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Even harmonic lasing

Description: Operation of a free-electron laser at harmonics of the fundamental frequency is explored with the numerical simulation code HELEX. This code includes coupling to the harmonics caused by misalignment of the electrons with the optical beam and coupling due to transverse gradients. Albeit weak, the transverse gradients produce the dominant coupling of the electrons to the even-harmonic light. Even-harmonic lasing occurs in a TEM{sub 0,2m+1}-like mode where the field on axis is zero. As bunching of the electron beam progresses, radiation at the higher odd harmonics is suppressed owing to the absence of higher-order odd-harmonic Fourier components in the bunch. Growth of the even-harmonic power from small signal requires suppression of competing harmonics (including the fundamental) that have higher gain. Lasing at an even harmonic has yet to be experimentally demonstrated in an open resonator (i.e. optical cavity). Strategies to make such an experiment possible are discussed. 9 refs., 5 figs., 1 tab.
Date: January 1, 1991
Creator: Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

Three-dimensional simulations of harmonic radiation and harmonic lasing

Description: Characteristics of the harmonic emission from free-electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission regimes, the interaction of the radiation fields with the electrons must be treated self-consistently. Here, a single-frequency distributed transverse source function for each electron is used in the harmonic version of the 3-D code FELEX to model the harmonic radiation. The code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiple-pass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored. 11 refs., 9 figs.
Date: January 1, 1990
Creator: Schmitt, M.J. & McVey, B.D.
Partner: UNT Libraries Government Documents Department

Spontaneous emission from free electron lasers

Description: Characteristics of the fundamental and harmonic emission from free-electron lasers (FELs) is examined in the spontaneous emission regime. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. For wigglers with many wiggle periods, calculation of the SE by integrating an ensemble of electrons along their exact trajectories becomes exceedingly cumbersome. Therefore, a different technique is used in which the far-field radiation pattern of a single electron is manipulated in transform space to include the effects if emittance. The effects of energy spread can be included by weighted sum over the energy distribution. The program execution time for wigglers of arbitrary length is negligible. The transverse radiation patterns including the transverse frequency dependences, are given. How this radiation is modeled in FEL simulation codes is discussed. 8 refs., 5 figs.
Date: January 1, 1991
Creator: Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

XUV harmonic enhancement by magnetic fields

Description: We examine three ways to enhance harmonic output of an XUV planar free-electron laser (FEL) operating in the Compton regime. The first method is to increase the rms static magnetic field, making it as large as possible. The second is by adding effective magnetic fields at the harmonics, thereby increasing the coupling to the harmonics. The third is by phase programming; i.e. programming the magnetic field to introduce jumps in the phase of the electrons as they move through phase space.
Date: September 1, 1986
Creator: Elliott, C.J. & Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

Free electron lasers using stable-unstable ring resonators

Description: The free electron laser (FEL) simulation code FELEX is used to examine the operation of stable-unstable FEL resonators. These resonators are stable along one transverse axis and unstable along the orthogonal transverse axis. The simulations utilize a ring resonator with an intracavity focus in the unstable plane near the center of the wiggler (close to the same axial position as the waist in the stable plane) thereby enhancing the coupling between the optical and electron beams. Asymmetric output scraping is performed in the back leg of the ring using a reflective mirror inserted from one side of the unstable axis. Resonators with relatively low equivalent Fresnel number (/vert bar/N/sub eq//vert bar/ less than or equal to 10) and magnification (/vert bar/M/sub x//vert bar/ approx. = 1.2) are examined. Optical characteristics including the cavity mode profile at various positions inside the resonator are shown. 8 refs., 8 figs.
Date: January 1, 1989
Creator: Schmitt, M.J. & Paxton, A.H.
Partner: UNT Libraries Government Documents Department

