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Optics, Diagnostics and Applications for Fourth-Generation Light Sources

Description: The Linac Coherent Light Source (LCLS) is a 1.5 to 15 {angstrom}-wavelength free-electron laser (FEL), proposed for the Stanford Linear Accelerator Centre (SLAC). The photon output consists of high brightness, transversely coherent pulses with duration < 300 fs, together with a broad spontaneous spectrum with total power comparable to the coherent output. The output fluence, and pulse duration, pose special challenges for optical component and diagnostic designs. We first discuss the specific requirements for the initial scientific experiments, and our proposed solutions. We then describe the supporting research and development program that includes: (1) radiation field modeling, (2) experimental and theoretical material damage studies, (3) high resolution, high fluence-tolerant optical design, fabrication, and testing, (including material manufacturing), and (4) diagnostic design and testing.
Date: February 5, 2003
Creator: Wootton, A; Barbee, T; Bionta, R; Chapman, H; Ditmire, T; Dyer, G et al.
Partner: UNT Libraries Government Documents Department

Infrared FEL photochemistry: Multiple-photon dissociation of Freon gas

Description: Wavelength tunability, synchrotron sidebands, and picosecond pulse structure are inherent FEL characteristics that should be advantageous for photochemistry involving infrared multiple-photon photodissociation. Tuned to an absorption resonance, the FEL sideband structure will overlap the broad, excited-state spectral absorption and should lead to enhanced dissociation. The Los Alamos APEX FEL was operated with and without sidebands to test this hypothesis on CFCl{sub 3} (Freon 11), an inert chlorofluorocarbon widely used in refrigeration systems and one of the gases implicated as depleting the ozone in the Earth`s stratospheric layer. The FEL wavelength was set at the C-Cl stretch absorption resonance at 11.8-{mu}m, the oscillator cavity length was detuned first to minimize and then to maximize the spectral bandwidth, and the beam was focused through a pair of test cells (1.0 Torr Freon+1.7 Torr air). Comparison of final and initial absorbance spectra indicated the CFCl{sub 3} photodissociation yield was 1.2% for the cell exposed with sideband spectra (3% FWHM) and 9-ns micropulse separation. Negligible effect was seen without sidebands, albeit at lower total beam fluence. Although the result of this single experiment is not large enough to be conclusive, it does provide a basis for optimizing the FEL temporal and spectral parameters to attain higher photodissociation yield in future tests.
Date: October 1, 1993
Creator: Newnam, B. E.; Early, J. W. & Lyman, J. L.
Partner: UNT Libraries Government Documents Department

X-ray beam lines and beam line components for the SLAC Linac Coherent Light Source (LCLS)

Description: The LCLS is a novel high-brightness x-ray source designed to operate in the 300--400 eV range. In contrast to conventional synchrotron radiation sources, its output pulses will be characterized by unprecedented levels of brevity and peak power. In this paper we present recently-developed beam line layouts and design features intended to optimize the delivery of the LCLS photons to various experimental stations.
Date: April 1, 1993
Creator: Tatchyn, R. & Pianetta, P.
Partner: UNT Libraries Government Documents Department

Design considerations for a 60 meter permanent magnet undulator for the SLAC Linac Coherent Light Source (LCLS)

Description: In this paper we describe design, fabrication, and measurement aspects of a pure permanent magnet (PM) insertion device designed to operate as an FEL at a 1st harmonic energy of 300 eV and an electron energy of 7 GeV in the Self-Amplified Spontaneous Emission (SASE) regime.
Date: April 1, 1993
Creator: Tatchyn, R.; Boyce, R.; Halbach, K.; Nuhn, H. D.; Seeman, J.; Winick, H. et al.
Partner: UNT Libraries Government Documents Department

Numerical simulation studies of the design and performance of the AFEL for high average power operation

