija; Grego, Timor; Bibić, Juraj; Heinrich, Zdravko

2014-12-01

Dosimetry for Gamma-Knife requires detectors with high spatial resolution and minimal angular dependence of response. Angular dependence and end effect time for p-type silicon detectors (PTW Diode P and Diode E) and PTW PinPoint ionization chamber were measured with Gamma-Knife beams. Weighted angular dependence correction factors were calculated for each detector. The Gamma-Knife output factors were corrected for angular dependence and end effect time. For Gamma-Knife beams angle range of 84°-54°. Diode P shows considerable angular dependence of 9% and 8% for the 18 mm and 14, 8, 4 mm collimator, respectively. For Diode E this dependence is about 4% for all collimators. PinPoint ionization chamber shows angular dependence of less than 3% for 18, 14 and 8 mm helmet and 10% for 4 mm collimator due to volumetric averaging effect in a small photon beam. Corrected output factors for 14 mm helmet are in very good agreement (within ±0.3%) with published data and values recommended by vendor (Elekta AB, Stockholm, Sweden). For the 8 mm collimator diodes are still in good agreement with recommended values (within ±0.6%), while PinPoint gives 3% less value. For the 4 mm helmet Diodes P and E show over-response of 2.8% and 1.8%, respectively. For PinPoint chamber output factor of 4 mm collimator is 25% lower than Elekta value which is generally not consequence of angular dependence, but of volumetric averaging effect and lack of lateral electronic equilibrium. Diodes P and E represent good choice for Gamma-Knife dosimetry. Copyright © 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Efficient creation of electron vortex beams for high resolution STEM imaging.

PubMed

Béché, A; Juchtmans, R; Verbeeck, J

2017-07-01

The recent discovery of electron vortex beams carrying quantised angular momentum in the TEM has led to an active field of research, exploring a variety of potential applications including the possibility of mapping magnetic states at the atomic scale. A prerequisite for this is the availability of atomic sized electron vortex beams at high beam current and mode purity. In this paper we present recent progress showing that by making use of the Aharonov-Bohm effect near the tip of a long single domain ferromagnetic Nickel needle, a very efficient aperture for the production of electron vortex beams can be realised. The aperture transmits more than 99% of all electrons and provides a vortex mode purity of up to 92%. Placing this aperture in the condenser plane of a state of the art Cs corrected microscope allows us to demonstrate atomic resolution HAADF STEM images with spatial resolution better than 1 Angström, in agreement with theoretical expectations and only slightly inferior to the performance of a non-vortex probe on the same instrument. Copyright © 2016 Elsevier B.V. All rights reserved.

Soft X-ray Spectrometer for Characterization of Electron Beam Driven WDM

NASA Astrophysics Data System (ADS)

Ramey, Nicholas; Coleman, Joshua; Perry, John

2017-10-01

A preliminary design study is being performed on a soft X-ray spectrometer to measure K-shell spectra emitted by a warm dense plasma generated by an intense, relativistic electron beam interacting with a thin, low-Z metal foil. A 100-ns-long electron pulse with a beam current of 1.7 kA and energy of 19.8 MeV deposits energy into the thin metal foil heating it to a warm dense plasma. The collisional ionization of the target by the electron beam produces an anisotropic angular distribution of K-shell radiation and a continuum of both scattered electrons and Bremsstrahlung up to the beam energy of 19.8 MeV. A proof-of-principle Bragg-type spectrometer has been built to measure the Ti K- α and K- β lines. The goal of the spectrometer is to measure the temperature and density of this warm dense plasma for the first time with this heating technique. This work was supported by the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. DE-AC52-06NA25396.

A simple model of electron beam initiated dielectric breakdown

NASA Technical Reports Server (NTRS)

Beers, B. L.; Daniell, R. E.; Delmer, T. N.

1985-01-01

A steady state model that describes the internal charge distribution of a planar dielectric sample exposed to a uniform electron beam was developed. The model includes the effects of charge deposition and ionization of the beam, separate trap-modulated mobilities for electrons and holes, electron-hole recombination, and pair production by drifting thermal electrons. If the incident beam current is greater than a certain critical value (which depends on sample thickness as well as other sample properties), the steady state solution is non-physical.

Tests of the module array of the ECAL0 electromagnetic calorimeter for the COMPASS experiment with the electron beam at ELSA

NASA Astrophysics Data System (ADS)

Anfimov, N.; Anosov, V.; Barth, J.; Chalyshev, V.; Chirikov-Zorin, I.; Dziewiecki, M.; Elsner, D.; Frolov, V.; Frommberger, F.; Guskov, A.; Hillert, W.; Klein, F.; Krumshteyn, Z.; Kurjata, R.; Marzec, J.; Nagaytsev, A.; Olchevski, A.; Orlov, I.; Rezinko, T.; Rybnikov, A.; Rychter, A.; Selyunin, A.; Zaremba, K.; Ziembicki, M.

2015-07-01

The array of 3 × 3 modules of the electromagnetic calorimeter ECAL0 of the COMPASS experiment at CERN has been tested with an electron beam of the ELSA (Germany) facility. The dependence of the response and the energy resolution of the calorimeter from the angle of incidence of the electron beam has been studied. A good agreement between the experimental data and the results of Monte Carlo simulation has been obtained. It will significantly expand the use of simulation to optimize event reconstruction algorithms.

Modeling of projection electron lithography

NASA Astrophysics Data System (ADS)

Mack, Chris A.

2000-07-01

Projection Electron Lithography (PEL) has recently become a leading candidate for the next generation of lithography systems after the successful demonstration of SCAPEL by Lucent Technologies and PREVAIL by IBM. These systems use a scattering membrane mask followed by a lens with limited angular acceptance range to form an image of the mask when illuminated by high energy electrons. This paper presents an initial modeling system for such types of projection electron lithography systems. Monte Carlo modeling of electron scattering within the mask structure creates an effective mask 'diffraction' pattern, to borrow the standard optical terminology. A cutoff of this scattered pattern by the imaging 'lens' provides an electron energy distribution striking the wafer. This distribution is then convolved with a 'point spread function,' the results of a Monte Carlo scattering calculation of a point beam of electrons striking the resist coated substrate and including the effects of beam blur. Resist exposure and development models from standard electron beam lithography simulation are used to simulate the final three-dimensional resist profile.

Calibration of the ART-XC mirror modules at MSFC

NASA Astrophysics Data System (ADS)

Krivonos, R.; Tkachenko, A.; Burenin, R.; Filippova, E.; Lapshov, I.; Mereminskiy, I.; Molkov, S.; Pavlinsky, M.; Sazonov, S.; Gubarev, M.; Kolodziejczak, J.; O'Dell, S. L.; Swartz, D.; Zavlin, Vyacheslav E.; Ramsey, B. D.

2017-10-01

The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module.

Electron scattering by highly polar molecules. III - CsCl

NASA Technical Reports Server (NTRS)

Vuskovic, L.; Srivastava, S. K.

1981-01-01

Utilizing a crossed electron-beam-molecular-beam scattering geometry, relative values of differential electron scattering cross sections for cesium chloride at 5 and 20 eV electron impact energies and at scattering angles between 10 and 120 deg have been measured. These relative cross sections have been normalized to the cross section at 15 deg scattering angle calculated by the hybrid S-matrix technique. In the angular range between 0 and 10 deg and between 120 and 180 deg extrapolations have been made to obtain integral and momentum transfer cross sections. An energy-loss spectrum is also presented which gives various spectral features lying between the 4 and 10 eV regions in CsCl.

Uniaxial angular accelerometers

NASA Astrophysics Data System (ADS)

Seleznev, A. V.; Shvab, I. A.

1985-05-01

The basic mechanical components of an angular accelerometer are the sensor, the damper, and the transducer. Penumatic dampers are simplest in construction, but the viscosity of air is very low and, therefore, dampers with special purpose oils having a high temperature stability (synthetic silicon or organosilicon oils) are most widely used. The most common types of viscous dampers are lamellar with meshed opposed arrays of fixed and movable vanes in the dashpot, piston dampers regulated by an adjustable-length capillary tube, and dampers with paddle wheel in closed tank. Another type of damper is an impact-inertial one with large masses absorbing the rotational energy upon collision with the sensor. Conventional measuring elements are resistive, capacitive, electromagnetic, photoelectric, and penumatic or hydraulic. Novel types of angular accelerometers are based on inertia of gas jets, electron beams, and ion beams, the piezoelectric effect in p-n junctions of diode and transistors, the electrokinetic effect in fluids, and cryogenic suspension of the sensor.

High-speed acoustic communication by multiplexing orbital angular momentum

PubMed Central

Shi, Chengzhi; Dubois, Marc; Wang, Yuan

2017-01-01

Long-range acoustic communication is crucial to underwater applications such as collection of scientific data from benthic stations, ocean geology, and remote control of off-shore industrial activities. However, the transmission rate of acoustic communication is always limited by the narrow-frequency bandwidth of the acoustic waves because of the large attenuation for high-frequency sound in water. Here, we demonstrate a high-throughput communication approach using the orbital angular momentum (OAM) of acoustic vortex beams with one order enhancement of the data transmission rate at a single frequency. The topological charges of OAM provide intrinsically orthogonal channels, offering a unique ability to multiplex data transmission within a single acoustic beam generated by a transducer array, drastically increasing the information channels and capacity of acoustic communication. A high spectral efficiency of 8.0 ± 0.4 (bit/s)/Hz in acoustic communication has been achieved using topological charges between −4 and +4 without applying other communication modulation techniques. Such OAM is a completely independent degree of freedom which can be readily integrated with other state-of-the-art communication modulation techniques like quadrature amplitude modulation (QAM) and phase-shift keying (PSK). Information multiplexing through OAM opens a dimension for acoustic communication, providing a data transmission rate that is critical for underwater applications. PMID:28652341

On the feasibility of sub-100 nm rad emittance measurement in plasma accelerators using permanent magnetic quadrupoles

NASA Astrophysics Data System (ADS)

Li, F.; Wu, Y. P.; Nie, Z.; Guo, B.; Zhang, X. H.; Huang, S.; Zhang, J.; Cheng, Z.; Ma, Y.; Fang, Y.; Zhang, C. J.; Wan, Y.; Xu, X. L.; Hua, J. F.; Pai, C. H.; Lu, W.; Gu, Y. Q.

2018-01-01

Low emittance (sub-100 nm rad) measurement of electron beams in plasma accelerators has been a challenging issue for a while. Among various measurement schemes, measurements based on single-shot quad-scan using permanent magnetic quadrupoles (PMQs) has been recently reported with emittance as low as ˜200 nm Weingartner (2012 Phys. Rev. Spec. Top. Accel. Beams 15 111302). However, the accuracy and reliability of this method have not been systematically analyzed. Such analysis is critical for evaluating the potential of sub-100 nm rad emittance measurement using any scheme. In this paper, we analyze the effects of various nonideal physical factors on the accuracy and reliability using the PMQ method. These factors include aberration induced by a high order field, PMQ misalignment and angular fluctuation of incoming beams. Our conclusions are as follows: (i) the aberrations caused by high order fields of PMQs are relatively weak for low emittance measurement as long as the PMQs are properly constructed. A series of PMQs were manufactured and measured at Tsinghua University, and using numerical simulations their high order field effects were found to be negligible . (ii) The largest measurement error of emittance is caused by the angular misalignment between PMQs. For low emittance measurement of ˜100 MeV beams, an angular alignment accuracy of 0.1° is necessary. This requirement can be eased for beams with higher energies. (iii) The transverse position misalignment of PMQs and angular fluctuation of incoming beams only cause a translational and rotational shift of measured signals, respectively, therefore, there is no effect on the measured value of emittance. (iv) The spatial resolution and efficiency of the detection system need to be properly designed to guarantee the accuracy of sub-100 nm rad emittance measurement.

Spatial control of photoemitted electron beams using a microlens-array transverse-shaping technique

DOE PAGES

Halavanau, A.; Qiang, G.; Ha, G.; ...

2017-10-26

A transversely inhomogeneous laser distribution on the photocathode surface generally produces electron beams with degraded beam quality. In this paper, we explore the use of microlens arrays to dramatically improve the transverse uniformity of an ultraviolet drive-laser pulse used in a photoinjector. Here, we also demonstrate a capability of microlens arrays to generate transversely modulated electron beams and present an application of such a feature to diagnose the properties of a magnetized beam.

Demonstration of Cascaded Modulator-Chicane Microbunching of a Relativistic Electron Beam

DOE PAGES

Sudar, N.; Musumeci, P.; Gadjev, I.; ...

2018-03-15

Here, we present results of an experiment showing the first successful demonstration of a cascaded microbunching scheme. Two modulator-chicane prebunchers arranged in series and a high power mid-IR laser seed are used to modulate a 52 MeV electron beam into a train of sharp microbunches phase locked to the external drive laser. This configuration is shown to greatly improve matching of the beam into the small longitudinal phase space acceptance of short-wavelength accelerators. We demonstrate trapping of nearly all (96%) of the electrons in a strongly tapered inverse free-electron laser accelerator, with an order-of-magnitude reduction in injection losses compared tomore » the classical single-buncher scheme. These results represent a critical advance in laser-based longitudinal phase space manipulations and find application in high gradient advanced acceleration as well as in high peak and average power coherent radiation sources.« less

Shielding calculations for industrial 5/7.5MeV electron accelerators using the MCNP Monte Carlo Code

NASA Astrophysics Data System (ADS)

Peri, Eyal; Orion, Itzhak

2017-09-01

High energy X-rays from accelerators are used to irradiate food ingredients to prevent growth and development of unwanted biological organisms in food, and by that extend the shelf life of the products. The production of X-rays is done by accelerating 5 MeV electrons and bombarding them into a heavy target (high Z). Since 2004, the FDA has approved using 7.5 MeV energy, providing higher production rates with lower treatments costs. In this study we calculated all the essential data needed for a straightforward concrete shielding design of typical food accelerator rooms. The following evaluation is done using the MCNP Monte Carlo code system: (1) Angular dependence (0-180°) of photon dose rate for 5 MeV and 7.5 MeV electron beams bombarding iron, aluminum, gold, tantalum, and tungsten targets. (2) Angular dependence (0-180°) spectral distribution simulations of bremsstrahlung for gold, tantalum, and tungsten bombarded by 5 MeV and 7.5 MeV electron beams. (3) Concrete attenuation calculations in several photon emission angles for the 5 MeV and 7.5 MeV electron beams bombarding a tantalum target. Based on the simulation, we calculated the expected increase in dose rate for facilities intending to increase the energy from 5 MeV to 7.5 MeV, and the concrete width needed to be added in order to keep the existing dose rate unchanged.

Electron Beam Pattern Rotation as a Method of Tunable Bunch Train Generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halavanau, A.; Piot, P.

Transversely modulated electron beams can be formed in photo injectors via microlens array (MLA) UV laser shap- ing technique. Microlenses can be arranged in polygonal lattices, with resulting transverse electron beam modula- tion mimicking the lenses pattern. Conventionally, square MLAs are used for UV laser beam shaping, and generated electron beam patterns form square beamlet arrays. The MLA setup can be placed on a rotational mount, thereby rotating electron beam distribution. In combination with transverse-to-longitudinal emittance exchange (EEX) beam line, it allows to vary beamlets horizontal projection and tune electron bunch train. In this paper, we extend the technique tomore » the case of different MLA lattice arrangements and explore the benefits of its rotational symmetries.« less

Dosimetric characterization of a synthetic single crystal diamond detector in a clinical 62 MeV ocular therapy proton beam

NASA Astrophysics Data System (ADS)

Marinelli, Marco; Pompili, F.; Prestopino, G.; Verona, C.; Verona-Rinati, G.; Cirrone, G. A. P.; Cuttone, G.; La Rosa, R. M.; Raffaele, L.; Romano, F.; Tuvè, C.

2014-12-01

A synthetic single crystal diamond based Schottky photodiode was tested at INFN-LNS on the proton beam line (62 MeV) dedicated to the radiation treatment of ocular disease. The diamond detector response was studied in terms of pre-irradiation dose, linearity with dose and dose rate, and angular dependence. Depth dose curves were measured for the 62 MeV pristine proton beam and for three unmodulated range-shifted proton beams; furthermore, the spread-out Bragg peak was measured for a modulated therapeutic proton beam. Beam parameters, recommended by the ICRU report 78, were evaluated to analyze depth-dose curves from diamond detector. Measured dose distributions were compared with the corresponding dose distributions acquired with reference plane-parallel ionization chambers. Field size dependence of the output factor (dose per monitor unit) in a therapeutic modulated proton beam was measured with the diamond detector over the range of ocular proton therapy collimator diameters (5-30 mm). Output factors measured with the diamond detector were compared to the ones by a Markus ionization chamber, a Scanditronix Hi-p Si stereotactic diode and a radiochromic EBT2 film. Signal stability within 0.5% was demonstrated for the diamond detector with no need of any pre-irradiation dose. Dose and dose rate dependence of the diamond response was measured: deviations from linearity resulted to be within ±0.5% over the investigated ranges of 0.5-40.0 Gy and 0.3-30.0 Gy/min respectively. Output factors from diamond detector measured with the smallest collimator (5 mm in diameter) showed a maximum deviation of about 3% with respect to the high resolution radiochromic EBT2 film. Depth-dose curves measured by diamond for unmodulated and modulated beams were in good agreement with those from the reference plane-parallel Markus chamber, with relative differences lower than ±1% in peak-to-plateau ratios, well within experimental uncertainties. A 2.5% variation in diamond detector response was observed in angular dependence measurements carried-out by varying the proton beam incidence angle in the polar direction. The dosimetric characterization of the tested synthetic single crystal diamond detector clearly indicates its suitability for relative dosimetry in ocular therapy proton beams, with no need of any correction factors accounting for dose rate and linear energy transfer dependence.

Gigatron microwave amplifier

DOEpatents

McIntyre, P.M.

1993-07-13

An electron tube for achieving high power at high frequency with high efficiency is described, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot there through for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

Gigatron microwave amplifier

DOEpatents

McIntyre, Peter M.

1993-01-01

An electron tube for achieving high power at high frequency with high efficiency, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot therethrough for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

Transverse Mode Electron Beam Microwave Generator

NASA Technical Reports Server (NTRS)

Wharton, Lawrence E.

1994-01-01

An electron beam microwave device having an evacuated interaction chamber to which are coupled a resonant cavity which has an opening between the resonant cavity and the evacuated interaction chamber and an electron gun which causes a narrow beam of electrons to traverse the evacuated interaction chamber. The device also contains a mechanism for feeding back a microwave electromagnetic field from the resonant cavity to the evacuated interaction chamber in such a way as to modulate the direction of propagation of the electron beam, thereby further amplifyjng the microwave electromagnetic field. Furthermore, provision is made for coupling the electromagnetic field out of the electron beam microwave device.

Production of hard X rays in a plasma focus

NASA Technical Reports Server (NTRS)

Newman, C. E.; Petrosian, V.

1975-01-01

A model of a plasma focus is examined wherein large axial electric fields are produced by an imploding current sheet during the final nanoseconds of the collapse phase and where the fields provide a mechanism for creating a beam of electrons of highly suprathermal energies. The expected bremsstrahlung radiation above 100 keV is calculated for such a beam, which has a power-law spectrum, both from electron-deuteron collisions in the focused plasma and when the beam reaches the wall of the device. It is concluded that, since the experimental results indicate little or no radiation above 100 keV originating in the walls, that the electrons in the beam must be decelerated after leaving the plasma and before reaching the wall. Comparisons with the results and the total energy of the device yield qualitative agreement with the expected angular distribution of hard X-rays and reasonable agreement with the total energy in accelerated electrons required to produce the observed total energy in hard X-rays by this mechanism.

Improved grating angular sensor for LISA and MGRS

NASA Astrophysics Data System (ADS)

Sun, Ke-Xun; Lu, Patrick; Byer, Robert L.

2009-03-01

LISA requires high precision angular beam pointing and telescope steering. In this paper, we report recent results for an improved grating angular sensor. We have achieved better than 0.2 nrad/Hz1/2 at 1 kHz with 14 mW of incident power, a factor of 5 improvement over our previously reported results. At 1 Hz we achieved 1-2 nrad/Hz1/2. We realized these improvements by enclosing the grating angular sensor assembly in a vacuum chamber and mounting the optics components on a zerodur glass plate, thereby lowering the noise floor at low frequencies. Furthermore, by upgrading the electronics and thus the detector power handing capability, we also investigated sensitivity scaling versus incident laser power. The results will benefit the design of grating angular sensors.

Self-referenced locking of optical coherence by single-detector electronic-frequency tagging

NASA Astrophysics Data System (ADS)

Shay, T. M.; Benham, Vincent; Spring, Justin; Ward, Benjamin; Ghebremichael, F.; Culpepper, Mark A.; Sanchez, Anthony D.; Baker, J. T.; Pilkington, D.; Berdine, Richard

2006-02-01

We report a novel coherent beam combining technique. This is the first actively phase locked optical fiber array that eliminates the need for a separate reference beam. In addition, only a single photodetector is required. The far-field central spot of the array is imaged onto the photodetector to produce the phase control loop signals. Each leg of the fiber array is phase modulated with a separate RF frequency, thus tagging the optical phase shift for each leg by a separate RF frequency. The optical phase errors for the individual array legs are separated in the electronic domain. In contrast with the previous active phase locking techniques, in our system the reference beam is spatially overlapped with all the RF modulated fiber leg beams onto a single detector. The phase shift between the optical wave in the reference leg and in the RF modulated legs is measured separately in the electronic domain and the phase error signal is feedback to the LiNbO 3 phase modulator for that leg to minimize the phase error for that leg relative to the reference leg. The advantages of this technique are 1) the elimination of the reference beam and beam combination optics and 2) the electronic separation of the phase error signals without any degradation of the phase locking accuracy. We will present the first theoretical model for self-referenced LOCSET and describe experimental results for a 3 x 3 array.

Orbital angular momentum of photons, plasmons and neutrinos in a plasma

NASA Astrophysics Data System (ADS)

Mendonca, J. T.; Thidé, Bo; Then, H.; Ali, S.

2009-11-01

We study the exchange of angular momentum between electromagnetic and electrostatic waves in a plasma, due to the stimulated Raman and Brillouin backscatering processes [1]. Angular momentum states for plasmon and phonon fields are introduced for the first time. We demonstrate that these states can be excited by nonlinear wave mixing, associated with the scattering processes. This could be relevant for plasma diagnostics, both in laboratory and in space. Nonlinearly coupled paraxial equations and instability growth rates are derived. The characteristic features of the plasmon modes with finite angular momentum are also discussed. The potential problem is solved and the angular momentum is explicitly calculated [2]. Finally, it is shown that an electron-neutrino beam, propagating in a background plasma, can be decomposed into orbital momentum states, similar to that of photon states. Coupling between different neutrino states, in the presence of a plasma vortex, is considered. We show that plasma vorticity can be transfered to the neutrino beam, which is relevant to the understanding of the neutrino sources in astrophysics. [1] J.T. Mendonca et al., PRL 102, 185005 (2009). [2] S. Ali and J.T. Mendonca, PoP (2009) submitted. [3] J.T. Mendonca and B. Thide, Europhys. Lett. 84, 41001 (2008).

Low energy electron spectroscopy of C60 in collisions with fast bare ions: Observation of GDPR peak and its angular distribution

NASA Astrophysics Data System (ADS)

Kelkar, A. H.; Misra, D.; Chatterjee, S.; Kasthurirangan, S.; Agnihotri, A.; Tribedi, L. C.

2009-11-01

We report the first direct measurement of GDPR peak in heavy ion (4 MeV/u F9+) induced secondary electron DDCS (double differential cross section) spectrum of C60 fullerene. A peak corresponding to GDPR is seen at all angles and the angular distribution, showing a dip at 90°, is in contrast with ion-atom collisions, indicating plasmon oscillations along beam direction. A comparison has also been done between C60 and other gaseous targets as well as with state-of-the art theoretical models, based on density functional methods.

Optical transition radiation used in the diagnostic of low energy and low current electron beams in particle accelerators.

PubMed

Silva, T F; Bonini, A L; Lima, R R; Maidana, N L; Malafronte, A A; Pascholati, P R; Vanin, V R; Martins, M N

2012-09-01

Optical transition radiation (OTR) plays an important role in beam diagnostics for high energy particle accelerators. Its linear intensity with beam current is a great advantage as compared to fluorescent screens, which are subject to saturation. Moreover, the measurement of the angular distribution of the emitted radiation enables the determination of many beam parameters in a single observation point. However, few works deals with the application of OTR to monitor low energy beams. In this work we describe the design of an OTR based beam monitor used to measure the transverse beam charge distribution of the 1.9-MeV electron beam of the linac injector of the IFUSP microtron using a standard vision machine camera. The average beam current in pulsed operation mode is of the order of tens of nano-Amps. Low energy and low beam current make OTR observation difficult. To improve sensitivity, the beam incidence angle on the target was chosen to maximize the photon flux in the camera field-of-view. Measurements that assess OTR observation (linearity with beam current, polarization, and spectrum shape) are presented, as well as a typical 1.9-MeV electron beam charge distribution obtained from OTR. Some aspects of emittance measurement using this device are also discussed.

BEaTriX, expanded x-ray beam facility for testing modular elements of telescope optics: an update

NASA Astrophysics Data System (ADS)

Pelliciari, C.; Spiga, D.; Bonnini, E.; Buffagni, E.; Ferrari, C.; Pareschi, G.; Tagliaferri, G.

2015-09-01

We present in this paper an update on the design of BEaTriX (Beam Expander Testing X-ray facility), an X-ray apparatus to be realized at INAF/OAB and that will generate an expanded, uniform and parallel beam of soft X-rays. BEaTriX will be used to perform the functional tests of X-ray focusing modules of large X-ray optics such as those for the ATHENA X-ray observatory, using the Silicon Pore Optics (SPO) as a baseline technology, and Slumped Glass Optics (SGO) as a possible alternative. Performing the tests in X-rays provides the advantage of an in-situ, at-wavelength quality control of the optical modules produced in series by the industry, performing a selection of the modules with the best angular resolution, and, in the case of SPOs, there is also the interesting possibility to align the parabolic and the hyperbolic stacks directly under X-rays, to minimize the aberrations. However, a parallel beam with divergence below 2 arcsec is necessary in order to measure mirror elements that are expected to reach an angular resolution of about 4 arcsec, since the ATHENA requirement for the entire telescope is 5 arcsec. Such a low divergence over the typical aperture of modular optics would require an X-ray source to be located in a several kilometers long vacuum tube. In contrast, BEaTriX will be compact enough (5 m x 14 m) to be housed in a small laboratory, will produce an expanded X-ray beam 60 mm x 200 mm broad, characterized by a very low divergence (1.5 arcsec HEW), strong polarization, high uniformity, and X-ray energy selectable between 1.5 keV and 4.5 keV. In this work we describe the BEaTriX layout and show a performance simulation for the X-ray energy of 4.5 keV.

Modeling of a Compact Terahertz Source based on the Two-Stream Instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Svimonishvili, Tengiz

2016-05-17

THz radiation straddles the microwave and infrared bands of the electromagnetic spectrum, thus combining the penetrating power of lower-frequency waves and imaging capabilities of higher-energy infrared radiation. THz radiation is employed in various elds such as cancer research, biology, agriculture, homeland security, and environmental monitoring. Conventional vacuum electronic sources of THz radiation (e.g., fast- and slow-wave devices) either require very small structures or are bulky and expensive to operate. Optical sources necessitate cryogenic cooling and are presently capable of producing milliwatt levels of power at THz frequencies. We propose a millimeter and sub-millimeter wave source based on a well-known phenomenonmore » called the two-stream instability. The two-beam source relies on lowenergy and low-current electron beams for operation. Also, it is compact, simple in design, and does not contain expensive parts that require complex machining and precise alignment. In this dissertation, we perform 2-D particle-in-cell (PIC) simulations of the interaction region of the two-beam source. The interaction region consists of a beam pipe of radius ra and two electron beams of radius rb co-propagating and interacting inside the pipe. The simulations involve the interaction of unmodulated (no initial energy modulation) and modulated (energy-modulated, seeded at a given frequency) electron beams. In addition, both cold (monoenergetic) and warm (Gaussian) beams are treated.« less

Transverse profile of the electron beam for the RHIC electron lenses

DOE PAGES

Gu, X.; Altinbas, Z.; Costanzo, M.; ...

2015-07-10

To compensate for the beam-beam effects from the proton-proton interactions at the two interaction points IP6 and IP8 in the Relativistic Heavy Ion Collider (RHIC), we are constructing two electron lenses (e-lenses) that we plan to install in the interaction region IR10. Before installing them, the electron gun, collector, instrumentation were tested and the electron beam properties were qualified on an electron lens test bench. We will present the test results and discuss our measurement of the electron beam current and of the electron gun perveance. We achieved a maximum current of 1 A with 5 kV energy for bothmore » the pulsed- and the DC-beam (which is a long turn-by-turn pulse beam). We measured beam transverse profiles with an Yttrium Aluminum Garnet (YAG) screen and pinhole detector, and compared those to simulated beam profiles. Measurements of the pulsed electron beam stability were obtained by measuring the modulator voltage.« less

Neutron production at 0° from the 40Ca+H reaction at Elab=357A and 565A MeV

NASA Astrophysics Data System (ADS)

Tuvè, C.; Albergo, S.; Boemi, D.; Caccia, Z.; Chen, C.-X.; Costa, S.; Crawford, H. J.; Cronqvist, M.; Engelage, J.; Greiner, L.; Guzik, T. G.; Insolia, A.; Knott, C. N.; Lindstrom, P. J.; Mitchell, J. W.; Potenza, R.; Reito, S.; Romanski, J.; Russo, G. V.; Soutoul, A.; Testard, O.; Tull, C. E.; Waddington, C. J.; Webber, W. R.; Wefel, J. P.

1997-08-01

Neutrons produced in the 40Ca+H reaction at Elab=357A and 565A MeV have been detected using a three-module version of the multifunctional neutron spectrometer MUFFINS. The detector covered a narrow angular range around the beam in the forward direction (0°-3.2°). Semi-inclusive neutron production cross sections, at the two energies, are reported together with neutron energy spectra, angular, rapidity, and transverse momentum distributions. Comparison with a Boltzmann-Nordheim-Vlasov approach + phase space coalescence model is discussed.

Inertial fusion program and national laser users facility program

NASA Astrophysics Data System (ADS)

1995-01-01

This is the 1994 annual report for the University of Rochester, Laboratory for Laser Energetics. The report is presented as a series of research type reports. The titles emphasize the breadth of work carried out. They are: stability analysis of unsteady ablation fronts; characterization of laser-produced plasma density profiles using grid image refractometry; transport and sound waves in plasmas with light and heavy ions; three-halves-harmonic radiation from long-scale-length plasmas revisited; OMEGA upgrade status report; target imaging and backlighting diagnosis; effect of electron collisions on ion-acoustic waves and heat flow; particle-in-cell code simulations of the interaction of gaussian ultrashort laser pulses with targets of varying initial scale lengths; characterization of thick cryogenic fuel layers: compensation for the lens effect using convergent beam interferometry; compact, multijoule-output, Nd:Glass, large-aperture ring amplifier; atomic force microscopy observation of water-induced morphological changes in Y2O3 monolayer coatings; observation of longitudinal acceleration of electrons born in a high-intensity laser focus; spatial intensity nonuniformities of an OMEGA beam due to nonlinear beam propagation; calculated X-ray backlighting images of mixed imploded targets; evaluation of cosmic rays for use in the monitoring of the MEDUSA scintillator-photomultiplier diagnostic array; highly efficient second-harmonic generation of ultra-intense Nd:Glass laser pulses multiple cutoff wave numbers of the ablative Rayleigh-Taylor instability; ultrafast, all-silicon light modulator; angular dependence of the stimulated Brillouin scattering in homogeneous plasma; and femtosecond excited-state dynamics of a conjugated ladder polymer.

RF Jitter Modulation Alignment Sensing

NASA Astrophysics Data System (ADS)

Ortega, L. F.; Fulda, P.; Diaz-Ortiz, M.; Perez Sanchez, G.; Ciani, G.; Voss, D.; Mueller, G.; Tanner, D. B.

2017-01-01

We will present the numerical and experimental results of a new alignment sensing scheme which can reduce the complexity of alignment sensing systems currently used, while maintaining the same shot noise limited sensitivity. This scheme relies on the ability of electro-optic beam deflectors to create angular modulation sidebands in radio frequency, and needs only a single-element photodiode and IQ demodulation to generate error signals for tilt and translation degrees of freedom in one dimension. It distances itself from current techniques by eliminating the need for beam centering servo systems, quadrant photodetectors and Gouy phase telescopes. RF Jitter alignment sensing can be used to reduce the complexity in the alignment systems of many laser optical experiments, including LIGO and the ALPS experiment.

Mechanical evidence of the orbital angular momentum to energy ratio of vortex beams.

PubMed

Demore, Christine E M; Yang, Zhengyi; Volovick, Alexander; Cochran, Sandy; MacDonald, Michael P; Spalding, Gabriel C

2012-05-11

We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We experimentally determine this ratio using simultaneous measurements of both the levitation force and the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a 1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the angular momentum current of the beam to the power should be given by the ratio of the beam's topological charge to its angular frequency. This direct experimental observation that the ratio of the torque to power does convincingly match the expected value (given by the topological charge to angular frequency ratio of the beam) is a fundamental result.

Microwave accelerator E-beam pumped laser

DOEpatents

Brau, Charles A.; Stein, William E.; Rockwood, Stephen D.

1980-01-01

A device and method for pumping gaseous lasers by means of a microwave accelerator. The microwave accelerator produces a relativistic electron beam which is applied along the longitudinal axis of the laser through an electron beam window. The incident points of the electron beam on the electron beam window are varied by deflection coils to enhance the cooling characteristics of the foil. A thyratron is used to reliably modulate the microwave accelerator to produce electron beam pulses which excite the laser medium to produce laser pulse repetition frequencies not previously obtainable. An aerodynamic window is also disclosed which eliminates foil heating problems, as well as a magnetic bottle for reducing laser cavity length and pressures while maintaining efficient energy deposition.

Theory of Self-Phase Modulation and Spectral Broadening

NASA Astrophysics Data System (ADS)

Shen, Y. R.; Yang, Guo-Zhen

Self-phase modulation refers to the phenomenon in which a laser beam propagating in a medium interacts with the medium and imposes a phase modulation on itself. It is one of those very fascinating effects discovered in the early days of nonlinear optics (Bloembergen and Lallemand, 1966; Brewer, 1967; Cheung et al., 1968; Lallemand, 1966; Jones and Stoicheff, 1964; Shimizu, 1967; Stoicheff, 1963). The physical origin of the phenomenon lies in the fact that the strong field of a laser beam is capable of inducing an appreciable intensity-dependent refractive index change in the medium. The medium then reacts back and inflicts a phase change on the incoming wave, resulting in self-phase modulation (SPM). Since a laser beam has a finite cross section, and hence a transverse intensity profile, SPM on the beam should have a transverse spatial dependence, equivalent to a distortion of the wave front. Consequently, the beam will appear to have self-diffracted. Such a self-diffraction action, resulting from SPM in space, is responsible for the well-known nonlinear optical phenomena of self-focusing and self-defocusing (Marburger, 1975; Shen, 1975). It can give rise to a multiple ring structure in the diffracted beam if the SPM is sufficiently strong (Durbin et al., 1981; Santamato and Shen, 1984). In the case of a pulsed laser input, the temporal variation of the laser intensity leads to an SPM in time. Since the time derivative of the phase of a wave is simply the angular frequency of the wave, SPM also appears as a frequency modulation. Thus, the output beam appears with a self-induced spectral broadening (Cheung et al., 1968; Gustafson et al., 1969; Shimizu, 1967).

Controlling neutron orbital angular momentum

NASA Astrophysics Data System (ADS)

Clark, Charles W.; Barankov, Roman; Huber, Michael G.; Arif, Muhammad; Cory, David G.; Pushin, Dmitry A.

2015-09-01

The quantized orbital angular momentum (OAM) of photons offers an additional degree of freedom and topological protection from noise. Photonic OAM states have therefore been exploited in various applications ranging from studies of quantum entanglement and quantum information science to imaging. The OAM states of electron beams have been shown to be similarly useful, for example in rotating nanoparticles and determining the chirality of crystals. However, although neutrons--as massive, penetrating and neutral particles--are important in materials characterization, quantum information and studies of the foundations of quantum mechanics, OAM control of neutrons has yet to be achieved. Here, we demonstrate OAM control of neutrons using macroscopic spiral phase plates that apply a `twist' to an input neutron beam. The twisted neutron beams are analysed with neutron interferometry. Our techniques, applied to spatially incoherent beams, demonstrate both the addition of quantum angular momenta along the direction of propagation, effected by multiple spiral phase plates, and the conservation of topological charge with respect to uniform phase fluctuations. Neutron-based studies of quantum information science, the foundations of quantum mechanics, and scattering and imaging of magnetic, superconducting and chiral materials have until now been limited to three degrees of freedom: spin, path and energy. The optimization of OAM control, leading to well defined values of OAM, would provide an additional quantized degree of freedom for such studies.

Range imaging laser radar

DOEpatents

Scott, Marion W.

1990-01-01

A laser source is operated continuously and modulated periodically (typicy sinusoidally). A receiver imposes another periodic modulation on the received optical signal, the modulated signal being detected by an array of detectors of the integrating type. Range to the target determined by measuring the phase shift of the intensity modulation on the received optical beam relative to a reference. The receiver comprises a photoemitter for converting the reflected, periodically modulated, return beam to an accordingly modulated electron stream. The electron stream is modulated by a local demodulation signal source and subsequently converted back to a photon stream by a detector. A charge coupled device (CCD) array then averages and samples the photon stream to provide an electrical signal in accordance with the photon stream.

Range imaging laser radar

DOEpatents

Scott, M.W.

1990-06-19

A laser source is operated continuously and modulated periodically (typically sinusoidally). A receiver imposes another periodic modulation on the received optical signal, the modulated signal being detected by an array of detectors of the integrating type. Range to the target determined by measuring the phase shift of the intensity modulation on the received optical beam relative to a reference. The receiver comprises a photoemitter for converting the reflected, periodically modulated, return beam to an accordingly modulated electron stream. The electron stream is modulated by a local demodulation signal source and subsequently converted back to a photon stream by a detector. A charge coupled device (CCD) array then averages and samples the photon stream to provide an electrical signal in accordance with the photon stream. 2 figs.

Transfer of Orbital and Spin angular momentum from non-paraxial optical vortex to atomic BEC

NASA Astrophysics Data System (ADS)

Bhowmik, Anal; Mondal, Pradip Kumar; Majumder, Sonjoy; Deb, Bimalendu

2017-04-01

Allen and co-workers first brought up the realization that optical vortex can carry well defined orbital angular momentum (OAM) associated with its spatial mode. Spin angular momentum (SAM) of the light, associated with the polarization, interacts with the internal electronic motion of the atom. The exchange of orbital angular momentum (OAM) between optical vortex and the center-of-mass (CM) motion of an atom or molecule is well known in paraxial approximation. We show that, how the total angular momentum (TAM) of non-paraxial optical vortex is shared with atom, in terms of OAM and SAM. Both the angular momenta are now possible to be transferred to the internal electronic and external CM motion of atom. Here we have studied how the Rabi frequencies of the excitations of two-photon Raman transitions with respect to focusing angles. Also, we investigate the properties of the vortex superposed state for a Bose-Einstein condensate condensate by a single non-paraxial vortex beam. The density distribution of the vortex-antivortex superposed state has a petal structure which is determined by the quantum circulations and proportion of the vortex and antivortex.

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

NASA Astrophysics Data System (ADS)

Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

2012-06-01

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

Momentum-imaging apparatus for the study of dissociative electron attachment dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moradmand, A.; Williams, J. B.; Landers, A. L.

An ion-momentum spectrometer is used to study the dissociative dynamics of electron attachment to molecules. A skimmed, supersonic gas jet is crossed with a pulsed beam of low-energy electrons, and the resulting negative ions are extracted toward a time- and position-sensitive detector. Calculations of the momentum in three dimensions may be used to determine the angular dependence of dissociative attachment as well as the energetics of the reaction.

Extreme Ultraviolet Fractional Orbital Angular Momentum Beams from High Harmonic Generation

PubMed Central

Turpin, Alex; Rego, Laura; Picón, Antonio; San Román, Julio; Hernández-García, Carlos

2017-01-01

We investigate theoretically the generation of extreme-ultraviolet (EUV) beams carrying fractional orbital angular momentum. To this end, we drive high-order harmonic generation with infrared conical refraction (CR) beams. We show that the high-order harmonic beams emitted in the EUV/soft x-ray regime preserve the characteristic signatures of the driving beam, namely ringlike transverse intensity profile and CR-like polarization distribution. As a result, through orbital and spin angular momentum conservation, harmonic beams are emitted with fractional orbital angular momentum, and they can be synthesized into structured attosecond helical beams –or “structured attosecond light springs”– with rotating linear polarization along the azimuth. Our proposal overcomes the state of the art limitations for the generation of light beams far from the visible domain carrying non-integer orbital angular momentum and could be applied in fields such as diffraction imaging, EUV lithography, particle trapping, and super-resolution imaging. PMID:28281655

Development of an Annular Electron Beam HPM Amplifier

DTIC Science & Technology

1994-09-01

34, Phys.Rev.Lett., 64(19), ppgs 2320-2323, 7 May 1990 9. Lau, Y.Y. and Chernin, D., "A review of the ac space - charge effect in electron-circuit interactions...the Child-Lanamuir, space - charge limiting current in the beam line. This removes the potential of torming a virtual cathode (Ref. 19). The...propagates the electron beam through a single modulating gap, with a specified voltage, frequency, and gap extent. The beam space charge is an input

Generation of 300 MeV Quasi-Monochromatic Electron Beams from Laser Wakefield and Initiation of Photonuclear Reactions

NASA Astrophysics Data System (ADS)

Maksimchuk, A.; Beene, J. R.

