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Survey Talk--New Laser and Optical RadiationDiagnostics

Description: New techniques am reported for electron beam monitoring, that rely either on the analysis of the properties of wiggler radiation (from static magnetic fields as well as from laser "undulators", also referred to as Thomson scattering) or on the non-linear mixing of laser radiation with electron beam radiation. The different techniques reviewed are capable of providing information on femtosecond time scales and micron or even sub-micron spatial scales. The laser undulator is also proposed as a useful tool for non- destructive measurement of high power electron beams. An example is given of measuring electron beam energy and energy spread through spectral filtering of spontaneous wiggler radiation [1]. A novel technique based on fluctuational characteristics of radiation is described, for single shot, nondestructive measurement of the electron beam bunch length [2,3]. Thomson scattering based beam monitoring techniques are discussed which, through analysis of the radiated beam properties, allow non-destructive detailed measurement of transverse and longitudinal distributions of relativistic electron beams [4]. Two new techniques are discussed which rely on non-linear optical mixing of laser radiation with electron bunch emission: differential optical gating (DOG) [5] and electron bunch length measurement in a storage ring based on sum-frequency generation [6].
Date: September 1, 1998
Creator: Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Working Group VI Summary Report: New Ideas Employing High-Power Lasers

Description: The objectives of this working group were to provide the ''Future Light Source Community'' information on: Electron-Laser interaction based sources; Plasma based radiation sources and accelerators; and Present and future high-power laser technology. A summary of presentations, discussions and opinions is presented next. At the end of this report, a few references are given. The list is very far from being complete but is meant as a start for further exploring the various topics discussed in this working group. Based on presentations and discussions during the workshop, a summarizing table of the performance of three different types of laser systems has been made. The emphasis is on listing performance parameters of solid state, FEL and gas based lasers, relevant to the development of a future fourth generation light source. Two types of solid state lasers capable of producing peak power in the multi-terawatt range are described: Nd:glass and Ti:sapphire lasers [1]. The main development for these lasers is towards higher average power levels: from the 10 W to the > 100 W level. An infrared FEL has recently produced 1 kW average power but with peak power on the order of 0.1 GW [2]. A terawatt class, short pulse CO{sub 2} based gas laser is under development at the Advanced Test Facility at BNL [3].
Date: April 9, 1999
Creator: Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Laser based sub-picosecond electron bunch characterization using 90{degree} Thomson scattering

Description: X-rays produced by 90{degree} Thomson scattering of a femtosecond, near infrared, terawatt laser pulse off a 50 MeV electron beam are shown to be an effective diagnostic to measure transverse and longitudinal density distributions of an electron beam (e-beam) with subpicosecond time resolution. The laser beam was focused onto the e-beam waist, generating 30 keV x-rays in the forward direction. The transverse and longitudinal e-beam structure have been obtained by measuring the intensity of the x-ray beam, while scanning the laser beam across the e-beam in space and time. The e-beam divergence has been obtained through measurement of spatial and spectral characteristics of the scattered x-ray beam.
Date: May 1, 1997
Creator: Leemans, W.P.; Volfbeyn, P. & Zolotorev, M.
Partner: UNT Libraries Government Documents Department

Femtosecond x-rays from Thomson scattering using laser wakefield accelerators

Description: The possibility of producing femtosecond x-rays through Thomson scattering high power laser beams off laser wakefield generated relativistic electron beams is discussed. The electron beams are produced with either a self-modulated laser wakefield accelerator (SM-LWFA) or through a standard laser wakefield accelerator (LWFA) with optical injection. For a SM-LWFA (LWFA) produced electron beam, a broad (narrow) energy distribution is assumed, resulting in X-ray spectra that are broadband (monochromatic). Designs are presented for 3-100 fs x-ray pulses and the expected flux and brightness of these sources are compared.
Date: March 1, 2001
Creator: Catravas, P.; Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Betatron radiation from electron beams in plasma focusing channels