Theory of harmonic radiation using a single-electron source model

Description: Significant progress has recently been made toward the understanding of the various mechanisms that generate harmonic radiation in plane-polarized free electron lasers. Within the context of a single-frequency coherent-spontaneous emission model, a distributed transverse source function for a single electron has been derived. This source is multiply peaked, with the number of peaks being equal to the harmonic number. The peaks and nulls in the radiation source are analogous to the radiation peaks seen in the spontaneous radiation pattern of a single electron. When the distributed source function is averaged over transverse space, the simplified one-dimensional results are recovered. The distributed source function model predicts the generation of even harmonic radiation with odd-symmetry in the electron wiggle plane (for electrons traveling along the wiggler axis) and odd harmonic radiation patterns with even transverse symmetry. A method for modeling the multi-pole nature of the harmonic radiation on a discrete grid is described. When the transverse electron beam distribution is slowly varying, all the harmonics can be adequately modeled with multi-poles having only a few peaks. This model has been incorporated into the 3-D FEL simulation code FELEX. Simulations of the Los Alamos and Stanford FEL oscillators have been performed. How the harmonic transverse spatial electric field profiles change for different operating conditions is examined. 11 refs., 5 figs.
Date: January 1, 1989
Creator: Schmitt, M.J. & Elliott, C.J.
Partner: UNT Libraries Government Documents Department

Small signal gain based on analytic models of thin intense electron beams

Description: We develop the free-electron laser theory of the effective energy distribution and the small signal gain for a thin electron beam. The assumption of thinness allows us to treat various transverse locations and electron beam trajectory angles as introducing phase shifts that have the same effect as those introduced by a change in energy of the electron. We have extended these ideas in five important ways. The first is the ability to treat electron beams with three different classes of matching or symmetry conditions: (1) electron beams with separate betatron matching in each plane, (2) those with aspect ratio matching, and (3) crossed matched beams. Manifestations of these symmetries include elliptical cross sections and electron beams that have modulated spatial profiles. Second, two emittance parameters for the electron beam are shown to consolidate into a single parameter that describes most of the energy variation of the effective energy distributions. Third, these calculations extend to energy distributions, angular distributions, and spatial distributions that all follow gaussian profiles. Fourth, this model incorporates the description of the incident gaussian optical beam and the above electron beam dynamics into a single influence function kernal. Fifth, three-dimensional profiles of the optical fields are computed. In this work the parameters of the incident optical beam are included. The resulting transverse dependence of the fields may be characterized by an optical beam radius. This optical beam width starts out large compared to the thin electron beam and then, in the example given, contracts to a size that becomes so small that the thin beam assumption is violated. 10 refs., 5 figs.
Date: January 1, 1990
Creator: Elliott, C.J.; McVey, B. & Schmitt, M.
Partner: UNT Libraries Government Documents Department

Assessment of Infrared Remote Chemical Sensing Systems with Numeric Simulations

Description: A general approach to the evaluation of remote chemical sensors is described that can be used to provide evaluation of the chemical detection in a particular chemical scenario. It will be used to make comparisons of a CO{sub 2} laser differential absorption lidar sensor and a passive thermal FTIR sensor. The focus of the study will be to evaluate the advantage of the FTIR sensor's increased spectral coverage and number of frequency channels.
Date: November 1, 1998
Creator: Fry, H.; McVey, B. & Schmitt, M.
Partner: UNT Libraries Government Documents Department

Atmospheric effects on CO{sub 2} differential absorption lidar sensitivity

Description: The ambient atmosphere between the laser transmitter and the target can affect CO{sub 2} differential absorption lidar (DIAL) measurement sensitivity through a number of different processes. In this work, we will address two of the sources of atmospheric interference with CO{sub 2} DIAL measurements: effects due to beam propagation through atmospheric turbulence and extinction due to absorption by atmospheric gases. Measurements of atmospheric extinction under different atmospheric conditions are presented and compared to a standard atmospheric transmission model (FASCODE). We have also investigated the effects of atmospheric turbulence on system performance. Measurements of the effective beam size after propagation are compared to model predictions using simultaneous measurements of atmospheric turbulence as input to the model. These results are also discussed in the context of the overall effect of beam propagation through atmospheric turbulence on the sensitivity of DIAL measurements.
Date: March 1, 1996
Creator: Petrin, R.R.; Nelson, D.H. & Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