2005-10-01

In the interaction of 30 fs, 40 TW Ti:sapphire Hercules laser at the University of Michigan, which is focused to the intensity of 10^19 W/cm^2 onto a supersonic He gas jet with electron density close to the resonant density, we observed quasi-monoenergetic electron beams with energy up to 300 MeV and angular divergence of about 10 mrad. The results on characterization of relativistic electron beam in terms of energy spread, its charge, divergence and pointing stability will be presented. 2D PIC simulations performed for the parameters close to the experimental conditions show the evolution of the laser pulse in plasma, electron injection, and the specifics of electron acceleration observed in experiments. Resulted relativistic electron beams have been used to perform gamma-neutron activation of ^12C and ^63Cu and photo-fission of ^238U. We demonstrated that approximately 10^6 reaction per shot has been produced in each case. This work was supported by the NSF through the Physics Frontier Center FOCUS. JRB, DRS, DWS, and CRV acknowledge support by the DOE under contract DE-AC05-00OR22725 with UT-Battelle, LLC.

Energy Weighted Angular Correlations Between Hadrons Produced in Electron-Positron Annihilation.

NASA Astrophysics Data System (ADS)

Strharsky, Roger Joseph

Electron-positron annihilation at large center of mass energy produces many hadronic particles. Experimentalists then measure the energies of these particles in calorimeters. This study investigated correlations between the angular locations of one or two such calorimeters and the angular orientation of the electron beam in the laboratory frame of reference. The calculation of these correlations includes weighting by the fraction of the total center of mass energy which the calorimeter measures. Starting with the assumption that the reaction proceeeds through the intermediate production of a single quark/anti-quark pair, a simple statistical model was developed to provide a phenomenological description of the distribution of final state hadrons. The model distributions were then used to calculate the one- and two-calorimeter correlation functions. Results of these calculations were compared with available data and several predictions were made for those quantities which had not yet been measured. Failure of the model to reproduce all of the data was discussed in terms of quantum chromodynamics, a fundamental theory which includes quark interactions.

Angular distribution measurements of photo-neutron yields produced by 2.0 GeV electrons incident on thick targets.

PubMed

Lee, Hee-Seock; Ban, Syuichi; Sanami, Toshiya; Takahashi, Kazutoshi; Sato, Tatsuhiko; Shin, Kazuo; Chung, Chinwha

2005-01-01

A study of differential photo-neutron yields by irradiation with 2 GeV electrons has been carried out. In this extension of a previous study in which measurements were made at an angle of 90 degrees relative to incident electrons, the differential photo-neutron yield was obtained at two other angles, 48 degrees and 140 degrees, to study its angular characteristics. Photo-neutron spectra were measured using a pulsed beam time-of-flight method and a BC418 plastic scintillator. The reliable range of neutron energy measurement was 8-250 MeV. The neutron spectra were measured for 10 Xo-thick Cu, Sn, W and Pb targets. The angular distribution characteristics, together with the previous results for 90 degrees, are presented in the study. The experimental results are compared with Monte Carlo calculation results. The yields predicted by MCNPX 2.5 tend to underestimate the measured ones. The same trend holds for the comparison results using the EGS4 and PICA3 codes.

Superoscillating electron wave functions with subdiffraction spots

NASA Astrophysics Data System (ADS)

Remez, Roei; Tsur, Yuval; Lu, Peng-Han; Tavabi, Amir H.; Dunin-Borkowski, Rafal E.; Arie, Ady

2017-03-01

Almost one and a half centuries ago, Abbe [Arch. Mikrosk. Anat. 9, 413 (1873), 10.1007/BF02956173] and shortly after Lord Rayleigh [Philos. Mag. Ser. 5 8, 261 (1879), 10.1080/14786447908639684] showed that, when an optical lens is illuminated by a plane wave, a diffraction-limited spot with radius 0.61 λ /sinα is obtained, where λ is the wavelength and α is the semiangle of the beam's convergence cone. However, spots with much smaller features can be obtained at the focal plane when the lens is illuminated by an appropriately structured beam. Whereas this concept is known for light beams, here, we show how to realize it for a massive-particle wave function, namely, a free electron. We experimentally demonstrate an electron central spot of radius 106 pm, which is more than two times smaller than the diffraction limit of the experimental setup used. In addition, we demonstrate that this central spot can be structured by adding orbital angular momentum to it. The resulting superoscillating vortex beam has a smaller dark core with respect to a regular vortex beam. This family of electron beams having hot spots with arbitrarily small features and tailored structures could be useful for studying electron-matter interactions with subatomic resolution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malashko, Ya I; Khabibulin, V M

We have derived analytical expressions, verified by the methods of numerical simulation, to evaluate the angular divergence of nondiffractive laser beams containing smooth aberrations, i.e., spherical defocusing, astigmatism and toroid. Using these expressions we have formulated the criteria for admissible values of smooth aberrations. (laser applications and other topics in quantum electronics)

Characterising laser beams with liquid crystal displays

NASA Astrophysics Data System (ADS)

Dudley, Angela; Naidoo, Darryl; Forbes, Andrew

2016-02-01

We show how one can determine the various properties of light, from the modal content of laser beams to decoding the information stored in optical fields carrying orbital angular momentum, by performing a modal decomposition. Although the modal decomposition of light has been known for a long time, applied mostly to pattern recognition, we illustrate how this technique can be implemented with the use of liquid-crystal displays. We show experimentally how liquid crystal displays can be used to infer the intensity, phase, wavefront, Poynting vector, and orbital angular momentum density of unknown optical fields. This measurement technique makes use of a single spatial light modulator (liquid crystal display), a Fourier transforming lens and detector (CCD or photo-diode). Such a diagnostic tool is extremely relevant to the real-time analysis of solid-state and fibre laser systems as well as mode division multiplexing as an emerging technology in optical communication.

Multi-beam linear accelerator EVT

NASA Astrophysics Data System (ADS)

Teryaev, Vladimir E.; Kazakov, Sergey Yu.; Hirshfield, Jay L.

2016-09-01

A novel electron multi-beam accelerator is presented. The accelerator, short-named EVT (Electron Voltage Transformer) belongs to the class of two-beam accelerators. It combines an RF generator and essentially an accelerator within the same vacuum envelope. Drive beam-lets and an accelerated beam are modulated in RF modulators and then bunches pass into an accelerating structure, comprising uncoupled with each other and inductive tuned cavities, where the energy transfer from the drive beams to the accelerated beam occurs. A phasing of bunches is solved by choice correspond distances between gaps of the adjacent cavities. Preliminary results of numerical simulations and the initial specification of EVT operating in S-band, with a 60 kV gun and generating a 2.7 A, 1.1 MV beam at its output is presented. A relatively high efficiency of 67% and high design average power suggest that EVT can find its use in industrial applications.

Multi-beam linear accelerator EVT

DOE PAGES

Teryaev, Vladimir E.; Kazakov, Sergey Yu.; Hirshfield, Jay L.

2016-03-29

A novel electron multi-beam accelerator is presented. The accelerator, short-named EVT (Electron Voltage Transformer) belongs to the class of two-beam accelerators. It combines an RF generator and essentially an accelerator within the same vacuum envelope. Drive beam-lets and an accelerated beam are modulated in RF modulators and then bunches pass into an accelerating structure, comprising uncoupled with each other and inductive tuned cavities, where the energy transfer from the drive beams to the accelerated beam occurs. A phasing of bunches is solved by choice correspond distances between gaps of the adjacent cavities. Preliminary results of numerical simulations and the initialmore » specification of EVT operating in S-band, with a 60 kV gun and generating a 2.7 A, 1.1 MV beam at its output is presented. Furthermore, a relatively high efficiency of 67% and high design average power suggest that EVT can find its use in industrial applications.« less

Arbitrary optical wavefront shaping via spin-to-orbit coupling

NASA Astrophysics Data System (ADS)

Larocque, Hugo; Gagnon-Bischoff, Jérémie; Bouchard, Frédéric; Fickler, Robert; Upham, Jeremy; Boyd, Robert W.; Karimi, Ebrahim

2016-12-01

Converting spin angular momentum to orbital angular momentum has been shown to be a practical and efficient method for generating optical beams carrying orbital angular momentum and possessing a space-varying polarized field. Here, we present novel liquid crystal devices for tailoring the wavefront of optical beams through the Pancharatnam-Berry phase concept. We demonstrate the versatility of these devices by generating an extensive range of optical beams such as beams carrying ±200 units of orbital angular momentum along with Bessel, Airy and Ince-Gauss beams. We characterize both the phase and the polarization properties of the generated beams, confirming our devices’ performance.

Low-dimensional organization of angular momentum during walking on a narrow beam.

PubMed

Chiovetto, Enrico; Huber, Meghan E; Sternad, Dagmar; Giese, Martin A

2018-01-08

Walking on a beam is a challenging motor skill that requires the regulation of upright balance and stability. The difficulty in beam walking results from the reduced base of support compared to that afforded by flat ground. One strategy to maintain stability and hence avoid falling off the beam is to rotate the limb segments to control the body's angular momentum. The aim of this study was to examine the coordination of the angular momentum variations during beam walking. We recorded movement kinematics of participants walking on a narrow beam and computed the angular momentum contributions of the body segments with respect to three different axes. Results showed that, despite considerable variability in the movement kinematics, the angular momentum was characterized by a low-dimensional organization based on a small number of segmental coordination patterns. When the angular momentum was computed with respect to the beam axis, the largest fraction of its variation was accounted for by the trunk segment. This simple organization was robust and invariant across all participants. These findings support the hypothesis that control strategies for complex balancing tasks might be easier to understand by investigating angular momentum instead of the segmental kinematics.

A 120kV IGBT modulator for driving a pierce electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Earley, L. M.; Brown, R. W.; Carlson, R. L.

2004-01-01

An IGBT modulator has been developed to drive a 120 kV, 23 A Pierce electron gun. The modulator is capable of producing pulses up to 10 {mu}s in width at repetition rates up to 10Hz with no active reset. The pulse rise time on the electron gun will be approximately 2 {mu}s and the remaining 8 {mu}s of flattop is tuned to have a ripple of less than 1 percent rms. The modulator technology was developed from a previous 50 kV prototype. The modulator consists of six boards, each with one EUPEC IGBT that drives a single common step-up transformermore » wound on METGLAS 2605SC cores. The six transformer cores share a common bi-filar output secondary winding. The modulator uses a fiber optic trigger system and has a high voltage cable output with an epoxy receptacle on the oil end and a ceramic receptacle on the vacuum end. The 120 kV electron gun was manufactured by MDS Co. and will be used to generate sheet electron beams from the standard pencil beam produced by the Pierce electron gun.« less

Measurement of angularly dependent spectra of betatron gamma-rays from a laser plasma accelerator with quadrant-sectored range filters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Jong Ho, E-mail: jhjeon07@ibs.re.kr; Nakajima, Kazuhisa, E-mail: naka115@dia-net.ne.jp; Rhee, Yong Joo

Measurement of angularly dependent spectra of betatron gamma-rays radiated by GeV electron beams from laser wakefield accelerators (LWFAs) are presented. The angle-resolved spectrum of betatron radiation was deconvolved from the position dependent data measured for a single laser shot with a broadband gamma-ray spectrometer comprising four-quadrant sectored range filters and an unfolding algorithm, based on the Monte Carlo code GEANT4. The unfolded gamma-ray spectra in the photon energy range of 0.1–10 MeV revealed an approximately isotropic angular dependence of the peak photon energy and photon energy-integrated fluence. As expected by the analysis of betatron radiation from LWFAs, the results indicate thatmore » unpolarized gamma-rays are emitted by electrons undergoing betatron motion in isotropically distributed orbit planes.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verschuur, G. L.; Schmelz, J. T., E-mail: gverschu@naic.edu

Small-scale features observed by Wilkinson Microwave Anisotropy Probe  ( WMAP ) and PLANCK in the frequency range of 22–90 GHz show a nearly flat spectrum, which meets with expectations that they originate in the early universe. However, free–free emission from electrons in small angular scale galactic sources that suffer beam dilution very closely mimic the observed spectrum in this frequency range. Fitting such a model to the PLANCK and WMAP data shows that the angular size required to fit the data is comparable to the angular width of associated H i filaments found in the Galactic Arecibo L-Band Feed Array-Hmore » isurvey data. Also, the temperature of the electrons is found to be in the range of 100–300 K. The phenomenon revealed by these data may contribute to a more precise characterization of the foreground masks required to interpret the cosmological aspect of PLANCK and WMAP data.« less

Coherent Lienard-Wiechert fields produced by free electron lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elias, L.R.; Gallardo, J.C.

1981-12-01

Results are presented here of a three-dimensional numerical analysis of the radiation fields produced in a free electron laser. The method used here to obtain the spatial and temporal behavior of the radiated fields is based on the coherent superposition of the exact Lienard-Wiechert fields produced by each electron in the beam. Interference effects are responsible for the narrow angular radiation patterns obtained and for the high degree of monochromaticity of the radiated field.

Source brightness and useful beam current of carbon nanotubes and other very small emitters

NASA Astrophysics Data System (ADS)

Kruit, P.; Bezuijen, M.; Barth, J. E.

2006-01-01

The potential application of carbon nanotubes as electron sources in electron microscopes is analyzed. The resolution and probe current that can be obtained from a carbon nanotube emitter in a low-voltage scanning electron microscope are calculated and compared to the state of the art using Schottky electron sources. Many analytical equations for probe-size versus probe-current relations in different parameter regimes are obtained. It is shown that for most carbon nanotube emitters, the gun lens aberrations are larger than the emitters' virtual source size and thus restrict the microscope's performance. The result is that the advantages of the higher brightness of nanotube emitters are limited unless the angular emission current is increased over present day values or the gun lens aberrations are decreased. For some nanotubes with a closed cap, it is known that the emitted electron beam is coherent over the full emission cone. We argue that for such emitters the parameter ``brightness'' becomes meaningless. The influence of phase variations in the electron wave front emitted from such a nanotube emitter on the focusing of the electron beam is analyzed.

Modulational instability of helicon waves in a magnetoactive semiconductor n-InSb

NASA Astrophysics Data System (ADS)

Salimullah, M.; Ferdous, T.

1984-03-01

In this paper the modulational instabilithy of a beam of high amplitude helicon wave in a magnetoactive piezoelectric semiconductor is studied. The nonlinear response of electrons in the semiconductor plasma has been found by following the fluid model of homogeneous plasmas. The low frequency nonlinearity has been taken through the ponderomotive force on electrons, whereas the nonlinearity in the scattered helicon waves arises through the nonlinear current densities of electrons. For typical plasma parameters in n-type indium antimonide and for a considerable power density (approximately 20 kW/sq cm) of the incident helicon beam, the growth rate of the modulational instability is quite high (approximately 10 to the 7th rad/s).

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

NASA Astrophysics Data System (ADS)

Lu, Chao; Jiang, Tao; Liu, Shengguang; Wang, Rui; Zhao, Lingrong; Zhu, Pengfei; Liu, Yaqi; Xu, Jun; Yu, Dapeng; Wan, Weishi; Zhu, Yimei; Xiang, Dao; Zhang, Jie

2018-03-01

An accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ˜3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10-19 s m, about 2 orders of magnitude higher than that achieved with state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.

Extraction of highly charged ions from the Berlin Electron Beam Ion Trap for interactions with a gas target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, F.I.; Biedermann, C.; Radtke, R.

2006-03-15

Highly charged ions are extracted from the Berlin Electron Beam Ion Trap for investigations of charge exchange with a gas target. The classical over-the-barrier model for slow highly charged ions describes this process, whereby one or more electrons are captured from the target into Rydberg states of the ion. The excited state relaxes via a radiative cascade of the electron to ground energy. The cascade spectra are characteristic of the capture state. We investigate x-ray photons emitted as a result of interactions between Ar{sup 17+} ions at energies {<=}5q keV with Ar atoms. Of particular interest is the velocity dependencemore » of the angular momentum capture state l{sub c}.« less

Dynamics of modulated beams in spectral domain

DOE PAGES

Yampolsky, Nikolai A.

2017-07-16

General formalism for describing dynamics of modulated beams along linear beamlines is developed. We describe modulated beams with spectral distribution function which represents Fourier transform of the conventional beam distribution function in the 6-dimensional phase space. The introduced spectral distribution function is localized in some region of the spectral domain for nearly monochromatic modulations. It can be characterized with a small number of typical parameters such as the lowest order moments of the spectral distribution. We study evolution of the modulated beams in linear beamlines and find that characteristic spectral parameters transform linearly. The developed approach significantly simplifies analysis ofmore » various schemes proposed for seeding X-ray free electron lasers. We use this approach to study several recently proposed schemes and find the bandwidth of the output bunching in each case.« less

Dosimetric characteristics of a MOSFET dosimeter for clinical electron beams.

PubMed

Manigandan, D; Bharanidharan, G; Aruna, P; Devan, K; Elangovan, D; Patil, Vikram; Tamilarasan, R; Vasanthan, S; Ganesan, S

2009-09-01

The fundamental dosimetric characteristics of commercially available metal oxide semiconductor field effect transistor (MOSFET) detectors were studied for clinical electron beam irradiations. MOSFET showed excellent linearity against doses measured using an ion chamber in the dose range of 20-630cGy. MOSFET reproducibility is better at high doses compared to low doses. The output factors measured with the MOSFET were within +/-3% when compared with those measured with a parallel plate chamber. From 4 to 12MeV, MOSFETs showed a large angular dependence in the tilt directions and less in the axial directions. MOSFETs do not show any dose-rate dependence between 100 and 600MU/min. However, MOSFETs have shown under-response when the dose per pulse of the beam is decreased. No measurable effect in MOSFET response was observed in the temperature range of 23-40 degrees C. The energy dependence of a MOSFET dosimeter was within +/-3.0% for 6-18MeV electron beams and 5.5% for 4MeV ones. This study shows that MOSFET detectors are suitable for dosimetry of electron beams in the energy range of 4-18MeV.

Beam test of CSES silicon strip detector module

NASA Astrophysics Data System (ADS)

Zhang, Da-Li; Lu, Hong; Wang, Huan-Yu; Li, Xin-Qiao; Xu, Yan-Bing; An, Zheng-Hua; Yu, Xiao-xia; Wang, Hui; Shi, Feng; Wang, Ping; Zhao, Xiao-Yun

2017-05-01

The silicon-strip tracker of the China Seismo-Electromagnetic Satellite (CSES) consists of two double-sided silicon strip detectors (DSSDs) which provide incident particle tracking information. A low-noise analog ASIC VA140 was used in this study for DSSD signal readout. A beam test on the DSSD module was performed at the Beijing Test Beam Facility of the Beijing Electron Positron Collider (BEPC) using a 400-800 MeV/c proton beam. The pedestal analysis results, RMSE noise, gain correction, and intensity distribution of incident particles of the DSSD module are presented. Supported by the XXX Civil Space Programme

Coulomb repulsion and the electron beam directed energy weapon

NASA Astrophysics Data System (ADS)

Retsky, Michael W.

2004-09-01

Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into small spots at large distances from defining apertures. A classic example is the 1970s era "Star Wars" study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Based on estimates, the nonreversible terms should be small - of the order of 0.1 mm. If this is true, it is possible to design a practical electron beam directed weapon not limited by Coulomb repulsion.

Position, spin, and orbital angular momentum of a relativistic electron

NASA Astrophysics Data System (ADS)

Bliokh, Konstantin Y.; Dennis, Mark R.; Nori, Franco

2017-08-01

Motivated by recent interest in relativistic electron vortex states, we revisit the spin and orbital angular momentum properties of Dirac electrons. These are uniquely determined by the choice of the position operator for a relativistic electron. We consider two main approaches discussed in the literature: (i) the projection of operators onto the positive-energy subspace, which removes the Zitterbewegung effects and correctly describes spin-orbit interaction effects, and (ii) the use of Newton-Wigner-Foldy-Wouthuysen operators based on the inverse Foldy-Wouthuysen transformation. We argue that the first approach [previously described in application to Dirac vortex beams in K. Y. Bliokh et al., Phys. Rev. Lett. 107, 174802 (2011), 10.1103/PhysRevLett.107.174802] has a more natural physical interpretation, including spin-orbit interactions and a nonsingular zero-mass limit, than the second one [S. M. Barnett, Phys. Rev. Lett. 118, 114802 (2017), 10.1103/PhysRevLett.118.114802].

Beam by design: Laser manipulation of electrons in modern accelerators

NASA Astrophysics Data System (ADS)

Hemsing, Erik; Stupakov, Gennady; Xiang, Dao; Zholents, Alexander

2014-07-01

Accelerator-based light sources such as storage rings and free-electron lasers use relativistic electron beams to produce intense radiation over a wide spectral range for fundamental research in physics, chemistry, materials science, biology, and medicine. More than a dozen such sources operate worldwide, and new sources are being built to deliver radiation that meets with the ever-increasing sophistication and depth of new research. Even so, conventional accelerator techniques often cannot keep pace with new demands and, thus, new approaches continue to emerge. In this article, a variety of recently developed and promising techniques that rely on lasers to manipulate and rearrange the electron distribution in order to tailor the properties of the radiation are reviewed. Basic theories of electron-laser interactions, techniques to create microstructures and nanostructures in electron beams, and techniques to produce radiation with customizable waveforms are reviewed. An overview of laser-based techniques for the generation of fully coherent x rays, mode-locked x-ray pulse trains, light with orbital angular momentum, and attosecond or even zeptosecond long coherent pulses in free-electron lasers is presented. Several methods to generate femtosecond pulses in storage rings are also discussed. Additionally, various schemes designed to enhance the performance of light sources through precision beam preparation including beam conditioning, laser heating, emittance exchange, and various laser-based diagnostics are described. Together these techniques represent a new emerging concept of "beam by design" in modern accelerators, which is the primary focus of this article.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murokh, A.

VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission FEL, which achieved saturation at 840 nm within a single-pass 4-m undulator. A gain length shorter than 18 cm has been obtained, yielding the gain of 2 x 10{sup 8} at saturation. The FEL performance, including spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. The results are compared to 3-D SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL system. Detailed agreement between simulations and experimental results is obtained over the wide range of themore » electron beam parameters.« less

Simulation of angular and energy distributions of the PTB beta secondary standard.

PubMed

Faw, R E; Simons, G G; Gianakon, T A; Bayouth, J E

1990-09-01

Calculations and measurements have been performed to assess radiation doses delivered by the PTB Secondary Standard that employs 147Pm, 204Tl, and 90Sr:90Y sources in prescribed geometries, and features "beam-flattening" filters to assure uniformity of delivered doses within a 5-cm radius of the axis from source to detector plane. Three-dimensional, coupled, electron-photon Monte Carlo calculations, accounting for transmission through the source encapsulation and backscattering from the source mounting, led to energy spectra and angular distributions of electrons penetrating the source encapsulation that were used in the representation of pseudo sources of electrons for subsequent transport through the atmosphere, filters, and detectors. Calculations were supplemented by measurements made using bare LiF TLD chips on a thick polymethyl methacrylate phantom. Measurements using the 204Tl and 90Sr:90Y sources revealed that, even in the absence of the beam-flattening filters, delivered dose rates were very uniform radially. Dosimeter response functions (TLD:skin dose ratios) were calculated and confirmed experimentally for all three beta-particle sources and for bare LiF TLDs ranging in mass thickness from 10 to 235 mg cm-2.

Excitation of terahertz radiation by an electron beam in a dielectric lined waveguide with rippled dielectric surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tripathi, Deepak; Uma, R.; Tripathi, V. K.

A relativistic electron beam propagating through a dielectric lined waveguide, with ripple on the dielectric surface, excites a free electron laser type instability where ripple acts as a wiggler. The spatial modulation of permittivity in the ripple region couples a terahertz radiation mode to a driven mode of lower phase velocity, where the beam is in Cerenkov resonance with the slow mode. Both the modes grow at the expanse of beam energy. The terahertz frequency increases as the beam velocity increases. The growth rate of the instability goes as one third power of beam density.

Orbital-angular-momentum transfer to optically levitated microparticles in vacuum

NASA Astrophysics Data System (ADS)

Mazilu, Michael; Arita, Yoshihiko; Vettenburg, Tom; Auñón, Juan M.; Wright, Ewan M.; Dholakia, Kishan

2016-11-01

We demonstrate the transfer of orbital angular momentum to an optically levitated microparticle in vacuum. The microparticle is placed within a Laguerre-Gaussian beam and orbits the annular beam profile with increasing angular velocity as the air drag coefficient is reduced. We explore the particle dynamics as a function of the topological charge of the levitating beam. Our results reveal that there is a fundamental limit to the orbital angular momentum that may be transferred to a trapped particle, dependent upon the beam parameters and inertial forces present.

New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

NASA Technical Reports Server (NTRS)

Nishikawa, Ken-Ichi; Buneman, Oscar; Neubert, Torsten

1994-01-01

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence, (2) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, and (3) the parallel phase velocity of the whistler wave is smaller than that of the beam mode. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is also involved in the generation of whistler waves.

Optical metrology for Starlight Separated Spacecraft Stellar Interferometry Mission

NASA Technical Reports Server (NTRS)

Dubovitsky, S.; Lay, O. P.; Peters, R. D.; Abramovici, A.; Asbury, C. G.; Kuhnert, A. C.; Mulder, J. L.

2002-01-01

We describe a high-precision inter-spacecraft metrology system designed for NASA 's StarLight mission, a space-based separated-spacecraft stellar interferometer. It consists of dual-target linear metrology, based on a heterodyne interferometer with carrier phase modulation, and angular metrology designed to sense the pointing of the laser beam and provides bearing information. The dual-target operation enables one metrology beam to sense displacement of two targets independently. We present the current design, breadboard implementation of the Metrology Subsystem in a stellar interferometer testbed and the present state of development of flight qualifiable subsystem components.

Independent Manipulation of Topological Charges and Polarization Patterns of Optical Vortices

PubMed Central

Yang, Ching-Han; Chen, Yuan-Di; Wu, Shing-Trong; Fuh, Andy Ying-Guey

2016-01-01

We present a simple and flexible method to generate various vectorial vortex beams (VVBs) with a Pancharatnam phase based on the scheme of double reflections from a single liquid crystal spatial light modulator (SLM). In this configuration, VVBs are constructed by the superposition of two orthogonally polarized orbital angular momentum (OAM) eigenstates. To verify the optical properties of the generated beams, Stokes polarimetry is developed to measure the states of polarization (SOP) over the transverse plane, while a Shack–Hartmann wavefront sensor is used to measure the OAM charge of beams. It is shown that both the simulated and the experimental results are in good qualitative agreement. In addition, polarization patterns and OAM charges of generated beams can be controlled independently using the proposed method. PMID:27526858

Can Coulomb repulsion for charged particle beams be overcome?

NASA Astrophysics Data System (ADS)

Retsky, Michael W.

2004-01-01

Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into a small spots at large distances from the defining apertures. A classic example is the 1970s era "Star Wars" study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Since the nonreversible terms should be small, it might be possible to construct an electron beam directed energy weapon.

Critical appraisal of volumetric-modulated arc therapy compared with electrons for the radiotherapy of cutaneous Kaposi's sarcoma of lower extremities with bone sparing.

PubMed

Nicolini, G; Abraham, S; Fogliata, A; Jordaan, A; Clivio, A; Vanetti, E; Cozzi, L

2013-03-01

To evaluate the use of volumetric-modulated arc therapy [VMAT, RapidArc® (RA); Varian Medical Systems, Palo Alto, CA] for the treatment of cutaneous Kaposi's sarcoma (KS) of lower extremities with adequate target coverage and high bone sparing, and to compare VMAT with electron beam therapy. 10 patients were planned with either RA or electron beams. The dose was prescribed to 30 Gy, 10 fractions, to mean the planning target volume (PTV), and significant maximum dose to bone was limited to 30 Gy. Plans were designed for 6-MV photon beams for RA and 6 MeV for electrons. Dose distributions were computed with AcurosXB® (Varian Medical Systems) for photons and with a Monte Carlo algorithm for electrons. V(90%) was 97.3±1.2 for RA plans and 78.2±2.6 for electrons; similarly, V(107%) was 2.5±2.2 and 37.7±3.4, respectively. RA met coverage criteria. Concerning bone sparing, D(2%) was 29.6±1.1 for RA and 31.0±2.4 for electrons. Although acceptable for bone involvement, pronounced target coverage violations were obtained for electron plans. Monitor units were similar for electrons and RA, although for the latter they increased when superior bone sparing was imposed. Delivery times were 12.1±4.0 min for electrons and 4.8±1.3 min for the most modulated RA plans. High plan quality was shown for KS in the lower extremities using VMAT, and this might simplify their management in comparison with the more conventional usage of electrons, particularly in institutes with limited staff resources and heavy workloads. VMAT is also dosimetrically extremely advantageous in a typology of treatments where electron beam therapy is mainly considered to be effective owing to the limited penetration of the beams.

Design of a double-anode magnetron-injection gun for the W-band gyrotron

NASA Astrophysics Data System (ADS)

Jang, Kwang Ho; Choi, Jin Joo; So, Joon Ho

2015-07-01

A double-anode magnetron-injection gun (MIG) was designed. The MIG is for a W-band 10-kW gyrotron. Analytic equations based on adiabatic theory and angular momentum conservation were used to examine the initial design parameters such as the cathode angle, and the radius of the beam emitting surface. The MIG's performances were predicted by using an electron trajectory code, the EGUN code. The beam spread of the axial velocity, Δvz/vz, obtained from the EGUN code was observed to be 1.34% at α = 1.3. The cathode edge emission and the thermal effect were modeled. The cathode edge emission was found to have a major effect on the velocity spread. The electron beam's quality was significantly improved by affixing non-emissive cylinders to the cathode.

LLE 1994 annual report, October 1993--September 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1995-01-01

This is the 1994 annual report for the University of Rochester, Laboratory for Laser Energetics. The report is presented as a series of research type reports. The titles emphasize the breadth of work carried out. They are: stability analysis of unsteady ablation fronts; characterization of laser-produced plasma density profiles using grid image refractometry; transport and sound waves in plasmas with light and heavy ions; three-halves-harmonic radiation from long-scale-length plasmas revisited; OMEGA upgrade status report; target imaging and backlighting diagnosis; effect of electron collisions on ion-acoustic waves and heat flow; particle-in-cell code simulations of the interaction of gaussian ultrashort laser pulsesmore » with targets of varying initial scale lengths; characterization of thick cryogenic fuel layers: compensation for the lens effect using convergent beam interferometry; compact, multijoule-output, Nd:Glass, large-aperture ring amplifier; atomic force microscopy observation of water-induced morphological changes in Y{sub 2}O{sub 3} monolayer coatings; observation of longitudinal acceleration of electrons born in a high-intensity laser focus; spatial intensity nonuniformities of an OMEGA beam due to nonlinear beam propagation; calculated X-ray backlighting images of mixed imploded targets; evaluation of cosmic rays for use in the monitoring of the MEDUSA scintillator-photomultiplier diagnostic array; highly efficient second-harmonic generation of ultra-intense Nd:Glass laser pulses multiple cutoff wave numbers of the ablative Rayleigh-Taylor instability; ultrafast, all-silicon light modulator; angular dependence of the stimulated Brillouin scattering in homogeneous plasma; femtosecond excited-state dynamics of a conjugated ladder polymer.« less

Amplitude Control of Solid-State Modulators for Precision Fast Kicker Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, J A; Anaya, R M; Caporaso, G C

2002-11-15

A solid-state modulator with very fast rise and fall times, pulse width agility, and multi-pulse burst and intra-pulse amplitude adjustment capability for use with high speed electron beam kickers has been designed and tested at LLNL. The modulator uses multiple solid-state modules stacked in an inductive-adder configuration. Amplitude adjustment is provided by controlling individual modules in the adder, and is used to compensate for transverse e-beam motion as well as the dynamic response and beam-induced steering effects associated with the kicker structure. A control algorithm calculates a voltage based on measured e-beam displacement and adjusts the modulator to regulate beammore » centroid position. This paper presents design details of amplitude control along with measured performance data from kicker operation on the ETA-II accelerator at LLNL.« less

Integrated development facility for the calibration of low-energy charged particle flight instrumentation

NASA Technical Reports Server (NTRS)

Biddle, A. P.; Reynolds, J. M.

1986-01-01

The design of a low-energy ion facility for development and calibration of thermal ion instrumentation is examined. A directly heated cathode provides the electrons used to produce ions by impact ionization and an applied magnetic field increases the path length followed by the electrons. The electrostatic and variable geometry magnetic mirror configuration in the ion source is studied. The procedures for the charge neutralization of the beam and the configuration and function of the 1.4-m drift tube are analyzed. A microcomputer is utilized to control and monitor the beam energy and composition, and the mass- and angle-dependent response of the instrument under testing. The facility produces a high-quality ion beam with an adjustable range of energies up to 150 eV; the angular divergence and uniformity of the beam is obtained from two independent retarding potential analyzers. The procedures for calibrating the instrument being developed are described.

The 1.06 micrometer wideband laser modulator: Fabrication and life testing

NASA Technical Reports Server (NTRS)

Teague, J. R.

1975-01-01

The design, fabrication, testing and delivery of an optical modulator which will operate with a mode-locked Nd:YAG laser at 1.06 micrometers were performed. The system transfers data at a nominal rate of 400 Mbps. This wideband laser modulator can transmit either Pulse Gated Binary Modulation (PGBM) or Pulse Polarization Binary Modulation (PPBM) formats. The laser beam enters the modulator and passes through both crystals; approximately 1% of the transmitted beam is split from the main beam and analyzed for the AEC signal; the remaining part of the beam exits the modulator. The delivered modulator when initially aligned and integrated with laser and electronics performed very well. The optical transmission was 69.5%. The static extinction ratio was 69:1. A 1000 hour life test was conducted with the delivered modulator. A 63 bit pseudorandom code signal was used as a driver input. At the conclusion of the life test the modulator optical transmission was 71.5% and the static extinction ratio 65:1.

Plasma-anode electron gun

NASA Astrophysics Data System (ADS)

Santoru, Joseph; Schumacher, Robert W.; Gregoire, Daniel J.

1994-11-01

The plasma-anode electron gun (PAG) is an electron source in which the thermionic cathode is replaced with a cold, secondary-electron-emitting electrode. Electron emission is stimulated by bombarding the cathode with high-energy ions. Ions are injected into the high-voltage gap through a gridded structure from a plasma source (gas pressure less than or equal to 50 mTorr) that is embedded in the anode electrode. The gridded structure serves as both a cathode for the plasma discharge and as an anode for the PAG. The beam current is modulated at near ground potential by modulating the plasma source, eliminating the need for a high-voltage modulator system. During laboratory tests, the PAG has demonstrated square-wave, 17-microsecond-long beam pulses at 100 kV and 10 A, and it has operated stably at 70 kV and 2.5 A for 210 microsecond pulse lengths without gap closure.

Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halavanau, A.; Qiang, G.; Ha, G.

2017-07-24

A common issue encountered in photoemission electron sources used in electron accelerators is the transverse inhomogeneity of the laser distribution resulting from the laser-amplification process and often use of frequency up conversion in nonlinear crystals. A inhomogeneous laser distribution on the photocathode produces charged beams with lower beam quality. In this paper, we explore the possible use of microlens arrays (fly-eye light condensers) to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes. We also demonstrate the use of such microlens arrays to generate transversely-modulated electron beams and present a possible application to diagnose the propertiesmore » of a magnetized beam.« less

Diffracted diffraction radiation and its application to beam diagnostics

NASA Astrophysics Data System (ADS)

Goponov, Yu. A.; Shatokhin, R. A.; Sumitani, K.; Syshchenko, V. V.; Takabayashi, Y.; Vnukov, I. E.

2018-03-01

We present theoretical considerations for diffracted diffraction radiation and also propose an application of this process to diagnosing ultra-relativistic electron (positron) beams for the first time. Diffraction radiation is produced when relativistic particles move near a target. If the target is a crystal or X-ray mirror, diffraction radiation in the X-ray region is expected to be diffracted at the Bragg angle and therefore be detectable. We present a scheme for applying this process to measurements of the beam angular spread, and consider how to conduct a proof-of-principle experiment for the proposed method.

Spectrum of coherent transition radiation generated by a modulated electron beam

NASA Astrophysics Data System (ADS)

Naumenko, G. A.; Potylitsyn, A. P.; Karataev, P. V.; Shipulya, M. A.; Bleko, V. V.

2017-07-01

The spectrum of coherent transition radiation has been recorded with the use of a Martin-Puplett interferometer. It has been shown that the spectrum includes monochromatic lines that are caused by the modulation of an electron beam with the frequency of an accelerating radio-frequency field νRF and correspond to resonances at ν k = kνRF k ≤ 10. To determine the length of an electron bunch from the measurement of the spectrum from a single bunch, it is necessary to use a spectrometer with the resolution Δνsp > νRF.

Retro-modulators and fast beam steering for free-space optical communications

NASA Astrophysics Data System (ADS)

Chan, Trevor Keith

Free-space optical (FSO) communications is a means of secure, high bandwidth communication through the use of a modulated laser beam in free-space as the information medium. The chaotic nature of the atmosphere and the motion of the communication nodes make laser alignment a crucial concern. The employment of retro-reflecting modulators makes the bidirectional quality of a communication link into a one sided alignment problem. While there are existing retro-reflecting modulators, their trade-offs create a lack of abilities (such as aperture size, angular range, high modulation speeds, economic viability) which do not fulfill the requirements for certain applications. Also, the beam must be directed towards the intended receiver. Form mobile or scintillated communication links, beam direction must be adaptable in real time. Once again, this area suffers from trade-offs where beamsteering speed is often limited. Research used to mitigate the trade-offs and adapt the devices into viable options for a wider range of applications is explored in this dissertation. Two forms of retro-modulators were explored; a MEMS deformable mirror retro-modulator and a solid silicon retro-modulator that modulated the light by frustrated total internal reflection (FTIR). The MEMS version offered a high speed, scalable, wavelength/angle insensitive retro-modulator which can be massed produced at low cost, while the solid retro-modulator offered a large field of view with low cost as well. Both modulator's design, simulated performances, fabrication and experimental characterization are described in this dissertation. An ultra-fast beamscanner was also designed using 2-dimensional dispersion. By using wavelength switching for directional control, a beamscanner was developed that could switch light faster than pre-existing beamscanners while the beams characteristics (most importantly its aperture) could be freely adjusted by the independent optics. This beamscanner was preceded by our work on a large channel wavelength demultiplexer which combined two orthogonally oriented wavelength demultiplexers. This created a 2-dimensional array of spots in free-space. The light was directed be a collimating lens into a specific direction based on its wavelength. The performance of this beamscanner was simulated by modeling the dispersive properties of the components.

Diffraction effects and inelastic electron transport in angle-resolved microscopic imaging applications.

PubMed

Winkelmann, A; Nolze, G; Vespucci, S; Naresh-Kumar, G; Trager-Cowan, C; Vilalta-Clemente, A; Wilkinson, A J; Vos, M

2017-09-01

We analyse the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Specifically, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolour orientation imaging using multiple, angle-resolving detectors. Consequently, diffraction effects of the incident beam and their impact on the subsequent coherent and incoherent electron transport need to be taken into account for an in-depth theoretical modelling of the energy- and momentum distribution of electrons backscattered from crystalline sample regions. Our findings have implications for the level of theoretical detail that can be necessary for the interpretation of complex imaging modalities such as electron channelling contrast imaging (ECCI) of defects in crystals. If the solid angle of detection is limited to specific regions of the backscattered electron momentum distribution, the image contrast that is observed in ECCI and similar applications can be strongly affected by incident beam diffraction and topographic effects from the sample surface. As an application, we demonstrate characteristic changes in the resulting images if different properties of the backscattered electron distribution are used for the analysis of a GaN thin film sample containing dislocations. © 2017 The Authors. Journal of Microscopy published by JohnWiley & Sons Ltd on behalf of Royal Microscopical Society.

Bremsstrahlung hard x-ray source driven by an electron beam from a self-modulated laser wakefield accelerator

NASA Astrophysics Data System (ADS)

Lemos, N.; Albert, F.; Shaw, J. L.; Papp, D.; Polanek, R.; King, P.; Milder, A. L.; Marsh, K. A.; Pak, A.; Pollock, B. B.; Hegelich, B. M.; Moody, J. D.; Park, J.; Tommasini, R.; Williams, G. J.; Chen, Hui; Joshi, C.

2018-05-01

An x-ray source generated by an electron beam produced using a Self-Modulated Laser Wakefield Accelerator (SM-LWFA) is explored for use in high energy density science facilities. By colliding the electron beam, with a maximum energy of 380 MeV, total charge of >10 nC and a divergence of 64 × 100 mrad, from a SM-LWFA driven by a 1 ps 120 J laser, into a high-Z foil, an x/gamma-ray source was generated. A broadband bremsstrahlung energy spectrum with temperatures ranging from 0.8 to 2 MeV was measured with an almost 2 orders of magnitude flux increase when compared with other schemes using LWFA. GEANT4 simulations were done to calculate the source size and divergence.

Effect of an angular trajectory kick in a high-gain free-electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baxevanis, Panagiotis; Huang, Zhirong; Stupakov, Gennady

In a free-electron laser, a transverse momentum offset (or “kick”) results in an oscillation of the centroid of the electron beam about the undulator axis. Studying the influence of this effect on the free-electron laser (FEL) interaction is important both from a tolerance point of view and for its potential diagnostic applications. In this paper, we present a self-consistent theoretical analysis of a high-gain FEL driven by such a “kicked” beam. In particular, we derive a solution to the three-dimensional, linearized initial value problem of the FEL through an orthogonal expansion technique and also describe a variational method for calculatingmore » the average FEL growth rate. Lastly, our results are benchmarked with genesis simulations and provide a robust theoretical background for a comparison with previous analytical results.« less

Effect of an angular trajectory kick in a high-gain free-electron laser

DOE PAGES

Baxevanis, Panagiotis; Huang, Zhirong; Stupakov, Gennady

2017-04-18

In a free-electron laser, a transverse momentum offset (or “kick”) results in an oscillation of the centroid of the electron beam about the undulator axis. Studying the influence of this effect on the free-electron laser (FEL) interaction is important both from a tolerance point of view and for its potential diagnostic applications. In this paper, we present a self-consistent theoretical analysis of a high-gain FEL driven by such a “kicked” beam. In particular, we derive a solution to the three-dimensional, linearized initial value problem of the FEL through an orthogonal expansion technique and also describe a variational method for calculatingmore » the average FEL growth rate. Lastly, our results are benchmarked with genesis simulations and provide a robust theoretical background for a comparison with previous analytical results.« less

Electron scattering by highly polar molecules. II - LiF

NASA Technical Reports Server (NTRS)

Vuskovic, L.; Srivastavas, S. K.; Trajmar, S.