Description: AFEL (Advanced Free-Electron Laser) at Los Alamos is a compact free-electron laser oscillator which utilizes a very high-brightness electron beam generated by a high gradient linac whose source of electrons is a photocathode injector. This device has been operating, with 15--17 MeV electrons, at optical wavelengths in the 4.5--6.0 {mu}m range, since April of 1993 with a one-centimeter-period, permanent-magnet wiggler which is 24 periods long. The linac produces about 12 {mu}s macropulses at a normal repetition rate of one Hz, while the micropulse repetition rate within a macropulse is 108.33 Mhz which is consistent with the optical cavity length of about 138.5 cm. A program is now underway to upgrade the subsystems of this laser in order to allow it to produce long-time-average optical output powers in the range of 0.1 to 1.0 kW. In this communication, we briefly indicate the details of the equipment upgrades, describe a new high-extraction-efficiency wiggler, and present the results of numerical simulation studies of the design.
Date: October 1, 1994
Creator: Goldstein, J. C.; Takeda, H. & Nguyen, D. C.
Partner: UNT Libraries Government Documents Department

Common analysis of the relativistic klystron and the standing-wave free-electron laser two-beam accelerator

Description: This paper summarizes a new formalism which makes the analysis and understanding of both the relativistic klystron (RK) and the standing-wave free-electron laser (SWFEL) two-beam accelerator (TBA) available to a wide audience of accelerator physicists. A ``coupling impedance`` for both the RK and SWFEL is introduced, which can include realistic cavity features, such as beam and vacuum ports, in a simple manner. The RK and SWFEL macroparticle equations, which govern the energy and phase evolution of successive bunches in the beam, are of identical form, differing only by multiplicative factors. The analysis allows, for the first time, a relative comparison of the RF and SWFEL TBAs.
Date: July 1, 1992
Creator: Wurtele, J. S.; Whittum, D. H. & Sessler, A. M.
Partner: UNT Libraries Government Documents Department

Physically transparent formulation of a free-electron laser in the linear gain regime

Description: The recent 2-dimensional analytic theories of a free-electron laser (FEL) in the linear regime are reformulated in terms of three dimensionless ratios that describe the degree to which the characteristics of the electron beam deviate from the cold beam limit of a beam with no emittance or energy spread. In terms of these ratios, algebraic model equations of a fit that combines features of both of the 2-dimensional analyses are given as a convenient computational tool. Graphs of the FEL gain eigenvalue computed with the combined 2-D formulation illustrate that the gain and the output power at saturation are reduced from the 1-D value, when any of the ratios is larger than unity.
Date: August 1, 1992
Creator: Barletta, W. A.; Sessler, A. M. & Yu, L. H.
Partner: UNT Libraries Government Documents Department

Photon pulse filtering and modulation based on the extreme temporal compression and correlated energy spread of the electron bunches in the SLAC Linac Coherent Light Source (LCLS)

Description: The LCLS photon pulses are expected to attain unprecedented levels of brightness and brevity in the 300--400eV range. Nominally, the photon pulse length will be dominated by the electron bunch length, while the performance of conventional x-ray reflecting and band-shaping optics will be limited by : 1) peak power damage, and 2) transform-limited monochromatization. In this paper we describe how: 1) the correlated energy spread in the electron bunch can be used to selectably compress the LCLS photon pulses to below their nominal length; 2) gas optics can be used to mitigate peak damage problems; 3) the LCLS pulse structure can, in principle, accommodate schemes based on ``disposable`` optics; and 4) pulse lengthening schemes can be used to extend the attainable degree of monochromatization.
Date: May 1, 1993
Creator: Tatchyn, R.
Partner: UNT Libraries Government Documents Department

A proposal for the generation of ultra-short x-ray pulses

Description: In this paper it is shown that optical stochastic cooling in a 150 MeV electron storage ring will allow production of a beam with longitudinal emittance 4.5 {times} 10{sup {minus}6} MeV{center_dot}m. Such a small emittance accompanied with a bunch compression technique based upon the transformation in the longitudinal phase space will allow achieving a bunch length 30 {mu}m. This bunch could then be used for the generation of ultra-short x-ray pulses by the Compton scattering of laser photons.
Date: August 1, 1994
Creator: Zholents, A. A. & Zolotorev, M. S.
Partner: UNT Libraries Government Documents Department