Description: Spontaneous radiation emitted from an electron undergoing betatron motion is a plasma focusing channel is analyzed and applications to plasma wakefield accelerator experiments and to the ion channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and in an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter a{sub {beta}}, which plays a similar role to that of the wiggler strength parameter in a conventional FEL. For a{sub {beta}} {approx_gt} 1, radiation is emitted in numerous harmonics. Furthermore, a{sub {beta}} is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. This places serious limits on the possibility of realizing an ICL.
Date: June 1, 2000
Creator: Esarey, E.; Catravas, P. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Experimental studies of laser guiding in plasma channels

Description: The authors present results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme is proposed and experimentally tested in hydrogen and nitrogen. It makes use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows, creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a > 5 {times} 10{sup 17} W/cm{sup 2}, 75 fs laser pulse.
Date: July 1, 1998
Creator: Volfbeyn, P. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Guiding of high intensity ultrashort laser pulses in plasma channels produced with the dual laser pulse ignitor-heater technique

Description: The authors present results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme is proposed and experimentally tested in hydrogen and nitrogen. It makes use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a > 5 {times} 10{sup 17} W/cm{sup 2}, 75 fs laser pulse.
Date: July 1, 1998
Creator: Volfbeyn, P. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Electron beam conditioning by Thomson scattering

Description: A method is proposed for conditioning electron beams via Thomson scattering. The conditioning provides a quadratic correlation between the electron energy deviation and the betatron amplitude of the electrons, which results in enhanced gain in free-electron lasers. Quantum effects imply conditioning must occur at high laser fluence and moderate electron energy. Conditioning of x-ray free-electron lasers should be achievable with present laser technology, leading to significant size and cost reductions of these large-scale facilities.
Date: November 25, 2003
Creator: Schroeder, C.B.; Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Laser Wakefield diagnostic using holographic longitudinal interferometry

Description: We propose a diagnostic technique for wakefield measurement in plasma channels. A new technique for plasma channel creation, the Ignitor Heater scheme was proposed and experimentally tested in hydrogen and nitrogen previously. It makes use of two laser pulses. The Ignitor, an ultrashort (sub 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used to heat the existing spark via in-verse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. Laser pulses injected into such plasma channels produce a plasma wake that has a phase velocity close to the speed of light. A discussion of plasma wake measurements, using a Longitudinal Interferometry Wakefield Diagnostic Based on Time Domain Rayleigh Refractometry with Holographic Inversion, will be presented.
Date: March 26, 1999
Creator: Volfbeyn, P.; Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation from electron beams in plasma focusing channels

Description: Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma focusing channel is analyzed and application to plasma wakefield accelerator experiments and to the ion channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter alpha-beta, which plays a similar role to that of the wiggler strength parameter in a conventional FEL. For alpha-beta > 1, radiation is emitted in numerous harmonics. Furthermore, alpha-beta is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. The radiation spectrum emitted from an electron beam is calculated by averaging the single electron spectrum over the electron distribution. This leads to a frequency broadening of the radiation spectrum, which places serious limits on the possibility of realizing an ICL.
Date: December 6, 2001
Creator: Esarey, E.; Shadwick, B.A.; Catravas, P. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Radiation sources and diagnostics with ultrashort electron bunches

Description: The basic principles and design of radiation sources (transition radiation, Cerenkov radiation, radiation from periodic structures, etc.) and radiation-based diagnostics will be discussed, with emphasis on radiation from ultra-short electron bunches. Ultra-short electron bunches have the potential to produce high peak flux radiation sources that cover wavelength regimes where sources are currently not widely available (coherent THz/IR) as well as ultrashort X-ray pulses (3-100 fs). While radiation from the electron bunch contains the full signature of the electron beam and/or medium it has travelled through, the deconvolution of a single property of interest can be difficult due to a large number of contributing properties. The experimental implementation of novel solutions to this problem will be described for beams from 30 MeV to 30 GeV, including fluctuational interferometry, source imaging, phase matched cone angles and laser-based techniques, which utilize optical transition radiation, wiggler and Cerenkov radiation, and Thomson scattering. These novel diagnostic methods have the potential to resolve fs bunch durations, slice emittance on fs scales, etc. The advantages and novel features of these techniques will be discussed.
Date: November 2, 2001
Creator: Catravas, P.; Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Experimental test of hole-coupled FEL resonator designs using a CW-HeNe laser