Muon interactions at 490 GeV

Description: E665 is a new, high-energy muon scattering experiment at Fermilab. Data were taken with a 490 GeV muon beam incident on deuterium, hydrogen, and xenon targets during the 1987--88 fixed target run. These data are being analyzed with various physics objectives in mind, and a number of preliminary results have been obtained. This paper presents four of results, specifically the small {chi}{sub Bj} ratio of xenon and deuterium cross sections, inclusive hadron distributions, two jet signals, and exclusive {rho}{sup 0} production.
Date: June 1, 1990
Creator: Schmitt, M. (Fermi National Accelerator Lab., Batavia, IL (USA) Harvard Univ., Cambridge, MA (USA))
Partner: UNT Libraries Government Documents Department

Three-dimensional simulations of the generation of one Angstrom radiation by a self-amplified spontaneous emission free-electron laser

Description: Three-dimensional numerical simulations of the generation of one Angstrom x-rays by a free-electron laser operating in the self-amplified spontaneous emission mode have been performed. Using model electron beam and wiggler parameters, we have investigated the length of wiggler needed to just avoid bandwidth broadening effects associated with gain saturation, and we have also obtained requirements for wiggler field errors to avoid significant loss of performance. 14 refs., 5 figs., 1 tab.
Date: January 1, 1990
Creator: Goldstein, J.C.; Elliott, C.J. & Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

Overtone production of soft x-rays with free-electron lasers

Description: Two one-dimensional free-electron laser codes have recently been written that include harmonic generation. A comparison of the results of these codes show that a self-consistent treatment of the harmonic interaction is not required in the presence of a strong fundamental field. Use of these codes to predict the effects of emittance on harmonic production have been conducted. The effects of wiggler-field amplitude fluctuations and odd-harmonic wiggler-field components on the harmonic-radiation production are also discussed.
Date: January 1, 1986
Creator: Schmitt, M.J.; Elliott, C.J.; Lee, K. & McVey, B.D.
Partner: UNT Libraries Government Documents Department

Free electron laser physical process code (FELPPC)

Description: Even at the conceptual level, the strong coupling between subsystem elements complicates the understanding and design of a free electron laser (FEL). Given the requirements for high-performance FELS, the coupling between subsystems must be included to obtain a realistic picture of the potential operational capability. The concept of an Integrated Numerical Experiment (INEX) was implemented to accurately calculate the coupling between the FEL subsystems. During the late 1980`s, the INEX approach was successfully applied to a large number of accelerator and FEL experiments. Unfortunately, because of significant manpower and computational requirements, the integrated approach is difficult to apply to trade-off and initial design studies. However, the INEX codes provided a base from which realistic accelerator, wiggler, optics, and control models could be developed. The Free Electron Laser Physical Process Code (FELPPC) includes models developed from the INEX codes, provides coupling between the subsystem models, and incorporates application models relevant to a specific study. In other words, FELPPC solves the complete physical process model using realistic physics and technology constraints. FELPPC can calculate complex FEL configurations including multiple accelerator and wiggler combinations. When compared with the INEX codes, the subsystem models have been found to be quite accurate over many orders-of-magnitude. As a result, FELPPC has been used for the initial design studies of a large number of FEL applications: high-average-power ground, space, plane, and ship based FELS; beacon and illuminator FELS; medical and compact FELS; and XUV FELS.
Date: February 1, 1995
Creator: Thode, L. E.; Chan, K. C. D. & Schmitt, M. J.
Partner: UNT Libraries Government Documents Department

Tevatron-for-LHC Report: Preparations for Discoveries

Description: This is the ''TeV4LHC'' report of the ''Physics Landscapes'' Working Group, focused on facilitating the start-up of physics explorations at the LHC by using the experience gained at the Tevatron. We present experimental and theoretical results that can be employed to probe various scenarios for physics beyond the Standard Model.
Date: August 1, 2006
Creator: Buescher, V.; Carena, Marcela S.; Dobrescu, Bogdan A.; Mrenna, S.; Rainwater, D. & Schmitt, M.
Partner: UNT Libraries Government Documents Department

Precision measurement of a particle mass at the linear collider

Description: Precision measurement of the stop mass at the ILC is done in a method based on cross-sections measurements at two different center-of-mass energies. This allows to minimize both the statistical and systematic errors. In the framework of the MSSM, a light stop, compatible with electro-weak baryogenesis, is studied in its decay into a charm jet and neutralino, the Lightest Supersymmetric Particle (LSP), as a candidate of dark matter. This takes place for a small stop-neutralino mass difference.
Date: June 1, 2007
Creator: Milstene, C.; /Fermilab; Freitas, A.; U., /Zurich; Schmitt, M.; U., /Northwestern et al.
Partner: UNT Libraries Government Documents Department