1978-01-01

The crossed electron-beam - molecular-beam scattering technique has been used to measure relative values of differential 'elastic' scattering cross sections at electron impact energies of 5.4 and 20 eV for the angular range from 20 to 130 deg. The absolute values of these cross sections have been obtained by normalization to the classical perturbation theory of Dickinson (1977) at a scattering angle of 40 deg. These differential cross sections have then been used to calculate the integral and momentum-transfer cross sections. An energy-loss spectrum at 100 eV electron impact energy and 15 deg scattering angle has also been obtained. Two weak features at the energy losses of 6.74 and 8.82 eV appear. Their energy positions are compared with the recent calculations of Kahn et al. (1974).

Modeling of electron-specimen interaction in scanning electron microscope for e-beam metrology and inspection: challenges and perspectives

NASA Astrophysics Data System (ADS)

Suzuki, Makoto; Kameda, Toshimasa; Doi, Ayumi; Borisov, Sergey; Babin, Sergey

2018-03-01

The interpretation of scanning electron microscopy (SEM) images of the latest semiconductor devices is not intuitive and requires comparison with computed images based on theoretical modeling and simulations. For quantitative image prediction and geometrical reconstruction of the specimen structure, the accuracy of the physical model is essential. In this paper, we review the current models of electron-solid interaction and discuss their accuracy. We perform the comparison of the simulated results with our experiments of SEM overlay of under-layer, grain imaging of copper interconnect, and hole bottom visualization by angular selective detectors, and show that our model well reproduces the experimental results. Remaining issues for quantitative simulation are also discussed, including the accuracy of the charge dynamics, treatment of beam skirt, and explosive increase in computing time.

Design of a fast multileaf collimator for radiobiological optimized IMRT with scanned beams of photons, electrons, and light ions.

PubMed

Svensson, Roger; Larsson, Susanne; Gudowska, Irena; Holmberg, Rickard; Brahme, Anders

2007-03-01

Intensity modulated radiation therapy is rapidly becoming the treatment of choice for most tumors with respect to minimizing damage to the normal tissues and maximizing tumor control. Today, intensity modulated beams are most commonly delivered using segmental multileaf collimation, although an increasing number of radiation therapy departments are employing dynamic multileaf collimation. The irradiation time using dynamic multileaf collimation depends strongly on the nature of the desired dose distribution, and it is difficult to reduce this time to less than the sum of the irradiation times for all individual peak heights using dynamic leaf collimation [Svensson et al., Phys. Med. Biol. 39, 37-61 (1994)]. Therefore, the intensity modulation will considerably increase the total treatment time. A more cost-effective procedure for rapid intensity modulation is using narrow scanned photon, electron, and light ion beams in combination with fast multileaf collimator penumbra trimming. With this approach, the irradiation time is largely independent of the complexity of the desired intensity distribution and, in the case of photon beams, may even be shorter than with uniform beams. The intensity modulation is achieved primarily by scanning of a narrow elementary photon pencil beam generated by directing a narrow well focused high energy electron beam onto a thin bremsstrahlung target. In the present study, the design of a fast low-weight multileaf collimator that is capable of further sharpening the penumbra at the edge of the elementary scanned beam has been simulated, in order to minimize the dose or radiation response of healthy tissues. In the case of photon beams, such a multileaf collimator can be placed relatively close to the bremsstrahlung target to minimize its size. It can also be flat and thin, i.e., only 15-25 mm thick in the direction of the beam with edges made of tungsten or preferably osmium to optimize the sharpening of the penumbra. The low height of the collimator will minimize edge scatter from glancing incidence. The major portions of the collimator leafs can then be made of steel or even aluminum, so that the total weight of the multileaf collimator will be as low as 10 kg, which may even allow high-speed collimation in real time in synchrony with organ movements. To demonstrate the efficiency of this collimator design in combination with pencil beam scanning, optimal radiobiological treatments of an advanced cervix cancer were simulated. Different geometrical collimator designs were tested for bremsstrahlung, electron, and light ion beams. With a 10 mm half-width elementary scanned photon beam and a steel collimator with tungsten edges, it was possible to make as effective treatments as obtained with intensity modulated beams of full resolution, i.e., here 5 mm resolution in the fluence map. In combination with narrow pencil beam scanning, such a collimator may provide ideal delivery of photons, electrons, or light ions for radiation therapy synchronized to breathing and other organ motions. These high-energy photon and light ion beams may allow three-dimensional in vivo verification of delivery and thereby clinical implementation of the BioArt approach using Biologically Optimized three-dimensional in vivo predictive Assay based adaptive Radiation Therapy [Brahme, Acta Oncol. 42, 123-126 (2003)].

Imaging the dynamics of free-electron Landau states

PubMed Central

Schattschneider, P.; Schachinger, Th.; Stöger-Pollach, M.; Löffler, S.; Steiger-Thirsfeld, A.; Bliokh, K. Y.; Nori, Franco

2014-01-01

Landau levels and states of electrons in a magnetic field are fundamental quantum entities underlying the quantum Hall and related effects in condensed matter physics. However, the real-space properties and observation of Landau wave functions remain elusive. Here we report the real-space observation of Landau states and the internal rotational dynamics of free electrons. States with different quantum numbers are produced using nanometre-sized electron vortex beams, with a radius chosen to match the waist of the Landau states, in a quasi-uniform magnetic field. Scanning the beams along the propagation direction, we reconstruct the rotational dynamics of the Landau wave functions with angular frequency ~100 GHz. We observe that Landau modes with different azimuthal quantum numbers belong to three classes, which are characterized by rotations with zero, Larmor and cyclotron frequencies, respectively. This is in sharp contrast to the uniform cyclotron rotation of classical electrons, and in perfect agreement with recent theoretical predictions. PMID:25105563

Holography with a neutron interferometer

NASA Astrophysics Data System (ADS)

Sarenac, Dusan; Cory, David G.; Pushin, Dmitry A.; Heacock, Benjamin; Huber, Michael G.; Arif, M.; Clark, Charles W.; Shahi, Chandra B.; Cfref Collaboration

2017-01-01

We demonstrate the first neutron hologram of a macroscopic object. Using a Mach-Zehnder neutron interferometer in a configuration similar to the optical setup of Bazhenov et al., our reference beam passes through a fused silica prism that provides a linear phase gradient, and our object beam beam passes through an aluminum spiral phase plate with a topological charge of l = 2 , which was recently used in studies of neutron orbital angular momentum. Interference of reference and object beams in a two-dimensional imaging detector produces the hologram, which is a fork dislocation structure similar to those used to generate atomic and electronic vortex beams. Our neutron hologram is made in an interferometer in which at most one neutron is present at any given time.

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Chao; Jiang, Tao; Liu, Shengguang

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

DOE PAGES

Lu, Chao; Jiang, Tao; Liu, Shengguang; ...

2018-03-12

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

A beam optics study of a modular multi-source X-ray tube for novel computed tomography applications

NASA Astrophysics Data System (ADS)

Walker, Brandon J.; Radtke, Jeff; Chen, Guang-Hong; Eliceiri, Kevin W.; Mackie, Thomas R.

2017-10-01

A modular implementation of a scanning multi-source X-ray tube is designed for the increasing number of multi-source imaging applications in computed tomography (CT). An electron beam array coupled with an oscillating magnetic deflector is proposed as a means for producing an X-ray focal spot at any position along a line. The preliminary multi-source model includes three thermionic electron guns that are deflected in tandem by a slowly varying magnetic field and pulsed according to a scanning sequence that is dependent on the intended imaging application. Particle tracking simulations with particle dynamics analysis software demonstrate that three 100 keV electron beams are laterally swept a combined distance of 15 cm over a stationary target with an oscillating magnetic field of 102 G perpendicular to the beam axis. Beam modulation is accomplished using 25 μs pulse widths to a grid electrode with a reverse gate bias of -500 V and an extraction voltage of +1000 V. Projected focal spot diameters are approximately 1 mm for 138 mA electron beams and the stationary target stays within thermal limits for the 14 kW module. This concept could be used as a research platform for investigating high-speed stationary CT scanners, for lowering dose with virtual fan beam formation, for reducing scatter radiation in cone-beam CT, or for other industrial applications.

Transport Simulations for Fast Ignition on NIF

NASA Astrophysics Data System (ADS)

Strozzi, D. J.; Tabak, M.; Grote, D. P.; Town, R. P. J.; Kemp, A. J.

2009-11-01

Calculations of the transport and deposition of a relativistic electron beam into fast-ignition fuel configurations are presented. The hybrid PIC code LSP is used, run in implicit mode and with fluid background particles. The electron beam distribution is chosen based on explicit PIC simulations of the short-pulse LPI. These generally display two hot-electron temperatures, one close to the ponderomotive scaling and one that is much lower. Fast-electron collisions utilize the formulae of J. R. Davies [S. Atzeni et al., Plasma Phys. Controlled Fusion 51 (2009)], and are done with a conservative, relativistic grid-based method similar to Lemons et al., J. Comput. Phys. 228 (2009). We include energy loss off both bound and free electrons in partially-ionized media (such as a gold cone), and have started to use realistic ionization and non-ideal EOS models. We have found the fractional energy coupling into the dense fuel is higher for CD than DT targets, due to the enhanced resistivity and resulting magnetic fields. The coupling enhancement due to magnetic fields and beam characteristics (such as angular spectrum) will be quantified.

Three dimensional particle-in-cell simulations of electron beams created via reflection of intense laser light from a water target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngirmang, Gregory K., E-mail: ngirmang.1@osu.edu; Orban, Chris; Feister, Scott

We present 3D Particle-in-Cell (PIC) modeling of an ultra-intense laser experiment by the Extreme Light group at the Air Force Research Laboratory using the Large Scale Plasma (LSP) PIC code. This is the first time PIC simulations have been performed in 3D for this experiment which involves an ultra-intense, short-pulse (30 fs) laser interacting with a water jet target at normal incidence. The laser-energy-to-ejected-electron-energy conversion efficiency observed in 2D(3v) simulations were comparable to the conversion efficiencies seen in the 3D simulations, but the angular distribution of ejected electrons in the 2D(3v) simulations displayed interesting differences with the 3D simulations' angular distribution;more » the observed differences between the 2D(3v) and 3D simulations were more noticeable for the simulations with higher intensity laser pulses. An analytic plane-wave model is discussed which provides some explanation for the angular distribution and energies of ejected electrons in the 2D(3v) simulations. We also performed a 3D simulation with circularly polarized light and found a significantly higher conversion efficiency and peak electron energy, which is promising for future experiments.« less

Modulation instability and dissipative rogue waves in ion-beam plasma: Roles of ionization, recombination, and electron attachment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Shimin, E-mail: gsm861@126.com; Mei, Liquan, E-mail: lqmei@mail.xjtu.edu.cn

The amplitude modulation of ion-acoustic waves is investigated in an unmagnetized plasma containing positive ions, negative ions, and electrons obeying a kappa-type distribution that is penetrated by a positive ion beam. By considering dissipative mechanisms, including ionization, negative-positive ion recombination, and electron attachment, we introduce a comprehensive model for the plasma with the effects of sources and sinks. Via reductive perturbation theory, the modified nonlinear Schrödinger equation with a dissipative term is derived to govern the dynamics of the modulated waves. The effect of the plasma parameters on the modulation instability criterion for the modified nonlinear Schrödinger equation is numericallymore » investigated in detail. Within the unstable region, first- and second-order dissipative ion-acoustic rogue waves are present. The effect of the plasma parameters on the characteristics of the dissipative rogue waves is also discussed.« less

Super-resolution and ultra-sensitivity of angular rotation measurement based on SU(1,1) interferometers using homodyne detection

NASA Astrophysics Data System (ADS)

Liu, Jun; Li, Shitao; Wei, Dong; Gao, Hong; Li, Fuli

2018-02-01

We theoretically explore the angular rotation measurement sensitivity of SU(1,1) interferometers with a coherent beam and a vacuum beam input by using orbital angular momentum (OAM). Compared with the OAM in an SU(2) interferometer, the SU(1,1) interferometer employing homodyne detection can further surpass the angular rotation shot noise limit \\tfrac{1}{2l\\sqrt{N}} and improve the resolution and sensitivity of angular rotation measurement. Two models are considered, one is that OAM is carried by a probe beam and the other one is a pump beam with the OAM. The sensitivity can be improved by higher OAM and nonlinear process with a large gain. The resolution can be enhanced in the case that the pump beam has OAM. Moreover, we present a brief discussion on the variation of resolution and sensitivity in the presence of photon loss.

Sci-Thur AM: YIS – 04: Stopping power-to-Cherenkov power ratios and beam quality specification for clinical Cherenkov emission dosimetry of electrons: beam-specific effects and experimental validation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zlateva, Yana; Seuntjens, Jan; El Naqa, Issam

Purpose: To advance towards clinical Cherenkov emission (CE)-based dosimetry by investigating beam-specific effects on Monte Carlo-calculated electron-beam stopping power-to-CE power ratios (SCRs), addressing electron beam quality specification in terms of CE, and validating simulations with measurements. Methods: The EGSnrc user code SPRRZnrc, used to calculate Spencer-Attix stopping-power ratios, was modified to instead calculate SCRs. SCRs were calculated for 6- to 22-MeV clinical electron beams from Varian TrueBeam, Clinac 21EX, and Clinac 2100C/D accelerators. Experiments were performed with a 20-MeV electron beam from a Varian TrueBeam accelerator, using a diffraction grating spectrometer with optical fiber input and a cooled back-illuminated CCD.more » A fluorophore was dissolved in the water to remove CE signal anisotropy. Results: It was found that angular spread of the incident beam has little effect on the SCR (≤ 0.3% at d{sub max}), while both the electron spectrum and photon contamination increase the SCR at shallow depths and decrease it at large depths. A universal data fit of R{sub 50} in terms of C{sub 50} (50% CE depth) revealed a strong linear dependence (R{sup 2} > 0.9999). The SCR was fit with a Burns-type equation (R{sup 2} = 0.9974, NRMSD = 0.5%). Below-threshold incident radiation was found to have minimal effect on beam quality specification (< 0.1%). Experiments and simulations were in good agreement. Conclusions: Our findings confirm the feasibility of the proposed CE dosimetry method, contingent on computation of SCRs from additional accelerators and on further experimental validation. This work constitutes an important step towards clinical high-resolution out-of-beam CE dosimetry.« less

Angular Spacing Control for Segmented Data Pages in Angle-Multiplexed Holographic Memory

NASA Astrophysics Data System (ADS)

Kinoshita, Nobuhiro; Muroi, Tetsuhiko; Ishii, Norihiko; Kamijo, Koji; Kikuchi, Hiroshi; Shimidzu, Naoki; Ando, Toshio; Masaki, Kazuyoshi; Shimizu, Takehiro

2011-09-01

To improve the recording density of angle-multiplexed holographic memory, it is effective to increase the numerical aperture of the lens and to shorten the wavelength of the laser source as well as to increase the multiplexing number. The angular selectivity of a hologram, which determines the multiplexing number, is dependent on the incident angle of not only the reference beam but also the signal beam to the holographic recording medium. The actual signal beam, which is a convergent or divergent beam, is regarded as the sum of plane waves that have different propagation directions, angular selectivities, and optimal angular spacings. In this paper, focusing on the differences in the optimal angular spacing, we proposed a method to control the angular spacing for each segmented data page. We investigated the angular selectivity of a hologram and crosstalk for segmented data pages using numerical simulation. The experimental results showed a practical bit-error rate on the order of 10-3.

Observation of coherent Smith-Purcell and transition radiation driven by single bunch and micro-bunched electron beams

NASA Astrophysics Data System (ADS)

Liang, Yifan; Du, Yingchao; Su, Xiaolu; Wang, Dan; Yan, Lixin; Tian, Qili; Zhou, Zheng; Wang, Dong; Huang, Wenhui; Gai, Wei; Tang, Chuanxiang; Konoplev, I. V.; Zhang, H.; Doucas, G.

2018-01-01

Generation of coherent Smith-Purcell (cSPr) and transition/diffraction radiation using a single bunch or a pre-modulated relativistic electron beam is one of the growing research areas aiming at the development of radiation sources and beam diagnostics for accelerators. We report the results of comparative experimental studies of terahertz radiation generation by an electron bunch and micro-bunched electron beams and the spectral properties of the coherent transition and SP radiation. The properties of cSPr spectra are investigated and discussed, and excitations of the fundamental and second harmonics of cSPr and their dependence on the beam-grating separation are shown. The experimental and theoretical results are compared, and good agreement is demonstrated.

The Direct Digital Modulation of Traveling Wave Tubes

NASA Technical Reports Server (NTRS)

Radhamohan, Ranjan S.

2004-01-01

Traveling wave tube (TWT) technology, first described by Rudolf Kompfner in the early 1940s, has been a key component of space missions from the earliest communication satellites in the 1960s to the Cassini probe today. TWTs are essentially signal amplifiers that have the special capability of operating at microwave frequencies. The microwave frequency range, which spans from approximately 500 MHz to 300 GHz, is shared by many technologies including cellular phones, satellite television, space communication, and radar. TWT devices are superior in reliability, weight, and efficiency to solid-state amplifiers at the high power and frequency levels required for most space missions. TWTs have three main components -an electron gun, slow wave structure, and collector. The electron gun generates an electron beam that moves along the length of the tube axis, inside of the slow wave circuit. At the same time, the inputted signal is slowed by its travel through the coils of the helical slow wave circuit. The interaction of the electron beam and this slowed signal produces a transfer of kinetic energy to the signal, and in turn, amplification. At the end of its travel, the spent electron beam moves into the collector where its remaining energy is dissipated as heat or harnessed for reuse. TWTs can easily produce gains in the tens of decibels, numbers that are suitable for space missions. To date, however, TWTs have typically operated at fixed levels of gain. This gain is determined by various, unchanging, physical factors of the tube. Traditionally, to achieve varying gain, an input signal s amplitude has had to first be modulated by a separate device before being fed into the TWT. This is not always desirable, as significant distortion can occur in certain situations. My mentor, Mr. Dale Force, has proposed an innovative solution to this problem called direct digital modulation . The testing and implementation of this solution is the focus of my summer internship. The direct digital modulation of a TWT removes the need for a separate amplitude modulation device. Instead, different levels of gain are achieved by varying the electron beam current. The lower the current, the less kinetic energy is available to be transferred to the signal. To vary the current, a grid is placed in-between the electron gun and the slow wave circuit. By changing the voltage across the grid, the electron beam current can be controlled. Grid technology has mostly been used in pulse applications such as radar, where only two voltage states are necessary. For direct digital modulation, however, a continuous range of voltages is required.

An optical apparatus for rotation and trapping

PubMed Central

Gutiérrez-Medina, Braulio; Andreasson, Johan O. L.; Greenleaf, William J.; LaPorta, Arthur; Block, Steven M.

2010-01-01

We present details of the design, construction and testing of a single-beam optical tweezers apparatus capable of measuring and exerting torque, as well as force, on microfabricated, optically anisotropic particles (an ‘optical torque wrench’). The control of angular orientation is achieved by rotating the linear polarization of a trapping laser with an electro-optic modulator (EOM), which affords improved performance over previous designs. The torque imparted to the trapped particle is assessed by measuring the difference between left- and right-circular components of the transmitted light, and constant torque is maintained by feeding this difference signal back into a custom-designed electronic servo loop. The limited angular range of the EOM (±180°) is extended by rapidly reversing the polarization once a threshold angle is reached, enabling the torque clamp to function over unlimited, continuous rotations at high bandwidth. In addition, we developed particles suitable for rotation in this apparatus using microfabrication techniques. Altogether, the system allows for the simultaneous application of forces (~0.1–100 pN) and torques (~1–10,000 pN nm) in the study of biomolecules. As a proof of principle, we demonstrate how our instrument can be used to study the supercoiling of single DNA molecules. PMID:20627165

Spatially multiplexed orbital-angular-momentum-encoded single photon and classical channels in a free-space optical communication link.

PubMed

Ren, Yongxiong; Liu, Cong; Pang, Kai; Zhao, Jiapeng; Cao, Yinwen; Xie, Guodong; Li, Long; Liao, Peicheng; Zhao, Zhe; Tur, Moshe; Boyd, Robert W; Willner, Alan E

2017-12-01

We experimentally demonstrate spatial multiplexing of an orbital angular momentum (OAM)-encoded quantum channel and a classical Gaussian beam with a different wavelength and orthogonal polarization. Data rates as large as 100 MHz are achieved by encoding on two different OAM states by employing a combination of independently modulated laser diodes and helical phase holograms. The influence of OAM mode spacing, encoding bandwidth, and interference from the co-propagating Gaussian beam on registered photon count rates and quantum bit error rates is investigated. Our results show that the deleterious effects of intermodal crosstalk effects on system performance become less important for OAM mode spacing Δ≥2 (corresponding to a crosstalk value of less than -18.5  dB). The use of OAM domain can additionally offer at least 10.4 dB isolation besides that provided by wavelength and polarization, leading to a further suppression of interference from the classical channel.

Laser-based sensor for detection of hazardous gases in the air using waveguide CO2 laser.

PubMed

Gondal, Mohammed A; Bakhtiari, Imran A; Dastageer, Abdul K

2007-06-01

A spectrometer based on the principle of photoacoustic spectroscopy has been developed recently at our laboratory for the detection of hazardous gases such as O3, C2H4, SO2, NO2 and SF6. In most of our earlier works, we employed a mechanical chopper to modulate the laser beam and this chopper modulation has the crucial disadvantage of instability in the chopper frequency. Even a minor shift of about 1 Hz in the modulation frequency could significantly reduce the photoacoustic signal by an order of magnitude at the acoustic resonant mode of the photoacoustic cell. To overcome this problem, we developed a photoacoustic spectrometer where a wave guided CW CO2 laser beam is modulated electronically with the external frequency generator. Our preliminary results show that the electronic modulation of CO2 laser beam improved the sensitivity of our spectrometer by a factor of 6. The parametric dependence of photoacoustic signal on laser power, modulation frequency and trace gas concentration, was investigated and the comparison between the two modulation techniques is presented in this paper for detection of trace gases such as C2H4.

Angular distribution and polarization of atomic radiative emission in electric and magnetic fields

NASA Astrophysics Data System (ADS)

Jacobs, V. L.; Filuk, A. B.

1999-09-01

A density-matrix approach has been developed for the angular distribution and polarization of radiative emission during single-photon atomic transitions for a general set of steady-state excitation processes in an arbitrary arrangement of static (or quasistatic) electric and magnetic fields. Particular attention has been directed at spectroscopic observations in the intense fields of the high-power ion diodes on the Particle Beam Fusion Accelerator II (PBFA II) and SABRE devices at Sandia National Laboratories and at magnetic-field measurements in tokamak plasmas. The field-dependent atomic eigenstates are represented as expansions in a complete basis set of field-free bound and continuum eigenstates. Particular emphasis has been given to directed-electron collisional excitations, which may be produced by an anisotropic incident-electron velocity distribution. We have allowed for the possibility of the coherent excitation of the nearly degenerate field-dependent atomic substates, which can give rise to a complex spectral pattern of overlapping Stark-Zeeman components. Coherent excitations may be produced by a beam of electrons that are spin-polarized at an angle with respect to the propagation direction or by nonparallel electric and magnetic fields. Our main result is a general expression for the matrix elements of the photon-polarization density operator representing the total intensity, angular distribution, and polarization of the atomic radiative emission. For the observation of radiative emission in the direction of the magnetic field, the detection of linearly polarized emission, in addition to the usual circularly polarized radiation, can reveal the presence of a perpendicular electric field or a coherent excitation mechanism.

Angular distribution and polarization of atomic radiative emission in electric and magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobs, V.L.; Filuk, A.B.

A density-matrix approach has been developed for the angular distribution and polarization of radiative emission during single-photon atomic transitions for a general set of steady-state excitation processes in an arbitrary arrangement of static (or quasistatic) electric and magnetic fields. Particular attention has been directed at spectroscopic observations in the intense fields of the high-power ion diodes on the Particle Beam Fusion Accelerator II (PBFA II) and SABRE devices at Sandia National Laboratories and at magnetic-field measurements in tokamak plasmas. The field-dependent atomic eigenstates are represented as expansions in a complete basis set of field-free bound and continuum eigenstates. Particular emphasismore » has been given to directed-electron collisional excitations, which may be produced by an anisotropic incident-electron velocity distribution. We have allowed for the possibility of the coherent excitation of the nearly degenerate field-dependent atomic substates, which can give rise to a complex spectral pattern of overlapping Stark-Zeeman components. Coherent excitations may be produced by a beam of electrons that are spin-polarized at an angle with respect to the propagation direction or by nonparallel electric and magnetic fields. Our main result is a general expression for the matrix elements of the photon-polarization density operator representing the total intensity, angular distribution, and polarization of the atomic radiative emission. For the observation of radiative emission in the direction of the magnetic field, the detection of linearly polarized emission, in addition to the usual circularly polarized radiation, can reveal the presence of a perpendicular electric field or a coherent excitation mechanism.« less

Some new results on electron transport in the atmosphere. [Monte Carlo calculation of penetration, diffusion, and slowing down of electron beams in air

NASA Technical Reports Server (NTRS)

Berger, M. J.; Seltzer, S. M.; Maeda, K.

1972-01-01

The penetration, diffusion and slowing down of electrons in a semi-infinite air medium has been studied by the Monte Carlo method. The results are applicable to the atmosphere at altitudes up to 300 km. Most of the results pertain to monoenergetic electron beams injected into the atmosphere at a height of 300 km, either vertically downwards or with a pitch-angle distribution isotropic over the downward hemisphere. Some results were also obtained for various initial pitch angles between 0 deg and 90 deg. Information has been generated concerning the following topics: (1) the backscattering of electrons from the atmosphere, expressed in terms of backscattering coefficients, angular distributions and energy spectra of reflected electrons, for incident energies T(o) between 2 keV and 2 MeV; (2) energy deposition by electrons as a function of the altitude, down to 80 km, for T(o) between 2 keV and 2 MeV; (3) the corresponding energy depostion by electron-produced bremsstrahlung, down to 30 km; (4) the evolution of the electron flux spectrum as function of the atmospheric depth, for T(o) between 2 keV and 20 keV. Energy deposition results are given for incident electron beams with exponential and power-exponential spectra.

Design and development of line type modulators for high impedance electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixit, Kavita P.; Tillu, Abhijit; Chavan, Ramchandra

Conventional line type modulators are routinely used for powering pulsed power microwave devices such as magnetrons and klystrons used for radar, medical and scientific applications. The load impedance (operating point) is fairly well defined in these cases, and makes the design of the discharging circuit of the modulator straight forward. This paper describes the Line type modulators that have been developed and being routinely used for powering the Triode Electron Gun of industrial electron linacs. The beam parameters of such guns are user defined and the pulse current varies from few mA to 800mA (typ). The beam energies requirement variesmore » from 40 keV to 80 keV. Hence the impedance offered by the electron gun to the power source (modulator) is not well defined. The load capacitance which is inclusive of the various stray capacitances along with the intrinsic gun capacitance is ∼ 200-400 pF. This capacitance, which depends on the configuration, shunts the load and makes the effective load highly capacitive with the resistive part varying over a wide range. The paper describes the design and development of conventional line type modulators for powering Electron gun load of the type described above. (author)« less

Design and Development of Emittance Measurement Device by Using the Pepper-pot Technique

NASA Astrophysics Data System (ADS)

Pakluea, S.; Rimjaem, S.

2017-09-01

Transverse emittance of a charged particle beam is one of the most important properties that reveals the quality of the beam. It is related to charge density, transvers size and angular displacement of the beam in transverse phase space. There are several techniques to measure the transverse emittance value. One of practical methods is the pepper-pot technique, which can measure both horizontal and vertical emittance value in a single measurement. This research concentrates on development of a pepper-pot device to measure the transverse emittance of electron beam produced from an accelerator injector system, which consists of a thermionic cathode RF electron gun and an alpha magnet, at the Plasma and Beam Physics Research Facility, Chiang Mai University. Simulation of beam dynamics was conducted with programs PARMELA, ELEGANT and self-developed codes using C and MATLAB. The geometry, dimensions and location of the pepper-pot as well as its corresponding screen station position were included in the simulation. The result from this study will be used to design and develop a practical pepper-pot experimental station.

Prospects for applications of electron beams in processing of gas and oil hydrocarbons

NASA Astrophysics Data System (ADS)

Ponomarev, A. V.; Pershukov, V. A.; Smirnov, V. P.

2015-12-01

Waste-free processing of oil and oil gases can be based on electron-beam technologies. Their major advantage is an opportunity of controlled manufacturing of a wide range of products with a higher utility value at moderate temperatures and pressures. The work considers certain key aspects of electron beam technologies applied for the chain cracking of heavy crude oil, for the synthesis of premium gasoline from oil gases, and also for the hydrogenation, alkylation, and isomerization of unsaturated oil products. Electronbeam processing of oil can be embodied via compact mobile modules which are applicable for direct usage at distant oil and gas fields. More cost-effective and reliable electron accelerators should be developed to realize the potential of electron-beam technologies.

Theory for low-frequency modulated Langmuir wave packets

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Robinson, P. A.

1992-01-01

Langmuir wave packets with low frequency modulations (or beats) observed in the Jovian foreshock are argued to be direct evidence for the Langmuir wave decay L yields L-prime + S. In this decay, 'pump' Langmuir waves L, driven by an electron beam, produce backscattered product Langmuir waves L-prime and ion sound waves S. The L and L-prime waves beat at the frequency and wavevector of the S waves, thereby modulating the wave packets. Beam speeds calculated using the modulated Jovian wave packets (1) are reasonable, at 4-10 times the electron thermal speed, (2) are consistent with theoretical limits on the decay process, and (3) decrease with increasing foreshock depth, as expected theoretically. These results strongly support the theory. The modulation depth of some wave packets suggests saturation by the decay L yields L-prime + S. Applications to modulated Langmuir packets in the Venusian and terrestrial foreshocks and in a type III radio source are proposed.

SU-F-T-281: Monte Carlo Investigation of Sources of Dosimetric Discrepancies with 2D Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afifi, M; Deiab, N; El-Farrash, A

2016-06-15

Purpose: Intensity modulated radiation therapy (IMRT) poses a number of challenges for properly measuring commissioning data and quality assurance (QA). Understanding the limitations and use of dosimeters to measure these dose distributions is critical to safe IMRT implementation. In this work, we used Monte Carlo simulations to investigate the possible sources of discrepancy between our measurement with 2D array system and our dose calculation using our treatment planning system (TPS). Material and Methods: MCBEAM and MCSIM Monte Carlo codes were used for treatment head simulation and phantom dose calculation. Accurate modeling of a 6MV beam from Varian trilogy machine wasmore » verified by comparing simulated and measured percentage depth doses and profiles. Dose distribution inside the 2D array was calculated using Monte Carlo simulations and our TPS. Then Cross profiles for different field sizes were compared with actual measurements for zero and 90° gantry angle setup. Through the analysis and comparison, we tried to determine the differences and quantify a possible angular calibration factor. Results: Minimum discrepancies was seen in the comparison between the simulated and the measured profiles for the zero gantry angles at all studied field sizes (4×4cm{sup 2}, 10×10cm{sup 2}, 15×15cm{sup 2}, and 20×20cm{sup 2}). Discrepancies between our measurements and calculations increased dramatically for the cross beam profiles at the 90° gantry angle. This could ascribe mainly to the different attenuation caused by the layer of electronics at the base behind the ion chambers in the 2D array. The degree of attenuation will vary depending on the angle of beam incidence. Correction factors were implemented to correct the errors. Conclusion: Monte Carlo modeling of the 2D arrays and the derivation of angular dependence correction factors will allow for improved accuracy of the device for IMRT QA.« less

Operation modes for a linear array of optical flexible reflective analog modulators

NASA Astrophysics Data System (ADS)

Doucet, Michel; Picard, Francis; Niall, Keith K.; Jerominek, Hubert

2005-05-01

A unique MEMS based spatial light modulator has been developed by INO and its partners for projection display applications. This unique device incorporates a linear array of micromirrors. Each micromirror is a 25 μm x 25 μm microbridge. Electrostatic actuation allows the control of the curvature of each micromirror independently. Combined with appropriate optics, this allows display of images with well over a thousands columns at a frame rate of 60 Hz. Operation and performance of this modulator have already been reported in the literature (SPIE Proceeding, Vol. 4985, p. 44-55; SPIE Proceeding, Vol. 5289, p. 284-293). In the latter paper, a brief description of various possible operation modes of this modulator has been presented. The objective of the present article is to provide an in-depth study of these operation modes. The study is done using numerical simulations. Several methods are employed to propagate the laser beam illuminating the micromirrors through the optical system. The gaussian beam superposition method is used to propagate the laser beam from the system input to the micromirrors. The reflexion on the micromirrors is computed by ray tracing. Finally, the angular spectrum of plane waves method is used to propagate the reflected coherent beam through Schlieren optics which converts the curvature of the micromirror into gray levels. The simulated optical response of the system as a function of the micromirror curvature is provided for various operation modes.

Characterization of submillisecond response optical addressing phase modulator based on low light scattering polymer network liquid crystal

NASA Astrophysics Data System (ADS)

Xiangjie, Zhao; Cangli, Liu; Jiazhu, Duan; Dayong, Zhang; Yongquan, Luo

2015-01-01

Optically addressed conventional nematic liquid crystal spatial light modulator has attracted wide research interests. But the slow response speed limited its further application. In this paper, polymer network liquid crystal (PNLC) was proposed to replace the conventional nematic liquid crystal to enhance the response time to the order of submillisecond. The maximum light scattering of the employed PNLC was suppressed to be less than 2% at 1.064 μm by optimizing polymerization conditions and selecting large viscosity liquid crystal as solvent. The occurrence of phase ripple phenomenon due to electron diffusion and drift in photoconductor was found to deteriorate the phase modulation effect of the optical addressed PNLC phase modulator. The wavelength effect and AC voltage frequency effect on the on state dynamic response of phase change was investigated by experimental methods. These effects were interpreted by electron diffusion and drift theory based on the assumption that free electron was inhomogeneously distributed in accordance with the writing beam intensity distribution along the incident direction. The experimental results indicated that the phase ripple could be suppressed by optimizing the wavelength of the writing beam and the driving AC voltage frequency when varying the writing beam intensity to generate phase change in 2π range. The modulation transfer function was also measured.

Optical analysis of grazing incidence ring resonators for free-electron lasers

NASA Astrophysics Data System (ADS)

Gabardi, David R.; Shealy, David L.

1990-06-01

Two types of grazing incidence ring resonators for use with free-electron lasers have been investigated. These cavities utilize off-axis conical and flat mirrors and have been designed to operate in the extreme ultraviolet region of the spectrum. In this paper, a design algorithm that calculates the mirror parameters for propagation of Gaussian TEM mode beams in the two cavity types is presented. Results concerning the angular stability of each type are also shown.

Kikuchi ultrafast nanodiffraction in four-dimensional electron microscopy

PubMed Central

Yurtsever, Aycan; Zewail, Ahmed H.

2011-01-01

Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size of the beam used, typically on the micron scale, the detection of nanoscale propagating waves in extended structures hitherto has not been reported. For elastic waves of complex motions, Bragg intensities contain all polarizations and they are not straightforward to disentangle. Here, we introduce Kikuchi diffraction dynamics, using convergent-beam geometry in an ultrafast electron microscope, to selectively probe propagating transverse elastic waves with nanoscale resolution. It is shown that Kikuchi band shifts, which are sensitive only to the tilting of atomic planes, reveal the resonance oscillations, unit cell angular amplitudes, and the polarization directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of Kikuchi’s edges, and the magnitude of angular amplitude (0.3 mrad) and polarization elucidate the nature of the motion: one that preserves the mass density (i.e., no compression or expansion) but leads to sliding of planes in the antisymmetric shear eigenmode of the elastic waveguide. As such, the method of Kikuchi diffraction dynamics, which is unique to electron imaging, can be used to characterize the atomic motions of propagating waves and their interactions with interfaces, defects, and grain boundaries at the nanoscale. PMID:21245348

Development of a Multi-GeV spectrometer for laser-plasma experiment at FLAME

NASA Astrophysics Data System (ADS)

Valente, P.; Anelli, F.; Bacci, A.; Batani, D.; Bellaveglia, M.; Benocci, R.; Benedetti, C.; Cacciotti, L.; Cecchetti, C. A.; Clozza, A.; Cultrera, L.; Di Pirro, G.; Drenska, N.; Faccini, R.; Ferrario, M.; Filippetto, D.; Fioravanti, S.; Gallo, A.; Gamucci, A.; Gatti, G.; Ghigo, A.; Giulietti, A.; Giulietti, D.; Gizzi, L. A.; Koester, P.; Labate, L.; Levato, T.; Lollo, V.; Londrillo, P.; Martellotti, S.; Pace, E.; Pathak, N.; Rossi, A.; Tani, F.; Serafini, L.; Turchetti, G.; Vaccarezza, C.

2011-10-01

The advance in laser-plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular, the upcoming experiments with the 250 TW laser at the FLAME facility of the INFN Laboratori Nazionali di Frascati, will enter the GeV regime with more than 100 pC of electrons. At the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need for developing a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV), with still unknown angular divergences. Within the PlasmonX experiment at FLAME, a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence, present challenges in the design and construction of such a device. We present the design considerations for this spectrometer that lead to the use of scintillating fibers, multichannel photo-multipliers and a multiplexing electronics, a combination which is innovative in the field. We also present the experimental results obtained with a high intensity electron beam performed on a prototype at the LNF beam test facility.

Ultra-thin optical vortex phase plate based on the metasurface and the angular momentum transformation

NASA Astrophysics Data System (ADS)

Wang, Wei; Li, Yan; Guo, Zhongyi; Li, Rongzhen; Zhang, Jingran; Zhang, Anjun; Qu, Shiliang

2015-04-01

The ultra-thin optical vortex phase plate (VPP) has been designed and investigated based on the metasurface of the metal rectangular split-ring resonators (MRSRRs) array. The circularly polarized incident light can convert into corresponding cross-polarization transmission light, and the phase and the amplitude of cross-polarization transmission light can be simultaneously governed by modulating two arms of the MRSRR. The MRSRR has been arranged in a special order for forming an ultra-thin optical VPP that can covert a plane wave into a vortex beam with a variety of the topological charges, and the transformation between spin angular momentum (SAM) and orbital angular momentum (OAM) has been discussed in detail. The multi-spectral characteristics of the VPP have also been investigated, and the operating bandwidth of the designed VPP is 190 nm (in the range of 710-900 nm), which enable a potential implication for integrated optics and vortex optics.

Review of Negative Hydrogen Ion Sources

DTIC Science & Technology

1990-09-01

Kwan, A. L. Peratt, J. Kinross-Wright, F. W. Van Haaften , R. F. Hoeberling, R. Faehl, B. Carlsten, W. W. Destler*, and L. B. Warner Los Alamos...relativistic electron beams," J. Appl. Phys. 64 (2), 1 Oct. 1988, p. 3353. 4. F. W. Van Haaften , et al, "A high-voltage, high- current electron beam modulator

THz radiation from two electron-beams interaction within a bi-grating and a sub-wavelength holes array composite sandwich structure.

PubMed

Zhang, Yaxin; Zhou, Y; Dong, L

2013-09-23

Two electron-beams' interaction in a sandwich structure composed of a bi-grating and a sub-wavelength holes array is suggested to generate THz radiation in this paper. It shows that this system takes advantage of both bi-grating and sub-wavelength holes array structures. The results demonstrate that surface waves on a bi-grating can couple with mimicking surface plasmons of a sub-wavelength holes array so that the wave-coupling is strong and the field intensity is high in this structure. Moreover, compared with the interaction in the bi-grating structure and sub-wavelength holes array structure, respectively, it shows that in this composite system the two electron-beams' interaction is more efficient and the modulation depth and radiation intensity have been enhanced significantly. The modulation depth and efficiency can reach 22% and 4%, respectively, and the starting current density is only 12 A/cm². This radiation system may provide good opportunities for development of multi-electron beam-driven THz radiation sources.

Coherent Leinard-Wiechert fields produced by FELs (free-electron laser). Technical report, 14 January 1981-13 January 1982

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elias, L.R.

1981-12-01

Results are presented of a three-dimensional numerical analysis of the radiation fields produced in a free-electron laser. The method used here to obtain the spatial and temporal behavior of the radiated fields is based on the coherent superposition of the radiated fields is based on the coherent superposition of the exact Lienard-Wiechert fields produced by each electron in the beam. Interference effects are responsible for the narrow angular radiation patterns obtained and for the high degree of monochromaticity of the radiated fields.

SU-C-201-07: Towards Clinical Cherenkov Emission Dosimetry: Stopping Power-To-Cherenkov Power Ratios and Beam Quality Specification of Clinical Electron Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zlateva, Y; Seuntjens, J; El Naqa, I

Purpose: We propose a Cherenkov emission (CE)-based reference dosimetry method, which in contrast to ionization chamber-based dosimetry, employs spectrum-averaged electron restricted mass collision stopping power-to-Cherenkov power ratios (SCRs), and we examine Monte Carlo-calculated SCRs and beam quality specification of clinical electron beams. Methods: The EGSnrc user code SPRRZnrc was modified to compute SCRs instead of stopping-power ratios (single medium: water; cut-off: CE threshold (observing Spencer-Attix conditions); CE power: Frank-Tamm). SCRs are calculated with BEAMnrc for realistic electron beams with nominal energies of 6–22 MeV from three Varian accelerators (TrueBeam Clinac 21EX, Clinac 2100C/D) and for mono-energetic beams of energies equalmore » to the mean electron energy at the water surface. Sources of deviation between clinical and mono-energetic SCRs are analyzed quantitatively. A universal fit for the beam-quality index R{sub 50} in terms of the depth of 50% CE C{sub 50} is carried out. Results: SCRs at reference depth are overestimated by mono-energetic values by up to 0.2% for a 6-MeV beam and underestimated by up to 2.3% for a 22-MeV beam. The variation is mainly due to the clinical beam spectrum and photon contamination. Beam angular spread has a small effect across all depths and energies. The influence of the electron spectrum becomes increasingly significant at large depths, while at shallow depths and high beam energies photon contamination is predominant (up to 2.0%). The universal data fit reveals a strong linear correlation between R{sub 50} and C{sub 50} (ρ > 0.99999). Conclusion: CE is inherent to radiotherapy beams and can be detected outside the beam with available optical technologies, which makes it an ideal candidate for out-of-beam high-resolution 3D dosimetry. Successful clinical implementation of CE dosimetry hinges on the development of robust protocols for converting measured CE to radiation dose. Our findings constitute a key step towards clinical CE dosimetry.« less

Construction and first beam-tests of silicon-tungsten prototype modules for the CMS High Granularity Calorimeter for HL-LHC

NASA Astrophysics Data System (ADS)

Jain, S.