Description: We report on ongoing experiments and simulations which model the performance of hole-coupled resonators. We have previously studied a hole-coupled resonator which was well inside the stable region (stability parameter g = [minus]0.8). In the far field, good agreement between experiment and simulation was obtained for both the intracavity and outcoupled mode-profile. The present study involves a resonator with a stability parameter of [minus]0.987, identical to the stability parameter of the proposed Infrared Free Electron Laser (IRFEL) at Lawrence Berkeley Laboratory. The experiments were carried out with a frequency stabilized CW-HeNe laser beam at a wavelength of 632.8 nm. Both intracavity and outcoupled mode profiles and power levels were measured. The simulations were done using the code HOLD, which is based on the Fresnel approximation for the Huygens kernel. Within the experimental uncertainties, magnified due to the 1/(1+g) dependence of the mode characteristics on errors in measured resonator parameters, we have obtained fair agreement between experiment and simulation.
Date: January 1, 1993
Creator: Leemans, W.P.; Wallace, E.W.; Xie, M. & Kim, K.J.
Partner: UNT Libraries Government Documents Department

Experimental test of hole-coupled FEL resonator designs using a CW-HeNe laser

Description: We report on ongoing experiments and simulations which model the performance of hole-coupled resonators. We have previously studied a hole-coupled resonator which was well inside the stable region (stability parameter g = {minus}0.8). In the far field, good agreement between experiment and simulation was obtained for both the intracavity and outcoupled mode-profile. The present study involves a resonator with a stability parameter of {minus}0.987, identical to the stability parameter of the proposed Infrared Free Electron Laser (IRFEL) at Lawrence Berkeley Laboratory. The experiments were carried out with a frequency stabilized CW-HeNe laser beam at a wavelength of 632.8 nm. Both intracavity and outcoupled mode profiles and power levels were measured. The simulations were done using the code HOLD, which is based on the Fresnel approximation for the Huygens kernel. Within the experimental uncertainties, magnified due to the 1/(1+g) dependence of the mode characteristics on errors in measured resonator parameters, we have obtained fair agreement between experiment and simulation.
Date: January 1, 1993
Creator: Leemans, W. P.; Wallace, E. W.; Xie, M. & Kim, K. J.
Partner: UNT Libraries Government Documents Department

Characterization of the 50 MeV ALS linac beam with optical transition radiation

Description: First experimental results of the optical transition radiation diagnostic at the Beam Test Facility (BTF) are presented. The BTF uses the 50 MeV Advanced Light Source (ALS) injector. Using sensitive CCD cameras single shot energies, spot sizes and divergences can be measured for the lnC/bunch electron beam. The emittance was determined by analyzing optical transition radiation data for various currents of a quadrupole lens.
Date: June 1, 1994
Creator: de Loos, M. J.; van der Geer, S. B. & Leemans, W. P.
Partner: UNT Libraries Government Documents Department

Design of an XUV FEL Driven by the Laser-Plasma Accelerator at theLBNL LOASIS Facility

Description: We present a design for a compact FEL source of ultrafast, high-peak flux, soft x-ray pulses employing a high-current, GeV-energy electron beam from the existing laser-plasma accelerator at the LBNL LOASIS laser facility. The proposed ultra-fast source would be intrinsically temporally synchronized to the drive laser pulse, enabling pump-probe studies in ultra-fast science with pulse lengths of tens of fs. Owing both to the high current ({approx} 10 kA) and reasonable charge/pulse ({approx} 0.1-0.5 nC) of the laser-plasma-accelerated electron beams, saturated output fluxes are potentially 10{sup 13}--10{sup 14} photons/pulse. We examine devices based both on SASE and high-harmonic generated input seeds to give improved coherence and reduced undulator length, presenting both analytic scalings and numerical simulation results for expected FEL performance. A successful source would result in a new class of compact laser-driven FELs in which a conventional RF accelerator is replaced by a GeV-class laser-plasma accelerator whose active acceleration region is only a few cm in length.
Date: September 1, 2006
Creator: Schroeder, Carl B.; Fawley, W.M.; Esarey, Eric & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Femtosecond electron and x-ray generation by laser andplasma-based sources