Compact-beam stable-unstable resonator for free-electron laser. Phase 2, Final report

Description: A significant problem in the design of high-energy free-electron lasers (FELs) centers on the technique for outcoupling the output beam. FELs with currently achievable output power usually include a conventional stable resonator with output through a partially transmitting mirror which will not work for arbitrarily high average power. An alternate scheme must be found for high-energy FELs. A high- efficiency grating outcoupler is an attractive possibility, but it is difficult to manufacture. Other suggestions include unstable resonators with an intracavity focus and unstable resonators with an intracavity focus and beam rotation. The intensity distribution at the intracavity focus of a negative-branch unstable resonator has side-lobes that would be scraped off by the faces of the wiggler magnets or by the beam tube through the wiggler. The resulting power loss would be significant. Therefore, it is desirable to develop another type of resonator for use with FELs. The resonator that we have developed is the compact-beam stable-unstable ring resonator. It is a stable resonator in one transverse dimension and an unstable resonator with an intracavity focus in the orthogonal transverse dimension. A scraper mirror outcouples the output beam from one side of the mode only. The resonator can be configured so that it has a small beam waist at the center of the wiggler in the stable direction and has an intracavity focus in the unstable direction. The half- width of the central lobe of the focus is approximately the size of the stable beam waist. In the stable direction, the Gaussian amplitude distribution results in a small loss on the wiggler magnets, or on a beam tube that will fit within the wiggler, if one is used. The beam tube can have an elliptical shape to permit the passage of several side lobes in the unstable dimension. A mode of ...
Date: October 1, 1991
Creator: Paxton, A.H.; White, C.J.; Boyd, T.L.; Schmitt, M.J. & Aldrich, C.H.
Partner: UNT Libraries Government Documents Department

Aperture averaging of optical scintillations in CO{sub 2} DIAL

Description: Atmospheric turbulence causes several effects on a propagating laser beam. The authors have previously studied the effects of beam spreading and beam wander, and feel they have a good understanding of their impact on CO{sub 2} DIAL. Another effect is scintillation where atmospheric turbulence causes irradiance fluctuations within the envelope of the beam profile. They believe that scintillation at the target plays an important role in LIDAR return statistics. A Huygens-Fresnel wave optics computer simulation for propagating beams through atmospheric optical turbulence has been previously developed. They modify this simulation to include the effects of reflective speckle and examine its application in comparison with experimental data.
Date: October 1, 1997
Creator: Nelson, D.H.; Petrin, R.R.; Schmitt, M.J.; Whitehead, M.C. & Walters, D.L.
Partner: UNT Libraries Government Documents Department

CO{sub 2} dial transmitter/receiver noise characterization and related correlated noise issues

Description: Our approach concerning the development of hard target return CO{sub 2} DIAL transmitter/receiver systems is two phased- (i) through analysis and experiment, develop a fundamental understanding of the transmitter/receiver physics specific to DIAL systems and (ii) apply these fundamentals in the development of optimal performance DIAL transmitter/receiver systems. We present our progress and results towards these objectives with the following topics addressed: A general overview of the DIAL transmitter/receiver system characterization effort with a focus on transceiver noise processes. The effects of correlated noise on DIAL performance, especially those effecting statistical convergence over long sample structures, is , introduced. And, preliminary measurements of a low-noise, ``white`` receiver prototype are presented.
Date: February 1, 1996
Creator: Cooke, B.; Schmitt, M.; Goeller, R.; Czuchlewski, S.; Fuller, K.; Olivas, N. et al.
Partner: UNT Libraries Government Documents Department

Atmospheric effects on CO{sub 2} differential absorption lidar performance

Description: CO{sub 2} differential absorption lidar (DIAL) performance can be adversely affected by the ambient atmosphere between the laser transmitter and the target through a number of different processes. This work addresses two sources of atmospheric interference with multispectral CO{sub 2} DIAL measurements: effects due to beam propagation through atmospheric turbulence and extinction due to absorption by atmospheric gases. The authors compare measurements of the effective beam size after propagation to predictions from a beam propagation model that includes turbulence effects such as beam steering and beam spreading. They also compare the experimental measurements of atmospheric extinction to those predicted by both a standard atmospheric transmission model (FASCODE) and a chemometric analysis.
Date: May 1, 1996
Creator: Petrin, R.R.; Quagliano, J.R.; Nelson, D.H.; Schmitt, M.J.; Quick, C.R.; Sander, R.K. et al.
Partner: UNT Libraries Government Documents Department

HIGGS PHYSICS WITH A GAMMA GAMMA COLLIDER BASED ON CLIC 1*.