2017-03-01

The High Granularity Calorimeter (HGCAL) is the technology choice of the CMS collaboration for the endcap calorimetry upgrade planned to cope with the harsh radiation and pileup environment at the High Luminosity-LHC . The HGCAL is realized as a sampling calorimeter, including an electromagnetic compartment comprising 28 layers of silicon pad detectors with pad areas of 0.5-01. cm2 interspersed with absorbers made from tungsten and copper to form a highly compact and granular device. Prototype modules, based on hexagonal silicon pad sensors, with 128 channels, have been constructed and tested in beams at FNAL and at CERN. The modules include many of the features required for this challenging detector, including a PCB glued directly to the sensor, using through-hole wire-bonding for signal readout and 5 mm spacing between layers—including the front-end electronics and all services. Tests in 2016 have used an existing front-end chip —Skiroc2 (designed for the CALICE experiment for ILC). We present results from first tests of these modules both in the laboratory and with beams of electrons, pions and protons, including noise performance, calibration with mips and electron signals.

Coincidence studies of diffraction structures in binary encounter electron spectra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao, C.; Hagmann, S.; Richard, P.

The authors have measured binary encounter electron (BEe) production in collisions of 0.3 MeV/u Cu{sup q+} (q=4,12) projectiles on H{sub 2} targets from 0 to 70 degrees with respect to the beam direction. Prominent features are the appearance of the BEe peak splitting and a very strong forward peaked angular distribution which are attributed to the diffractive scattering of the quasifree target electrons in the short range potential of the projectile. Using electron-projectile final charge state coincidence techniques, different collision reaction channels can be separated. Measurements of this type are being pursued.

Quantum scattering beyond the plane-wave approximation

NASA Astrophysics Data System (ADS)

Karlovets, Dmitry

2017-12-01

While a plane-wave approximation in high-energy physics works well in a majority of practical cases, it becomes inapplicable for scattering of the vortex particles carrying orbital angular momentum, of Airy beams, of the so-called Schrödinger cat states, and their generalizations. Such quantum states of photons, electrons and neutrons have been generated experimentally in recent years, opening up new perspectives in quantum optics, electron microscopy, particle physics, and so forth. Here we discuss the non-plane-wave effects in scattering brought about by the novel quantum numbers of these wave packets. For the well-focused electrons of intermediate energies, already available at electron microscopes, the corresponding contribution can surpass that of the radiative corrections. Moreover, collisions of the cat-like superpositions of such focused beams with atoms allow one to probe effects of the quantum interference, which have never played any role in particle scattering.

Integration of the GET electronics for the CHIMERA and FARCOS devices

NASA Astrophysics Data System (ADS)

De Filippo, E.; Acosta, L.; Auditore, L.; Boiano, C.; Cardella, G.; Castoldi, A.; D’Andrea, M.; De Luca, S.; Favela, F.; Fichera, F.; Giudice, N.; Gnoffo, B.; Grimaldi, A.; Guazzoni, C.; Lanzalone, G.; Librizzi, F.; Litrico, P.; Maiolino, C.; Maffesanti, S.; Martorana, NS; Pagano, A.; Pagano, EV; Papa, M.; Parsani, T.; Passaro, G.; Pirrone, S.; Politi, G.; Previdi, F.; Quattrocchi, L.; Rizzo, F.; Russotto, P.; Saccà, G.; Salemi, G.; Sciliberto, D.; Trifirò, A.; Trimarchi, M.

2018-05-01

A new front-end based on digital GET electronics has been adopted for the readout of the CsI(Tl) detectors of the CHIMERA 4π multi-detector and for the new modular Femtoscopy Array for Correlation and Spectroscopy (FARCOS). It is expected that the coupling of CHIMERA with the FARCOS array, featuring high angular and energy resolution, and the adoption of the new digital electronics will be well suited for improving specific future data analysis, with the full shape storage of the signals, in the field of heavy ion reactions with stable and exotic beams around the Fermi energies domain. Integration of the GET electronics with CHIMERA and FARCOS devices and with the local analog data acquisition will be briefly discussed. We present some results from previous experimental tests and from the first in-beam experiment (Hoyle-Gamma) with the coupled GET+CHIMERA data acquisition.

A simple model of space radiation damage in GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Stith, J. J.; Stock, L. V.

1983-01-01

A simple model is derived for the radiation damage of shallow junction gallium arsenide (GaAs) solar cells. Reasonable agreement is found between the model and specific experimental studies of radiation effects with electron and proton beams. In particular, the extreme sensitivity of the cell to protons stopping near the cell junction is predicted by the model. The equivalent fluence concept is of questionable validity for monoenergetic proton beams. Angular factors are quite important in establishing the cell sensitivity to incident particle types and energies. A fluence of isotropic incidence 1 MeV electrons (assuming infinite backing) is equivalent to four times the fluence of normal incidence 1 MeV electrons. Spectral factors common to the space radiations are considered, and cover glass thickness required to minimize the initial damage for a typical cell configuration is calculated. Rough equivalence between the geosynchronous environment and an equivalent 1 MeV electron fluence (normal incidence) is established.

Generation of first hard X-ray pulse at Tsinghua Thomson Scattering X-ray Source.

PubMed

Du, Yingchao; Yan, Lixin; Hua, Jianfei; Du, Qiang; Zhang, Zhen; Li, Renkai; Qian, Houjun; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2013-05-01

Tsinghua Thomson Scattering X-ray Source (TTX) is the first-of-its-kind dedicated hard X-ray source in China based on the Thomson scattering between a terawatt ultrashort laser and relativistic electron beams. In this paper, we report the experimental generation and characterization of the first hard X-ray pulses (51.7 keV) via head-on collision of an 800 nm laser and 46.7 MeV electron beams. The measured yield is 1.0 × 10(6) per pulse with an electron bunch charge of 200 pC and laser pulse energy of 300 mJ. The angular intensity distribution and energy spectra of the X-ray pulse are measured with an electron-multiplying charge-coupled device using a CsI scintillator and silicon attenuators. These measurements agree well with theoretical and simulation predictions. An imaging test using the X-ray pulse at the TTX is also presented.

Pattern manipulation via on-chip phase modulation between orbital angular momentum beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Huanlu; School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LP; Strain, Michael J.

2015-08-03

An integrated approach to thermal modulation of relative phase between two optical vortices with opposite chirality has been demonstrated on a silicon-on-insulator substrate. The device consists of a silicon-integrated optical vortex emitter and a phase controlled 3 dB coupler. The relative phase between two optical vortices can be actively modulated on chip by applying a voltage on the integrated heater. The phase shift is shown to be linearly proportional to applied electrical power, and the rotation angle of the interference pattern is observed to be inversely proportional to topological charge. This scheme can be used in lab-on-chip, communications and sensing applications.more » It can be intentionally implemented with other modulation elements to achieve more complicated applications.« less

Fractional Fourier transform of Lorentz-Gauss vortex beams

NASA Astrophysics Data System (ADS)

Zhou, GuoQuan; Wang, XiaoGang; Chu, XiuXiang

2013-08-01

An analytical expression for a Lorentz-Gauss vortex beam passing through a fractional Fourier transform (FRFT) system is derived. The influences of the order of the FRFT and the topological charge on the normalized intensity distribution, the phase distribution, and the orbital angular momentum density of a Lorentz-Gauss vortex beam in the FRFT plane are examined. The order of the FRFT controls the beam spot size, the orientation of the beam spot, the spiral direction of the phase distribution, the spatial orientation of the two peaks in the orbital angular momentum density distribution, and the magnitude of the orbital angular momentum density. The increase of the topological charge not only results in the dark-hollow region becoming large, but also brings about detail changes in the beam profile. The spatial orientation of the two peaks in the orbital angular momentum density distribution and the phase distribution also depend on the topological charge.

Critical appraisal of volumetric-modulated arc therapy compared with electrons for the radiotherapy of cutaneous Kaposi’s sarcoma of lower extremities with bone sparing

PubMed Central

Abraham, S; Fogliata, A; Jordaan, A; Clivio, A; Vanetti, E; Cozzi, L

2013-01-01

Objective: To evaluate the use of volumetric-modulated arc therapy [VMAT, RapidArc® (RA); Varian Medical Systems, Palo Alto, CA] for the treatment of cutaneous Kaposi’s sarcoma (KS) of lower extremities with adequate target coverage and high bone sparing, and to compare VMAT with electron beam therapy. Methods: 10 patients were planned with either RA or electron beams. The dose was prescribed to 30 Gy, 10 fractions, to mean the planning target volume (PTV), and significant maximum dose to bone was limited to 30 Gy. Plans were designed for 6-MV photon beams for RA and 6 MeV for electrons. Dose distributions were computed with AcurosXB® (Varian Medical Systems) for photons and with a Monte Carlo algorithm for electrons. Results: V90% was 97.3±1.2 for RA plans and 78.2±2.6 for electrons; similarly, V107% was 2.5±2.2 and 37.7±3.4, respectively. RA met coverage criteria. Concerning bone sparing, D2% was 29.6±1.1 for RA and 31.0±2.4 for electrons. Although acceptable for bone involvement, pronounced target coverage violations were obtained for electron plans. Monitor units were similar for electrons and RA, although for the latter they increased when superior bone sparing was imposed. Delivery times were 12.1±4.0 min for electrons and 4.8±1.3 min for the most modulated RA plans. Conclusion: High plan quality was shown for KS in the lower extremities using VMAT, and this might simplify their management in comparison with the more conventional usage of electrons, particularly in institutes with limited staff resources and heavy workloads. Advances in knowledge: VMAT is also dosimetrically extremely advantageous in a typology of treatments where electron beam therapy is mainly considered to be effective owing to the limited penetration of the beams. PMID:23392192

Multisource inverse-geometry CT. Part II. X-ray source design and prototype

PubMed Central

Neculaes, V. Bogdan; Caiafa, Antonio; Cao, Yang; De Man, Bruno; Edic, Peter M.; Frutschy, Kristopher; Gunturi, Satish; Inzinna, Lou; Reynolds, Joseph; Vermilyea, Mark; Wagner, David; Zhang, Xi; Zou, Yun; Pelc, Norbert J.; Lounsberry, Brian

2016-01-01

Purpose: This paper summarizes the development of a high-power distributed x-ray source, or “multisource,” designed for inverse-geometry computed tomography (CT) applications [see B. De Man et al., “Multisource inverse-geometry CT. Part I. System concept and development,” Med. Phys. 43, 4607–4616 (2016)]. The paper presents the evolution of the source architecture, component design (anode, emitter, beam optics, control electronics, high voltage insulator), and experimental validation. Methods: Dispenser cathode emitters were chosen as electron sources. A modular design was adopted, with eight electron emitters (two rows of four emitters) per module, wherein tungsten targets were brazed onto copper anode blocks—one anode block per module. A specialized ceramic connector provided high voltage standoff capability and cooling oil flow to the anode. A matrix topology and low-noise electronic controls provided switching of the emitters. Results: Four modules (32 x-ray sources in two rows of 16) have been successfully integrated into a single vacuum vessel and operated on an inverse-geometry computed tomography system. Dispenser cathodes provided high beam current (>1000 mA) in pulse mode, and the electrostatic lenses focused the current beam to a small optical focal spot size (0.5 × 1.4 mm). Controlled emitter grid voltage allowed the beam current to be varied for each source, providing the ability to modulate beam current across the fan of the x-ray beam, denoted as a virtual bowtie filter. The custom designed controls achieved x-ray source switching in <1 μs. The cathode-grounded source was operated successfully up to 120 kV. Conclusions: A high-power, distributed x-ray source for inverse-geometry CT applications was successfully designed, fabricated, and operated. Future embodiments may increase the number of spots and utilize fast read out detectors to increase the x-ray flux magnitude further, while still staying within the stationary target inherent thermal limitations. PMID:27487878

Multisource inverse-geometry CT. Part II. X-ray source design and prototype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neculaes, V. Bogdan, E-mail: neculaes@ge.com; Caia

2016-08-15

Purpose: This paper summarizes the development of a high-power distributed x-ray source, or “multisource,” designed for inverse-geometry computed tomography (CT) applications [see B. De Man et al., “Multisource inverse-geometry CT. Part I. System concept and development,” Med. Phys. 43, 4607–4616 (2016)]. The paper presents the evolution of the source architecture, component design (anode, emitter, beam optics, control electronics, high voltage insulator), and experimental validation. Methods: Dispenser cathode emitters were chosen as electron sources. A modular design was adopted, with eight electron emitters (two rows of four emitters) per module, wherein tungsten targets were brazed onto copper anode blocks—one anode blockmore » per module. A specialized ceramic connector provided high voltage standoff capability and cooling oil flow to the anode. A matrix topology and low-noise electronic controls provided switching of the emitters. Results: Four modules (32 x-ray sources in two rows of 16) have been successfully integrated into a single vacuum vessel and operated on an inverse-geometry computed tomography system. Dispenser cathodes provided high beam current (>1000 mA) in pulse mode, and the electrostatic lenses focused the current beam to a small optical focal spot size (0.5 × 1.4 mm). Controlled emitter grid voltage allowed the beam current to be varied for each source, providing the ability to modulate beam current across the fan of the x-ray beam, denoted as a virtual bowtie filter. The custom designed controls achieved x-ray source switching in <1 μs. The cathode-grounded source was operated successfully up to 120 kV. Conclusions: A high-power, distributed x-ray source for inverse-geometry CT applications was successfully designed, fabricated, and operated. Future embodiments may increase the number of spots and utilize fast read out detectors to increase the x-ray flux magnitude further, while still staying within the stationary target inherent thermal limitations.« less

Orbit-induced localized spin angular momentum in strong focusing of optical vectorial vortex beams

NASA Astrophysics Data System (ADS)

Li, Manman; Cai, Yanan; Yan, Shaohui; Liang, Yansheng; Zhang, Peng; Yao, Baoli

2018-05-01

Light beams may carry optical spin or orbital angular momentum, or both. The spin and orbital parts manifest themselves by the ellipticity of the state of polarization and the vortex structure of phase of light beams, separately. Optical spin and orbit interaction, arising from the interaction between the polarization and the spatial structure of light beams, has attracted enormous interest recently. The optical spin-to-orbital angular momentum conversion under strong focusing is well known, while the converse process, orbital-to-spin conversion, has not been reported so far. In this paper, we predict in theory that the orbital angular momentum can induce a localized spin angular momentum in strong focusing of a spin-free azimuthal polarization vortex beam. This localized longitudinal spin of the focused field can drive the trapped particle to spin around its own axis. This investigation provides a new degree of freedom for spinning particles by using a vortex phase, which may have considerable potentials in optical spin and orbit interaction, light-beam shaping, or optical manipulation.

Performance of the 2 × 4-cell superconducting linac module for the THz-FEL facility

NASA Astrophysics Data System (ADS)

Kui, Zhou; Chenglong, Lao; Dai, Wu; Xing, Luo; Jianxin, Wang; Dexin, Xiao; Lijun, Shan; Tianhui, He; Xuming, Shen; Sifen, Lin; Linde, Yang; Hanbin, Wang; Xingfan, Yang; Ming, Li; Xiangyang, Lu

2018-07-01

A high average power THz radiation facility has been developed by the China Academy of Engineering Physics. It is the first CW THz user facility based on superconducting accelerator technology in China. The superconducting linac module, which contains two 4-cell 1.3 GHz TESLA-like superconducting radio frequency cavities, is a major component of this facility. The expected electron energy gain is 6-8 MeV with a field gradient of 8-10 MV/m. The design and fabrication of the linac module is complete. This paper discusses its assembly and results from cyromodule tests and beam commissioning. At 2 K, the cryomodule works smoothly and stably. Both cavities have achieved effective field gradients of 10 MV/m. In beam loading experiments, 8 MeV, 5 mA electron beams with an energy spread less than 0.2% have been produced, which satisfies our requirements.

Time-resolved characteristics of deuteron-beam generated by plasma focus discharge.

PubMed

Lim, Lian-Kuang; Yap, Seong-Ling; Bradley, D A

2018-01-01

The plasma focus device discussed herein is a Z-pinch pulsed-plasma arrangement. In this, the plasma is heated and compressed into a cylindrical column, producing a typical density of > 1025 particles/m3 and a temperature of (1-3) × 107 oC. The plasma focus has been widely investigated as a radiation source, including as ion-beams, electron-beams and as a source of x-ray and neutron production, providing considerable scope for use in a variety of technological situations. Thus said, the nature of the radiation emission depends on the dynamics of the plasma pinch. In this study of the characteristics of deuteron-beam emission, in terms of energy, fluence and angular distribution were analyzed. The 2.7 kJ plasma focus discharge has been made to operate at a pressure of less than 1 mbar rather than at its more conventional operating pressure of a few mbar. Faraday cup were used to determine deuteron-beam energy and deuteron-beam fluence per shot while CR-39 solid-state nuclear track detectors were employed in studying the angular distribution of deuteron emission. Beam energy and deuteron-beam fluence per shot have been found to be pressure dependent. The largest value of average deuteron energy measured for present conditions was found to be (52 ± 7) keV, while the deuteron-beam fluence per shot was of the order of 1015 ions/m2 when operated at a pressure of 0.2 mbar. The deuteron-beam emission is in the forward direction and is observed to be highly anisotropic.

Time-resolved characteristics of deuteron-beam generated by plasma focus discharge

PubMed Central

Bradley, D. A.

2018-01-01

The plasma focus device discussed herein is a Z-pinch pulsed-plasma arrangement. In this, the plasma is heated and compressed into a cylindrical column, producing a typical density of > 1025 particles/m3 and a temperature of (1–3) × 107 oC. The plasma focus has been widely investigated as a radiation source, including as ion-beams, electron-beams and as a source of x-ray and neutron production, providing considerable scope for use in a variety of technological situations. Thus said, the nature of the radiation emission depends on the dynamics of the plasma pinch. In this study of the characteristics of deuteron-beam emission, in terms of energy, fluence and angular distribution were analyzed. The 2.7 kJ plasma focus discharge has been made to operate at a pressure of less than 1 mbar rather than at its more conventional operating pressure of a few mbar. Faraday cup were used to determine deuteron-beam energy and deuteron-beam fluence per shot while CR-39 solid-state nuclear track detectors were employed in studying the angular distribution of deuteron emission. Beam energy and deuteron-beam fluence per shot have been found to be pressure dependent. The largest value of average deuteron energy measured for present conditions was found to be (52 ± 7) keV, while the deuteron-beam fluence per shot was of the order of 1015 ions/m2 when operated at a pressure of 0.2 mbar. The deuteron-beam emission is in the forward direction and is observed to be highly anisotropic. PMID:29309425

A wide bandwidth free-electron laser with mode locking using current modulation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kur, E.; Dunning, D. J.; McNeil, B. W. J.

2011-01-20

A new scheme for mode locking a free-electron laser amplifier is proposed based on electron beam current modulation. It is found that certain properties of the original concept, based on the energy modulation of electrons, are improved including the spectral brightness of the source and the purity of the series of short pulses. Numerical comparisons are made between the new and old schemes and between a mode-locked free-electron laser and self-amplified spontaneous emission free-electron laser. Illustrative examples using a hypothetical mode-locked free-electron laser amplifier are provided. The ability to generate intense coherent radiation with a large bandwidth is demonstrated.

High resolution multiplexed functional imaging in live embryos (Conference Presentation)

NASA Astrophysics Data System (ADS)

Xu, Dongli; Zhou, Weibin; Peng, Leilei

2017-02-01

Fourier multiplexed fluorescence lifetime imaging (FmFLIM) scanning laser optical tomography (FmFLIM-SLOT) combines FmFLIM and Scanning laser optical tomography (SLOT) to perform multiplexed 3D FLIM imaging of live embryos. The system had demonstrate multiplexed functional imaging of zebrafish embryos genetically express Foster Resonant Energy Transfer (FRET) sensors. However, previous system has a 20 micron resolution because the focused Gaussian beam diverges quickly from the focused plane, makes it difficult to achieve high resolution imaging over a long projection depth. Here, we present a high-resolution FmFLIM-SLOT system with achromatic Bessel beam, which achieves 3 micron resolution in 3D deep tissue imaging. In Bessel-FmFLIM-SLOT, multiple laser excitation lines are firstly intensity modulated by a Michelson interferometer with a spinning polygon mirror optical delay line, which enables Fourier multiplexed multi-channel lifetime measurements. Then, a spatial light modulator and a prism are used to transform the modulated Gaussian laser beam to an achromatic Bessel beam. The achromatic Bessel beam scans across the whole specimen with equal angular intervals as sample rotated. After tomography reconstruction and the frequency domain lifetime analysis method, both the 3D intensity and lifetime image of multiple excitation-emission can be obtained. Using Bessel-FmFLIM-SLOT system, we performed cellular-resolution FLIM tomography imaging of live zebrafish embryo. Genetically expressed FRET sensors in these embryo will allow non-invasive observation of multiple biochemical processes in vivo.

Active control of acoustic field-of-view in a biosonar system.

PubMed

Yovel, Yossi; Falk, Ben; Moss, Cynthia F; Ulanovsky, Nachum

2011-09-01

Active-sensing systems abound in nature, but little is known about systematic strategies that are used by these systems to scan the environment. Here, we addressed this question by studying echolocating bats, animals that have the ability to point their biosonar beam to a confined region of space. We trained Egyptian fruit bats to land on a target, under conditions of varying levels of environmental complexity, and measured their echolocation and flight behavior. The bats modulated the intensity of their biosonar emissions, and the spatial region they sampled, in a task-dependant manner. We report here that Egyptian fruit bats selectively change the emission intensity and the angle between the beam axes of sequentially emitted clicks, according to the distance to the target, and depending on the level of environmental complexity. In so doing, they effectively adjusted the spatial sector sampled by a pair of clicks-the "field-of-view." We suggest that the exact point within the beam that is directed towards an object (e.g., the beam's peak, maximal slope, etc.) is influenced by three competing task demands: detection, localization, and angular scanning-where the third factor is modulated by field-of-view. Our results suggest that lingual echolocation (based on tongue clicks) is in fact much more sophisticated than previously believed. They also reveal a new parameter under active control in animal sonar-the angle between consecutive beams. Our findings suggest that acoustic scanning of space by mammals is highly flexible and modulated much more selectively than previously recognized.

Kapton charging characteristics: Effects of material thickness and electron-energy distribution

NASA Technical Reports Server (NTRS)

Williamson, W. S.; Dulgeroff, C. R.; Hymann, J.; Viswanathan, R.

1985-01-01

Charging characteristics of polyimide (Kapton) of varying thicknesses under irradiation by a very-low-curent-density electron beam, with the back surface of the sample grounded are reported. These charging characteristics are in good agreement with a simple analytical model which predicts that in thin samples at low current density, sample surface potential is limited by conduction leakage through the bulk material. The charging of Kapton in a low-current-density electron beam in which the beam energy was modulated to simulate Maxwellian and biMaxwellian distribution functions is measured.

Strong higher-order resonant contributions to x-ray line polarization in hot plasmas

NASA Astrophysics Data System (ADS)

Shah, Chintan; Amaro, Pedro; Steinbrügge, Rene; Beilmann, Christian; Bernitt, Sven; Fritzsche, Stephan; Surzhykov, Andrey; Crespo López-Urrutia, José R.; Tashenov, Stanislav

2016-06-01

We studied angular distributions of x rays emitted in resonant recombination of highly charged iron and krypton ions, resolving dielectronic, trielectronic, and quadruelectronic channels. A tunable electron beam drove these processes, inducing x rays registered by two detectors mounted along and perpendicular to the beam axis. The measured emission asymmetries comprehensively benchmarked full-order atomic calculations. We conclude that accurate polarization diagnostics of hot plasmas can only be obtained under the premise of inclusion of higher-order processes that were neglected in earlier work.

Investigating PID shunting in polycrystalline silicon modules via multiscale, multitechnique characterization

DOE PAGES

Harvey, Steven P.; Moseley, John; Norman, Andrew; ...

2018-02-27

We investigated the potential-induced degradation (PID) shunting mechanism in multicrystalline-silicon photovoltaic modules by using a multiscale, multitechnique characterization approach. Both field-stressed modules and laboratory-stressed mini modules were studied. We used photoluminescence, electroluminescence, and dark lock-in thermography imaging to identify degraded areas at the module scale. Small samples were then removed from degraded areas, laser marked, and imaged by scanning electron microscopy. We used simultaneous electron-beam induced current imaging and focused ion beam milling to mark around PID shunts for chemical analysis by time-of-flight secondary-ion mass spectrometry or to isolate individual shunt defects for transmission electron microscopy and atom-probe tomography analysis.more » By spanning a range of 10 orders of magnitude in size, this approach enabled us to investigate the root-cause mechanisms for PID shunting. We observed a direct correlation between recombination active shunts and sodium content. The sodium content in shunted areas peaks at the SiNX/Si interface and is consistently observed at a concentration of 0.1% to 2% in shunted areas. Analysis of samples subjected to PID recovery, either activated by electron beam or thermal effects only, reveals that recovery of isolated shunts correlates with diffusion of sodium out of the structural defects to the silicon surface. We observed the role of oxygen and chlorine in PID shunting and found that those species - although sometimes present in structural defects where PID shunting was observed - do not play a consistent role in PID shunting.« less

Theoretical and numerical analyses of a slit-masked chicane for modulated bunch generation

DOE PAGES

Zhu, Xiaofang; Broemmelsiek, Daniel R.; Shin, Young -Min; ...

2015-10-28

Density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The beam modulation is studied with a masked chicane by the analytic model and simulations with the beam parameters of the Fermilab Accelerator Science and Technology (FAST) facility. With the chicane design parameters (bending angle of 18o, bending radius of 0.95 m and R 56 ~ –0.19 m) and a nominal beam of 3 ps bunch length, the analytic model showed that a slit-mask with slit period 900 μ m and aperture width 300 μ m induces a modulation of bunch-to-bunch spacingmore » ~ 100 μ m to the bunch with 2.4% correlated energy spread. With the designed slit mask and a 3 ps bunch, particle-in-cell (PIC) simulations, including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in beam modulation with bunch-to-bunch distance around 100 μ m and a corresponding modulation frequency of 3 THz. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by tracking code Elegant. The simulation analysis indicates that the sliced beam by the slit-mask with 3 ~ 6% correlated energy spread has modulation lengths about 187 μ m (0.25 nC), 270 μ m (1 nC) and 325 μ m (3.2 nC). As a result, the theoretical and numerical data proved the capability of the designed masked chicane in producing modulated bunch train with micro-bunch length around 100 fs.« less

Theoretical and numerical analyses of a slit-masked chicane for modulated bunch generation

NASA Astrophysics Data System (ADS)

Zhu, X.; Broemmelsiek, D. R.; Shin, Y.-M.

2015-10-01

Density modulations on electron beams can improve machine performance of beam-driven accelerators and FELs with resonance beam-wave coupling. The beam modulation is studied with a masked chicane by the analytic model and simulations with the beam parameters of the Fermilab Accelerator Science and Technology (FAST) facility. With the chicane design parameters (bending angle of 18o, bending radius of 0.95 m and R56 ~ -0.19 m) and a nominal beam of 3 ps bunch length, the analytic model showed that a slit-mask with slit period 900 μ m and aperture width 300 μ m induces a modulation of bunch-to-bunch spacing ~ 100 μ m to the bunch with 2.4% correlated energy spread. With the designed slit mask and a 3 ps bunch, particle-in-cell (PIC) simulations, including nonlinear energy distributions, space charge force, and coherent synchrotron radiation (CSR) effect, also result in beam modulation with bunch-to-bunch distance around 100 μ m and a corresponding modulation frequency of 3 THz. The beam modulation has been extensively examined with three different beam conditions, 2.25 ps (0.25 nC), 3.25 ps (1 nC), and 4.75 ps (3.2 nC), by tracking code Elegant. The simulation analysis indicates that the sliced beam by the slit-mask with 3 ~ 6% correlated energy spread has modulation lengths about 187 μ m (0.25 nC), 270 μ m (1 nC) and 325 μ m (3.2 nC). The theoretical and numerical data proved the capability of the designed masked chicane in producing modulated bunch train with micro-bunch length around 100 fs.

Kinetic theory of twisted waves: Application to space plasmas having superthermal population of species

NASA Astrophysics Data System (ADS)

Arshad, Kashif; Poedts, Stefaan; Lazar, Marian

2017-04-01

Nowadays electromagnetic (EM) fields have various applications in fundamental research, communication, and home appliances. Even though, there are still some subtle features of electromagnetic field known to us a century ago, yet to be utilized. It is because of the technical complexities to sense three dimensional electromagnetic field. An important characteristic of electromagnetic field is its orbital angular momentum (OAM). The angular momentum consists of two distinct parts; intrinsic part associated with the wave polarization or spin, and the extrinsic part associated with the orbital angular momentum (OAM). The orbital angular momentum (OAM) is inherited by helically phased light or helical (twisted) electric field. The investigations of Allen on lasers carrying orbital angular momentum (OAM), has initiated a new scientific and technological advancement in various growing fields, such as microscopy and imaging, atomic and nano-particle manipulation, ultra-fast optical communications, quantum computing, ionospheric radar facility to observe 3D plasma dynamics in ionosphere, photonic crystal fibre, OAM entanglement of two photons, twisted gravitational waves, ultra-intense twisted laser pulses and astrophysics. Recently, the plasma modes are also investigated with orbital angular momentum. The production of electron vortex beams and its applications are indicated by Verbeeck et al. The magnetic tornadoes (rotating magnetic field structures) exhibit three types of morphology i.e., spiral, ring and split. Leyser pumped helical radio beam carrying OAM into the Ionospheric plasma under High Frequency Active Auroral Research Program (HAARP) and characteristic ring shaped morphology is obtained by the optical emission spectrum of pumped plasma turbulence. The scattering phenomenon like (stimulated Raman and Brillouin backscattering) is observed to be responsible for the interaction between electrostatic and electromagnetic waves through orbital angular momentum. The ring shape morphology of a beam with orbital angular momentum (OAM) is ideal for the observation of solar corona around the sun where the intensity of the beam is minimum at the center, in solar experiments, and Earth's ionosphere. The twisted plasma modes carrying OAM are mostly studied either by the fluid theory or Maxwellian distributed Kinetic Theory. But most of the space plasmas and some laboratory plasmas have non-thermal distributions due to super-thermal population of the plasma particles. Therefore the Kinetic Theory of twisted plasma modes carrying OAM are recently studied using non-thermal (kappa) distribution of the super-thermal particles in the presence of the helical electric field and significant change in the damping rates are observed by tuning appropriate parameters.

Orbital and spin angular momentum in conical diffraction

NASA Astrophysics Data System (ADS)

Berry, M. V.; Jeffrey, M. R.; Mansuripur, M.

2005-11-01

The angular momentum Jinc of a light beam can be changed by passage through a slab of crystal. When the beam is incident along the optic axis of a biaxial crystal, which may also possess optical activity (chirality), the final angular momentum J can have both orbital (Jorb) and spin (Jsp) contributions, which we calculate paraxially exactly for arbitrary biaxiality and chirality and initially uniformly polarized beams with circular symmetry. For the familiar special case of a non-chiral crystal with fully developed conical-refraction rings, J is purely orbital and equal to Jinc/2, reflecting an interesting singularity structure in the beam. Explicit formulas and numerical computations are presented for a Gaussian incident beam. The change in angular momentum results in a torque on the crystal, along the axis of the incident beam. An additional, much larger, torque, about an axis lying in the slab, arises from the offset of the cone of conical refraction relative to the incident beam.

Skew chicane based betatron eigenmode exchange module

DOEpatents

Douglas, David

2010-12-28

A skewed chicane eigenmode exchange module (SCEEM) that combines in a single beamline segment the separate functionalities of a skew quad eigenmode exchange module and a magnetic chicane. This module allows the exchange of independent betatron eigenmodes, alters electron beam orbit geometry, and provides longitudinal parameter control with dispersion management in a single beamline segment with stable betatron behavior. It thus reduces the spatial requirements for multiple beam dynamic functions, reduces required component counts and thus reduces costs, and allows the use of more compact accelerator configurations than prior art design methods.

Ultrafast generation of skyrmionic defects with vortex beams: Printing laser profiles on magnets

NASA Astrophysics Data System (ADS)

Fujita, Hiroyuki; Sato, Masahiro

2017-02-01

Controlling electric and magnetic properties of matter by laser beams is actively explored in the broad region of condensed matter physics, including spintronics and magneto-optics. Here we theoretically propose an application of optical and electron vortex beams carrying intrinsic orbital angular momentum to chiral ferro- and antiferromagnets. We analyze the time evolution of spins in chiral magnets under irradiation of vortex beams by using the stochastic Landau-Lifshitz-Gilbert equation. We show that beam-driven nonuniform temperature leads to a class of ring-shaped magnetic defects, what we call skyrmion multiplex, as well as conventional skyrmions. We discuss the proper beam parameters and the optimal way of applying the beams for the creation of these topological defects. Our findings provide an ultrafast scheme of generating topological magnetic defects in a way applicable to both metallic and insulating chiral (anti-) ferromagnets.

Synthesis and characterization of attosecond light vortices in the extreme ultraviolet

PubMed Central

Géneaux, R.; Camper, A.; Auguste, T.; Gobert, O.; Caillat, J.; Taïeb, R.; Ruchon, T.

2016-01-01

Infrared and visible light beams carrying orbital angular momentum (OAM) are currently thoroughly studied for their extremely broad applicative prospects, among which are quantum information, micromachining and diagnostic tools. Here we extend these prospects, presenting a comprehensive study for the synthesis and full characterization of optical vortices carrying OAM in the extreme ultraviolet (XUV) domain. We confirm the upconversion rules of a femtosecond infrared helically phased beam into its high-order harmonics, showing that each harmonic order carries the total number of OAM units absorbed in the process up to very high orders (57). This allows us to synthesize and characterize helically shaped XUV trains of attosecond pulses. To demonstrate a typical use of these new XUV light beams, we show our ability to generate and control, through photoionization, attosecond electron beams carrying OAM. These breakthroughs pave the route for the study of a series of fundamental phenomena and the development of new ultrafast diagnosis tools using either photonic or electronic vortices. PMID:27573787

Synthesis and characterization of attosecond light vortices in the extreme ultraviolet

DOE PAGES

Géneaux, R.; Camper, A.; Auguste, T.; ...

2016-08-30

Infrared and visible light beams carrying orbital angular momentum (OAM) are currently thoroughly studied for their extremely broad applicative prospects, among which are quantum information, micromachining and diagnostic tools. Here we extend these prospects, presenting a comprehensive study for the synthesis and full characterization of optical vortices carrying OAM in the extreme ultraviolet (XUV) domain. We confirm the upconversion rules of a femtosecond infrared helically phased beam into its high-order harmonics, showing that each harmonic order carries the total number of OAM units absorbed in the process up to very high orders (57). This allows us to synthesize and characterizemore » helically shaped XUV trains of attosecond pulses. To demonstrate a typical use of these new XUV light beams, we show our ability to generate and control, through photoionization, attosecond electron beams carrying OAM. Furthermore, these breakthroughs pave the route for the study of a series of fundamental phenomena and the development of new ultrafast diagnosis tools using either photonic or electronic vortices.« less

Automated System Calibration and Verification of the Position Measurements for the Los Alamos Isotope Production Facility and the Switchyard Kicker Facilities

NASA Astrophysics Data System (ADS)

Barr, D.; Gilpatrick, J. D.; Martinez, D.; Shurter, R. B.

2004-11-01

The Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory has constructed both an Isotope Production Facility (IPF) and a Switchyard Kicker (XDK) as additions to the H+ and H- accelerator. These additions contain eleven Beam Position Monitors (BPMs) that measure the beam's position throughout the transport. The analog electronics within each processing module determines the beam position using the log-ratio technique. For system reliability, calibrations compensate for various temperature drifts and other imperfections in the processing electronics components. Additionally, verifications are periodically implemented by a PC running a National Instruments LabVIEW virtual instrument (VI) to verify continued system and cable integrity. The VI communicates with the processor cards via a PCI/MXI-3 VXI-crate communication module. Previously, accelerator operators performed BPM system calibrations typically once per day while beam was explicitly turned off. One of this new measurement system's unique achievements is its automated calibration and verification capability. Taking advantage of the pulsed nature of the LANSCE-facility beams, the integrated electronics hardware and VI perform calibration and verification operations between beam pulses without interrupting production beam delivery. The design, construction, and performance results of the automated calibration and verification portion of this position measurement system will be the topic of this paper.

Integral momenta of vortex Bessel-Gaussian beams in turbulent atmosphere.

PubMed

Lukin, Igor P

2016-04-20

The orbital angular momentum of vortex Bessel-Gaussian beams propagating in turbulent atmosphere is studied theoretically. The field of an optical beam is determined through the solution of the paraxial wave equation for a randomly inhomogeneous medium with fluctuations of the refraction index of the turbulent atmosphere. Peculiarities in the behavior of the total power of the vortex Bessel-Gaussian beam at the receiver (or transmitter) are examined. The dependence of the total power of the vortex Bessel-Gaussian beam on optical beam parameters, namely, the transverse wave number of optical radiation, amplitude factor radius, and, especially, topological charge of the optical beam, is analyzed in detail. It turns out that the mean value of the orbital angular momentum of the vortex Bessel-Gaussian beam remains constant during propagation in the turbulent atmosphere. It is shown that the variance of fluctuations of the orbital angular momentum of the vortex Bessel-Gaussian beam propagating in turbulent atmosphere calculated with the "mean-intensity" approximation is equal to zero identically. Thus, it is possible to declare confidently that the variance of fluctuations of the orbital angular momentum of the vortex Bessel-Gaussian beam in turbulent atmosphere is not very large.

A new evaluation method of electron optical performance of high beam current probe forming systems.

PubMed

Fujita, Shin; Shimoyama, Hiroshi

2005-10-01

A new numerical simulation method is presented for the electron optical property analysis of probe forming systems with point cathode guns such as cold field emitters and the Schottky emitters. It has long been recognized that the gun aberrations are important parameters to be considered since the intrinsically high brightness of the point cathode gun is reduced due to its spherical aberration. The simulation method can evaluate the 'threshold beam current I(th)' above which the apparent brightness starts to decrease from the intrinsic value. It is found that the threshold depends on the 'electron gun focal length' as well as on the spherical aberration of the gun. Formulas are presented to estimate the brightness reduction as a function of the beam current. The gun brightness reduction must be included when the probe property (the relation between the beam current l(b) and the probe size on the sample, d) of the entire electron optical column is evaluated. Formulas that explicitly consider the gun aberrations into account are presented. It is shown that the probe property curve consists of three segments in the order of increasing beam current: (i) the constant probe size region, (ii) the brightness limited region where the probe size increases as d approximately I(b)(3/8), and (iii) the angular current intensity limited region in which the beam size increases rapidly as d approximately I(b)(3/2). Some strategies are suggested to increase the threshold beam current and to extend the effective beam current range of the point cathode gun into micro ampere regime.

Post-filamentation high-intensive light channels formation upon ultrashort laser pulses self-focusing in air

NASA Astrophysics Data System (ADS)

Geints, Yu. E.; Ionin, A. A.; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Zemlyanov, A. A.

2017-01-01

Experimental and theoretical study of the post-filamentation stage of focused high-power Ti:Sa laser pulses in air is presented. Angular divergence of the laser beam, as well as angular and spatial characteristics of specific spatially localized light structures, the post-filament channels (PFCs), under different initial focusing conditions and laser beam energy are investigated. We show that PFC angular divergence is always less than that of the whole laser beam and tends to decrease with laser pulse energy increase and beam focal length elongation.

Relativistic twistron based on backward-wave oscillator with modulating reflector and an efficiency of 56%

NASA Astrophysics Data System (ADS)

Totmeninov, E. M.; Pegel, I. V.; Tarakanov, V. P.

2017-06-01

Using numerical simulation, the operating mode of a relativistic Cherenkov microwave generator of the twistronic type has been demonstrated. The generator includes an electrodynamic system based on a backward-wave oscillator and modulating reflector with nonmonotonous, highly nonuniform energy exchange along the length of the system. The efficiency of power conversion from the electron beam to electromagnetic radiation is 56%, and the electronic efficiency is 66%. For an accelerating voltage of 340 kV and an electron beam current of 3.3 kA, the simulated generation power is 630 MW at a frequency of 9.7 GHz and a guiding magnetic field of 2.2 T.

Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry.

PubMed

Vadilonga, Simone; Zizak, Ivo; Roshchupkin, Dmitry; Evgenii, Emelin; Petsiuk, Andrei; Leitenberger, Wolfram; Erko, Alexei

2017-04-01

X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La 3 Ga 5 SiO 14 ) modulated by Λ = 3 µm Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space-time modulation of an X-ray beam.

Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry1

PubMed Central

Vadilonga, Simone; Zizak, Ivo; Roshchupkin, Dmitry; Evgenii, Emelin; Petsiuk, Andrei; Leitenberger, Wolfram; Erko, Alexei

2017-01-01

X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La3Ga5SiO14) modulated by Λ = 3 µm Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space–time modulation of an X-ray beam. PMID:28381976

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

NASA Technical Reports Server (NTRS)

Fischer, M. L.; Alsop, D. C.; Cheng, E. S.; Clapp, A. C.; Cottingham, D. A.; Gundersen, J. O.; Koch, T. C.; Kreysa, E.; Meinhold, P. R.; Lange, A. E.

1992-01-01

The performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0.3 to 3 deg is presented. The system represents a collaborative effort combining a low-background 1-m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3, 6, 9, and 12/cm (90, 180, 270, and 360 GHz). The telescope has been flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of about 0.00001 with detectors operated at 0.3 K.