Description: The generation of ultra-short x-rays by Thomson scattering intense laser pulses from electron beams is discussed, including recent experimental results and methods for enhancing the x-ray flux. A high flux of x-rays in a femtosecond pulse requires the generation of femtosecond electron bunches and a head-on Thomson scattering geometry. The generation of ultrashort electron bunches in a plasma-based accelerator with an injection technique that uses two colliding laser pulses is discussed. Simulations indicate the bunches as short as a few fs can be produced. Conversion of the fs electron pulse to a fs x-ray pulse can be accomplished by Bremsstrahlung or Thomson scattering.
Date: February 1, 2000
Creator: Esarey, E. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Improvement of electron beam quality in optical injection schemesusing negative plasma density gradients

Description: Enhanced electron trapping using plasma density down ramps as a method for improving the performance of laser injection schemes is proposed and analyzed. A decrease in density implies an increase in plasma wavelength, which can shift a relativistic electron from the defocusing to the focusing region of the accelerating wakefield, and a decrease in wake phase velocity, which lowers the trapping threshold. The specific method of two-pulse colliding pulse injector was examined using a three-dimensional test particle tracking code. A density down-ramp with a change of density on the order of tens of percent over distances greater than the plasma wavelength led to an enhancement of charge by two orders in magnitude or more, up to the limits imposed by beam loading. The accelerated bunches are ultrashort (fraction of the plasma wavelength, e.g., {approx}5 fs), high charge (&gt;20 pC at modest injection laser intensity 10{sup 17} W/cm{sup 2}), with a relative energy spread of a few percent at a mean energy of {approx}25 MeV, and a normalized root-mean square emittance on the order 0.5 mm mrad.
Date: July 26, 2005
Creator: Fubiani, G.; Esarey, E.; Schroeder, C.B. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Laser guiding at>1018 W/cm2 in plasma channels formed by theignitor heater method

Description: Experiments explore guiding of intense laser pulses, optimization using channel formation beams and gas jet targets, and the interplay of channel guiding and relativistic self guiding. Impact on laser wakefield particle acceleration is being assessed.
Date: May 1, 2004
Creator: Geddes, C.G.R.; Toth, C.; vanTilborg, J. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Trapping and dark current in plasma-based accelerators

Description: The trapping of thermal electrons in a nonlinear plasma wave of arbitrary phase velocity is investigated. The threshold plasma wave amplitude for trapping plasma electrons is calculated, thereby determining the fraction trapped and the expected dark current in a plasma-based accelerator. It is shown that the presence of a laser field (e.g., trapping in the self-modulated regime of the laser wakefield accelerator) increases the trapping threshold. Implications for experimental and numerical laser-plasma studies are discussed.
Date: June 1, 2004
Creator: Schroder, C.B.; Esarey, E.; Shadwick, B.A. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Raman forward scattering of high-intensity chirped laser pulses

Description: Raman forward scattering of a high-intensity, short-duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Relation of these results to recent experiments is discussed.
Date: June 23, 2002
Creator: Schroeder, C.B.; Esarey, E.; Shadwick, B.A. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Raman forward scattering of chirped laser pulses

Description: Raman scattering of a high-intensity, short duration, frequency-chirped laser pulse propagating in an underdense plasma is examined. The growth of the direct forward scattered light is calculated for a laser pulse with a linear frequency chirp in various spatio-temporal regimes. This includes a previously undescribed regime of strongly-coupled four-wave nonresonant interaction, which is important for relativistic laser intensities. In all regimes of forward scattering, it is shown that the growth rate increases (decreases) for positive (negative) frequency chirp. The effect of chirp on the growth rate is relatively minor, i.e., a few percent chirp yields few percent changes in the growth rates. Numerical solutions based on fully nonlinear cold Maxwell-fluid model are presented which confirm analytical predictions. Relation of these results to recent experiments is discussed.
Date: December 5, 2002
Creator: Schroeder, C.B.; Esarey, E.; Shadwick, B.A. & Leemans, W.P.
Partner: UNT Libraries Government Documents Department