Properties and Applications of Laser Generated X-Ray Sources

Description: The rapid development of laser technology and related progress in research using lasers is shifting the boundaries where laser based sources are preferred over other light sources particularly in the XUV and x-ray spectral region. Laser based sources have exceptional capability for short pulse and high brightness and with improvements in high repetition rate pulsed operation, such sources are also becoming more interesting for their average power capability. This study presents an evaluation of the current capabilities and near term future potential of laser based light sources and summarizes, for the purpose of comparison, the characteristics and near term prospects of sources based on synchrotron radiation and free electron lasers. Conclusions are drawn on areas where the development of laser based sources is most promising and competitive in terms of applications potential.
Date: February 25, 2002
Creator: Smith, R F & Key, M H
Partner: UNT Libraries Government Documents Department

Optical guiding and sideband suppression in the FEL and IFEL. Yearly technical progress report, July 1993--June 1994

Description: Several studies have been made of optical guiding and sideband effects that might occur using the hardware of certain experiments which are scheduled to operate in late 1994 at the Accelerator Test Facility at Brookhaven. We find that experimental observations of optical guiding and sidebanding would be fruitful in connection with the blue-green FEL oscillator experiment. Should the data bear out our expectations (obtained from TDA code runs described below), then some confidence would be established in our tentative conclusion --based upon the code as well as analytic theory-- that neither optical guiding nor sidebands are to be expected in connection with the IFEL accelerator.
Date: October 1, 1994
Creator: Marshall, T. C. & Bhattacharjee, A.
Partner: UNT Libraries Government Documents Department

Accelerator Technology Division progress report, FY 1993

Description: This report discusses the following topics: A Next-Generation Spallation-Neutron Source; Accelerator Performance Demonstration Facility; APEX Free-Electron Laser Project; The Ground Test Accelerator (GTA) Program; Intense Neutron Source for Materials Testing; Linac Physics and Special Projects; Magnetic Optics and Beam Diagnostics; Radio-Frequency Technology; Accelerator Controls and Automation; Very High-Power Microwave Sources and Effects; and GTA Installation, Commissioning, and Operation.
Date: December 31, 1993
Creator: Schriber, S. O.; Hardekopf, R. A. & Heighway, E. A.
Partner: UNT Libraries Government Documents Department

Fabrication of high-field short-period permanent magnet wigglers

Description: A permanent magnet wiggler is described that has been designed to lase at unusually short wavelengths. Its novel features include the following: all magnets are magnetized parallel to the wiggler`s axis; only two pairs per period are used; the gap occupied by the electron beam is very small; the magnet arrangement is optimized for lasing on the third harmonic; the assembly of the magnets is carried out during continuous measurements of the field integrals; field gradients are measured with equal care; and residual errors are corrected by gluing small correcting magnets to appropriate places. The assembly, testing, and trimming of this wiggler was accomplished in less than a week. The wiggler has been used to lase successfully at 0.375 {mu}m wavelength.
Date: September 1, 1993
Creator: Warren, R. W. & Fortgang, C. M.
Partner: UNT Libraries Government Documents Department

Initial performance of Los Alamos Advanced Free Electron Laser

Description: The Los Alamos compact Advanced FEL has lased at 4.7 and 5.2 {mu}m with a 1-cm period wiggler and a high-brightness electron beam at 16.8 and 15.8 MeV, respectively. The measured electron beam normalized emittance is 1.7 {pi}{center_dot}mm{center_dot}mrad at a peak current of 100 A, corresponding to a beam brightness greater than 2 {times} 10{sup 12} A/m{sup 2}rad{sup 2}. Initial results indicate that the AFEL small signal gain is {approximately}8% at 0.3 nC (30 A peak). The maximum output energy is 7 mJ over a 2-{mu}s macropulse. The AFEL performance can be significantly enhanced by improvements in the rf and drive laser stability.
Date: September 1, 1993
Creator: Nguyen, D. C.; Austin, R. H. & Chan, K. C. D.
Partner: UNT Libraries Government Documents Department

Performance of the high brightness linac for the Advanced Free Electron Laser Initiative at Los Alamos