SU-D-213-06: Dosimetry of Modulated Electron Radiation Therapy Using Fricke Gel Dosimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gawad, M Abdel; Elgohary, M; Hassaan, M

Purpose: Modulated electron radiation therapy (MERT) has been proposed as an effective modality for treatment of superficial targets. MERT utilizes multiple beams of different energies which are intensity modulated to deliver optimized dose distribution. Energy independent dosimeters are thus needed for quantitative evaluations of MERT dose distributions and measurements of absolute doses delivered to patients. Thus in the current work we study the feasibility of Fricke gel dosimeters in MERT dosimetry. Methods: Batches of radiation sensitive Fricke gel is fabricated and poured into polymethyl methacrylate cuvettes. The samples were irradiated in solid water phantom and a thick layer of bolusmore » was used as a buildup. A spectrophotometer system was used for measuring the color changes (the absorbance) before and after irradiation and then we calculate net absorbance. We constructed calibration curves to relate the measured absorbance in terms of absorbed dose for all available electron energies. Dosimetric measurements were performed for mixed electron beam delivery and we also performed measurement for segmented field delivery with the dosimeter placed at the junction of two adjacent electron beams of different energies. Dose measured by our gel dosimetry is compared to that calculation from our precise treatment planning system. We also initiated a Monte Carlo study to evaluate the water equivalence of our dosimeters. MCBEAM and MCSIM codes were used for treatment head simulation and phantom dose calculation. PDDs and profiles were calculated for electron beams incident on a phantom designed with 1cm slab of Fricke gel. Results: The calibration curves showed no observed energy dependence with all studied electron beam energies. Good agreement was obtained between dose calculated and that obtained by gel dosimetry. Monte Carlo results illustrated the tissue equivalency of our Gel dosimeters. Conclusion: Fricke Gel dosimeters represent a good option for the dosimetric quality assurance prior to MERT application.« less

Status and Perspectives for a Slow Positron Beam Facility at the HH—NIPNE Bucharest

NASA Astrophysics Data System (ADS)

Constantin, Florin; Craciun, Liviu Stefan; Constantinescu, Olimpiu; Ghita, Ionica Alina; Ionescu, Cristina; Racolta, Petru Mihai; Straticiuc, Mihai; Vasilescu, Angela; Braic, Viorel; Zoita, Catalin; Kiss, Adrian; Bojin, Dionezie

2009-03-01

The development of a positron annihilation spectroscopy laboratory at the HH-NIPNE Bucharest-to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high-vacuum dedicated beam line with two options: a 25 mCi 22NaCl source and in line with the NIPNE-cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source- moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8-1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8-50 keV and a CDBS analysis chamber. The moderator proposed—is tungsten as a foil of about 3 μm prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100 W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3 M diffractometer, with a Co tube (λKα = 1.7903 A)—the angular regions studied were around 34° (1 0 0) and 69° (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set-up we used a home-made 22NaCl source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home- made biparametric system for CDBS measurements will be reported, also.

Status and Perspectives for a Slow Positron Beam Facility at the HH-NIPNE Bucharest

NASA Astrophysics Data System (ADS)

Straticiuc, Mihai; Craciun, Liviu Stefan; Constantinescu, Olimpiu; Ghita, Ionica Alina; Ionescu, Cristina; Racolta, Petru Mihai; Vasilescu, Angela; Braic, Viorel; Zoita, Catalin; Kiss, Adrian; Bojin, Dionezie

2009-03-01

The development of a positron annihilation spectroscopy laboratory at the HH-NIPNE Bucharest-to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high-vacuum dedicated beam line with two options: a 25 mCi 22NaCl source and in line with the NIPNE-cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source- moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8-1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8-50 keV and a CDBS analysis chamber. The moderator proposed-is tungsten as a foil of about 3 μm prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100 W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3 M diffractometer, with a Co tube (λKα = 1.7903 A)-the angular regions studied were around 34° (1 0 0) and 69° (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set-up we used a home-made 22NaCl source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home- made biparametric system for CDBS measurements will be reported, also.

Orbital angular momentum (OAM) spectrum correction in free space optical communication.

PubMed

Liu, Yi-Dong; Gao, Chunqing; Qi, Xiaoqing; Weber, Horst

2008-05-12

Orbital angular momentum (OAM) of laser beams has potential application in free space optical communication, but it is sensitive against pointing instabilities of the beam, i.e. shift (lateral displacement) and tilt (deflection of the beam). This work proposes a method to correct the distorted OAM spectrum by using the mean square value of the orbital angular momentum as an indicator. Qualitative analysis is given, and the numerical simulation is carried out for demonstration. The results show that the mean square value can be used to determine the beam axis of the superimposed helical beams. The initial OAM spectrum can be recovered.

BBU design of linear induction accelerator cells for radiography application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shang, C.C.; Chen, Y.J.; Gaporaso, G.J.

1997-05-06

There is an ongoing effort to develop accelerating modules for high-current electron accelerators for advanced radiography application. Accelerating modules with low beam-cavity coupling impedances along with gap designs with acceptable field stresses comprise a set of fundamental design criteria. We examine improved cell designs which have been developed for accelerator application in several radiographic operating regimes. We evaluate interaction impedances, analyze the effects of beam structure coupling on beam dynamics (beam break-up instability and corkscrew motion). We also provide estimates of coupling through interesting new high-gradient insulators and evaluate their potential future application in induction cells.

Numerical simulation of ion charge breeding in electron beam ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, L., E-mail: zhao@far-tech.com; Kim, Jin-Soo

2014-02-15

The Electron Beam Ion Source particle-in-cell code (EBIS-PIC) tracks ions in an EBIS electron beam while updating electric potential self-consistently and atomic processes by the Monte Carlo method. Recent improvements to the code are reported in this paper. The ionization module has been improved by using experimental ionization energies and shell effects. The acceptance of injected ions and the emittance of extracted ion beam are calculated by extending EBIS-PIC to the beam line transport region. An EBIS-PIC simulation is performed for a Cs charge-breeding experiment at BNL. The charge state distribution agrees well with experiments, and additional simulation results ofmore » radial profiles and velocity space distributions of the trapped ions are presented.« less

A Monte Carlo investigation of contaminant electrons due to a novel in vivo transmission detector.

PubMed

Asuni, G; Jensen, J M; McCurdy, B M C

2011-02-21

A novel transmission detector (IBA Dosimetry, Germany) developed as an IMRT quality assurance tool, intended for in vivo patient dose measurements, is studied here. The goal of this investigation is to use Monte Carlo techniques to characterize treatment beam parameters in the presence of the detector and to compare to those of a plastic block tray (a frequently used clinical device). Particular attention is paid to the impact of the detector on electron contamination model parameters of two commercial dose calculation algorithms. The linac head together with the COMPASS transmission detector (TRD) was modeled using BEAMnrc code. To understand the effect of the TRD on treatment beams, the contaminant electron fluence, energy spectra, and angular distributions at different SSDs were analyzed for open and non-open (i.e. TRD and block tray) fields. Contaminant electrons in the BEAMnrc simulations were separated according to where they were created. Calculation of surface dose and the evaluation of contributions from contaminant electrons were performed using the DOSXYZnrc user code. The effect of the TRD on contaminant electrons model parameters in Eclipse AAA and Pinnacle(3) dose calculation algorithms was investigated. Comparisons of the fluence of contaminant electrons produced in the non-open fields versus open field show that electrons created in the non-open fields increase at shorter SSD, but most of the electrons at shorter SSD are of low energy with large angular spread. These electrons are out-scattered or absorbed in air and contribute less to surface dose at larger SSD. Calculated surface doses with the block tray are higher than those with the TRD. Contribution of contaminant electrons to dose in the buildup region increases with increasing field size. The additional contribution of electrons to surface dose increases with field size for TRD and block tray. The introduction of the TRD results in a 12% and 15% increase in the Gaussian widths used in the contaminant electron source model of the Eclipse AAA dose algorithm. The off-axis coefficient in the Pinnacle(3) dose calculation algorithm decreases in the presence of TRD compared to without the device. The electron model parameters were modified to reflect the increase in electron contamination with the TRD, a necessary step for accurate beam modeling when using the device.

Effects of the circularly polarized beam of linearized gravitational waves

NASA Astrophysics Data System (ADS)

Barker, W.

2017-08-01

Solutions of the linearized Einstein equations are found that describe a transversely confined beam of circularly polarized gravitational waves on a Minkowski backdrop. By evaluating the cycle-averaged stress-energy-momentum pseudotensor of Landau & Lifshitz it is found that the angular momentum density is concentrated in the ‘skin’ at the edge of the beam where the intensity falls, and that the ratio of angular momentum to energy per unit length of the beam is 2/ω , where ω is the wave frequency, as expected for a beam of spin-2 gravitons. For sharply-defined, uniform, axisymmetric beams, the induced background metric is shown to produce the gravitomagnetic field and frame-dragging effects of a gravitational solenoid, whilst the angular momentum current helically twists the space at infinite radius along the beam axis.

Integrated optical modulator manipulating the polarization and rotation handedness of Orbital Angular Momentum states.

PubMed

Mousavi, S Faezeh; Nouroozi, Rahman; Vallone, Giuseppe; Villoresi, Paolo

2017-06-19

Recent studies demonstrated that the optical channels encoded by Orbital Angular Momentum (OAM) are capable candidates for improving the next generation of communication systems. OAM states can enhance the capacity and security of high-dimensional communication channels in both classical and quantum regimes based on optical fibre and free space. Hence, fast and precise control of the beams encoded by OAM can provide their commercial applications in the compatible communication networks. Integrated optical devices are good miniaturized options to perform this issue. This paper proposes a numerically verified integrated high-frequency electro-optical modulator for manipulation of the guided modes encoded in both OAM and polarization states. The proposed modulator is designed as an electro-optically active Lithium Niobate (LN) core photonic wire with silica as its cladding in a LN on Insulator (LNOI) configuration. It consists of two successive parts; a phase shifter to reverse the rotation handedness of the input OAM state and a polarization converter to change the horizontally polarized OAM state to the vertically polarized one. It is shown that all four possible output polarization-OAM encoded states can be achieved with only 6 V and 7 V applied voltages to the electrodes in the two parts of the modulator.

Insertion device and method for accurate and repeatable target insertion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubeli, III, Joseph F.; Shinn, Michelle D.; Bevins, Michael E.

The present invention discloses a device and a method for inserting and positioning a target within a free electron laser, particle accelerator, or other such device that generates or utilizes a beam of energy or particles. The system includes a three-point registration mechanism that insures angular and translational accuracy and repeatability of positioning upon multiple insertions within the same structure.

Programmable graphene doping via electron beam irradiation.

PubMed

Zhou, Yangbo; Jadwiszczak, Jakub; Keane, Darragh; Chen, Ying; Yu, Dapeng; Zhang, Hongzhou

2017-06-29

Graphene is a promising candidate to succeed silicon based devices, and the conventional strategies for fabrication and testing of graphene-based electronics often utilise an electron beam. Here, we report on a systematic study of the effect of electron beam exposure on graphene devices. We realise reversible doping of on-chip graphene using a focused electron beam. Our results demonstrate site-specific control of carrier type and concentration achievable by modulating the charge distribution in the substrate. The effect of substrate-embedded charges on carrier mobility and conductivity of graphene is studied, with a dielectric screening model proposed to explain the effective n-type and p-type doping produced at different beam energies. Multiple logic operations are thus implemented in a single graphene sheet by using site-specific e-beam irradiation. We extend the phenomenon to MoS 2 , generalising it to conductive two-dimensional materials. Our results are of importance to imaging, in situ characterisation and lithographic techniques employed to investigate 2D materials.

New Insights on Subsurface Imaging of Carbon Nanotubes in Polymer Composites via Scanning Electron Microscopy

NASA Technical Reports Server (NTRS)

Zhao, Minhua; Ming, Bin; Kim, Jae-Woo; Gibbons, Luke J.; Gu, Xiaohong; Nguyen, Tinh; Park, Cheol; Lillehei, Peter T.; Villarrubia, J. S.; Vladar, Andras E.;

Conceptual design of hollow electron lenses for beam halo control in the Large Hadron Collider

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stancari, Giulio; Previtali, Valentina; Valishev, Alexander

Collimation with hollow electron beams is a technique for halo control in high-power hadron beams. It is based on an electron beam (possibly pulsed or modulated in intensity) guided by strong axial magnetic fields which overlaps with the circulating beam in a short section of the ring. The concept was tested experimentally at the Fermilab Tevatron collider using a hollow electron gun installed in one of the Tevatron electron lenses. We are proposing a conceptual design for applying this technique to the Large Hadron Collider at CERN. A prototype hollow electron gun for the LHC was built and tested. Themore » expected performance of the hollow electron beam collimator was based on Tevatron experiments and on numerical tracking simulations. Halo removal rates and enhancements of halo diffusivity were estimated as a function of beam and lattice parameters. Proton beam core lifetimes and emittance growth rates were checked to ensure that undesired effects were suppressed. Hardware specifications were based on the Tevatron devices and on preliminary engineering integration studies in the LHC machine. Required resources and a possible timeline were also outlined, together with a brief discussion of alternative halo-removal schemes and of other possible uses of electron lenses to improve the performance of the LHC.« less

Diode magnetic-field influence on radiographic spot size

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, Carl A. Jr.

2012-09-04

Flash radiography of hydrodynamic experiments driven by high explosives is a well-known diagnostic technique in use at many laboratories. The Dual-Axis Radiography for Hydrodynamic Testing (DARHT) facility at Los Alamos was developed for flash radiography of large hydrodynamic experiments. Two linear induction accelerators (LIAs) produce the bremsstrahlung radiographic source spots for orthogonal views of each experiment ('hydrotest'). The 2-kA, 20-MeV Axis-I LIA creates a single 60-ns radiography pulse. For time resolution of the hydrotest dynamics, the 1.7-kA, 16.5-MeV Axis-II LIA creates up to four radiography pulses by slicing them out of a longer pulse that has a 1.6-{micro}s flattop. Bothmore » axes now routinely produce radiographic source spot sizes having full-width at half-maximum (FWHM) less than 1 mm. To further improve on the radiographic resolution, one must consider the major factors influencing the spot size: (1) Beam convergence at the final focus; (2) Beam emittance; (3) Beam canonical angular momentum; (4) Beam-motion blur; and (5) Beam-target interactions. Beam emittance growth and motion in the accelerators have been addressed by careful tuning. Defocusing by beam-target interactions has been minimized through tuning of the final focus solenoid for optimum convergence and other means. Finally, the beam canonical angular momentum is minimized by using a 'shielded source' of electrons. An ideal shielded source creates the beam in a region where the axial magnetic field is zero, thus the canonical momentum zero, since the beam is born with no mechanical angular momentum. It then follows from Busch's conservation theorem that the canonical angular momentum is minimized at the target, at least in principal. In the DARHT accelerators, the axial magnetic field at the cathode is minmized by using a 'bucking coil' solenoid with reverse polarity to cancel out whatever solenoidal beam transport field exists there. This is imperfect in practice, because of radial variation of the total field across the cathode surface, solenoid misalignments, and long-term variability of solenoid fields for given currents. Therefore, it is useful to quantify the relative importance of canonical momentum in determining the focal spot, and to establish a systematic methodology for tuning the bucking coils for minimum spot size. That is the purpose of this article. Section II provides a theoretical foundation for understanding the relative importance of the canonical momentum. Section III describes the results of simulations used to quantify beam parameters, including the momentum, for each of the accelerators. Section IV compares the two accelerators, especially with respect to mis-tuned bucking coils. Finally, Section IV concludes with a methodology for optimizing the bucking coil settings.« less

Tracking Efficiency And Charge Sharing of 3D Silicon Sensors at Different Angles in a 1.4T Magnetic Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gjersdal, H.; /Oslo U.; Bolle, E.

2012-05-07

A 3D silicon sensor fabricated at Stanford with electrodes penetrating throughout the entire silicon wafer and with active edges was tested in a 1.4 T magnetic field with a 180 GeV/c pion beam at the CERN SPS in May 2009. The device under test was bump-bonded to the ATLAS pixel FE-I3 readout electronics chip. Three readout electrodes were used to cover the 400 {micro}m long pixel side, this resulting in a p-n inter-electrode distance of {approx} 71 {micro}m. Its behavior was confronted with a planar sensor of the type presently installed in the ATLAS inner tracker. Time over threshold, chargemore » sharing and tracking efficiency data were collected at zero and 15{sup o} angles with and without magnetic field. The latest is the angular configuration expected for the modules of the Insertable B-Layer (IBL) currently under study for the LHC phase 1 upgrade expected in 2014.« less

Cryogenic Flow Sensor

NASA Technical Reports Server (NTRS)

Justak, John

2010-01-01

An acousto-optic cryogenic flow sensor (CFS) determines mass flow of cryogens for spacecraft propellant management. The CFS operates unobtrusively in a high-pressure, high-flowrate cryogenic environment to provide measurements for fluid quality as well as mass flow rate. Experimental hardware uses an optical plane-of-light (POL) to detect the onset of two-phase flow, and the presence of particles in the flow of water. Acousto-optic devices are used in laser equipment for electronic control of the intensity and position of the laser beam. Acousto-optic interaction occurs in all optical media when an acoustic wave and a laser beam are present. When an acoustic wave is launched into the optical medium, it generates a refractive index wave that behaves like a sinusoidal grating. An incident laser beam passing through this grating will diffract the laser beam into several orders. Its angular position is linearly proportional to the acoustic frequency, so that the higher the frequency, the larger the diffracted angle. If the acoustic wave is traveling in a moving fluid, the fluid velocity will affect the frequency of the traveling wave, relative to a stationary sensor. This frequency shift changes the angle of diffraction, hence, fluid velocity can be determined from the diffraction angle. The CFS acoustic Bragg grating data test indicates that it is capable of accurately determining flow from 0 to 10 meters per second. The same sensor can be used in flow velocities exceeding 100 m/s. The POL module has successfully determined the onset of two-phase flow, and can distinguish vapor bubbles from debris.

Optical spin-to-orbital angular momentum conversion in ultra-thin metasurfaces with arbitrary topological charges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bouchard, Frédéric; De Leon, Israel; Schulz, Sebastian A.

Orbital angular momentum associated with the helical phase-front of optical beams provides an unbounded “space” for both classical and quantum communications. Among the different approaches to generate and manipulate orbital angular momentum states of light, coupling between spin and orbital angular momentum allows a faster manipulation of orbital angular momentum states because it depends on manipulating the polarisation state of light, which is simpler and generally faster than manipulating conventional orbital angular momentum generators. In this work, we design and fabricate an ultra-thin spin-to-orbital angular momentum converter, based on plasmonic nano-antennas and operating in the visible wavelength range that ismore » capable of converting spin to an arbitrary value of orbital angular momentum ℓ. The nano-antennas are arranged in an array with a well-defined geometry in the transverse plane of the beam, possessing a specific integer or half-integer topological charge q. When a circularly polarised light beam traverses this metasurface, the output beam polarisation switches handedness and the orbital angular momentum changes in value by ℓ=±2qℏ per photon. We experimentally demonstrate ℓ values ranging from ±1 to ±25 with conversion efficiencies of 8.6% ± 0.4%. Our ultra-thin devices are integratable and thus suitable for applications in quantum communications, quantum computations, and nano-scale sensing.« less

Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaoze; Song, Wei; Tan, Weibing

2016-07-15

A high efficiency relativistic backward wave oscillator working at a low guiding magnetic field is designed and simulated. A trapezoidal resonant reflector is used to reduce the modulation field in the resonant reflector to avoid overmodulation of the electron beam which will lead to a large momentum spread and then low conversion efficiency. The envelope of the inner radius of the slow wave structure (SWS) increases stepwise to keep conformal to the trajectory of the electron beam which will alleviate the bombardment of the electron on the surface of the SWS. The length of period of the SWS is reducedmore » gradually to make a better match between phase velocity and electron beam, which decelerates continually and improves the RF current distribution. Meanwhile the modulation field is reduced by the introduction of nonuniform SWS also. The particle in cell simulation results reveal that a microwave with a power of 1.8 GW and a frequency of 14.7 GHz is generated with an efficiency of 47% when the diode voltage is 620 kV, the beam current 6.1 kA, and the guiding magnetic field 0.95 T.« less

The impact of positrons beam on the propagation of super freak waves in electron-positron-ion plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali Shan, S.; National Centre for Physics; Pakistan Institute of Engineering and Applied Sciences

2016-07-15

In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positronmore » beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.« less

Eigenmode multiplexing with SLM for volume holographic data storage

NASA Astrophysics Data System (ADS)

Chen, Guanghao; Miller, Bo E.; Takashima, Yuzuru

2017-08-01

The cavity supports the orthogonal reference beam families as its eigenmodes while enhancing the reference beam power. Such orthogonal eigenmodes are used as additional degree of freedom to multiplex data pages, consequently increase storage densities for volume Holographic Data Storage Systems (HDSS) when the maximum number of multiplexed data page is limited by geometrical factor. Image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at multiple Bragg angles by using Liquid Crystal on Silicon (LCOS) spatial light modulators (SLMs) in reference arms. Total of nine holograms are recorded with three angular and three eigenmode.

Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light.

PubMed

Quinteiro, G F; Tamborenea, P I; Berakdar, J

2011-12-19

We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics.

Suppression of the Transit -Time Instability in Large-Area Electron Beam Diodes

NASA Astrophysics Data System (ADS)

Myers, Matthew C.; Friedman, Moshe; Swanekamp, Stephen B.; Chan, Lop-Yung; Ludeking, Larry; Sethian, John D.

2002-12-01

Experiment, theory, and simulation have shown that large-area electron-beam diodes are susceptible to the transit-time instability. The instability modulates the electron beam spatially and temporally, producing a wide spread in electron energy and momentum distributions. The result is gross inefficiency in beam generation and propagation. Simulations indicate that a periodic, slotted cathode structure that is loaded with resistive elements may be used to eliminate the instability. Such a cathode has been fielded on one of the two opposing 60 cm × 200 cm diodes on the NIKE KrF laser at the Naval Research Laboratory. These diodes typically deliver 600 kV, 500 kA, 250 ns electron beams to the laser cell in an external magnetic field of 0.2 T. We conclude that the slotted cathode suppressed the transit-time instability such that the RF power was reduced by a factor of 9 and that electron transmission efficiency into the laser gas was improved by more than 50%.

Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways

NASA Astrophysics Data System (ADS)

Sang, Xiahan; Lupini, Andrew R.; Ding, Jilai; Kalinin, Sergei V.; Jesse, Stephen; Unocic, Raymond R.

2017-03-01

Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i.e. image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. “Archimedean” spirals, with a constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.

Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways.

PubMed

Sang, Xiahan; Lupini, Andrew R; Ding, Jilai; Kalinin, Sergei V; Jesse, Stephen; Unocic, Raymond R

2017-03-08

Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i.e. image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. "Archimedean" spirals, with a constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.

Optical vortex beam transmission with different OAM in scattering beads and brain tissue media

NASA Astrophysics Data System (ADS)

Wang, W. B.; Shi, Lingyan; Lindwasser, Lukas; Marque, Paulo; Lavery, M. P. J.; Alfano, R. R.

2016-03-01

Light transmission of Laguerre Gaussian (LG) vortex beams with different orbital angular momentum (OAM) values (L) in scattering beads and mouse brain tissue media were experimentally investigated for the first time in comparison with Gaussian (G) beams. The LG beams with different OAM were generated using a spatial light modulator (SLM) in reflection mode. The scattering beads media consist of various sizes and concentrations of latex beads in water solutions. The transmissions of LG and G beams through scattering beads and brain tissue media were measured with different ratios of sample thicknesses (z) to scattering mean free path (ls) of the turbid media, z/ls. The results indicate that within the ballistic region where z/ls is small, the LG and G beams show no significant difference, while in the diffusive region where z/ls is higher, the vortex beams show higher transmission than G beams. In the diffusive region, the LG beams with higher L values show higher transmission than the beams with lower L values due to the eigen channels in the media. The transition points from the ballistic to diffusive regions for different scattering beads and brain tissue media were studied.

Random wandering of laser beams with orbital angular momentum during propagation through atmospheric turbulence.

PubMed

Aksenov, Valerii P; Kolosov, Valeriy V; Pogutsa, Cheslav E

2014-06-10

The propagation of laser beams having orbital angular momenta (OAM) in the turbulent atmosphere is studied numerically. The variance of random wandering of these beams is investigated with the use of the Monte Carlo technique. It is found that, among various types of vortex laser beams, such as the Laguerre-Gaussian (LG) beam, modified Bessel-Gaussian beam, and hypergeometric Gaussian beam, having identical initial effective radii and OAM, the LG beam occupying the largest effective volume in space is the most stable one.

A Beat Frequency RF Modulator for Generation of Low Repetition Rate Electron Microbunches for the CEBAF Polarized Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

John Musson; Reza Kazimi; Benard Poelker

2007-06-25

Fiber-based drive lasers now produce all of the spin-polarized electron beams at CEBAF/Jefferson Lab. The flexibility of these drive lasers, combined with the existing three-beam CEBAF photoinjector Chopper, provides a means to implement a beat frequency technique to produce long time intervals between individual electron microbunches (tens of nanoseconds) by merely varying the nominal 499 MHz drive laser frequency by < 20%. This submission describes the RF Laser modulator that uses a divider and heterodyne scheme to maintain coherence with the accelerator Master Oscillator (MO), while providing delay resolution in increments of 2ns. Some possible uses for such a beammore » are discussed as well as intended future development.« less

High brightness diode lasers controlled by volume Bragg gratings

NASA Astrophysics Data System (ADS)

Glebov, Leonid

2017-02-01

Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass are holographic optical elements that are effective spectral and angular filters withstanding high power laser radiation. Reflecting VBGs are narrow-band spectral filters while transmitting VBGs are narrow-band angular filters. The use of these optical elements in external resonators of semiconductor lasers enables extremely resonant feedback that provides dramatic spectral and angular narrowing of laser diodes radiation without significant power and efficiency penalty. Spectral narrowing of laser diodes by reflecting VBGs demonstrated in wide spectral region from near UV to 3 μm. Commercially available VBGs have spectral width ranged from few nanometers to few tens of picometers. Efficient spectral locking was demonstrated for edge emitters (single diodes, bars, modules, and stacks), vertical cavity surface emitting lasers (VCSELs), grating coupled surface emitting lasers (GCSELs), and interband cascade lasers (ICLs). The use of multiplexed VBGs provides multiwavelength emission from a single emitter. Spectrally locked semiconductor lasers demonstrated CW power from milliwatts to a kilowatt. Angular narrowing by transmitting VBGs enables single transverse mode emission from wide aperture diode lasers having resonators with great Fresnel numbers. This feature provides close to diffraction limit divergence along a slow axis of wide stripe edge emitters. Radiation exchange between lasers by means of spatially profiled or multiplexed VBGs enables coherent combining of diode lasers. Sequence of VBGs or multiplexed VBGs enable spectral combining of spectrally narrowed diode lasers or laser modules. Thus the use of VBGs for diode lasers beam control provides dramatic increase of brightness.

Alignment of the Pixel and SCT Modules for the 2004 ATLAS Combined Test Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

ATLAS Collaboration; Ahmad, A.; Andreazza, A.

2008-06-02

A small set of final prototypes of the ATLAS Inner Detector silicon tracking system(Pixel Detector and SemiConductor Tracker), were used to take data during the 2004 Combined Test Beam. Data were collected from runs with beams of different flavour (electrons, pions, muons and photons) with a momentum range of 2 to 180 GeV/c. Four independent methods were used to align the silicon modules. The corrections obtained were validated using the known momenta of the beam particles and were shown to yield consistent results among the different alignment approaches. From the residual distributions, it is concluded that the precision attained inmore » the alignmentof the silicon modules is of the order of 5 mm in their most precise coordinate.« less

Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

DOE PAGES

Rusz, Jan; Idrobo, Juan -Carlos; Bhowmick, Somnath

2014-09-30

The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strongmore » as those obtained by nanodiffraction methods.« less

The cosmology large angular scale surveyor (CLASS): 40 GHz optical design

NASA Astrophysics Data System (ADS)

Eimer, Joseph R.; Bennett, Charles L.; Chuss, David T.; Marriage, Tobias; Wollack, Edward J.; Zeng, Lingzhen

2012-09-01

The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19° x 14° with a resolution for each beam on the sky of 1.5° FWHM.

The Cosmology Large Angular Scale Surveyor (CLASS): 40 GHz Optical Design

NASA Technical Reports Server (NTRS)

Eimer, Joseph R.; Bennett, Charles L.; Chuss, David T.; Marriage, Tobias; Wollack, Edward J.; Zeng, Lingzhen

2012-01-01

The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19 deg x 14 deg with a resolution for each beam on the sky of 1.5 deg. FWHM.

Computational study of radiation doses at UNLV accelerator facility

NASA Astrophysics Data System (ADS)

Hodges, Matthew; Barzilov, Alexander; Chen, Yi-Tung; Lowe, Daniel

2017-09-01

A Varian K15 electron linear accelerator (linac) has been considered for installation at University of Nevada, Las Vegas (UNLV). Before experiments can be performed, it is necessary to evaluate the photon and neutron spectra as generated by the linac, as well as the resulting dose rates within the accelerator facility. A computational study using MCNPX was performed to characterize the source terms for the bremsstrahlung converter. The 15 MeV electron beam available in the linac is above the photoneutron threshold energy for several materials in the linac assembly, and as a result, neutrons must be accounted for. The angular and energy distributions for bremsstrahlung flux generated by the interaction of the 15 MeV electron beam with the linac target were determined. This source term was used in conjunction with the K15 collimators to determine the dose rates within the facility.

Active Control of Acoustic Field-of-View in a Biosonar System

PubMed Central

Yovel, Yossi; Falk, Ben; Moss, Cynthia F.; Ulanovsky, Nachum

2011-01-01

Active-sensing systems abound in nature, but little is known about systematic strategies that are used by these systems to scan the environment. Here, we addressed this question by studying echolocating bats, animals that have the ability to point their biosonar beam to a confined region of space. We trained Egyptian fruit bats to land on a target, under conditions of varying levels of environmental complexity, and measured their echolocation and flight behavior. The bats modulated the intensity of their biosonar emissions, and the spatial region they sampled, in a task-dependant manner. We report here that Egyptian fruit bats selectively change the emission intensity and the angle between the beam axes of sequentially emitted clicks, according to the distance to the target, and depending on the level of environmental complexity. In so doing, they effectively adjusted the spatial sector sampled by a pair of clicks—the “field-of-view.” We suggest that the exact point within the beam that is directed towards an object (e.g., the beam's peak, maximal slope, etc.) is influenced by three competing task demands: detection, localization, and angular scanning—where the third factor is modulated by field-of-view. Our results suggest that lingual echolocation (based on tongue clicks) is in fact much more sophisticated than previously believed. They also reveal a new parameter under active control in animal sonar—the angle between consecutive beams. Our findings suggest that acoustic scanning of space by mammals is highly flexible and modulated much more selectively than previously recognized. PMID:21931535

A proposed measurement of optical orbital and spin angular momentum and its implications for photon angular momentum

NASA Astrophysics Data System (ADS)

Leader, Elliot

2018-04-01

The expression for the total angular momentum carried by a laser optical vortex beam, splits, in the paraxial approximation, into two terms which seem to represent orbital and spin angular momentum respectively. There are, however, two very different competing versions of the formula for the spin angular momentum, one based on the use of the Poynting vector, as in classical electrodynamics, the other related to the canonical expression for the angular momentum which occurs in Quantum Electrodynamics. I analyze the possibility that a sufficiently sensitive optical measurement could decide which of these corresponds to the actual physical angular momentum carried by the beam.

Study of nonlinear interaction between bunched beam and intermediate cavities in a relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Wu, Y.; Xu, Z.; Li, Z. H.; Tang, C. X.

2012-07-01

In intermediate cavities of a relativistic klystron amplifier (RKA) driven by intense relativistic electron beam, the equivalent circuit model, which is widely adopted to investigate the interaction between bunched beam and the intermediate cavity in a conventional klystron design, is invalid due to the high gap voltage and the nonlinear beam loading in a RKA. According to Maxwell equations and Lorentz equation, the self-consistent equations for beam-wave interaction in the intermediate cavity are introduced to study the nonlinear interaction between bunched beam and the intermediate cavity in a RKA. Based on the equations, the effects of modulation depth and modulation frequency of the beam on the gap voltage amplitude and its phase are obtained. It is shown that the gap voltage is significantly lower than that estimated by the equivalent circuit model when the beam modulation is high. And the bandwidth becomes wider as the beam modulation depth increases. An S-band high gain relativistic klystron amplifier is designed based on the result. And the corresponding experiment is carried out on the linear transformer driver accelerator. The peak output power has achieved 1.2 GW with an efficiency of 28.6% and a gain of 46 dB in the corresponding experiment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, Steven P.; Moseley, John; Norman, Andrew

We investigated the potential-induced degradation (PID) shunting mechanism in multicrystalline-silicon photovoltaic modules by using a multiscale, multitechnique characterization approach. Both field-stressed modules and laboratory-stressed mini modules were studied. We used photoluminescence, electroluminescence, and dark lock-in thermography imaging to identify degraded areas at the module scale. Small samples were then removed from degraded areas, laser marked, and imaged by scanning electron microscopy. We used simultaneous electron-beam induced current imaging and focused ion beam milling to mark around PID shunts for chemical analysis by time-of-flight secondary-ion mass spectrometry or to isolate individual shunt defects for transmission electron microscopy and atom-probe tomography analysis.more » By spanning a range of 10 orders of magnitude in size, this approach enabled us to investigate the root-cause mechanisms for PID shunting. We observed a direct correlation between recombination active shunts and sodium content. The sodium content in shunted areas peaks at the SiNX/Si interface and is consistently observed at a concentration of 0.1% to 2% in shunted areas. Analysis of samples subjected to PID recovery, either activated by electron beam or thermal effects only, reveals that recovery of isolated shunts correlates with diffusion of sodium out of the structural defects to the silicon surface. We observed the role of oxygen and chlorine in PID shunting and found that those species - although sometimes present in structural defects where PID shunting was observed - do not play a consistent role in PID shunting.« less

Pulsed depressed collector

DOEpatents

Kemp, Mark A

2015-11-03

A high power RF device has an electron beam cavity, a modulator, and a circuit for feed-forward energy recovery from a multi-stage depressed collector to the modulator. The electron beam cavity include a cathode, an anode, and the multi-stage depressed collector, and the modulator is configured to provide pulses to the cathode. Voltages of the electrode stages of the multi-stage depressed collector are allowed to float as determined by fixed impedances seen by the electrode stages. The energy recovery circuit includes a storage capacitor that dynamically biases potentials of the electrode stages of the multi-stage depressed collector and provides recovered energy from the electrode stages of the multi-stage depressed collector to the modulator. The circuit may also include a step-down transformer, where the electrode stages of the multi-stage depressed collector are electrically connected to separate taps on the step-down transformer.

GHz laser-free time-resolved transmission electron microscopy: A stroboscopic high-duty-cycle method

DOE PAGES

Qiu, Jiaqi; Zhu, Yimei; Ha, Gwanghui; ...

2015-11-10

In this study, a device and a method for producing ultrashort electron pulses with GHz repetition rates via pulsing an input direct current (dc) electron beam are provided. The device and the method are based on an electromagnetic-mechanical pulser (EMMP) that consists of a series of transverse deflecting cavities and magnetic quadrupoles. The EMMP modulates and chops the incoming dc electron beam and converts it into pico- and sub-pico-second electron pulse sequences (pulse trains) at >1 GHz repetition rates, as well as controllably manipulates the resulting pulses. Ultimately, it leads to negligible electron pulse phase-space degradation compared to the incomingmore » dc beam parameters. The temporal pulse length and repetition rate for the EMMP can be continuously tunable over wide ranges.« less

Acceleration of electron bunches by intense laser pulse in vacuum

NASA Astrophysics Data System (ADS)

Hua, J. F.; Ho, Y. K.; Lin, Y. Z.; Cao, N.

2003-08-01

This paper addresses the output characteristics of real electron bunches accelerated with ultra-intense laser pulse in vacuum by the capture & acceleration scenario (CAS) scheme (see, e.g., Phys. Rev. E66 (2002) 066501). Normally, the size of an electron bunch is much larger than that of a tightly focused and compressed laser pulse. We examine in detail the features of the intersection region, the distribution of electrons which can experience an intense laser field and be accelerated to high energy. Furthermore, the output properties of the accelerated CAS electrons, such as the energy spectra, the angular distributions, the energy-angle correlations, the acceleration gradient, the energy which can be reached with this scheme, the emittances of the outgoing electron bunches, and the dependence of the output properties on the incident electron beam qualities such as the emittance, focusing status, etc. were studied and explained. We found that with intense laser systems and electron beam technology currently available nowadays, the number of CAS electrons can reach 10 4-10 5, when the total number of incident electrons in the practical bunch reaches ˜10 8. These results demonstrate that CAS is promising to become a novel mechanism of vacuum laser accelerators.

Combining experiment and optical simulation in coherent X-ray nanobeam characterization of Si/SiGe semiconductor heterostructures

DOE PAGES

Tilka, J. A.; Park, J.; Ahn, Y.; ...

2016-07-06

Here, the highly coherent and tightly focused x-ray beams produced by hard x-ray light sources enable the nanoscale characterization of the structure of electronic materials but are accompanied by significant challenges in the interpretation of diffraction and scattering patterns. X-ray nanobeams exhibit optical coherence combined with a large angular divergence introduced by the x-ray focusing optics. The scattering of nanofocused x-ray beams from intricate semiconductor heterostructures produces a complex distribution of scattered intensity. We report here an extension of coherent xray optical simulations of convergent x-ray beam diffraction patterns to arbitrary x-ray incident angles to allow the nanobeam diffraction patternsmore » of complex heterostructures to be simulated faithfully. These methods are used to extract the misorientation of lattice planes and the strain of individual layers from synchrotron x-ray nanobeam diffraction patterns of Si/SiGe heterostructures relevant to applications in quantum electronic devices. The systematic interpretation of nanobeam diffraction patterns from semiconductor heterostructures presents a new opportunity in characterizing and ultimately designing electronic materials.« less

Atomic Clock Based on Opto-Electronic Oscillator

NASA Technical Reports Server (NTRS)

Maleki, Lute; Yu, Nan

2005-01-01

A proposed highly accurate clock or oscillator would be based on the concept of an opto-electronic oscillator (OEO) stabilized to an atomic transition. Opto-electronic oscillators, which have been described in a number of prior NASA Tech Briefs articles, generate signals at frequencies in the gigahertz range characterized by high spectral purity but not by longterm stability or accuracy. On the other hand, the signals generated by previously developed atomic clocks are characterized by long-term stability and accuracy but not by spectral purity. The proposed atomic clock would provide high spectral purity plus long-term stability and accuracy a combination of characteristics needed to realize advanced developments in communications and navigation. In addition, it should be possible to miniaturize the proposed atomic clock. When a laser beam is modulated by a microwave signal and applied to a photodetector, the electrical output of the photodetector includes a component at the microwave frequency. In atomic clocks of a type known as Raman clocks or coherent-population-trapping (CPT) clocks, microwave outputs are obtained from laser beams modulated, in each case, to create two sidebands that differ in frequency by the amount of a hyperfine transition in the ground state of atoms of an element in vapor form in a cell. The combination of these sidebands produces a transparency in the population of a higher electronic level that can be reached from either of the two ground-state hyperfine levels by absorption of a photon. The beam is transmitted through the vapor to a photodetector. The components of light scattered or transmitted by the atoms in the two hyperfine levels mix in the photodetector and thereby give rise to a signal at the hyperfine- transition frequency. The proposed atomic clock would include an OEO and a rubidium- or cesium- vapor cell operating in the CPT/Raman regime (see figure). In the OEO portion of this atomic clock, as in a typical prior OEO, a laser beam would pass through an electro-optical modulator, the modulated beam would be fed into a fiber-optic delay line, and the delayed beam would be fed to a photodetector. The electrical output of the photodetector would be detected, amplified, filtered, and fed back to the microwave input port of the modulator. The laser would be chosen to have the same wavelength as that of the pertinent ground-state/higher-state transition of the atoms in the vapor. The modulator/ filter combination would be designed to operate at the microwave frequency of the hyperfine transition. Part of the laser beam would be tapped from the fiberoptic loop of the OEO and introduced into the vapor cell. After passing through the cell, this portion of the beam would be detected differentially with a tapped portion of the fiber-optically-delayed beam. The electrical output of the photodetector would be amplified and filtered in a loop that would control a DC bias applied to the modulator. In this manner, the long-term stability and accuracy of the atomic transition would be transferred to the OEO.

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary.

PubMed

Azzam, R M A

2015-12-01

Conditions for achieving equal and opposite angular deflections of a light beam by reflection and refraction at an air-dielectric boundary are determined. Such angularly symmetric beam splitting (ASBS) is possible only if the angle of incidence is >60° by exactly one third of the angle of refraction. This simple law, plus Snell's law, leads to several analytical results that clarify all aspects of this phenomenon. In particular, it is shown that the intensities of the two symmetrically deflected beams can be equalized by proper choice of the prism refractive index and the azimuth of incident linearly polarized light. ASBS enables a geometrically attractive layout of optical systems that employ multiple prism beam splitters.

Generation of electron Airy beams.

PubMed

Voloch-Bloch, Noa; Lereah, Yossi; Lilach, Yigal; Gover, Avraham; Arie, Ady

2013-02-21

Within the framework of quantum mechanics, a unique particle wave packet exists in the form of the Airy function. Its counterintuitive properties are revealed as it propagates in time or space: the quantum probability wave packet preserves its shape despite dispersion or diffraction and propagates along a parabolic caustic trajectory, even though no force is applied. This does not contradict Newton's laws of motion, because the wave packet centroid propagates along a straight line. Nearly 30 years later, this wave packet, known as an accelerating Airy beam, was realized in the optical domain; later it was generalized to an orthogonal and complete family of beams that propagate along parabolic trajectories, as well as to beams that propagate along arbitrary convex trajectories. Here we report the experimental generation and observation of the Airy beams of free electrons. These electron Airy beams were generated by diffraction of electrons through a nanoscale hologram, which imprinted on the electrons' wavefunction a cubic phase modulation in the transverse plane. The highest-intensity lobes of the generated beams indeed followed parabolic trajectories. We directly observed a non-spreading electron wavefunction that self-heals, restoring its original shape after passing an obstacle. This holographic generation of electron Airy beams opens up new avenues for steering electronic wave packets like their photonic counterparts, because the wave packets can be imprinted with arbitrary shapes or trajectories.

Development and application of a water calorimeter for the absolute dosimetry of short-range particle beams.