Experiment and simulation of hole-coupled resonator modes with a CW HeNe laser

Description: The Infrared Free Electron Laser (IRFEL) for the proposed Chemical Dynamics Laboratory at Lawrence Berkeley Laboratory will operate from 3 - 50 [mu]m and use all-metal optics. This choice of optics allows for broad tuning and has excellent power-handling capabilities. A hole-coupling approach for the optical resonator was adopted after extensive computer simulations verified that it fully met the design requirements. To bench-test the simulations we have carried out a scaled cavity experiment utilizing a visible (632.8 nm) continuous wave (CW) HeNe laser. Two cases have been studied: (a) a Gaussian near-concentric symmetric resonator and (b) a hole-coupled resonator with degenerate higher order modes. The simple geometry of the former case allows for a direct comparison with analytical theory and is useful for bench marking the diagnostic equipment. Since mode degeneracy should be avoided for good operation of an FEL, gaining an understanding of the latter case is important. Furthermore, it provides a good test case for evaluating the code performance. After discussing the theoretical model used in the simulations, we describe the cavity parameters and the experimental set-up. We proceed by comparing, for both case (a) and (b), the experimental results with theoretical predictions and simulations. This is followed by the summary and conclusions of these experiments.
Date: August 1, 1992
Creator: Leemans, W.P.; Xie, M.; Edighoffer, J.A.; Wallace, E.; Kim, K.J. & Chattopadhyay, S.
Partner: UNT Libraries Government Documents Department

A technique for single-pulse spectrum and pulse width measurements for an IR-FEL

Description: A diagnostic system has been designed to measure the spectrum and pulse width of infrared FEL pulses. Use of an image dissector [1] and a single element high speed detector with integrating sphere, allows one to obtain spectral or temporal information for each individual micro-pulse inside the pulse train. The spectral diagnostic consists of a mode matching telescope, a high resolution spectrometer, an imaging telescope and an image dissector system. The imaging telescope between the spectrograph and the image dissector provides for variable magnification (and hence resolution) of the spectrum onto the image dissector. The pulse width measurement uses single pulse autocorrelation through non-collinear optical mixing in a frequency doubling crystal [2], an imaging telescope and again an image dissector system. Here, the imaging telescope relays the image of the region in the nonlinear crystal in which second harmonic light was generated onto the image dissector. The design and implementation of these diagnostics for the 1--11 {mu}m on the IR-FEL at Stanford University are discussed.
Date: August 1, 1992
Creator: Leemans, W. P.; Edighoffer, J. A.; Kim, K. J.; Chattopadhyay, S. & Schwettman, H. A.
Partner: UNT Libraries Government Documents Department

Experiment and simulation of hole-coupled resonator modes with a CW HeNe laser

Description: The Infrared Free Electron Laser (IRFEL) for the proposed Chemical Dynamics Laboratory at Lawrence Berkeley Laboratory will operate from 3 - 50 {mu}m and use all-metal optics. This choice of optics allows for broad tuning and has excellent power-handling capabilities. A hole-coupling approach for the optical resonator was adopted after extensive computer simulations verified that it fully met the design requirements. To bench-test the simulations we have carried out a scaled cavity experiment utilizing a visible (632.8 nm) continuous wave (CW) HeNe laser. Two cases have been studied: (a) a Gaussian near-concentric symmetric resonator and (b) a hole-coupled resonator with degenerate higher order modes. The simple geometry of the former case allows for a direct comparison with analytical theory and is useful for bench marking the diagnostic equipment. Since mode degeneracy should be avoided for good operation of an FEL, gaining an understanding of the latter case is important. Furthermore, it provides a good test case for evaluating the code performance. After discussing the theoretical model used in the simulations, we describe the cavity parameters and the experimental set-up. We proceed by comparing, for both case (a) and (b), the experimental results with theoretical predictions and simulations. This is followed by the summary and conclusions of these experiments.
Date: August 1, 1992
Creator: Leemans, W. P.; Xie, M.; Edighoffer, J. A.; Wallace, E.; Kim, K. J. & Chattopadhyay, S.
Partner: UNT Libraries Government Documents Department