Description: The AFEL accelerator has produced beams of greater than 2 {times} 10{sup 12} A/m{sup 2} at 1 nC (brightness = 2*I/{var_epsilon}{sup 2}, with I greater than 100 A and {var_epsilon} of than 2 {pi} mm-mrad normalized ms emittance). The 1300 MHz standing-wave accelerator uses on-axis coupling cells. The electron source is a photoinjector with a CsK{sub 2}Sb photocathode. The photoinjector is an integral part of a single 11-cell accelerator structure. The accelerator operates between 12 and 18 MeV. The beam emittance growth in the accelerator is minimized by using a photoinjector, a focusing solenoid to correct the emittance growth due to space charge, and a special design of the coupling slots between accelerator cavities to minimize quadrupole effects. This paper describes the experimental results and compares those results with PARMELA simulation. The simulation code PARMELA was modified for this effort. This modified version uses SUPERFISH files for the accelerator cavity fields, MAFIA files for the fields due to the coupling slots in the accelerator cells, and POISSON files for the solenoid field in the gun region.
Date: September 1, 1993
Creator: Sheffield, R. L.; Austin, R. H.; Chan, K. D. C.; Gierman, S. M.; Kinross-Wright, J. M.; Kong, S. H. et al.
Partner: UNT Libraries Government Documents Department

Inverse Free Electron Laser beat-wave accelerator research: Annual progress report

Description: In the past twelve-month period, we have completed our experimental study of the inverse-FEL autoaccelerator. The IFEL accelerates electrons by stimulated absorption of a laser pulse passing along an electron beam in an undulator; the autoaccelerator is a configuration we have developed at Columbia to test the principle of resonant absorption and acceleration. This report discusses the progress of this research.
Date: August 1, 1992
Creator: Marshall, T. C. & Bhattacharjee, A.
Partner: UNT Libraries Government Documents Department

Demonstration of ultraviolet lasing with a low energy electron beam

Description: We report on the design details of the first ultraviolet (UV) free-electron laser (FEL) oscillator driven by low-energy electrons from a radio-frequency linear accelerator. In our experiment we used a high-current, high brightness electon beam in combination with a wiggler of novel design to produce an FEL that lased at wavelengths from 369--380 nm using 45.9--45.2 MeV electrons. In addition we performed a proof-of principle experiment that demonstrated the first ever photolithography on a photoresist-coated silicon wafer using an FEL light source.
Date: August 10, 1993
Creator: O`Shea, P. G.; Bender, S. C. & Byrd, D. A.
Partner: UNT Libraries Government Documents Department

Variable-field permanent magnet dipole

Description: A new concept for a variable-field permanent-magnet dipole (VFPMD) has been designed, fabricated, and tested at Los Alamos. The VFPMD is a C-shaped sector magnet with iron poles separated by a large block of magnet material (SmCo). The central field can be continuously varied from 0.07 T to 0.3 T by moving an iron shunt closer or further away from the back of the magnet. The shunt is specially shaped to make the dependence of the dipole field strength on the shunt position as linear as possible. The dipole has a 2.8 cm high by 8 cm wide aperture with {approximately}10 cm long poles.
Date: October 1, 1993
Creator: Barlow, D. B.; Kraus, R. H. Jr. & Meyer, R. E.
Partner: UNT Libraries Government Documents Department

Infrared (IR) vs x-ray power generation in the SLAC Linac Coherent Light Source (LCLS)

Description: The LCLS, a Free-Electron Laser (FEL) designed for operation at a first harmonic energy of 300 eV ({lambda} {congruent} 40{Angstrom}) in the Self-Amplified Spontaneous Emission (SASE) regime, will utilize electron bunches compressed down to durations of <0.5ps, or lengths of <150 {mu}. It is natural to inquire whether coherent radiation of this (and longer) wavelength will constitute a significant component of the total coherent output of the FEL. In this paper a determination of a simple upper bound on the IR that can be generated by the compressed bunches is outlines. Under the assumed operating parameters of the LCLS undulator, it is shown that that IR component of the coherent output should be strongly dominated by the x-ray component.
Date: May 1, 1993
Creator: Tatchyn, R.
Partner: UNT Libraries Government Documents Department

Demonstration of resonant photopumping of Mo VII by Mo XII for a VUV laser near 600 {Angstrom}