PubMed

Renaud, J; Rossomme, S; Sarfehnia, A; Vynckier, S; Palmans, H; Kacperek, A; Seuntjens, J

2016-09-21

In this work, we describe a new design of water calorimeter built to measure absorbed dose in non-standard radiation fields with reference depths in the range of 6-20 mm, and its initial testing in clinical electron and proton beams. A functioning calorimeter prototype with a total water equivalent thickness of less than 30 mm was constructed in-house and used to obtain measurements in clinical accelerator-based 6 MeV and 8 MeV electron beams and cyclotron-based 60 MeV monoenergetic and modulated proton beams. Corrections for the conductive heat transfer due to dose gradients and non-water materials was also accounted for using a commercial finite element method software package. Absorbed dose to water was measured with an associated type A standard uncertainty of approximately 0.4% and 0.2% for the electron and proton beam experiments, respectively. In terms of thermal stability, drifts were on the order of a couple of hundred µK min -1 , with a short-term variation of 5-10 µK. Heat transfer correction factors ranged between 1.021 and 1.049. The overall combined standard uncertainty on the absorbed dose to water was estimated to be 0.6% for the 6 MeV and 8 MeV electron beams, as well as for the 60 MeV monoenergetic protons, and 0.7% for the modulated 60 MeV proton beam. This study establishes the feasibility of developing an absorbed dose transfer standard for short-range clinical electrons and protons and forms the basis for a transportable dose standard for direct calibration of ionization chambers in the user's beam. The largest contributions to the combined standard uncertainty were the positioning (⩽0.5%) and the correction due to conductive heat transfer (⩽0.4%). This is the first time that water calorimetry has been used in such a low energy proton beam.

Development and application of a water calorimeter for the absolute dosimetry of short-range particle beams

NASA Astrophysics Data System (ADS)

Renaud, J.; Rossomme, S.; Sarfehnia, A.; Vynckier, S.; Palmans, H.; Kacperek, A.; Seuntjens, J.

2016-09-01

In this work, we describe a new design of water calorimeter built to measure absorbed dose in non-standard radiation fields with reference depths in the range of 6-20 mm, and its initial testing in clinical electron and proton beams. A functioning calorimeter prototype with a total water equivalent thickness of less than 30 mm was constructed in-house and used to obtain measurements in clinical accelerator-based 6 MeV and 8 MeV electron beams and cyclotron-based 60 MeV monoenergetic and modulated proton beams. Corrections for the conductive heat transfer due to dose gradients and non-water materials was also accounted for using a commercial finite element method software package. Absorbed dose to water was measured with an associated type A standard uncertainty of approximately 0.4% and 0.2% for the electron and proton beam experiments, respectively. In terms of thermal stability, drifts were on the order of a couple of hundred µK min-1, with a short-term variation of 5-10 µK. Heat transfer correction factors ranged between 1.021 and 1.049. The overall combined standard uncertainty on the absorbed dose to water was estimated to be 0.6% for the 6 MeV and 8 MeV electron beams, as well as for the 60 MeV monoenergetic protons, and 0.7% for the modulated 60 MeV proton beam. This study establishes the feasibility of developing an absorbed dose transfer standard for short-range clinical electrons and protons and forms the basis for a transportable dose standard for direct calibration of ionization chambers in the user’s beam. The largest contributions to the combined standard uncertainty were the positioning (⩽0.5%) and the correction due to conductive heat transfer (⩽0.4%). This is the first time that water calorimetry has been used in such a low energy proton beam.

Evolution from Rydberg gas to ultracold plasma in a supersonic atomic beam of Xe

NASA Astrophysics Data System (ADS)

Hung, J.; Sadeghi, H.; Schulz-Weiling, M.; Grant, E. R.

2014-08-01

A Rydberg gas of xenon, entrained in a supersonic atomic beam, evolves slowly to form an ultracold plasma. In the early stages of this evolution, when the free-electron density is low, Rydberg atoms undergo long-range \\ell -mixing collisions, yielding states of high orbital angular momentum. The development of high-\\ell states promotes dipole-dipole interactions that help to drive Penning ionization. The electron density increases until it reaches the threshold for avalanche. Ninety μs after the production of a Rydberg gas with the initial state, {{n}_{0}}{{\\ell }_{0}}=42d, a 432 V cm-1 electrostatic pulse fails to separate charge in the excited volume, an effect which is ascribed to screening by free electrons. Photoexcitation cross sections, observed rates of \\ell -mixing, and a coupled-rate-equation model simulating the onset of the electron-impact avalanche point consistently to an initial Rydberg gas density of 5\\times {{10}^{8}}\\;c{{m}^{-3}}.

Ionization Injection of Electrons into a Plasma Wakefield Accelerator at FACET

NASA Astrophysics Data System (ADS)

Clayton, Chris; E-200 At Facet Collaboration

2013-10-01

In the PWFA experiments at FACET, a low ionization-potential (IP) metal vapor gas (Li) is confined within a heat-pipe oven by a higher IP buffer gas (typically He). The Li is easily field-ionized by the FACET beam. A non-linear wake is formed in the blowout regime when the 20.3 GeV bunch containing 2e10 electrons in a σz ~ 30 μm is focused to a (vacuum) σr < 25 near the ~ 10cm-long boundary region. There the Li density rises from zero up to the oven's 30cm-long flat-topped density of 2.5e17 cm-3. To obtain a mono-energetic beam from accelerated ionization-injected electrons at the far end of the oven--the goal of this experiment--it is necessary for the FACET beam to have a betatron pinch just where the flat-topped region begins; i.e., where the wake wavelength is no longer changing. If the buffer gas contains a mixture of He and a moderate IP gas, the ``impurity'' gases will also be field ionized and potentially contribute more charge to the injected bunch than with He alone. Moderate IP gases were added to the He buffer gas: 10%, 20%, and 50% Ar (balance He) and 30% Ne (balance He) have been used. Evidence for ionization injection and acceleration appears through the observation of distinct features, characterized by their very narrow size and thus angular spread, at the image plane of a magnetic imaging spectrometer. Analysis aimed at characterizing these features with respect to energy, charge, and angular spread is underway and will be presented. This work was supported by the DOE and the NSF.

Evaluation of beam tracking strategies for the THOR-CSW solar wind instrument

NASA Astrophysics Data System (ADS)

De Keyser, Johan; Lavraud, Benoit; Prech, Lubomir; Neefs, Eddy; Berkenbosch, Sophie; Beeckman, Bram; Maggiolo, Romain; Fedorov, Andrei; Baruah, Rituparna; Wong, King-Wah; Amoros, Carine; Mathon, Romain; Génot, Vincent

2017-04-01

We compare different beam tracking strategies for the Cold Solar Wind (CSW) plasma spectrometer on the ESA M4 THOR mission candidate. The goal is to intelligently select the energy and angular windows the instrument is sampling and to adapt these windows as the solar wind properties evolve, with the aim to maximize the velocity distribution acquisition rate while maintaining excellent energy and angular resolution. Using synthetic data constructed using high-cadence measurements by the Faraday cup instrument on the Spektr-R mission (30 ms resolution), we test the performance of energy beam tracking with or without angular beam tracking. The algorithm can be fed both by data acquired by the plasma spectrometer during the previous measurement cycle, or by data from another instrument, in casu the Faraday Cup (FAR) instrument foreseen on THOR. We verify how these beam tracking algorithms behave for different sizes of the energy and angular windows, and for different data integration times, in order to assess the limitations of the algorithm and to avoid situations in which the algorithm loses track of the beam.

Projecting light beams with 3D waveguide arrays

NASA Astrophysics Data System (ADS)

Crespi, Andrea; Bragheri, Francesca

2017-01-01

Free-space light beams with complex intensity patterns, or non-trivial phase structure, are demanded in diverse fields, ranging from classical and quantum optical communications, to manipulation and imaging of microparticles and cells. Static or dynamic spatial light modulators, acting on the phase or intensity of an incoming light wave, are the conventional choices to produce beams with such non-trivial characteristics. However, interfacing these devices with optical fibers or integrated optical circuits often requires difficult alignment or cumbersome optical setups. Here we explore theoretically and with numerical simulations the potentialities of directly using the output of engineered three-dimensional waveguide arrays, illuminated with linearly polarized light, to project light beams with peculiar structures. We investigate through a collection of illustrative configurations the far field distribution, showing the possibility to achieve orbital angular momentum, or to produce elaborate intensity or phase patterns with several singularity points. We also simulate the propagation of the projected beam, showing the possibility to concentrate light. We note that these devices should be at reach of current technology, thus perspectives are open for the generation of complex free-space optical beams from integrated waveguide circuits.

Propagation characteristics of partially coherent anomalous elliptical hollow Gaussian beam propagating through atmospheric turbulence along a slant path

NASA Astrophysics Data System (ADS)

Tian, Huanhuan; Xu, Yonggen; Yang, Ting; Ma, Zairu; Wang, Shijian; Dan, Youquan

2017-02-01

Based on the extended Huygens-Fresnel principal and the Wigner distribution function, the root mean square (rms) angular width and propagation factor (M2-factor) of partially coherent anomalous elliptical hollow Gaussian (PCAEHG) beam propagating through atmospheric turbulence along a slant path are studied in detail. Analytical formulae of the rms angular width and M2-factor of PCAEHG beam are derived. Our results show that the rms angular width increases with increasing of wavelength and zenith angle and with decreasing of transverse coherence length, beam waist sizes and inner scale. The M2-factor increases with increasing of zenith angle and with decreasing of wavelength, transverse coherence length, beam waist sizes and inner scale. The saturation propagation distances (SPDs) increase as zenith angle increases. The numerical calculations also indicate that the SPDs of rms angular width and M2-factor for uplink slant paths with zenith angle of π/12 are about 0.2 and 20 km, respectively.

A study of angular spectrum and limited diffraction beams for calculation of field of array transducers

NASA Astrophysics Data System (ADS)

Cheng, Jiqi; Lu, Jian-Yu

2002-05-01

Angular spectrum is one of the most powerful tools for field calculation. It is based on linear system theory and the Fourier transform and is used for the calculation of propagating sound fields at different distances. In this report, the generalization and interpretation of the angular spectrum and its intrinsic relationship with limited diffraction beams are studied. With an angular spectrum, the field at the surface of a transducer is decomposed into limited diffractions beams. For an array transducer, a linear relationship between the quantized fields at the surface of elements of the array and the propagating field at any point in space can be established. For an annular array, the field is decomposed into limited diffraction Bessel beams [P. D. Fox and S. Holm, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 49, 85-93 (2002)], while for a two-dimensional (2-D) array the field is decomposed into limited diffraction array beams [J-y. Lu and J. Cheng, J. Acoust. Soc. Am. 109, 2397-2398 (2001)]. The angular spectrum reveals the intrinsic link between these decompositions. [Work supported in part by Grant 5RO1 HL60301 from NIH.

Interaction of doughnut-shaped laser pulses with glasses

DOE PAGES

Zhukov, Vladimir P.; Rubenchik, Alexander M.; Fedoruk, Mikhail P.; ...

2017-01-26

Non-Gaussian laser beams can open new opportunities for microfabrication, including ultrashort laser direct writing. By using a model based on Maxwell’s equations, we investigate the dynamics of doughnut-shaped laser beams focused inside fused silica glass, in comparison with Gaussian pulses of the same energy. The laser propagation dynamics reveals intriguing features of beam splitting and sudden collapse toward the beam axis, overcoming the intensity clamping effect. The resulting structure of light absorption represents a very hot, hollow nanocylinder, which can lead to an implosion process that brings matter to extreme thermodynamic states. Furthermore, by monitoring the simulations of the lasermore » beam scattering we see a considerable difference in both the blueshift and the angular distribution of scattered light for different laser energies, suggesting that investigations of the spectra of scattered radiation can be used as a diagnostic of laser-produced electron plasmas in transparent materials.« less

Imaging electron flow from collimating contacts in graphene

NASA Astrophysics Data System (ADS)

Bhandari, S.; Lee, G. H.; Watanabe, K.; Taniguchi, T.; Kim, P.; Westervelt, R. M.

2018-04-01

The ballistic motion of electrons in graphene opens exciting opportunities for electron-optic devices based on collimated electron beams. We form a collimating contact in a hBN-encapsulated graphene hall bar by adding zigzag contacts on either side of an electron emitter that absorb stray electrons; collimation can be turned off by floating the zig-zag contacts. The electron beam is imaged using a liquid-He cooled scanning gate microscope (SGM). The tip deflects electrons as they pass from the collimating contact to a receiving contact on the opposite side of the channel, and an image of electron flow can be made by displaying the change in transmission as the tip is raster scanned across the sample. The angular half width Δθ of the electron beam is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. The images reveal that the electron flow from the collimating contact drops quickly at B  =  0.05 T when the electron orbits miss the receiving contact. The flow for the non-collimating case persists longer, up to B  =  0.19 T, due to the broader range of entry angles. Ray-tracing simulations agree well with the experimental images. By fitting the fields B at which the magnitude of electron flow drops in the experimental SGM images, we find Δθ  =  9° for electron flow from the collimating contact, compared with Δθ  =  54° for the non-collimating case.

Analysis of Shot Noise Suppression for Electron Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ratner, Daniel; /Stanford U., Appl. Phys. Dept.; Huang, Zhirong

2012-05-07

Shot noise can affect the performance of free-electron lasers (FELs) by driving instabilities (e.g., the microbunching instability) or by competing with seeded density modulations. Recent papers have proposed suppressing shot noise to enhance FEL performance. In this paper we use a one-dimensional (1D) model to calculate the noise amplification from an energy modulation (e.g., electron interactions from space charge or undulator radiation) followed by a dispersive section. We show that, for a broad class of interactions, selecting the correct dispersive strength suppresses shot noise across a wide range of frequencies. The final noise level depends on the beam's energy spreadmore » and the properties of the interaction potential. We confirm and illustrate our analytical results with 1D simulations.« less

Characterization of submillisecond response optical addressing phase modulator based on low light scattering polymer network liquid crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiangjie, Zhao, E-mail: zxjdouble@163.com, E-mail: zxjdouble@gmail.com; Cangli, Liu; Jiazhu, Duan

Optically addressed conventional nematic liquid crystal spatial light modulator has attracted wide research interests. But the slow response speed limited its further application. In this paper, polymer network liquid crystal (PNLC) was proposed to replace the conventional nematic liquid crystal to enhance the response time to the order of submillisecond. The maximum light scattering of the employed PNLC was suppressed to be less than 2% at 1.064 μm by optimizing polymerization conditions and selecting large viscosity liquid crystal as solvent. The occurrence of phase ripple phenomenon due to electron diffusion and drift in photoconductor was found to deteriorate the phase modulationmore » effect of the optical addressed PNLC phase modulator. The wavelength effect and AC voltage frequency effect on the on state dynamic response of phase change was investigated by experimental methods. These effects were interpreted by electron diffusion and drift theory based on the assumption that free electron was inhomogeneously distributed in accordance with the writing beam intensity distribution along the incident direction. The experimental results indicated that the phase ripple could be suppressed by optimizing the wavelength of the writing beam and the driving AC voltage frequency when varying the writing beam intensity to generate phase change in 2π range. The modulation transfer function was also measured.« less

Coherent control of plasma dynamics

NASA Astrophysics Data System (ADS)

He, Zhaohan

2014-10-01

The concept of coherent control - precise measurement or determination of a process through control of the phase of an applied oscillating field - has been applied to numerous systems with great success. Here, we demonstrate the use of coherent control on plasma dynamics in a laser wakefield electron acceleration experiment. A tightly focused femtosecond laser pulse (10 mJ, 35 fs) was used to generate electron beams by plasma wakefield acceleration in the density down ramp. The technique is based on optimization of the electron beam using a deformable mirror adaptive optical system with an iterative evolutionary genetic algorithm. The image of the electrons on a scintillator screen was processed and used in a fitness function as direct feedback for the optimization algorithm. This coherent manipulation of the laser wavefront leads to orders of magnitude improvement to the electron beam properties such as the peak charge and beam divergence. The laser beam optimized to generate the best electron beam was not the one with the ``best'' focal spot. When a particular wavefront of laser light interacts with plasma, it can affect the plasma wave structures and trapping conditions of the electrons in a complex way. For example, Raman forward scattering, envelope self-modulation, relativistic self-focusing, and relativistic self-phase modulation and many other nonlinear interactions modify both the pulse envelope and phase as the pulse propagates, in a way that cannot be easily predicted and that subsequently dictates the formation of plasma waves. The optimal wavefront could be successfully determined via the heuristic search under laser-plasma conditions that were not known a priori. Control and shaping of the electron energy distribution was found to be less effective, but was still possible. Particle-in-cell simulations were performed to show that the mode structure of the laser beam can affect the plasma wave structure and trapping conditions of electrons, which subsequently produces electron beams with a different divergence. The proof-of-principle demonstration of coherent control for plasmas opens new possibilities for future laser-based accelerators and their applications. This study should also enable a significantly improved understanding of the complex dynamics of laser plasma interactions. This work was supported by DARPA under Contract No. N66001-11-1-4208, the NSF under Contract No. 0935197 and MCubed at the University of Michigan.

Measurement of Two-Plasmon-Decay Dependence on Plasma Density Scale Length

NASA Astrophysics Data System (ADS)

Haberberger, D.

2013-10-01

An accurate understanding of the plasma scale-length (Lq) conditions near quarter-critical density is important in quantifying the hot electrons generated by the two-plasmon-decay (TPD) instability in long-scale-length plasmas. A novel target platform was developed to vary the density scale length and an innovative diagnostic was implemented to measure the density profiles above 1021 cm-3 where TPD is expected to have the largest growth. A series of experiments was performed using the four UV (351-nm) beams on OMEGA EP that varied the Lq by changing the radius of curvature of the target while maintaining a constant Iq/Tq. The fraction of laser energy converted to hot electrons (fhot) was observed to increase rapidly from 0.005% to 1% by increasing the plasma scale length from 130 μm to 300 μm, corresponding to target diameters of 0.4 mm to 8 mm. A new diagnostic was developed based on refractometry using angular spectral filters to overcome the large phase accumulation in standard interferometric techniques. The angular filter refractometer measures the refraction angles of a 10-ps, 263-nm probe laser after propagating through the plasma. An angular spectral filter is used in the Fourier plane of the probe beam, where the refractive angles of the rays are mapped to space. The edges of the filter are present in the image plane and represent contours of constant refraction angle. These contours are used to infer the phase of the probe beam, which are used to calculate the plasma density profile. In long-scale-length plasmas, the diagnostic currently measures plasma densities from ~1019 cm-3 to ~2 × 1021 cm-3. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. In collaboration with D. H. Edgell, S. X. Hu, S. Ivancic, R. Boni, C. Dorrer, and D. H. Froula (Laboratory for Laser Energetics, U. of Rochester).

Collective field accelerator

DOEpatents

Luce, John S.

1978-01-01

A collective field accelerator which operates with a vacuum diode and utilizes a grooved cathode and a dielectric anode that operates with a relativistic electron beam with a .nu./.gamma. of .about. 1, and a plurality of dielectric lenses having an axial magnetic field thereabout to focus the collectively accelerated electrons and ions which are ejected from the anode. The anode and lenses operate as unoptimized r-f cavities which modulate and focus the beam.

Network of Porosity Formed in Ultrafine-Grained Copper Produced by Equal Channel Angular Pressing

NASA Astrophysics Data System (ADS)

Ribbe, Jens; Baither, Dietmar; Schmitz, Guido; Divinski, Sergiy V.

2009-04-01

Radiotracer experiments on diffusion of Ni63 and Rb86 in severely deformed commercially pure copper (8 passes of equal channel angular pressing) reveal unambiguously the existence of ultrafast transport paths. A fraction of these paths remains in the material even after complete recrystallization. Scanning electron microscopy and focused ion beam techniques are applied. Deep grooves are found which are related to original high-energy interfaces. In-depth sectioning near corresponding triple junctions reveals clearly multiple microvoids or microcracks caused by the severe deformation. Long-range tracer penetration over tens of micrometers proves that these submicrometer-large defects are connected by highly diffusive paths and that they appear with significant frequency.

Geometrical optics of beams with vortices: Berry phase and orbital angular momentum Hall effect.

PubMed

Bliokh, Konstantin Yu

2006-07-28

We consider propagation of a paraxial beam carrying the spin angular momentum (polarization) and intrinsic orbital angular momentum (IOAM) in a smoothly inhomogeneous isotropic medium. It is shown that the presence of IOAM can dramatically enhance and rearrange the topological phenomena that previously were considered solely in connection to the polarization of transverse waves. In particular, the appearance of a new type of Berry phase that describes the parallel transport of the beam structure along a curved ray is predicted. We derive the ray equations demonstrating the splitting of beams with different values of IOAM. This is the orbital angular momentum Hall effect, which resembles the Magnus effect for optical vortices. Unlike the spin Hall effect of photons, it can be much larger in magnitude and is inherent to waves of any nature. Experimental means to detect the phenomena are discussed.

The stonehenge technique: a new method of crystal alignment for coherent bremsstrahlung experiments

NASA Astrophysics Data System (ADS)

Livingston, Kenneth

2005-08-01

In the coherent bremsstrahlung technique a thin diamond crystal oriented correctly in an electron beam can produce photons with a high degree of linear polarization.1 The crystal is mounted on a goniometer to control its orientation and it is necessary to measure the angular offsets a) between the crystal axes and the goniometer axes and b) between the goniometer and the electron beam axis. A method for measuring these offsets and aligning the crystal was developed by Lohman et al, and has been used successfully in Mainz.2 However, recent attempts to investigate new crystals have shown that this approach has limitations which become more serious at higher beam energies where more accurate setting of the crystal angles, which scale with l/Ebeam, is required. (Eg. the recent installation of coherent bremsstrahlung facility at Jlab, with Ebeam = 6 GeV ) This paper describes a new, more general alignment technique, which overcomes these limitations. The technique is based on scans where the horizontal and vertical rotation axes of the goniometer are adjusted in a series of steps to make the normal to the crystal describe a cone of a given angle. For each step in the scan, the photon energy spectrum is measured using a tagging spectrometer, and the offsets between the electron beam and the crystal lattice are inferred from the resulting 2D plot. Using this method, it is possible to align the crystal with the beam quickly, and hence to set any desired orientation of the crystal relative to the beam. This is essential for any experiment requiring linearly polarized photons produced via coherent bremsstrahlung, and is also required for a systematic study of the channeling radiation produced by the electron beam incident on the crystal.

Superwide-angle coverage code-multiplexed optical scanner.

PubMed

Riza, Nabeel A; Arain, Muzammil A

2004-05-01

A superwide-angle coverage code-multiplexed optical scanner is presented that has the potential to provide 4 pi-sr coverage. As a proof-of-concept experiment, an angular scan range of 288 degrees for six randomly distributed beams is demonstrated. The proposed scanner achieves its superwide coverage by exploiting a combination of phase-encoded transmission and reflection holography within an in-line hologram recording-retrieval geometry. The basic scanner unit consists of one phase-only digital mode spatial light modulator for code entry (i.e., beam scan control) and a holographic material from which we obtained what we believe is the first-of-a-kind extremely wide coverage, low component count, high speed (e.g., microsecond domain), and large aperture (e.g., > 1-cm diameter) scanner.

Electronic quenching of O({sup 1}D) by Xe: Oscillations in the product angular distribution and their dependence on collision energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garofalo, Lauren A.; Smith, Mica C.; Dagdigian, Paul J., E-mail: pjdagdigian@jhu.edu

2015-08-07

The dynamics of the O({sup 1}D) + Xe electronic quenching reaction was investigated in a crossed beam experiment at four collision energies. Marked large-scale oscillations in the differential cross sections were observed for the inelastic scattering products, O({sup 3}P) and Xe. The shape and relative phases of the oscillatory structure depend strongly on collision energy. Comparison of the experimental results with time-independent scattering calculations shows qualitatively that this behavior is caused by Stueckelberg interferences, for which the quantum phases of the multiple reaction pathways accessible during electronic quenching constructively and destructively interfere.

Choosing a therapy electron accelerator target.

PubMed

Hutcheon, R M; Schriber, S O; Funk, L W; Sherman, N K

1979-01-01

Angular distributions of photon depth dose produced by 25-MeV electrons incident on several fully stopping single-element targets (C, Al, Cu, Mo, Ta, Pb) and two composite layered targets (Ni-Al, W-Al) were studied. Depth-dose curves measured using TLD-700 (thermoluminescent dosimeter) chips embedded in lucite phantoms. Several useful therapy electron accelerator design curves were determined, including relative flattener thickness as a function of target atomic number, "effective" bremsstrahlung endpoint energy or beam "hardness" as a function of target atomic number and photon emission angle, and estimates of shielding thickness as a function of angle required to reduce the radiation outside the treatment cone to required levels.

An Electro-Optic Spatial Light Modulator for Thermoelastic Generation of Programmably Focused Ultrasound.

DTIC Science & Technology

1984-12-01

The concept proposed is an electro - optic technique that would make it possible to spatially modulate a high power pulsed laser beam to thermoelastically induce focused ultrasound in a test material. Being a purely electro - optic device, the modulator, and therefore the depth at which the acoustic focus occurs, can be programmed electronically at electronic speeds. If successful, it would become possible to scan ultrasound continuously in three dimensions within the component or structure under test. (Author)

An electro-optic spatial light modulator for thermoelastic generation of programmably focused ultrasound

NASA Astrophysics Data System (ADS)

1984-12-01

The concept proposed is an electro-optic technique that would make it possible to spatially modulate a high power pulsed laser beam to thermoelastically induce focused ultrasound in a test material. Being a purely electro-optic device, the modulator, and therefore the depth at which the acoustic focus occurs, can be programmed electronically at electronic speeds. If successful, it would become possible to scan ultrasound continuously in three dimensions within the component or structure under test.

Simulations of electron transport and ignition for direct-drive fast-ignition targets

NASA Astrophysics Data System (ADS)

Solodov, A. A.; Anderson, K. S.; Betti, R.; Gotcheva, V.; Myatt, J.; Delettrez, J. A.; Skupsky, S.; Theobald, W.; Stoeckl, C.

2008-11-01

The performance of high-gain, fast-ignition fusion targets is investigated using one-dimensional hydrodynamic simulations of implosion and two-dimensional (2D) hybrid fluid-particle simulations of hot-electron transport, ignition, and burn. The 2D/3D hybrid-particle-in-cell code LSP [D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)] and the 2D fluid code DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)] are integrated to simulate the hot-electron transport and heating for direct-drive fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. The self-generated resistive magnetic field is found to collimate the hot-electron beam, increase the coupling efficiency of hot electrons with the target, and reduce the minimum energy required for ignition. Resistive filamentation of the hot-electron beam is also observed. The minimum energy required for ignition is found for hot electrons with realistic angular spread and Maxwellian energy-distribution function.

Imaging method based on attenuation, refraction and ultra-small-angle-scattering of x-rays

DOEpatents

Wernick, Miles N.; Chapman, Leroy Dean; Oltulu, Oral; Zhong, Zhong

2005-09-20

A method for detecting an image of an object by measuring the intensity at a plurality of positions of a transmitted beam of x-ray radiation emitted from the object as a function of angle within the transmitted beam. The intensity measurements of the transmitted beam are obtained by a crystal analyzer positioned at a plurality of angular positions. The plurality of intensity measurements are used to determine the angular intensity spectrum of the transmitted beam. One or more parameters, such as an attenuation property, a refraction property and a scatter property, can be obtained from the angular intensity spectrum and used to display an image of the object.

Characterization of the Exradin W1 scintillator for use in radiotherapy.

PubMed

Carrasco, P; Jornet, N; Jordi, O; Lizondo, M; Latorre-Musoll, A; Eudaldo, T; Ruiz, A; Ribas, M

2015-01-01

To evaluate the main characteristics of the Exradin W1 scintillator as a dosimeter and to estimate measurement uncertainties when used in radiotherapy. We studied the calibration procedure, energy and modality dependence, short-term repeatability, dose-response linearity, angular dependence, temperature dependence, time to reach thermal equilibrium, dose-rate dependence, water-equivalent depth of the effective measurement point, and long-term stability. An uncertainty budget was derived for relative and absolute dose measurements in photon and electron beams. Exradin W1 showed a temperature dependence of -0.225% °C(-1). The loss of sensitivity with accumulated dose decreased with use. The sensitivity of Exradin W1 was energy independent for high-energy photon and electron beams. All remaining dependencies of Exradin W1 were around or below 0.5%, leading to an uncertainty budget of about 1%. When a dual channel electrometer with automatic trigger was not used, timing effects became significant, increasing uncertainties by one order of magnitude. The Exradin W1 response is energy independent for high energy x-rays and electron beams, and only one calibration coefficient is needed. A temperature correction factor should be applied to keep uncertainties around 2% for absolute dose measurements and around 1% for relative measurements in high-energy photon and electron beams. The Exradin W1 scintillator is an excellent alternative to detectors such as diodes for relative dose measurements.

Sub-micron resolution selected area electron channeling patterns.

PubMed

Guyon, J; Mansour, H; Gey, N; Crimp, M A; Chalal, S; Maloufi, N

2015-02-01

Collection of selected area channeling patterns (SACPs) on a high resolution FEG-SEM is essential to carry out quantitative electron channeling contrast imaging (ECCI) studies, as it facilitates accurate determination of the crystal plane normal with respect to the incident beam direction and thus allows control the electron channeling conditions. Unfortunately commercial SACP modes developed in the past were limited in spatial resolution and are often no longer offered. In this contribution we present a novel approach for collecting high resolution SACPs (HR-SACPs) developed on a Gemini column. This HR-SACP technique combines the first demonstrated sub-micron spatial resolution with high angular accuracy of about 0.1°, at a convenient working distance of 10mm. This innovative approach integrates the use of aperture alignment coils to rock the beam with a digitally calibrated beam shift procedure to ensure the rocking beam is maintained on a point of interest. Moreover a new methodology to accurately measure SACP spatial resolution is proposed. While column considerations limit the rocking angle to 4°, this range is adequate to index the HR-SACP in conjunction with the pattern simulated from the approximate orientation deduced by EBSD. This new technique facilitates Accurate ECCI (A-ECCI) studies from very fine grained and/or highly strained materials. It offers also new insights for developing HR-SACP modes on new generation high-resolution electron columns. Copyright © 2014 Elsevier B.V. All rights reserved.

Results of 2007 test beam of AMS-02 Electromagnetic Calorimeter

NASA Astrophysics Data System (ADS)

di Falco, Stefano

2010-01-01

The AMS-02 experiment will be delivered by the Space Shuttle Discovery to the ISS in summer 2010. The main goals of the experiment are search for antimatter and dark matter, high precision measurement of charged cosmic ray spectra and fluxes and study of gamma rays, in the GeV to TeV energy range. In AMS-02 the Electromagnetic Calorimeter (ECAL) is required to measure e+,e- and gamma energy and to discriminate electromagnetic showers from hadronic cascades. ECAL is based on a lead/scintillating fiber sandwich, providing a 3D imaging reconstruction of the showers. The electronics equipping the detector has low power consumption, low noise, large dynamic range readout and full double redundancy. The calorimeter successfully got through several space qualification tests concerning the mechanical and thermal stability, the electromagnetic compatibility and radiation hardness. The ECAL Flight Model was calibrated during Summer 2007 in a test beam at CERN, using 6-250 GeV electron and proton beams: angular and energy resolutions, obtained from these data, are reported.

Progress of plasma wakefield self-modulation experiments at FACET

NASA Astrophysics Data System (ADS)

Adli, E.; Berglyd Olsen, V. K.; Lindstrøm, C. A.; Muggli, P.; Reimann, O.; Vieira, J. M.; Amorim, L. D.; Clarke, C. I.; Gessner, S. J.; Green, S. Z.; Hogan, M. J.; Litos, M. D.; O`Shea, B. D.; Yakimenko, V.; Clayton, C.; Marsh, K. A.; Mori, W. B.; Joshi, C.; Vafaei-Najafabadi, N.; Williams, O.

2016-09-01

Simulations and theory predict that long electron and positron beams may under favorable conditions self-modulate in plasmas. We report on the progress of experiments studying the self-modulation instability in plasma wakefield experiments at FACET. The experimental results obtained so far, while not being fully conclusive, appear to be consistent with the presence of the self-modulation instability.

Shapes of rotating superfluid helium nanodroplets

DOE PAGES

Bernando, Charles; Tanyag, Rico Mayro P.; Jones, Curtis; ...

2017-02-16

Rotating superfluid He droplets of approximately 1 μm in diameter were obtained in a free nozzle beam expansion of liquid He in vacuum and were studied by single-shot coherent diffractive imaging using an x-ray free electron laser. The formation of strongly deformed droplets is evidenced by large anisotropies and intensity anomalies (streaks) in the obtained diffraction images. The analysis of the images shows that in addition to previously described axially symmetric oblate shapes, some droplets exhibit prolate shapes. Forward modeling of the diffraction images indicates that the shapes of rotating superfluid droplets are very similar to their classical counterparts, givingmore » direct access to the droplet angular momenta and angular velocities. Here, the analyses of the radial intensity distribution and appearance statistics of the anisotropic images confirm the existence of oblate metastable superfluid droplets with large angular momenta beyond the classical bifurcation threshold.« less

Electrostatic twisted modes in multi-component dusty plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ayub, M. K.; National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000; Pohang University of Sciences and Technology, Pohang, Gyeongbuk 790-784

Various electrostatic twisted modes are re-investigated with finite orbital angular momentum in an unmagnetized collisionless multi-component dusty plasma, consisting of positive/negative charged dust particles, ions, and electrons. For this purpose, hydrodynamical equations are employed to obtain paraxial equations in terms of density perturbations, while assuming the Gaussian and Laguerre-Gaussian (LG) beam solutions. Specifically, approximated solutions for potential problem are studied by using the paraxial approximation and expressed the electric field components in terms of LG functions. The energy fluxes associated with these modes are computed and corresponding expressions for orbital angular momenta are derived. Numerical analyses reveal that radial/angular modemore » numbers as well as dust number density and dust charging states strongly modify the LG potential profiles attributed to different electrostatic modes. Our results are important for understanding particle transport and energy transfer due to wave excitations in multi-component dusty plasmas.« less

Shapes of rotating superfluid helium nanodroplets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernando, Charles; Tanyag, Rico Mayro P.; Jones, Curtis

Rotating superfluid He droplets of approximately 1 μm in diameter were obtained in a free nozzle beam expansion of liquid He in vacuum and were studied by single-shot coherent diffractive imaging using an x-ray free electron laser. The formation of strongly deformed droplets is evidenced by large anisotropies and intensity anomalies (streaks) in the obtained diffraction images. The analysis of the images shows that in addition to previously described axially symmetric oblate shapes, some droplets exhibit prolate shapes. Forward modeling of the diffraction images indicates that the shapes of rotating superfluid droplets are very similar to their classical counterparts, givingmore » direct access to the droplet angular momenta and angular velocities. Here, the analyses of the radial intensity distribution and appearance statistics of the anisotropic images confirm the existence of oblate metastable superfluid droplets with large angular momenta beyond the classical bifurcation threshold.« less

Laser radiation wavefront conjugation in fiber optic lightguides

NASA Astrophysics Data System (ADS)

Chertkov, A. A.

1986-02-01

Wavefront conjugation precision during stimulated brillouin scattering is investigated in a monofiber with spatially homogeneous and inhomogeneous beams at lambda = 106 micrometer. A Q-modulated YAG:Nd sup 3+ laser with initial transmission of 25% was employed as the radiation source. The energy of the incident and reflected radiation was measured by means of F-28 photoelements outputting their signals to an S8-12 oscilloscope. The behavior of the coefficient of reflection from the stimulated Brillouin scattering mirror as a function of the amount by which the pumping energy exceeded the threshold was found to be the same for all types of fibers, and to be independent of astigmatism and angular beam divergence. The wavefront conjugation quality as a function of the energy level was also the same for all of the lightguides employed: quartz, silicate and silicate-quartz. The good wavefront conjugation observed for astigmatic and spatially inhomogeneous beams make it possible to compensate satisfactorily for inhomogeneities in the distorting wavefront of the beam.

The atom-molecule reaction D plus H2 yields HD plus H studied by molecular beams

NASA Technical Reports Server (NTRS)

Geddes, J.; Krause, H. F.; Fite, W. L.

1972-01-01

Collisions between deuterium atoms and hydrogen molecules were studied in a modulated crossed beam experiment. The relative signal intensity and the signal phase for the product HD from reactive collisions permitted determination of both the angular distribution and HD mean velocity as a function of angle. From these a relative differential reactive scattering cross section in center-of-mass coordinates was deduced. The experiment indicates that reactively formed HD which has little or no internal excitation departs from the collision anisotropically, with maximum amplitude 180 deg from the direction of the incident D beam in center-of-mass coordinates, which shows that the D-H-H reacting configuration is short-lived compared to its rotation time. Non reactive scattering of D by H2 was used to assign absolute values to the differential reactive scattering cross sections.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Speckle suppression using a liquid-crystal cell

NASA Astrophysics Data System (ADS)

Andreev, A. L.; Kompanets, I. N.; Minchenko, M. V.; Pozhidaev, E. P.; Andreeva, T. B.

2008-12-01

A simple method for suppressing speckles in images produced by laser projectors is proposed. The coherence of the laser beam and, therefore, speckles can be destroyed when the beam passes through an electrooptical cell in which a special ferroelectric liquid crystal is used as a modulating medium. The effect is achieved due to the spatially inhomogeneous phase modulation of light when specially shaped bipolar electric pulses are applied to the cell.

Reactive Collisions in Crossed Molecular Beams

DOE R&D Accomplishments Database

Herschbach, D. R.

1962-02-01

The distribution of velocity vectors of reaction products is discussed with emphasis on the restrictions imposed by the conservation laws. The recoil velocity that carries the products away from the center of mass shows how the energy of reaction is divided between internal excitation and translation. Similarly, the angular distributions, as viewed from the center of mass, reflect the partitioning of the total angular momentum between angular momenta of individual molecules and orbital angular momentum associated with their relative motion. Crossed-beam studies of several reactions of the type M + RI yields R + MI are described, where M = K, Rb, Cs, and R = CH{sub 3}, C{sub 3}H{sub 5}, etc. The results show that most of the energy of reaction goes into internal excitation of the products and that the angular distribution is quite anisotropic, with most of the MI recoiling backward (and R forward) with respect to the incoming K beam. (auth)

Grating angle magnification enhanced angular sensor and scanner

NASA Technical Reports Server (NTRS)

Sun, Ke-Xun (Inventor); Byer, Robert L. (Inventor)

2009-01-01

An angular magnification effect of diffraction is exploited to provide improved sensing and scanning. This effect is most pronounced for a normal or near-normal incidence angle in combination with a grazing diffraction angle, so such configurations are preferred. Angular sensitivity can be further enhanced because the width of the diffracted beam can be substantially less than the width of the incident beam. Normal incidence configurations with two symmetric diffracted beams are preferred, since rotation and vertical displacement can be readily distinguished. Increased sensitivity to vertical displacement can be provided by incorporating an interferometer into the measurement system. Quad cell detectors can be employed to provide sensitivity to rotation about the grating surface normal. A 2-D grating can be employed to provide sensitivity to angular displacements in two different planes (e.g., pitch and yaw). Combined systems can provide sensitivity to vertical displacement and to all three angular degrees of freedom.

Radially dependent angular acceleration of twisted light.

PubMed

Webster, Jason; Rosales-Guzmán, Carmelo; Forbes, Andrew

2017-02-15

While photons travel in a straight line at constant velocity in free space, the intensity profile of structured light may be tailored for acceleration in any degree of freedom. Here we propose a simple approach to control the angular acceleration of light. Using Laguerre-Gaussian modes as our twisted beams carrying orbital angular momentum, we show that superpositions of opposite handedness result in a radially dependent angular acceleration as they pass through a focus (waist plane). Due to conservation of orbital angular momentum, we find that propagation dynamics are complex despite the free-space medium: the outer part of the beam (rings) rotates in an opposite direction to the inner part (petals), and while the outer part accelerates, the inner part decelerates. We outline the concepts theoretically and confirm them experimentally. Such exotic structured light beams are topical due to their many applications, for instance in optical trapping and tweezing, metrology, and fundamental studies in optics.

Quantum coherent optical phase modulation in an ultrafast transmission electron microscope.

PubMed

Feist, Armin; Echternkamp, Katharina E; Schauss, Jakob; Yalunin, Sergey V; Schäfer, Sascha; Ropers, Claus

2015-05-14

Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven 'quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.

Quantum coherent optical phase modulation in an ultrafast transmission electron microscope

NASA Astrophysics Data System (ADS)

Feist, Armin; Echternkamp, Katharina E.; Schauss, Jakob; Yalunin, Sergey V.; Schäfer, Sascha; Ropers, Claus

2015-05-01

Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven `quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.

Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sang, Xiahan; Lupini, Andrew R.; Ding, Jilai

Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i.e. image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. “Archimedean” spirals, with amore » constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.« less

Precision controlled atomic resolution scanning transmission electron microscopy using spiral scan pathways

DOE PAGES

Sang, Xiahan; Lupini, Andrew R.; Ding, Jilai; ...

2017-03-08

Atomic-resolution imaging in an aberration-corrected scanning transmission electron microscope (STEM) can enable direct correlation between atomic structure and materials functionality. The fast and precise control of the STEM probe is, however, challenging because the true beam location deviates from the assigned location depending on the properties of the deflectors. To reduce these deviations, i.e. image distortions, we use spiral scanning paths, allowing precise control of a sub-Å sized electron probe within an aberration-corrected STEM. Although spiral scanning avoids the sudden changes in the beam location (fly-back distortion) present in conventional raster scans, it is not distortion-free. “Archimedean” spirals, with amore » constant angular frequency within each scan, are used to determine the characteristic response at different frequencies. We then show that such characteristic functions can be used to correct image distortions present in more complicated constant linear velocity spirals, where the frequency varies within each scan. Through the combined application of constant linear velocity scanning and beam path corrections, spiral scan images are shown to exhibit less scan distortion than conventional raster scan images. The methodology presented here will be useful for in situ STEM imaging at higher temporal resolution and for imaging beam sensitive materials.« less

Superficial dosimetry imaging based on Čerenkov emission for external beam radiotherapy with megavoltage x-ray beam

PubMed Central

Zhang, Rongxiao; Glaser, Adam K.; Gladstone, David J.; Fox, Colleen J.; Pogue, Brian W.

2013-01-01

Purpose: Čerenkov radiation emission occurs in all tissue, when charged particles (either primary or secondary) travel at velocity above the threshold for the Čerenkov effect (about 220 KeV in tissue for electrons). This study presents the first examination of optical Čerenkov emission as a surrogate for the absorbed superficial dose for MV x-ray beams. Methods: In this study, Monte Carlo simulations of flat and curved surfaces were studied to analyze the energy spectra of charged particles produced in different regions near the surfaces when irradiated by MV x-ray beams. Čerenkov emission intensity and radiation dose were directly simulated in voxelized flat and cylindrical phantoms. The sampling region of superficial dosimetry based on Čerenkov radiation was simulated in layered skin models. Angular distributions of optical emission from the surfaces were investigated. Tissue mimicking phantoms with flat and curved surfaces were imaged with a time domain gating system. The beam field sizes (50 × 50–200 × 200 mm2), incident angles (0°–70°) and imaging regions were all varied. Results: The entrance or exit region of the tissue has nearly homogeneous energy spectra across the beam, such that their Čerenkov emission is proportional to dose. Directly simulated local intensity of Čerenkov and radiation dose in voxelized flat and cylindrical phantoms further validate that this signal is proportional to radiation dose with absolute average discrepancy within 2%, and the largest within 5% typically at the beam edges. The effective sampling depth could be tuned from near 0 up to 6 mm by spectral filtering. The angular profiles near the theoretical Lambertian emission distribution for a perfect diffusive medium, suggesting that angular correction of Čerenkov images may not be required even for curved surface. The acquisition speed and signal to noise ratio of the time domain gating system were investigated for different acquisition procedures, and the results show there is good potential for real-time superficial dose monitoring. Dose imaging under normal ambient room lighting was validated, using gated detection and a breast phantom. Conclusions: This study indicates that Čerenkov emission imaging might provide a valuable way to superficial dosimetry imaging in real time for external beam radiotherapy with megavoltage x-ray beams. PMID:24089916

Tests with beam setup of the TileCal phase-II upgrade electronics

NASA Astrophysics Data System (ADS)

Reward Hlaluku, Dingane

2017-09-01

The LHC has planned a series of upgrades culminating in the High Luminosity LHC which will have an average luminosity 5-7 times larger than the nominal Run-2 value. The ATLAS Tile calorimeter plans to introduce a new readout architecture by completely replacing the back-end and front-end electronics for the High Luminosity LHC. The photomultiplier signals will be fully digitized and transferred for every bunch crossing to the off-detector Tile PreProcessor. The Tile PreProcessor will further provide preprocessed digital data to the first level of trigger with improved spatial granularity and energy resolution in contrast to the current analog trigger signals. A single super-drawer module commissioned with the phase-II upgrade electronics is to be inserted into the real detector to evaluate and qualify the new readout and trigger concepts in the overall ATLAS data acquisition system. This new super-drawer, so-called hybrid Demonstrator, must provide analog trigger signals for backward compatibility with the current system. This Demonstrator drawer has been inserted into a Tile calorimeter module prototype to evaluate the performance in the lab. In parallel, one more module has been instrumented with two other front-end electronics options based on custom ASICs (QIE and FATALIC) which are under evaluation. These two modules together with three other modules composed of the current system electronics were exposed to different particles and energies in three test-beam campaigns during 2015 and 2016.

Angular aberration in the problem of power beaming to geostationary satellites through the atmosphere.

PubMed

Baryshnikov, F F

1995-10-20

The influence of angular aberration of radiation as a result of the difference in speed of a geostationary satellite and the speed of the Earth's surface on laser power beaming to satellites is considered. Angular aberration makes it impossible to direct the energy to the satellite, and additional beam rotation is necessary. Because the Earth's rotation may cause bad phase restoration, we face a serious problem: how to transfer incoherent radiation to remote satellites. In the framework of the Kolmogorov turbulence model simple conditions of energy transfer are derived and discussed.

Fundamental Parameters Line Profile Fitting in Laboratory Diffractometers

PubMed Central

Cheary, R. W.; Coelho, A. A.; Cline, J. P.

2004-01-01

The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes. Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers. The refined parameters are determined by the diffractometer configuration. In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample. In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits. The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters. Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function. One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer. Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile. PMID:27366594

A bolometric millimeter-wave system for observations of anisotropy in the cosmic microwave background radiation on medium angular scales

NASA Technical Reports Server (NTRS)

Fischer, M. L.; Alsop, D. C.; Cheng, E. S.; Clapp, A. C.; Cottingham, D. A.; Gundersen, J. O.; Koch, T. C.; Kreysa, E.; Meinhold, P. R.; Lange, A. E.

1992-01-01

We report the performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0 deg 3 min to 3 deg. The system represents a collaborative effort combining a low-background 1 m diameter balloon-borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four-channel bolometric receiver with passbands centered near frequencies of 3 (90), 6 (180), 9 (270), and 12 (360) cm(exp -1) (GHz). The telescope was flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of Delta(T)/T(sub CMB) is approximately equal to 10(exp -5) with detectors operated at T = 0.3 K.

A new multidimensional diagnostic method for measuring the properties of intense ion beams

NASA Astrophysics Data System (ADS)

Yasuike, Kazuhito; Miyamoto, Shuji; Nakai, Sadao

1996-02-01

A new arrayed pinhole camera (APC) diagnostic method for intense ion beams has been developed. The APC diagnostic technique permits the acquisition of the angular divergences and the ion fluxes of high intensity ion beams, in one shot, with a spatial resolution on the source of better than 1 mm and an effective angular divergence resolution of better than 10 mrad. A prototype time integrated APC has been designed and evaluated. The demonstration experiments have been performed on a Reiden-IV, 1 MV and 1 Ω pulsed power machine [1 T W (tera-watt or trillion watts)]. Proton beams of 0.7 MeV, with a pulse duration of ˜50 ns and an ion current density of about 100 A/cm2, were generated in an applied-Br type ion diode source using paraffin-filled grooves. These experimental results show that the APC can measure nonuniformities in the ion beam intensity generated from the ion source and the dependence of beam angular divergence on ion beam intensity.

SEE Observations of Ionospheric Heating from HAARP Using Orbital Angular Momentum

NASA Astrophysics Data System (ADS)

Briczinski, S. J.; Bernhardt, P. A.; Siefring, C. L.

2013-12-01

High power HF radio waves exciting the ionosphere provide aeronomers with a unique space-based laboratory capability. The High-Frequency Active Auroral Research Program (HAARP) in Gakona, Alaksa is the world's largest heating facility, providing effective radiated powers in the gigawatt range. Experiments performed at HAARP have allowed researchers to study many non-linear effects of wave-plasma interactions. Stimulated Electromagnetic Emission (SEE) is of interest to the ionospheric community for its diagnostic purposes. Typical SEE experiments at HAARP have focused on characterizing the parametric decay of the electromagnetic pump wave into several different wave modes such as upper and lower hybrid, ion acoustic, ion-Bernstein and electron-Bernstein. These production modes have been extensively studied at HAARP using traditional beam heating patterns and SEE detection. New results are present from HAARP experiments using an excitation mode that attempts to impart orbital angular momentum (OAM) into the heating region. This OAM mode is also referred to as a 'twisted beam.' Previous analysis of twisted beam heating shows that the SEE results obtained are nearly identical to the modes without OAM. Recent twisted beam heating experiments have produced SEE modes not previously characterized. These new modes are presented and discussed. One difference in the twisted beam mode is the heating region produced is in the shape of a ring as opposed to the more traditional 'solid spot' region. The ring heating pattern may be more conducive to the creation of artificial ionization clouds. The results of these runs include artificial ionization creation and evolution as pertaining to the twisted beam pattern.

Grain Refinement of Freeform Fabricated Ti-6Al-4V Alloy Using Beam/Arc Modulation

NASA Technical Reports Server (NTRS)

Mitzner, Scott; Liu, Stephen; Domack, Marcia S.; Hafley, Robert A.

2012-01-01

Grain refinement can significantly improve the mechanical properties of freeform-fabricated Ti-6Al-4V alloy, promoting increased strength and enhanced isotropy compared with coarser grained material. Large beta-grains can lead to a segregated microstructure, in regard to both alpha-phase morphology and alpha-lath orientation. Beam modulation, which has been used in conventional fusion welding to promote grain refinement, is explored in this study for use in additive manufacturing processes including electron beam freeform fabrication (EBF(sup 3)) and gas-tungsten arc (GTA) deposition to alter solidification behavior and produce a refined microstructure. The dynamic molten pool size induced by beam modulation causes rapid heat flow variance and results in a more competitive grain growth environment, reducing grain size. Consequently, improved isotropy and strength can be achieved with relatively small adjustments to deposition parameters.

Low-Absorption Liquid Crystals for Infrared Beam Steering

DTIC Science & Technology

2015-09-30

liquid crystals for infrared laser beam steering applications. To suppress the optical loss in MW1R and LW1R, we have investigated following...dielectric anisotropy, and low optical loss nematic liquid crystals for infrared laser beam steering applications. To suppress the optical loss in MWIR and...modulators. 1. Objective The main objective of this program is to develop low-loss liquid crystals for electronic laser beam steering in the infrared

Planck 2013 results. VII. HFI time response and beams

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bowyer, J. W.; Bridges, M.; Bucher, M.; Burigana, C.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Haissinski, J.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hou, Z.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leonardi, R.; Leroy, C.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matsumura, T.; Matthai, F.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polegre, A. M.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rusholme, B.; Sandri, M.; Santos, D.; Sauvé, A.; Savini, G.; Scott, D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

This paper characterizes the effective beams, the effective beam window functions and the associated errors for the Planck High Frequency Instrument (HFI) detectors. The effective beam is theangular response including the effect of the optics, detectors, data processing and the scan strategy. The window function is the representation of this beam in the harmonic domain which is required to recover an unbiased measurement of the cosmic microwave background angular power spectrum. The HFI is a scanning instrument and its effective beams are the convolution of: a) the optical response of the telescope and feeds; b) the processing of the time-ordered data and deconvolution of the bolometric and electronic transfer function; and c) the merging of several surveys to produce maps. The time response transfer functions are measured using observations of Jupiter and Saturn and by minimizing survey difference residuals. The scanning beam is the post-deconvolution angular response of the instrument, and is characterized with observations of Mars. The main beam solid angles are determined to better than 0.5% at each HFI frequency band. Observations of Jupiter and Saturn limit near sidelobes (within 5°) to about 0.1% of the total solid angle. Time response residuals remain as long tails in the scanning beams, but contribute less than 0.1% of the total solid angle. The bias and uncertainty in the beam products are estimated using ensembles of simulated planet observations that include the impact of instrumental noise and known systematic effects. The correlation structure of these ensembles is well-described by five error eigenmodes that are sub-dominant to sample variance and instrumental noise in the harmonic domain. A suite of consistency tests provide confidence that the error model represents a sufficient description of the data. The total error in the effective beam window functions is below 1% at 100 GHz up to multipole ℓ ~ 1500, and below 0.5% at 143 and 217 GHz up to ℓ ~ 2000.

Examination of the properties of IMRT and VMAT beams and evaluation against pre-treatment quality assurance results

NASA Astrophysics Data System (ADS)

Crowe, S. B.; Kairn, T.; Middlebrook, N.; Sutherland, B.; Hill, B.; Kenny, J.; Langton, C. M.; Trapp, J. V.

2015-03-01

This study aimed to provide a detailed evaluation and comparison of a range of modulated beam evaluation metrics, in terms of their correlation with QA testing results and their variation between treatment sites, for a large number of treatments. Ten metrics including the modulation index (MI), fluence map complexity, modulation complexity score (MCS), mean aperture displacement (MAD) and small aperture score (SAS) were evaluated for 546 beams from 122 intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment plans targeting the anus, rectum, endometrium, brain, head and neck and prostate. The calculated sets of metrics were evaluated in terms of their relationships to each other and their correlation with the results of electronic portal imaging based quality assurance (QA) evaluations of the treatment beams. Evaluation of the MI, MAD and SAS suggested that beams used in treatments of the anus, rectum, head and neck were more complex than the prostate and brain treatment beams. Seven of the ten beam complexity metrics were found to be strongly correlated with the results from QA testing of the IMRT beams (p < 0.00008). For example, values of SAS (with multileaf collimator apertures narrower than 10 mm defined as ‘small’) less than 0.2 also identified QA passing IMRT beams with 100% specificity. However, few of the metrics are correlated with the results from QA testing of the VMAT beams, whether they were evaluated as whole 360° arcs or as 60° sub-arcs. Select evaluation of beam complexity metrics (at least MI, MCS and SAS) is therefore recommended, as an intermediate step in the IMRT QA chain. Such evaluation may also be useful as a means of periodically reviewing VMAT planning or optimiser performance.

Some computer graphical user interfaces in radiation therapy.

PubMed

Chow, James C L

2016-03-28

In this review, five graphical user interfaces (GUIs) used in radiation therapy practices and researches are introduced. They are: (1) the treatment time calculator, superficial X-ray treatment time calculator (SUPCALC) used in the superficial X-ray radiation therapy; (2) the monitor unit calculator, electron monitor unit calculator (EMUC) used in the electron radiation therapy; (3) the multileaf collimator machine file creator, sliding window intensity modulated radiotherapy (SWIMRT) used in generating fluence map for research and quality assurance in intensity modulated radiation therapy; (4) the treatment planning system, DOSCTP used in the calculation of 3D dose distribution using Monte Carlo simulation; and (5) the monitor unit calculator, photon beam monitor unit calculator (PMUC) used in photon beam radiation therapy. One common issue of these GUIs is that all user-friendly interfaces are linked to complex formulas and algorithms based on various theories, which do not have to be understood and noted by the user. In that case, user only needs to input the required information with help from graphical elements in order to produce desired results. SUPCALC is a superficial radiation treatment time calculator using the GUI technique to provide a convenient way for radiation therapist to calculate the treatment time, and keep a record for the skin cancer patient. EMUC is an electron monitor unit calculator for electron radiation therapy. Instead of doing hand calculation according to pre-determined dosimetric tables, clinical user needs only to input the required drawing of electron field in computer graphical file format, prescription dose, and beam parameters to EMUC to calculate the required monitor unit for the electron beam treatment. EMUC is based on a semi-experimental theory of sector-integration algorithm. SWIMRT is a multileaf collimator machine file creator to generate a fluence map produced by a medical linear accelerator. This machine file controls the multileaf collimator to deliver intensity modulated beams for a specific fluence map used in quality assurance or research. DOSCTP is a treatment planning system using the computed tomography images. Radiation beams (photon or electron) with different energies and field sizes produced by a linear accelerator can be placed in different positions to irradiate the tumour in the patient. DOSCTP is linked to a Monte Carlo simulation engine using the EGSnrc-based code, so that 3D dose distribution can be determined accurately for radiation therapy. Moreover, DOSCTP can be used for treatment planning of patient or small animal. PMUC is a GUI for calculation of the monitor unit based on the prescription dose of patient in photon beam radiation therapy. The calculation is based on dose corrections in changes of photon beam energy, treatment depth, field size, jaw position, beam axis, treatment distance and beam modifiers. All GUIs mentioned in this review were written either by the Microsoft Visual Basic.net or a MATLAB GUI development tool called GUIDE. In addition, all GUIs were verified and tested using measurements to ensure their accuracies were up to clinical acceptable levels for implementations.

High-power laser diodes with high polarization purity

NASA Astrophysics Data System (ADS)

Rosenkrantz, Etai; Yanson, Dan; Peleg, Ophir; Blonder, Moshe; Rappaport, Noam; Klumel, Genady

2017-02-01

Fiber-coupled laser diode modules employ power scaling of single emitters for fiber laser pumping. To this end, techniques such as geometrical, spectral and polarization beam combining (PBC) are used. For PBC, linear polarization with high degree of purity is important, as any non-perfectly polarized light leads to losses and heating. Furthermore, PBC is typically performed in a collimated portion of the beams, which also cancels the angular dependence of the PBC element, e.g., beam-splitter. However, we discovered that single emitters have variable degrees of polarization, which depends both on the operating current and far-field divergence. We present data to show angle-resolved polarization measurements that correlate with the ignition of high-order modes in the slow-axis emission of the emitter. We demonstrate that the ultimate laser brightness includes not only the standard parameters such as power, emitting area and beam divergence, but also the degree of polarization (DoP), which is a strong function of the latter. Improved slow-axis divergence, therefore, contributes not only to high brightness but also high beam combining efficiency through polarization.

Compensation for the orbital angular momentum of a vortex beam in turbulent atmosphere by adaptive optics

NASA Astrophysics Data System (ADS)

Li, Nan; Chu, Xiuxiang; Zhang, Pengfei; Feng, Xiaoxing; Fan, ChengYu; Qiao, Chunhong

2018-01-01

A method which can be used to compensate for a distorted orbital angular momentum and wavefront of a beam in atmospheric turbulence, simultaneously, has been proposed. To confirm the validity of the method, an experimental setup for up-link propagation of a vortex beam in a turbulent atmosphere has been simulated. Simulation results show that both of the distorted orbital angular momentum and the distorted wavefront of a beam due to turbulence can be compensated by an adaptive optics system with the help of a cooperative beacon at satellite. However, when the number of the lenslet of wavefront sensor (WFS) and the actuators of the deform mirror (DM) is small, satisfactory results cannot be obtained.

High efficiency tapered free-electron lasers with a prebunched electron beam

DOE PAGES

Emma, C.; Sudar, N.; Musumeci, P.; ...

2017-11-17

In this study we analyze the high gain, high efficiency tapered free-electron laser amplifier with a prebunched electron beam. Simple scaling laws are derived for the peak output power and extraction efficiency and verified using 1D simulations. These studies provide useful analytical expressions which highlight the benefits resulting from fine control of the initial conditions of the system, namely the initial electron beam bunching and input seed radiation. When time-dependent effects are included, the sideband instability is known to limit the radiation amplification due to particle detrapping. We discuss two different approaches to mitigate the sideband growth via 1-D timemore » dependent simulations. We find that a more aggressive taper enabled by strong prebunching and a modulation of the resonance condition are both effective methods for suppressing the sideband instability growth rate.« less

Angular dependence of the nanoDot OSL dosimeter.

PubMed

Kerns, James R; Kry, Stephen F; Sahoo, Narayan; Followill, David S; Ibbott, Geoffrey S

2011-07-01

Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.

Angular dependence of the nanoDot OSL dosimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan

Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight/OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system. Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, asmore » well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX. Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found. Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions.« less

Angular dependence of the nanoDot OSL dosimeter

PubMed Central

Kerns, James R.; Kry, Stephen F.; Sahoo, Narayan; Followill, David S.; Ibbott, Geoffrey S.

2011-01-01

Purpose: Optically stimulated luminescent detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The most abundant commercial OSLD is the InLight∕OSL system from Landauer, Inc. The purpose of this study was to examine the angular dependence of the nanoDot dosimeter, which is part of the InLight system.Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as a clinical proton beam. These measurements were done within a phantom at a depth beyond the build-up region. To verify the observed angular dependence, additional measurements were conducted as well as Monte Carlo simulations in MCNPX.Results: When irradiated with the incident photon beams parallel to the plane of the dosimeter, the nanoDot response was 4% lower at 6 MV and 3% lower at 18 MV than the response when irradiated with the incident beam normal to the plane of the dosimeter. Monte Carlo simulations at 6 MV showed similar results to the experimental values. Examination of the results in Monte Carlo suggests the cause as partial volume irradiation. In a clinical proton beam, no angular dependence was found.Conclusions: A nontrivial angular response of this OSLD was observed in photon beams. This factor may need to be accounted for when evaluating doses from photon beams incident from a variety of directions. PMID:21858992

A Laser Stabilization System for Rydberg Atom Physics

DTIC Science & Technology

2015-09-06

offset locking method which we did. For each system, a small amount of light from a 852 nm (780 nm) diode laser is picked off from the output beam ...this way, tunable sidebands, from 1-10 GHz, that are themselves modulated at .05-5 MHz, can be generated on the input laser beam . The light from the...phase modulation signal. This signal is fed back into the fast (10 MHz bandwidth) locking electronics of the diode laser system to lock the laser to

Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

National Institute of Standards and Technology Data Gateway

SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface

NASA Astrophysics Data System (ADS)

Jałochowski, M.; Kwapiński, T.; Łukasik, P.; Nita, P.; Kopciuszyński, M.

2016-07-01

Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed.

An X-band phase-locked relativistic backward wave oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Y.; Science and Technology on High Power Microwave Laboratory, Mianyang 621900; Li, Z. H.

2015-08-15

For the purpose of coherent high power microwave combining at high frequency band, an X-band phase-locked relativistic backward wave oscillator is presented and investigated. The phase-locking of the oscillator is accomplished by modulation of the electron beam before it reaches the oscillator. To produce a bunched beam with an acceptable injected RF power requirement, an overmoded input cavity is employed to provide initial density modulation. And a buncher cavity is introduced to further increase the modulation depth. When the beam enters the oscillator, the modulation depth is enough to lock the frequency and phase of the output microwave generated bymore » the oscillator. Particle-in-cell simulation shows that an input power of 90 kW is sufficient to lock the frequency and phase of 1.5 GW output microwave with locking bandwidth of 60 MHz.« less

Bunch modulation in LWFA blowout regime

NASA Astrophysics Data System (ADS)

Vyskočil, Jiří; Klimo, Ondřej; Vieira, Jorge; Korn, Georg

2015-05-01

Laser wakefield acceleration (LWFA) is able to produce high quality electron bunches interesting for many applications ranging from coherent light sources to high energy physics. The blow-out regime of LWFA provides excellent accelerating structure able to maintain small transverse emittance and energy spread of the accelerating electron beam if combined with localised injection. A modulation of the back of a self-injected electron bunch in the blowout regime of Laser Wakefield Acceleration appears 3D Particle-in-Cell simulations with the code OSIRIS. The shape of the modulation is connected to the polarization of the driving laser pulse, although the wavelength of the modulation is longer than that of the pulse. Nevertheless a circularly polarized laser pulse leads to a corkscrew-like modulation, while in the case of linear polarization, the modulation lies in the polarization plane.

(Surface engineering by high energy beams)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McHargue, C.J.

1989-10-23

A paper entitled Structure-Mechanical Property relationships in Ion-Implanted Ceramics'' was presented at the 2nd International Seminar on Surface Engineering by High Energy Beams in Lisbon, Portugal. This seminar was sponsored by the International Federation of Heat Treatment and Surface Engineering and included discussions on surface modifications using laser, electron, and ion beams. The visit to the University of Lisbon and LNETI-Sacavem included discussions regarding collaborative research in which Professor J.C. Soares and Dr. M.F. da Silva would conduct perturbed angular correlation (PAC) studies on ion-implanted samples supplied by the traveler. The collaboration between researchers at ORNL and the University Claudemore » Bernard-Lyon 1 (France) continues. Data were analyzed during this visit, plans for further experiments were developed, and a paper was drafted for publication.« less

The Gaussian Laser Angular Distribution in HYDRA's 3D Laser Ray Trace Package

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sepke, Scott M.

In this note, the angular distribution of rays launched by the 3D LZR ray trace package is derived for Gaussian beams (npower==2) with bm model=3±. Beams with bm model=+3 have a nearly at distribution, and beams with bm model=-3 have a nearly linear distribution when the spot size is large compared to the wavelength.

The gyrotron - a natural source of high-power orbital angular momentum millimeter-wave beams

NASA Astrophysics Data System (ADS)

Thumm, M.; Sawant, A.; Choe, M. S.; Choi, E. M.

2017-08-01

Orbital angular momentum (OAM) of electromagnetic-wave beams provides further diversity to multiplexing in wireless communication. The present report shows that higher-order mode gyrotrons are natural sources of high-power OAM millimeter (mm) wave beams. The well-defined OAM of their rotating cavity modes operating at near cutoff frequency has been derived by photonic and electromagnetic wave approaches.

Beam Normal Single Spin Asymmetry in Forward Angle Inelastic Electron-Proton Scattering using the Q-Weak Apparatus

DOE Office of Scientific and Technical Information (OSTI.GOV)

., Nuruzzaman

2014-12-01

The Q-weak experiment in Hall-C at the Thomas Jefferson National Accelerator Facility has made the first direct measurement of the weak charge of the proton through the precision measurement of the parity-violating asymmetry in elastic electron-proton scattering at low momentum transfer. There is also a parity conserving Beam Normal Single Spin Asymmetry or transverse asymmetry (B_n) on H_2 with a sin(phi)-like dependence due to two-photon exchange. If the size of elastic B_n is a few ppm, then a few percent residual transverse polarization in the beam, combined with small broken azimuthal symmetries in the detector, would require a few ppbmore » correction to the Q-weak data. As part of a program of B_n background studies, we made the first measurement of B_n in the N-to-Delta(1232) transition using the Q-weak apparatus. The final transverse asymmetry, corrected for backgrounds and beam polarization, was found to be B_n = 42.82 ± 2.45 (stat) ± 16.07 (sys) ppm at beam energy E_beam = 1.155 GeV, scattering angle theta = 8.3 deg, and missing mass W = 1.2 GeV. B_n from electron-nucleon scattering is a unique tool to study the gamma^* Delta Delta form factors, and this measurement will help to improve the theoretical models on beam normal single spin asymmetry and thereby our understanding of the doubly virtual Compton scattering process. To help correct false asymmetries from beam noise, a beam modulation system was implemented to induce small position, angle, and energy changes at the target to characterize detector response to the beam jitter. Two air-core dipoles separated by ~10 m were pulsed at a time to produce position and angle changes at the target, for virtually any tune of the beamline. The beam energy was modulated using an SRF cavity. The hardware and associated control instrumentation will be described in this dissertation. Preliminary detector sensitivities were extracted which helped to reduce the width of the measured asymmetry. The beam modulation system has also proven valuable for tracking changes in the beamline optics, such as dispersion at the target.« less

Stimulated scattering of electromagnetic waves carrying orbital angular momentum in quantum plasmas.

PubMed

Shukla, P K; Eliasson, B; Stenflo, L

2012-07-01

We investigate stimulated scattering instabilities of coherent circularly polarized electromagnetic (CPEM) waves carrying orbital angular momentum (OAM) in dense quantum plasmas with degenerate electrons and nondegenerate ions. For this purpose, we employ the coupled equations for the CPEM wave vector potential and the driven (by the ponderomotive force of the CPEM waves) equations for the electron and ion plasma oscillations. The electrons are significantly affected by the quantum forces (viz., the quantum statistical pressure, the quantum Bohm potential, as well as the electron exchange and electron correlations due to electron spin), which are included in the framework of the quantum hydrodynamical description of the electrons. Furthermore, our investigation of the stimulated Brillouin instability of coherent CPEM waves uses the generalized ion momentum equation that includes strong ion coupling effects. The nonlinear equations for the coupled CPEM and quantum plasma waves are then analyzed to obtain nonlinear dispersion relations which exhibit stimulated Raman, stimulated Brillouin, and modulational instabilities of CPEM waves carrying OAM. The present results are useful for understanding the origin of scattered light off low-frequency density fluctuations in high-energy density plasmas where quantum effects are eminent.

The effect of beam pre-bunching on the excitation of terahertz plasmons in a parallel plane guiding system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Suresh C.; Malik, Pratibha

2015-04-15

The excitation of terahertz (THz) plasmons by a pre-bunched relativistic electron beam propagating in a parallel plane semiconducting guiding system is studied. It is found that the n-InSb semiconductor strongly supports the confined surface plasmons in the terahertz frequency range. The growth rate and efficiency of the THz surface plasmons increase linearly with modulation index and show the largest value as modulation index approaches unity. Moreover, the growth rate of the instability scales as one-third power of the beam density and inverse one-third power of the THz radiation frequency.

X-ray radiation generated by a beam of relativistic electrons in composite structure

NASA Astrophysics Data System (ADS)

Blazhevich, S. V.; Noskov, A. V.

2018-04-01

The dynamic theory of coherent X-ray radiation generated by a beam of relativistic electrons in the three-layer structure consisting of an amorphous layer, a vacuum (air) layer and a single crystal has been developed. The phenomenon description is based on two main radiation mechanisms, namely, parametric X-ray radiation (PXR) and diffracted transition radiation (DTR). The possibility to increase the spectral-angular density of DTR under the condition of constructive interference of the transition radiation waves from different boundaries of such a structure has been demonstrated. It is shown that little changes in the layers thicknesses should not cause a considerable change in the interference picture, for example, the transition of constructive interference into destructive one. It means that in the considered process the conditions of constructive interference are enough stable to use them for increasing the intensity of X-ray source that can be created based on the interaction of relativistic electrons with such a structure.

Angularly resolved characterization of ion beams from laser-ultrathin foil interactions

NASA Astrophysics Data System (ADS)

Scullion, C.; Doria, D.; Romagnani, L.; Ahmed, H.; Alejo, A.; Ettlinger, O. C.; Gray, R. J.; Green, J.; Hicks, G. S.; Jung, D.; Naughton, K.; Padda, H.; Poder, K.; Scott, G. G.; Symes, D. R.; Kar, S.; McKenna, P.; Najmudin, Z.; Neely, D.; Zepf, M.; Borghesi, M.

2016-09-01

Methods and techniques used to capture and analyze beam profiles produced from the interaction of intense, ultrashort laser pulses and ultrathin foil targets using stacks of Radiochromic Film (RCF) and Columbia Resin #39 (CR-39) are presented. The identification of structure in the beam is particularly important in this regime, as it may be indicative of the dominance of specific acceleration mechanisms. Additionally, RCF can be used to deconvolve proton spectra with coarse energy resolution while mantaining angular information across the whole beam.

Variable Distance Angular Symbology Reader

NASA Technical Reports Server (NTRS)

Schramm, Harry F., Jr. (Inventor); Corder, Eric L. (Inventor)

2006-01-01

A variable distance angular symbology, reader utilizes at least one light source to direct light through a beam splitter and onto a target. A target may be angled relative to the impinging light beam up to and maybe even greater than 45deg. A reflected beam from the target passes through the beam splitter and is preferably directed 90deg relative to the light source through a telecentric lens to a scanner which records an image of the target such as a direct part marking code.

Kinetic Theory and Fast Wind Observations of the Electron Strahl

NASA Astrophysics Data System (ADS)

Horaites, Konstantinos; Boldyrev, Stanislav; Wilson, Lynn B., III; Viñas, Adolfo F.; Merka, Jan

2017-10-01

Measurements of the electron velocity distribution function (eVDF) in the solar wind exhibit a high-energy, field-aligned beam of electrons, known as the ``strahl''. We develop a kinetic model for the strahl population, based on the solution of the electron drift-kinetic equation at heliospheric distances where the plasma density, temperature, and the strength of the magnetic field decline as power-laws of the distance along a magnetic flux tube. We compare our model with the eVDF measured by the Wind satellite's SWE strahl detector. The model is successful at predicting the angular width of the strahl for the Wind data at 1 AU, in particular, the scaling of the width with particle energy and background density.

Numerical Study of Electrostatic Field Distortion on LPTPC End-Plates based on Bulk Micromegas Modules

NASA Astrophysics Data System (ADS)

Bhattacharya, Purba; Bhattacharya, Deb Sankar; Mukhopadhyay, Supratik; Majumdar, Nayana; Bhattacharya, Sudeb; Colas, Paul; Attié, David

2018-02-01

The R&D activities for the linear collider TPC (LC-TPC) are currently working on the adoption of the micro pattern devices for the gaseous amplification stage. Several beam tests have been carried out at DESY with a 5 GeV electron beam in a 1 T superconducting magnet. We worked on a large prototype TPC with an end-plate that was built, for the first time, using seven resistive bulk Micromegas modules. During experiments, reduced signal sensitivity was observed at the boundary of these modules. Electrostatic field distortion near the module boundaries was considered to be the possible major reason behind these observations. In the present work, we will explore this hypothesis through numerical simulation. Our aim has been to understand the origin of distortions observed close to the edges of the test beam modules and to explore the possibility of using the Garfield simulation framework for investigating a phenomenon as complex as distortion.

Quantum orbital angular momentum of elliptically symmetric light

NASA Astrophysics Data System (ADS)

Plick, William N.; Krenn, Mario; Fickler, Robert; Ramelow, Sven; Zeilinger, Anton

2013-03-01

We present a quantum-mechanical analysis of the orbital angular momentum of a class of recently discovered elliptically symmetric stable light fields—the so-called Ince-Gauss modes. We study, in a fully quantum formalism, how the orbital angular momentum of these beams varies with their ellipticity, and we discover several compelling features, including nonmonotonic behavior, stable beams with real continuous (noninteger) orbital angular momenta, and orthogonal modes with the same orbital angular momenta. We explore, and explain in detail, the reasons for this behavior. These features may have applications in quantum key distribution, atom trapping, and quantum informatics in general—as the ellipticity opens up an alternative way of navigating the spatial photonic Hilbert space.

Theory and applications of free-electron vortex states

NASA Astrophysics Data System (ADS)

Bliokh, K. Y.; Ivanov, I. P.; Guzzinati, G.; Clark, L.; Van Boxem, R.; Béché, A.; Juchtmans, R.; Alonso, M. A.; Schattschneider, P.; Nori, F.; Verbeeck, J.

2017-05-01

Both classical and quantum waves can form vortices : entities with helical phase fronts and circulating current densities. These features determine the intrinsic orbital angular momentum carried by localized vortex states. In the past 25 years, optical vortex beams have become an inherent part of modern optics, with many remarkable achievements and applications. In the past decade, it has been realized and demonstrated that such vortex beams or wavepackets can also appear in free electron waves, in particular, in electron microscopy. Interest in free-electron vortex states quickly spread over different areas of physics: from basic aspects of quantum mechanics, via applications for fine probing of matter (including individual atoms), to high-energy particle collision and radiation processes. Here we provide a comprehensive review of theoretical and experimental studies in this emerging field of research. We describe the main properties of electron vortex states, experimental achievements and possible applications within transmission electron microscopy, as well as the possible role of vortex electrons in relativistic and high-energy processes. We aim to provide a balanced description including a pedagogical introduction, solid theoretical basis, and a wide range of practical details. Special attention is paid to translating theoretical insights into suggestions for future experiments, in electron microscopy and beyond, in any situation where free electrons occur.

47 CFR 73.128 - AM stereophonic broadcasting.

Code of Federal Regulations, 2014 CFR

2014-10-01

... magnitude of the nth term of the difference signal ωsn=the nth order angular velocity of the sum signal ωdn=the nth order angular velocity of the difference signal ωc=the angular velocity of the carrier... presence of envelope modulation. (5) Maximum angular modulation, which occurs on negative peaks of the left...

Polarization of resonantly excited X-ray lines

NASA Astrophysics Data System (ADS)

Shah, Chintan; Amaro, Pedro; Steinbrügge, René; Bernitt, Sven; Fritzsche, Stephan; Surzhykov, Andrey; Crespo Lopez-Urrutia, José R.; Tashenov, Stanislav

2017-08-01

For a wide range of temperatures, resonantly captured electrons with energies below the excitation threshold are the strongest source of X-ray line excitation in hot plasmas containing highly charged Fe ions. The angular distribution and polarization of X-rays emitted due to these processes were experimentally studied using an electron beam ion trap. The electron-ion collision energy was scanned over the KLL dielectronic, trielectronic, and quadruelectronic recombination resonances of Fe18+..24+ and Kr28+..34+ with an exemplary resolution of ~6 eV. The angular distribution of induced X-ray fluorescence was measured along and perpendicular to the electron beam propagation direction [1]. Subsequently, the polarization of X-ray fluorescence was also measured using a novel Compton polarimeter [2, 3].The experimental data reveal the alignment of the populated excited states and exhibit a high sensitivity to the relativistic Breit interaction [2, 4]. We observed that most of the transitions lead to polarization, including hitherto-neglected trielectronic and quadruelectronic recombination channels. Furthermore, these channels dominate the polarization of the prominent Kα X-rays emitted by hot anisotropic plasmas in a wide temperature range. The present experimental results comprehensively benchmark full-order atomic calculations carried out with the FAC [5] and RATIP [6] codes. We conclude that accurate polarization diagnostics of hot anisotropic plasmas, e.~g., of solar flares and active galactic nuclei, and laboratory fusion plasmas of tokamaks can only be obtained under the premise of careful inclusion of relativistic effects and higher-order resonances which were often neglected in previous works [1]. The present experiments also demonstrate the suitability of the applied technique for accurate directional diagnostics of electron or ion beams in hot plasmas [7].[1] C. Shah et al., Phys. Rev. E 93, 061201 (R) (2016)[2] C. Shah et al., Phys. Rev. A 92, 042702 (2015)[3] S. Weber et al., Rev. Sci. Instr. 86, 093110 (2015)[4] P. Amaro et al., Phys. Rev. A 95, 022712 (2017)[5] M. F. Gu, Can. Phys. J 86, 675 (2008)[6] S. Fritzsche, Comput. Phys. Commu. 183, 1525-1559 (2012)[7] C. Shah et al., submitted (2017)

Unique Properties and Prospects: Quantum Theory of the Orbital Angular Momentum of Ince-Gauss Beams

NASA Astrophysics Data System (ADS)

Plick, William; Krenn, Mario; Fickler, Robert; Ramelow, Sven; Zeilinger, Anton

2012-02-01

The Ince-Gauss modes represent a new addition to the standard solutions to the paraxial wave equation. Parametrized by the ellipticity of the beam, they span the solution space between the Hermite-Gauss and the Laguerre-Gauss modes. These beams may be decomposed in either basis, and single photons in the Ince-Gauss modes exist naturally as superpositions of either Laguerre-Gauss or Hermite-Gauss modes. We present the fully quantum theory of the orbital angular momentum of these beams. Interesting features that arise are: stable beams with fractional orbital angular momentum, non-monotonic behavior of the OAM with respect to ellipticity, and the possibility of orthogonal modes possessing the same OAM. We believe that these modes may open up a fully new parameter space for quantum informatics and communication, and thus are worthy of thorough study.

Control of Angular Intervals for Angle-Multiplexed Holographic Memory

NASA Astrophysics Data System (ADS)

Kinoshita, Nobuhiro; Muroi, Tetsuhiko; Ishii, Norihiko; Kamijo, Koji; Shimidzu, Naoki

2009-03-01

In angle-multiplexed holographic memory, the full width at half maximum of the Bragg selectivity curves is dependent on the angle formed between the medium and incident laser beams. This indicates the possibility of high density and high multiplexing number by varying the angular intervals between adjacent holograms. We propose an angular interval scheduling for closely stacking holograms into medium even when the angle range is limited. We obtained bit error rates of the order of 10-4 under the following conditions: medium thickness of 1 mm, laser beam wavelength of 532 nm, and angular multiplexing number of 300.

Effects of Energy Chirp on Echo-Enabled Harmonic Generation Free-Electron Lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Z.; Ratner, D.; Stupakov, G.

2009-02-23

We study effects of energy chirp on echo-enabled harmonic generation (EEHG). Analytical expressions are compared with numerical simulations for both harmonic and bunching factors. We also discuss the EEHG free-electron laser bandwidth increase due to an energy-modulated beam and its pulse length dependence on the electron energy chirp.

Light beam shaping and homogenization (LSBH) by irregular microlens structure for medical applications

NASA Astrophysics Data System (ADS)

Semchishen, Vladimir A.; Mrochen, Michael; Seminogov, Vladimir N.; Panchenko, Vladislav Y.; Seiler, Theo

1998-04-01

Purpose: The increasing interest in a homogeneous Gaussian light beam profile for applications in ophthalmology e.g. photorefractive keratectomy (PRK) requests simple optical systems with low energy losses. Therefore, we developed the Light Shaping Beam Homogenizer (LSBH) working from UV up to mid-IR. Method: The irregular microlenses structure on a quartz surface was fabricated by using photolithography, chemical etching and chemical polishing processes. This created a three dimensional structure on the quartz substrate characterized in case of a Gaussian beam by random law distribution of individual irregularities tilts. The LSBH was realized for the 193 nm and the 2.94 micrometer wavelengths. Simulation results obtained by 3-D analysis for an arbitrary incident light beam were compared to experimental results. Results: The correlation to a numerical Gaussian fit is better than 94% with high uniformity for an incident beam with an intensity modulation of nearly 100%. In the far field the cross section of the beam shows always rotation symmetry. Transmittance and damage threshold of the LSBH are only dependent on the substrate characteristics. Conclusions: considering our experimental and simulation results it is possible to control the angular distribution of the beam intensity after LSBH with higher efficiency compared to diffraction or holographic optical elements.

Light-sheet generation in inhomogeneous media using self-reconstructing beams and the STED-principle.

PubMed

Gohn-Kreuz, Cristian; Rohrbach, Alexander

2016-03-21

Self-reconstruction of Bessel beams in inhomogeneous media is beneficial in light-sheet based microscopy. Although the beam's ring system enables propagation stability, the resulting image contrast is reduced. Here, we show that by a combination of two self-reconstructing beams with different orbital angular momenta it is possible to inhibit fluorescence from the ring system by using stimulated emission depletion (STED) even in strongly scattering media. Our theoretical study shows that the remaining fluorescence γ depends non-linearly on the beams' relative radial and orbital angular momenta. For various scattering media we demonstrate that γ remains remarkably stable over long beam propagation distances.

Nanofocusing of structured light for quadrupolar light-matter interactions.

PubMed

Sakai, Kyosuke; Yamamoto, Takeaki; Sasaki, Keiji

2018-05-17

The spatial structure of an electromagnetic field can determine the characteristics of light-matter interactions. A strong gradient of light in the near field can excite dipole-forbidden atomic transitions, e.g., electric quadrupole transitions, which are rarely observed under plane-wave far-field illumination. Structured light with a higher-order orbital angular momentum state may also modulate the selection rules in which an atom can absorb two quanta of angular momentum: one from the spin and another from the spatial structure of the beam. Here, we numerically demonstrate a strong focusing of structured light with a higher-order orbital angular momentum state in the near field. A quadrupole field was confined within a gap region of several tens of nanometres in a plasmonic tetramer structure. A plasmonic crystal surrounding the tetramer structure provides a robust antenna effect, where the incident structured light can be strongly coupled to the quadrupole field in the gap region with a larger alignment tolerance. The proposed system is expected to provide a platform for light-matter interactions with strong multipolar effects.

Experimental demonstration of beaconless beam displacement tracking for an orbital angular momentum multiplexed free-space optical link.

PubMed

Li, Long; Zhang, Runzhou; Xie, Guodong; Ren, Yongxiong; Zhao, Zhe; Wang, Zhe; Liu, Cong; Song, Haoqian; Pang, Kai; Bock, Robert; Tur, Moshe; Willner, Alan E

2018-05-15

In this Letter, we experimentally demonstrate beaconless beam displacement tracking for free-space optical communication link multiplexing multiple orbital angular momentum (OAM) beams, where the data-carrying OAM beams are used for position detection. 400 Gbit/s data transmission is demonstrated under emulated lateral displacement of up to ±10  mm with power penalties of less than 3 dB for all channels. Channel crosstalk is reduced by the beam tracking system to below -18  dB. Moreover, we investigate using a Gaussian beacon for beam displacement tracking, and achieve similar channel crosstalk and power penalties, compared with using the beaconless beam tracking.