Description: We present data of experiments on the resonant photopumping of Mo VII by Mo XII as a method of generating a coherent VUV source near 600 {angstrom}. The experiment is based on a scheme proposed by Feldman and Reader in which the 4p{sup 6} -- 4p{sup 5}6s transition in Mo VII in resonantly photopumped by the 5s {sup 2}S{sub 1/2} -- 4p {sup 2}P{sub 1/2} transition in Mo XII. Results of the laser produced plasma experiments show the successful enhancement of the population of the Mo VII 4p{sup 5}6s upper lasing level when pumped by an adjacent Mo VII plasma. No enhancement was seen in a control experiment where the Mo VII plasma was pumped by a Zr X plasma. Improvements of the intensity of the Mo XII pump source, achieved using an additional pump laser, lead to the generation of a population inversion for the VUV transition.
Date: September 1, 1993
Creator: Ilcisin, K. J.; Aumayr, F.; Schwob, J. L. & Suckewer, S.
Partner: UNT Libraries Government Documents Department

Wavelength and power stability measurements of the Stanford SCA/FEL

Description: Wavelength and power stability of the Stanford infrared SCA/FEL operating with the TRW wiggler have been measured using a high-resolution spectrometer and an image dissector system. The image dissector is capable of reading the spectrum of every single micropulse at 12 MHz throughout a macropulse of up to 2 ms duration. The intrinsic wavelength and power stability of the SCA/FEL are found to be {delta}{lambda}/{lambda}=0.035% and {delta}P/P=18%. The use of a feedback control system to stabilize the wavelength, and an acousto-optic modulator for output power smoothing, improves the performance to {delta}{lambda}/{lambda}=0.012% and {delta}P/P=7%.
Date: August 1, 1994
Creator: van der Geer, B.; de Loos, M. J.; Conde, M. E. & Leemans, W. P.
Partner: UNT Libraries Government Documents Department

Operational experience with a free-electron laser driven by an rf photoinjector linac

Description: For a number of years Los Alamos National Laboratory has been developing photocathode sources of high-brightness electron beams for FEL applications. The APEX FEL, which has been operational for over two years, was the first FEL to use a custom designed rf photoinjector as its electron source. The system consists of a 1.3 GHz, 6 MeV photoinjector with a multi-alkali photocathode illuminated by a frequency doubled ND:YLF drive-laser, followed by three separately powered accelerating structures that give a final electron energy of 40-MeV. The FEL has operated as an oscillator with either a permanent magnet or pulsed electromagnetic wigglers. Originally the FEL was designed to operate at a wavelengths near 3{mu}m, however the electron beam emittance and brightness are sufficient for harmonic lasing at much shorter wavelengths. We have demonstrated the tunability of the device from 0.37 to 11 {mu}m.
Date: October 1, 1993
Creator: O`Shea, P. G.
Partner: UNT Libraries Government Documents Department

The multi-cavity free-electron laser

Description: Consideration is made of a free-electron laser with many optical cavities where the cavities communicate with each other, not optically, but through the electron beam. Analysis is made in Ole one-dimensional approximation. A general expression is given for the growth rate in the exponential (high current) regime. In the regime where lethargy is important expressions are given in the two opposite limits of small and large numbers of cavities and bunches. Numerical simulation results, still in the one-dimensional approximation, but including non-linearities, are presented. The multi-cavity free-electron laser (MC/FEL) can be employed to avoid the slippage phenomena, and thus to make picosecond pulses of infra-red radiation. Three examples of this application are presented.
Date: July 1, 1992
Creator: Krishnagopal, S.; Rangarajan, G. & Sessler, A.
Partner: UNT Libraries Government Documents Department

Inverse free electron laser beat-wave accelerator research. Annual progress report, [August 1992--September 1993]

Description: A calculation on the stabilization of the sideband instability in the free electron laser (FEL) and inverse FEL (IFEL) was completed. The issue arises in connection with the use of a tapered (``variable-parameter``) undulator of extended length, such as might be used in an ``enhanced efficiency`` traveling-wave FEL or an IFEL accelerator. In addition, the FEL facility at Columbia was configured as a traveling wave amplifier for a 10-kW signal from a 24-GHz magnetron. The space charge field in the bunches of the FEL was measured. Completed work has been published.
Date: September 1, 1993
Creator: Marshall, T. C. & Bhattacharjee, A.
Partner: UNT Libraries Government Documents Department