Determination of electron beam polarization using electron detector in Compton polarimeter with less than 1% statistical and systematic uncertainty

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narayan, Amrendra

2015-05-01

The Q-weak experiment aims to measure the weak charge of proton with a precision of 4.2%. The proposed precision on weak charge required a 2.5% measurement of the parity violating asymmetry in elastic electron - proton scattering. Polarimetry was the largest experimental contribution to this uncertainty and a new Compton polarimeter was installed in Hall C at Jefferson Lab to make the goal achievable. In this polarimeter the electron beam collides with green laser light in a low gain Fabry-Perot Cavity; the scattered electrons are detected in 4 planes of a novel diamond micro strip detector while the back scatteredmore » photons are detected in lead tungstate crystals. This diamond micro-strip detector is the first such device to be used as a tracking detector in a nuclear and particle physics experiment. The diamond detectors are read out using custom built electronic modules that include a preamplifier, a pulse shaping amplifier and a discriminator for each detector micro-strip. We use field programmable gate array based general purpose logic modules for event selection and histogramming. Extensive Monte Carlo simulations and data acquisition simulations were performed to estimate the systematic uncertainties. Additionally, the Moller and Compton polarimeters were cross calibrated at low electron beam currents using a series of interleaved measurements. In this dissertation, we describe all the subsystems of the Compton polarimeter with emphasis on the electron detector. We focus on the FPGA based data acquisition system built by the author and the data analysis methods implemented by the author. The simulations of the data acquisition and the polarimeter that helped rigorously establish the systematic uncertainties of the polarimeter are also elaborated, resulting in the first sub 1% measurement of low energy (?1 GeV) electron beam polarization with a Compton electron detector. We have demonstrated that diamond based micro-strip detectors can be used for tracking in a high radiation environment and it has enabled us to achieve the desired precision in the measurement of the electron beam polarization which in turn has allowed the most precise determination of the weak charge of the proton.« less

Determination of electron beam polarization using electron detector in Compton polarimeter with less than 1% statistical and systematic uncertainty

NASA Astrophysics Data System (ADS)

Narayan, Amrendra

The Q-weak experiment aims to measure the weak charge of proton with a precision of 4.2%. The proposed precision on weak charge required a 2.5% measurement of the parity violating asymmetry in elastic electron - proton scattering. Polarimetry was the largest experimental contribution to this uncertainty and a new Compton polarimeter was installed in Hall C at Jefferson Lab to make the goal achievable. In this polarimeter the electron beam collides with green laser light in a low gain Fabry-Perot Cavity; the scattered electrons are detected in 4 planes of a novel diamond micro strip detector while the back scattered photons are detected in lead tungstate crystals. This diamond micro-strip detector is the first such device to be used as a tracking detector in a nuclear and particle physics experiment. The diamond detectors are read out using custom built electronic modules that include a preamplifier, a pulse shaping amplifier and a discriminator for each detector micro-strip. We use field programmable gate array based general purpose logic modules for event selection and histogramming. Extensive Monte Carlo simulations and data acquisition simulations were performed to estimate the systematic uncertainties. Additionally, the Moller and Compton polarimeters were cross calibrated at low electron beam currents using a series of interleaved measurements. In this dissertation, we describe all the subsystems of the Compton polarimeter with emphasis on the electron detector. We focus on the FPGA based data acquisition system built by the author and the data analysis methods implemented by the author. The simulations of the data acquisition and the polarimeter that helped rigorously establish the systematic uncertainties of the polarimeter are also elaborated, resulting in the first sub 1% measurement of low energy (~1GeV) electron beam polarization with a Compton electron detector. We have demonstrated that diamond based micro-strip detectors can be used for tracking in a high radiation environment and it has enabled us to achieve the desired precision in the measurement of the electron beam polarization which in turn has allowed the most precise determination of the weak charge of the proton.

Review Of E-Beam Electrical Test Techniques

NASA Astrophysics Data System (ADS)

Hohn, Fritz J.

1987-09-01

Electron beams as a viable technique for contactless testing of electrical functions and electrical integrity of different active devices in VLSI-chips has been demonstrated over the past years. This method of testing electronic networks, most widely used in the laboratory environment, is based on an electron probe which is deflected from point to point in the network. A current of secondary electrons emitted in response to the impingement of the electron probe is converted to a signal indicating the presence of a voltage or varying potential at the different points. Voltage contrast, electron beam induced current, dual potential approach, stroboscopic techniques and other methods have been developed and are used to detect different functional failures in devices. Besides the VLSI application, the contactless testing of three dimensional conductor networks of a 10cm x 10cm x .8cm multilayer ceramic module poses a different and new application for the electron beam test technique. A dual potential electron beam test system allows to generate electron beam induced voltage contrast. The same system at a different potential is used to detect this voltage contrast over the large area without moving the substrate and thus test for the electrical integrity of the networks. Less attention in most of the applications has been paid to the electron optical environment, mostly SEM's were upgraded or converted to do the job of a "voltage contrast" machine. This by no means will satisfy all requirements and more thoughts have to be given to aspects such as: low voltage electron guns: thermal emitter, Schottky emitter, field emitter, low voltage electron optics, two lens systems, different means of detection, signal processing - storage and others. This paper will review available E-beam test techniques, specific applications and some critical components.

Generation and Amplification of Coherent Radiation with Optical Orbital Angular Momentum in a Free-Electron Laser

NASA Astrophysics Data System (ADS)

Hemsing, Erik Willard

The object of this work is to examine how coherent light that carries orbital angular momentum (OAM) can be generated and amplified in a single pass, high-gain free-electron laser (FEL) at the fundamental operating frequency. This concept unites two rapidly expanding, but at present largely non-overlapping fields of study: high-order OAM light modes, which interact in new ways with matter, and FELs, in which a relativistically energetic electron beam emits coherent, ultra high-brightness, highly frequency-tunable light. The ability to generate OAM light in an FEL enables new regimes of laser interaction physics to be explored at wavelengths down to hard x-rays. The theoretical portion of this dissertation attempts to provide a new predictive mathematical framework. It builds on existing work, and describes the three-dimensional electromagnetic field of the high-gain FEL as a sum of OAM modes such that the amplification properties of individual modes can be characterized. The effects of uncorrelated energy spread, longitudinal space charge, energy detuning, and transverse emittance in the electron beam are included, as is the diffraction of the laser light. Theoretical predictions are corroborated by detailed numerical Genesis 1.3 simulations. When the theory is extended to frequency harmonics, a novel interaction is uncovered that generates a helical electron beam density distribution. These predictions are also supported by numerical Tredi simulations. This type of highly correlated structure is shown to naturally emit OAM light, and forms the basis of a new high-gain, high-mode generation (HGHMG) scheme proposed in its entirety here. The experimental section examines the helical microbunching concept in a proof-of-principle experiment dubbed HELIX, performed at the UCLA Neptune laboratory. We present detailed measurement of the coherent transition radiation emitted by the 12.5 MeV electron beam that is microbunched in a second harmonic interaction with an input laser and helical undulator. The predicted dependence of the CTR signal on the input laser polarization is observed, and is consistent with microbunching that has a periodicity near the 10.6 mum wavelength of the 30 MW CO2 laser pulse. Scans of the interaction energy bandwidth are consistent with predictions that indicate a dominant azimuthal density mode with a bunching factor of 10%, and thus provide indication of the first experimental evidence of helical microbunching. This result offers support for future successful realization of the proposed HGHMG scheme to generate OAM modes in high-gain FELs.

Pulse width modulation inverter with battery charger

DOEpatents

Slicker, James M.

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Pulse width modulation inverter with battery charger

NASA Technical Reports Server (NTRS)

Slicker, James M. (Inventor)

1985-01-01

An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.

78 FR 29387 - Government-Owned Inventions, Available for Licensing

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-20

... System for Physiologically Modulating Action Role-playing Open World Video Games and Simulations Which... Deposition Measurement for the Electron Beam Free Form Fabrication (EBF3) Process; NASA Case No.: LAR-17887-1... Modulating Videogames and Simulations Which Use Gesture and Body Image Sensing Control Input Devices; NASA...

Tilt-effect of holograms and images displayed on a spatial light modulator.

PubMed

Harm, Walter; Roider, Clemens; Bernet, Stefan; Ritsch-Marte, Monika

2015-11-16

We show that a liquid crystal spatial light modulator (LCOS-SLM) can be used to display amplitude images, or phase holograms, which change in a pre-determined way when the display is tilted, i.e. observed under different angles. This is similar to the tilt-effect (also called "latent image effect") known from various security elements ("kinegrams") on credit cards or bank notes. The effect is achieved without any specialized optical components, simply by using the large phase shifting capability of a "thick" SLM, which extends over several multiples of 2π, in combination with the angular dependence of the phase shift. For hologram projection one can use the fact that the phase of a monochromatic wave is only defined modulo 2π. Thus one can design a phase pattern extending over several multiples of 2π, which transforms at different readout angles into different 2π-wrapped phase structures, due to the angular dependence of the modulo 2π operation. These different beams then project different holograms at the respective readout angles. In amplitude modulation mode (with inserted polarizer) the intensity of each SLM pixel oscillates over several periods when tuning its control voltage. Since the oscillation period depends on the readout angle, it is possible to find a certain control voltage which produces two (or more) selectable gray levels at a corresponding number of pre-determined readout angles. This is done with all SLM pixels individually, thus constructing different images for the selected angles. We experimentally demonstrate the reconstruction of multiple (Fourier- and Fresnel-) holograms, and of different amplitude images, by readout of static diffractive patterns in a variable angular range between 0° and 60°.

Investigation of Microbunching Instabilities in Modern Recirculating Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Cheng

Particle accelerators are machines to accelerate and store charged particles, such as electrons or protons, to the energy levels for various scientific applications. A collection of charged particles usually forms a particle beam. There are three basic types of particle accelerators: linear accelerators (linac), storage-ring (or circular) accelerators, and recirculating accelerators. In a linac, particles are accelerated and pass through once along a linear or straight beamline. Storage-ring accelerators propel particles around a circular track and repetitively append the energy to the stored beam. The third type, also the most recent one in chronology, the recirculating accelerator, is designed tomore » accelerate the particle beam in a short section of linac, circulate the beam, and then either continue to accelerate for energy boost or decelerate it for energy recovery. The beam properties of a linac machine are set at best by the initial particle sources. For storage rings, the beam equilibria are instead determined by the overall machine design. The modern recirculating machines share with linacs the advantages to both accelerate and preserve the beam with high beam quality, as well as efficiently reuse the accelerating components. The beamline design in such a machine configuration can however be much more complicated than that of linacs. As modern accelerators push toward the high-brightness or high-intensity frontier by demanding particles in a highly charged bunch (about nano-Coulomb per bunch) to concentrate in an ever-decreasing beam phase space (transverse normalized emittance about 1 μm and relative energy spread of the order of 10^-5 in GeV beam energy), the interaction amongst particles via their self-generated electromagnetic fields can potentially lead to coherent instabilities of the beam and thus pose significant challenges to the machine design and operation. In the past decade and a half, microbunching instability (MBI) has been one of the most challenging issues for such high-brightness or high-intensity beam transport, as it would degrade lasing performance in the fourth-generation light sources, reduce cooling efficiency in electron cooling facilities, and compromise the luminosity of colliding beams in lepton or lepton-hadron colliders. The dissertation work will focus on the MBI in modern recirculating electron accelerators. It has been known that the collective interactions, the coherent synchrotron radiation (CSR) and the longitudinal space charge (LSC) forces, can drive MBI. The CSR effect is a collective phenomenon in which the electrons in a curved motion, e.g. a bending dipole, emit radiation at a scale comparable to the micro-bunched structure of the bunch distribution. The LSC effect stems from non-uniformity of the charge distribution, acts as plasma oscillation, and can eventually accumulate an amount of energy modulation when the beam traverses a long section of a beamline. MBI can be seeded by non-uniformity or shot noise of the beam, which originates from granularity of the elementary charge. Through the aforementioned collective effects, the modulation of the bunch sub-structure can be amplified and, once the beam-wave interaction formed a positive feedback, can result in MBI. The problem of MBI has been intensively studied for linac-based facilities and for storage-ring accelerators. However, systematic studies for recirculation machines are still very limited and form a knowledge gap. Because of the much more complicated machine configuration of the recirculating accelerators than that of linacs, the existing MBI analysis needs to be extended to accommodate the high-brightness particle beam transport in modern recirculating accelerators. This dissertation is focused on theoretical investigation of MBI in such machine configuration in the following seven themes: (1) Development and generalization of MBI theory The theoretical formulation has been extended so as to be applicable to a general linear beamline lattice including horizontal and vertical transport bending elements, and beam acceleration or deceleration. These featured generalizations are required for MBI analysis in recirculation accelerators. (2) Construction of CSR impedance models In addition to the steady-state CSR interaction, it has been found that the exit transient effect (or CSR drift) can even result in more serious MBI in high-brightness recirculation arcs. The onedimensional free-space CSR impedances, especially the exit transients, are derived. The steady-state CSR impedance is also extended to non-ultrarelativistic beam energy for MBI analysis of low-energy merger sections in recirculating accelerators. (3) Numerical implementation of the derived semi-analytical formulation This includes the development of a semi-analytical Vlasov solver for MBI analysis, and also benchmarking of the solver against massive particle tracking simulations. (4) Exploration of multistage amplification behavior of CSR microbunching development The CSR-induced MBI acts as an amplifier, which amplifies the sub-bunch modulation of a beam. The amplification is commonly quantified by the amplification gain. A beam transport system can be considered as a cascaded amplifier. Unlike the two-stage amplification of four-dipole bunch compressor chicanes employed in linacs, the recirculation arcs, which are usually constituted by several tens of bending magnets, show a distinguishing feature of up to six-stage microbunching amplification for our example arc lattices. That is, the maximal CSR amplification gain can be proportional to the peak bunch current up to sixth power. A method to compare lattice performance has been developed in terms of gain coefficients, which nearly depend on the lattice properties only. This method has also proven to be an effective way to quantify the current dependence of the maximal (5) Control of CSR MBI in multibend transport or recirculation arcs The existing mitigation schemes of MBI mostly aim to linac-based accelerators and may not be practical to the recirculating accelerator facilities. Thus a set of conditions for suppression of CSR MBI was proposed and examined for example lattices from low (~100 MeV) to high (~1 GeV) energies. (6) Study of more aspects of microbunched structures in beam phase spaces For a cascaded amplifier in circuit electronics, the total amplification gain can be estimated as the product of individual gains. In a beam transport line of an accelerator, the (scalar) gain multiplication was examined and found to under-estimate the overall microbunching amplification. The concept of gain matrix was developed, which includes the density, energy and transverse-longitudinal modulations in a beam phase space, and used to analyze MBI for a proposed recirculating machine. Throughout the gain matrix approach, it reasonably gives the upper limit of spectral MBI gain curves. This extended analysis can be employed to study multi-pass recirculation. (7) Study of MBI for magnetized beams Driven by a recent energy-recovery-linac based cooler design for electron cooling at Jefferson Lab Electron-Ion Collider Project, the generalized theoretical formulation for MBI to a transversely coupled beam has been developed and applied to this study. A magnetized beam in general features non-zero canonical angular momentum, thus considered to be a transversely coupled beam. A novel idea of utilizing magnetized beam transport was proposed for improvement of cooling efficiency and possible mitigation of collective effects. A concern of MBI regarding this design was studied and excluded. The large transverse beam size associated with the beam magnetization is found to help suppress MBI via the transverse-longitudinal correlation.« less

Observation of giant Goos-Hänchen and angular shifts at designed metasurfaces

PubMed Central

Yallapragada, Venkata Jayasurya; Ravishankar, Ajith P.; Mulay, Gajendra L.; Agarwal, Girish S.; Achanta, Venu Gopal

2016-01-01

Metasurfaces with sub-wavelength features are useful in modulating the phase, amplitude or polarization of electromagnetic fields. While several applications are reported for light manipulation and control, the sharp phase changes would be useful in enhancing the beam shifts at reflection from a metasurface. In designed periodic patterns on metal film, at surface plasmon resonance, we demonstrate Goos-Hanchen shift of the order of 70 times the incident wavelength and the angular shifts of several hundred microradians. We have designed the patterns using rigorous coupled wave analysis (RCWA) together with S-matrices and have used a complete vector theory to calculate the shifts as well as demonstrate a versatile experimental setup to directly measure the shifts. The giant shifts demonstrated could prove to be useful in enhancing the sensitivity of experiments ranging from atomic force microscopy to gravitational wave detection. PMID:26758471

Electron beam collimation with a photon MLC for standard electron treatments

NASA Astrophysics Data System (ADS)

Mueller, S.; Fix, M. K.; Henzen, D.; Frei, D.; Frauchiger, D.; Loessl, K.; Stampanoni, M. F. M.; Manser, P.

2018-01-01

Standard electron treatments are currently still performed using standard or molded patient-specific cut-outs placed in the electron applicator. Replacing cut-outs and electron applicators with a photon multileaf collimator (pMLC) for electron beam collimation would make standard electron treatments more efficient and would facilitate advanced treatment techniques like modulated electron radiotherapy (MERT) and mixed beam radiotherapy (MBRT). In this work, a multiple source Monte Carlo beam model for pMLC shaped electron beams commissioned at a source-to-surface distance (SSD) of 70 cm is extended for SSDs of up to 100 cm and validated for several Varian treatment units with field sizes typically used for standard electron treatments. Measurements and dose calculations agree generally within 3% of the maximal dose or 2 mm distance to agreement. To evaluate the dosimetric consequences of using pMLC collimated electron beams for standard electron treatments, pMLC-based and cut-out-based treatment plans are created for a left and a right breast boost, a sternum, a testis and a parotid gland case. The treatment plans consist of a single electron field, either alone (1E) or in combination with two 3D conformal tangential photon fields (1E2X). For each case, a pMLC plan with similar treatment plan quality in terms of dose homogeneity to the target and absolute mean dose values to the organs at risk (OARs) compared to a cut-out plan is found. The absolute mean dose to an OAR is slightly increased for pMLC-based compared to cut-out-based 1E plans if the OAR is located laterally close to the target with respect to beam direction, or if a 6 MeV electron beam is used at an extended SSD. In conclusion, treatment plans using cut-out collimation can be replaced by plans of similar treatment plan quality using pMLC collimation with accurately calculated dose distributions.

Interharmonic modulation products as a means to quantify nonlinear D-region interactions

NASA Astrophysics Data System (ADS)

Moore, Robert

Experimental observations performed during dual beam ionospheric HF heating experiments at the High frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska are used to quantify the relative importance of specific nonlinear interactions that occur within the D region ionosphere. During these experiments, HAARP broadcast two amplitude modulated HF beams whose center frequencies were separated by less than 20 kHz. One beam was sinusoidally modulated at 500 Hz while the second beam was sinusoidally modulated using a 1-7 kHz linear frequency-time chirp. ELF/VLF observations performed at two different locations (3 and 98 km from HAARP) provide clear evidence of strong interactions between all field components of the two HF beams in the form of low and high order interharmonic modulation products. From a theoretical standpoint, the observed interharmonic modulation products could be produced by several different nonlinearities. The two primary nonlinearities take the form of wave-medium interactions (i.e., cross modulation), wherein the ionospheric conductivity modulation produced by one signal crosses onto the other signal via collision frequency modification, and wave-wave interactions, wherein the conduction current associated with one wave mixes with the electric field of the other wave to produce electron temperature oscillations. We are able to separate and quantify these two different nonlinearities, and we conclude that the wave-wave interactions dominate the wave-medium interactions by a factor of two. These results are of great importance for the modeling of transioinospheric radio wave propagation, in that both the wave-wave and the wave-medium interactions could be responsible for a significant amount of anomalous absorption.

Micromachined mirrors for raster-scanning displays and optical fiber switches

NASA Astrophysics Data System (ADS)

Hagelin, Paul Merritt

Micromachines and micro-optics have the potential to shrink the size and cost of free-space optical systems, enabling a new generation of high-performance, compact projection displays and telecommunications equipment. In raster-scanning displays and optical fiber switches, a free-space optical beam can interact with multiple tilt- up micromirrors fabricated on a single substrate. The size, rotation angle, and flatness of the mirror surfaces determine the number of pixels in a raster-display or ports in an optical switch. Single-chip and two-chip optical raster display systems demonstrate static mirror curvature correction, an integrated electronic driver board, and dynamic micromirror performance. Correction for curvature caused by a stress gradient in the micromirror leads to resolution of 102 by 119 pixels in the single-chip display. The optical design of the two-chip display features in-situ mirror curvature measurement and adjustable image magnification with a single output lens. An electronic driver board synchronizes modulation of the optical source with micromirror actuation for the display of images. Dynamic off-axis mirror motion is shown to have minimal influence on resolution. The confocal switch, a free-space optical fiber cross- connect, incorporates micromirrors having a design similar to the image-refresh scanner. Two micromirror arrays redirect optical beams from an input fiber array to the output fibers. The switch architecture supports simultaneous switching of multiple wavelength channels. A 2x2 switch configuration, using single-mode optical fiber at 1550 mn, is demonstrated with insertion loss of -4.2 dB and cross-talk of -50.5 dB. The micromirrors have sufficient size and angular range for scaling to a 32x32 cross-connect switch that has low insertion-loss and low cross-talk.

Boundary conditions on the plasma emitter surface in the presence of a particle counter flow: I. Ion emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Astrelin, V. T., E-mail: V.T.Astrelin@inp.nsk.su; Kotelnikov, I. A.

Emission of positively charged ions from a plasma emitter irradiated by a counterpropagating electron beam is studied theoretically. A bipolar diode with a plasma emitter in which the ion temperature is lower than the electron temperature and the counter electron flow is extracted from the ion collector is calculated in the one-dimensional model. An analog of Bohm’s criterion for ion emission in the presence of a counterpropagating electron beam is derived. The limiting density of the counterpropagating beam in a bipolar diode operating in the space-charge-limited-emission regime is calculated. The full set of boundary conditions on the plasma emitter surfacemore » that are required for operation of the high-current optics module in numerical codes used to simulate charged particle sources is formulated.« less

Monte Carlo simulation of electron beams from an accelerator head using PENELOPE.

PubMed

Sempau, J; Sánchez-Reyes, A; Salvat, F; ben Tahar, H O; Jiang, S B; Fernández-Varea, J M

2001-04-01

The Monte Carlo code PENELOPE has been used to simulate electron beams from a Siemens Mevatron KDS linac with nominal energies of 6, 12 and 18 MeV. Owing to its accuracy, which stems from that of the underlying physical interaction models, PENELOPE is suitable for simulating problems of interest to the medical physics community. It includes a geometry package that allows the definition of complex quadric geometries, such as those of irradiation instruments, in a straightforward manner. Dose distributions in water simulated with PENELOPE agree well with experimental measurements using a silicon detector and a monitoring ionization chamber. Insertion of a lead slab in the incident beam at the surface of the water phantom produces sharp variations in the dose distributions, which are correctly reproduced by the simulation code. Results from PENELOPE are also compared with those of equivalent simulations with the EGS4-based user codes BEAM and DOSXYZ. Angular and energy distributions of electrons and photons in the phase-space plane (at the downstream end of the applicator) obtained from both simulation codes are similar, although significant differences do appear in some cases. These differences, however, are shown to have a negligible effect on the calculated dose distributions. Various practical aspects of the simulations, such as the calculation of statistical uncertainties and the effect of the 'latent' variance in the phase-space file, are discussed in detail.

The effect of electronically steering a phased array ultrasound transducer on near-field tissue heating.

PubMed

Payne, Allison; Vyas, Urvi; Todd, Nick; de Bever, Joshua; Christensen, Douglas A; Parker, Dennis L

2011-09-01

This study presents the results obtained from both simulation and experimental techniques that show the effect of mechanically or electronically steering a phased array transducer on proximal tissue heating. The thermal response of a nine-position raster and a 16-mm diameter circle scanning trajectory executed through both electronic and mechanical scanning was evaluated in computer simulations and experimentally in a homogeneous tissue-mimicking phantom. Simulations were performed using power deposition maps obtained from the hybrid angular spectrum (HAS) method and applying a finite-difference approximation of the Pennes' bioheat transfer equation for the experimentally used transducer and also for a fully sampled transducer to demonstrate the effect of acoustic window, ultrasound beam overlap and grating lobe clutter on near-field heating. Both simulation and experimental results show that electronically steering the ultrasound beam for the two trajectories using the 256-element phased array significantly increases the thermal dose deposited in the near-field tissues when compared with the same treatment executed through mechanical steering only. In addition, the individual contributions of both beam overlap and grating lobe clutter to the near-field thermal effects were determined through comparing the simulated ultrasound beam patterns and resulting temperature fields from mechanically and electronically steered trajectories using the 256-randomized element phased array transducer to an electronically steered trajectory using a fully sampled transducer with 40 401 phase-adjusted sample points. Three distinctly different three distinctly different transducers were simulated to analyze the tradeoffs of selected transducer design parameters on near-field heating. Careful consideration of design tradeoffs and accurate patient treatment planning combined with thorough monitoring of the near-field tissue temperature will help to ensure patient safety during an MRgHIFU treatment.

Experimental observation of acoustic emissions generated by a pulsed proton beam from a hospital-based clinical cyclotron.

PubMed

Jones, Kevin C; Vander Stappen, François; Bawiec, Christopher R; Janssens, Guillaume; Lewin, Peter A; Prieels, Damien; Solberg, Timothy D; Sehgal, Chandra M; Avery, Stephen

2015-12-01

To measure the acoustic signal generated by a pulsed proton spill from a hospital-based clinical cyclotron. An electronic function generator modulated the IBA C230 isochronous cyclotron to create a pulsed proton beam. The acoustic emissions generated by the proton beam were measured in water using a hydrophone. The acoustic measurements were repeated with increasing proton current and increasing distance between detector and beam. The cyclotron generated proton spills with rise times of 18 μs and a maximum measured instantaneous proton current of 790 nA. Acoustic emissions generated by the proton energy deposition were measured to be on the order of mPa. The origin of the acoustic wave was identified as the proton beam based on the correlation between acoustic emission arrival time and distance between the hydrophone and proton beam. The acoustic frequency spectrum peaked at 10 kHz, and the acoustic pressure amplitude increased monotonically with increasing proton current. The authors report the first observation of acoustic emissions generated by a proton beam from a hospital-based clinical cyclotron. When modulated by an electronic function generator, the cyclotron is capable of creating proton spills with fast rise times (18 μs) and high instantaneous currents (790 nA). Measurements of the proton-generated acoustic emissions in a clinical setting may provide a method for in vivo proton range verification and patient monitoring.

Some computer graphical user interfaces in radiation therapy

PubMed Central

Chow, James C L

2016-01-01

In this review, five graphical user interfaces (GUIs) used in radiation therapy practices and researches are introduced. They are: (1) the treatment time calculator, superficial X-ray treatment time calculator (SUPCALC) used in the superficial X-ray radiation therapy; (2) the monitor unit calculator, electron monitor unit calculator (EMUC) used in the electron radiation therapy; (3) the multileaf collimator machine file creator, sliding window intensity modulated radiotherapy (SWIMRT) used in generating fluence map for research and quality assurance in intensity modulated radiation therapy; (4) the treatment planning system, DOSCTP used in the calculation of 3D dose distribution using Monte Carlo simulation; and (5) the monitor unit calculator, photon beam monitor unit calculator (PMUC) used in photon beam radiation therapy. One common issue of these GUIs is that all user-friendly interfaces are linked to complex formulas and algorithms based on various theories, which do not have to be understood and noted by the user. In that case, user only needs to input the required information with help from graphical elements in order to produce desired results. SUPCALC is a superficial radiation treatment time calculator using the GUI technique to provide a convenient way for radiation therapist to calculate the treatment time, and keep a record for the skin cancer patient. EMUC is an electron monitor unit calculator for electron radiation therapy. Instead of doing hand calculation according to pre-determined dosimetric tables, clinical user needs only to input the required drawing of electron field in computer graphical file format, prescription dose, and beam parameters to EMUC to calculate the required monitor unit for the electron beam treatment. EMUC is based on a semi-experimental theory of sector-integration algorithm. SWIMRT is a multileaf collimator machine file creator to generate a fluence map produced by a medical linear accelerator. This machine file controls the multileaf collimator to deliver intensity modulated beams for a specific fluence map used in quality assurance or research. DOSCTP is a treatment planning system using the computed tomography images. Radiation beams (photon or electron) with different energies and field sizes produced by a linear accelerator can be placed in different positions to irradiate the tumour in the patient. DOSCTP is linked to a Monte Carlo simulation engine using the EGSnrc-based code, so that 3D dose distribution can be determined accurately for radiation therapy. Moreover, DOSCTP can be used for treatment planning of patient or small animal. PMUC is a GUI for calculation of the monitor unit based on the prescription dose of patient in photon beam radiation therapy. The calculation is based on dose corrections in changes of photon beam energy, treatment depth, field size, jaw position, beam axis, treatment distance and beam modifiers. All GUIs mentioned in this review were written either by the Microsoft Visual Basic.net or a MATLAB GUI development tool called GUIDE. In addition, all GUIs were verified and tested using measurements to ensure their accuracies were up to clinical acceptable levels for implementations. PMID:27027225

Bell’s measure and implementing quantum Fourier transform with orbital angular momentum of classical light

PubMed Central

Song, Xinbing; Sun, Yifan; Li, Pengyun; Qin, Hongwei; Zhang, Xiangdong

2015-01-01

We perform Bell’s measurement for the non-separable correlation between polarization and orbital angular momentum from the same classical vortex beam. The violation of Bell’s inequality for such a non-separable classical correlation has been demonstrated experimentally. Based on the classical vortex beam and non-quantum entanglement between the polarization and the orbital angular momentum, the Hadamard gates and conditional phase gates have been designed. Furthermore, a quantum Fourier transform has been implemented experimentally. PMID:26369424

Beam Conditioning and Harmonic Generation in Free ElectronLasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Charman, A.E.; Penn, G.; Wolski, A.

2004-07-05

The next generation of large-scale free-electron lasers (FELs) such as Euro-XFEL and LCLS are to be devices which produce coherent X-rays using Self-Amplified Spontaneous Emission (SASE). The performance of these devices is limited by the spread in longitudinal velocities of the beam. In the case where this spread arises primarily from large transverse oscillation amplitudes, beam conditioning can significantly enhance FEL performance. Future X-ray sources may also exploit harmonic generation starting from laser-seeded modulation. Preliminary analysis of such devices is discussed, based on a novel trial-function/variational-principle approach, which shows good agreement with more lengthy numerical simulations.

Off-Axis and Angular Impulse Measurements on a Lightcraft Engine

NASA Astrophysics Data System (ADS)

Libeau, Michael; Myrabo, Leik

2005-04-01

A laser pulse into a Lightcraft engine applies three linear impulses and three angular impulses to the vehicle that depend on the engine's position and orientation with respect to the laser beam. The magnitudes on this impulsive reaction determine the vehicle's autonomous beam-riding characteristics. The impulsive reaction applied to the laser Lightcraft is examined and a device capable of measuring the reaction is designed and tested. Previous work has examined only the linear impulse acting in the thrust direction but the new apparatus, termed the Angular Impulse Measuring Device (AIMD), experimentally measures the dominant side impulse and dominant pitching angular impulse generated by the engine after a laser-strike. Recent tests of an 11/10 scale Model 200 Lightcraft were conducted using a 10KW Army laser at White Sands Missile Range. The resulting measurements are presented as a function of laser beam position.

An End of Service Life Assessment of PMMA Lenses from Veteran Concentrator Photovoltaic Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, David C.; Khonkar, Hussameldin I.; Herrero, Rebecca

The optical performance of poly(methyl methacrylate) lenses from veteran concentrator photovoltaic modules was examined after the end of their service life. Lenses from the Martin-Marietta and Intersol module designs were examined from the 'Solar Village' site near Riyadh, Saudi Arabia, as well as the Phoenix Sky Harbor airport, followed by the Arizona Public Service Solar Test and Research (APS-STaR) center in Tempe, Arizona. The various lens specimens were deployed for 20, 27, and 22 years, respectively. Optical characterizations included lens efficiency (Solar Simulator instrument), material transmittance and haze (of coupons cut from veteran lenses, then measured again after their facetedmore » back surface was polished, and then measured again after the incident front surface was polished), and direct transmittance (as a function of detector's acceptance angle, using the Very Low Angular Beam Spread ('VLABS') instrument). Lens efficiency measurements compared the central region to the entire lens, also using hot and cold mirror measurements to diagnose differences in performance. A series of subsequent characterizations was performed because a decrease in performance of greater than 10% was observed for some of the veteran lenses. Surface roughness was examined using atomic force microscopy and scanning electron microscopy. Facet geometry (tip and valley radius) was quantified on cross-sectioned specimens. Molecular weight was compared between the incident and faceted surfaces of the lenses.« less

Electron beam observation opportunity

NASA Astrophysics Data System (ADS)

Raitt, John; Banks, Peter

Ionospheric researchers will have the opportunity to conduct coordinated radio, radar, and optical observations in conjunction with other space-based electron beam experiments as part of the upcoming Cooperative High-Altitude Rocket Gun Experiments (CHARGE) 3 rocket flight in November 1988 at White Sands Missile Range (WSMR, White Sands, N.Mex.). The flight will be particularly interesting because of the high power planned for the electron gun (3.5 kV at 5 A), which is based, in part, on technology developments planned for the successful Excede series of rockets.CHARGE 3 is the third in a series of U.S. flights made in collaboration with investigators from Utah State University (Logan), Stanford University (Stanford, Calif.), the Institute for Space and Astronautical Sciences (Sendai, Japan), and the University of Michigan (Ann Arbor). The general objectives for CHARGE 3 are fourfold: to study vehicle charging and diagnosecontributory effects at higher beam currents and energy,to study ELF/VLF wave generation and propagation from dc and modulated electron beams,to diagnose beam propagation remotely by studying E region ionization and optical excitation, andto investigate voltage and current distribution in an electrically tethered space vehicle system at higher beam currents.

Overview of Hall D Complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chudakov, Eugene A.

Hall D is a new experimental hall at Jefferson Lab, designed for experiments with a photon beam. The primary motivation for Hall D is the GlueX experiment [1,2], dedicated to meson spectroscopy. The Hall D complex consists of: An electron beam line used to extract the 5.5-pass electrons from the accelerator into the Tagger Hall. The designed beam energy is E e = 12 GeV;The Tagger Hall, where the electron beam passes through a thin radiator (~0.01% R.L.) and is deflected into the beam dump. The electrons that lost >30% of their energy in the radiator are detected with scintillatormore » hodoscopes providing a ~0.1% energy resolution for the tagged photons. Aligned diamond radiators allow to produce linearly polarized photons via the Coherent Bremsstrahlung. The beam dump is limited to 60 kW (5 µA at 12 GeV); The Collimator Cave contains a collimator for the photon beam and dipole magnets downstream in order to remove charged particles. The 3.4 mm diameter collimator, located about 75 m downstream of the radiator, selects the central cone of the photon beam increasing its average linear polarization, up to ~40%in the coherent peak at 9 GeV; Hall D contains several elements of the photon beam line, and themain spectrometer. A Pair Spectrometer consists of a thin converter, a dipole magnet, and a two-arm detector used to measure the energy spectrum of the photon beam. The main spectrometer is based on a 2-T superconducting solenoid, 4 m long and 1.85 m bore diameter. The liquid hydrogen target is located in the front part the solenoid. The charged tracks are detected with a set of drift chambers; photons are detected with two electromagnetic calorimeters. There are also scintillator hodoscopes for triggering and time-of-flight measurements. The spectrometer is nearly hermetic in an angular range of 1° < θ < 120 •. The momentum resolution is σ p /p ~ 1 ₋ ₋3% depending on the polar angle θ. The energy resolution of the electromagnetic calorimeters is about 7% at 1 GeV.« less

Angular dependence of Kβ/Kα intensity ratios of thick Ti and Cu pure elements from 10-25 keV electron bombardment

NASA Astrophysics Data System (ADS)

Singh, B.; Kumar, S.; Prajapati, S.; Singh, B. K.; Llovet, X.; Shanker, R.

2018-02-01

Measurements yielding the first results on angular dependence of Kβ/Kα X-ray intensity ratios of thick Ti (Z = 22) and Cu (Z = 29) targets induced by 10-25 keV electrons are presented. The measurements were done by rotating the target surface around the electron beam direction in the angular detection range 105° ≤ θ ≤ 165° in the reflection mode using an energy dispersive Si PIN photodiode detector. The measured angular dependence of Kβ/Kα intensity ratios is shown to be almost isotropic for Ti and Cu targets for the range of detection angles, 105° ≤ θ ≤ 150°, while there is a very weak increase beyond 150° for both targets. No dependence of Kβ/Kα intensity ratios on impact energy is observed; while on average, the value of the Kβ/Kα X-ray intensity ratio for Cu is larger by about 8% than that for Ti, which indicates a weak Z-dependence of the target. The experimental results are compared with those obtained from PENELOPE MC calculations and from the Evaluated Atomic Data Library (EADL) ratios. These results on Kβ/Kα X-ray intensity ratios are found to be in reasonable agreement in the detection angle range 105° ≤ θ ≤ 150° to within uncertainties, whereas the simulation and experimental results show a very slight increase in the intensity ratio with θ as the latter attains higher values. The results presented in this work provide a direct check on the accuracy of PENELOPE at oblique incidence angles for which there has been a lack of measurements in the literature until now.

Electronic sputtering of LiF, CaF2, LaF3 and UF4 with 197 MeV Au ions. Is the stoichiometry of atom emission preserved?

NASA Astrophysics Data System (ADS)

Toulemonde, M.; Assmann, W.; Muller, D.; Trautmann, C.

2017-09-01

Sputtering experiments with swift heavy ions in the electronic energy loss regime were performed by using the catcher technique in combination with elastic recoil detection analysis. Four different fluoride targets, LiF, CaF2, LaF3 and UF4 were irradiated in the electronic energy loss regime using 197 MeV Au ions. The angular distribution of particles sputtered from the surface of freshly cleaved LiF and CaF2 single crystals is composed of a broad cosine distribution superimposed by a jet-like peak that appears perpendicular to the surface independent of the angle of beam incidence. For LiF, the particle emission in the entire angular distribution (jet plus broad cosine component) is stoichiometric, whereas for CaF2 the ratio of the sputtered F to Ca particles is at large angles by a factor of two smaller than the stoichiometry of the crystal. For single crystalline LaF3 no jet component is observed and the angular distribution is non-stoichiometric with the number of sputtered F particles being slightly larger than the number of sputtered La particles. In the case of UF4, the target was polycrystalline and had a much rougher surface compared to cleaved crystals. This destroys the appearance of a possible jet component leading to a broad angular distribution. The ratio of sputtered U atoms compared to F atoms is in the order of 1-2, i.e. the number of collected particles on the catcher is also non-stoichiometric. Such unlike behavior of particles sputtered from different fluoride crystals creates new questions.

Tilt angle measurement with a Gaussian-shaped laser beam tracking

NASA Astrophysics Data System (ADS)

Šarbort, Martin; Řeřucha, Šimon; Jedlička, Petr; Lazar, Josef; Číp, Ondrej

2014-05-01

We have addressed the challenge to carry out the angular tilt stabilization of a laser guiding mirror which is intended to route a laser beam with a high energy density. Such an application requires good angular accuracy as well as large operating range, long term stability and absolute positioning. We have designed an instrument for such a high precision angular tilt measurement based on a triangulation method where a laser beam with Gaussian profile is reflected off the stabilized mirror and detected by an image sensor. As the angular deflection of the mirror causes a change of the beam spot position, the principal task is to measure the position on the image chip surface. We have employed a numerical analysis of the Gaussian intensity pattern which uses the nonlinear regression algorithm. The feasibility and performance of the method were tested by numeric modeling as well as experimentally. The experimental results indicate that the assembled instrument achieves a measurement error of 0.13 microradian in the range +/-0.65 degrees over the period of one hour. This corresponds to the dynamic range of 1:170 000.

Stern-Gerlach-like approach to electron orbital angular momentum measurement

DOE PAGES

Harvey, Tyler R.; Grillo, Vincenzo; McMorran, Benjamin J.

2017-02-28

Many methods now exist to prepare free electrons into orbital-angular-momentum states, and the predicted applications of these electron states as probes of materials and scattering processes are numerous. The development of electron orbital-angular-momentum measurement techniques has lagged behind. We show that coupling between electron orbital angular momentum and a spatially varying magnetic field produces an angular-momentum-dependent focusing effect. We propose a design for an orbital-angular-momentum measurement device built on this principle. As the method of measurement is noninterferometric, the device works equally well for mixed, superposed, and pure final orbital-angular-momentum states. The energy and orbital-angular-momentum distributions of inelastically scattered electronsmore » may be simultaneously measurable with this technique.« less

Stern-Gerlach-like approach to electron orbital angular momentum measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, Tyler R.; Grillo, Vincenzo; McMorran, Benjamin J.

Many methods now exist to prepare free electrons into orbital-angular-momentum states, and the predicted applications of these electron states as probes of materials and scattering processes are numerous. The development of electron orbital-angular-momentum measurement techniques has lagged behind. We show that coupling between electron orbital angular momentum and a spatially varying magnetic field produces an angular-momentum-dependent focusing effect. We propose a design for an orbital-angular-momentum measurement device built on this principle. As the method of measurement is noninterferometric, the device works equally well for mixed, superposed, and pure final orbital-angular-momentum states. The energy and orbital-angular-momentum distributions of inelastically scattered electronsmore » may be simultaneously measurable with this technique.« less

Solution of the Fokker-Planck equation with mixing of angular harmonics by beam-beam charge exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikkelsen, D.R.

1989-09-01

A method for solving the linear Fokker-Planck equation with anisotropic beam-beam charge exchange loss is presented. The 2-D equation is transformed to a system of coupled 1-D equations which are solved iteratively as independent equations. Although isotropic approximations to the beam-beam losses lead to inaccurate fast ion distributions, typically only a few angular harmonics are needed to include accurately the effect of the beam-beam charge exchange loss on the usual integrals of the fast ion distribution. Consequently, the algorithm converges very rapidly and is much more efficient than a 2-D finite difference method. A convenient recursion formula for the couplingmore » coefficients is given and generalization of the method is discussed. 13 refs., 2 figs.« less