Description: We present the machine parameters and physics capabilities of the CLIC Higgs Experiment (CLICHE), a low-energy {gamma}{gamma} collider based on CLIC 1, the demonstration project for the higher-energy two-beam accelerator CLIC. CLICHE is conceived as a factory capable of producing around 20,000 light Higgs bosons per year. We discuss the requirements for the CLIC 1 beams and a laser backscattering system capable of producing a {gamma}{gamma} total (peak) luminosity of 2.0 (0.36) x 10{sup 34} cm{sup -2} s{sup -1} with E{sub CM}({gamma}{gamma}) 115 GeV. We show how CLICHE could be used to measure accurately the mass, {bar b}b, WW and {gamma}{gamma} decays of a light Higgs boson. We illustrate how these measurements may distinguish between the Standard Model Higgs boson and those in supersymmetric and more general two-Higgs-doublet models, complementing the measurements to be made with other accelerators. We also comment on other prospects in {gamma}{gamma} and e{sup -}{gamma} physics with CLICHE.
Date: November 1, 2001
Creator: ASNER,D.; BURKHARDT,H.; DE ROECK,A.; ELLIS,J.; GRONBERG,J.; HEINEMEYER,S. et al.
Partner: UNT Libraries Government Documents Department

Integrated Numerical Experiments (INEX) and the Free-Electron Laser Physical Process Code (FELPPC)

Description: The strong coupling of subsystem elements, such as the accelerator, wiggler, and optics, greatly complicates the understanding and design of a free electron laser (FEL), even at the conceptual level. Given the requirements for high-performance FELs, the strong coupling between the laser subsystems must be included to obtain a realistic picture of the potential operational capability. To address the strong coupling character of the FEL the concept of an Integrated Numerical Experiment (INEX) was proposed. Unique features of the INEX approach are consistency and numerical equivalence of experimental diagnostics. The equivalent numerical diagnostics mitigates the major problem of misinterpretation that often occurs when theoretical and experimental data are compared. The INEX approach has been applied to a large number of accelerator and FEL experiments. Overall, the agreement between INEX and the experiments is very good. Despite the success of INEX, the approach is difficult to apply to trade-off and initial design studies because of the significant manpower and computational requirements. On the other hand, INEX provides a base from which realistic accelerator, wiggler, and optics models can be developed. The Free Electron Laser Physical Process Code (FELPPC) includes models developed from INEX, provides coupling between the subsystems models and incorporates application models relevant to a specific trade-off or design study.
Date: January 1, 1990
Creator: Thode, L.E.; Chan, K.C.D.; Schmitt, M.J.; McKee, J.; Ostic, J.; Elliott, C.J. et al.
Partner: UNT Libraries Government Documents Department

Simulation codes for modeling free-electron laser oscillators

Description: This paper reviews the basic characteristics of free-electron laser (FEL) oscillators, and describes a group of codes that have been developed to analyze and design rf-linac-driven FELs. The optical performance of an FEL has been treated using 1-D time-dependent (finite pulse) codes that describe the characteristics of the optical temporal pulse shape and spectrum during the evolution of the oscillator from, low-intensity small-signal gain conditions to high-intensity large-signal gain conditions. These codes can include frequency-dependent elements, such as narrow-band filters or grating rhombs. Diffraction effects, transverse optical and electron-beam mode properties, misalignments, as well as aberrations on optical elements are modeled with the 3-D code FELEX. This code has now been extended to include effects of imperfections in the wiggler magnetic field and light emission at higher optical harmonics. A separate accelerator modeling capability allows the use of a numerically-generated electron pulse in FELEX for 3-D integrated numerical FEL simulations. 26 refs., 10 figs.
Date: January 1, 1988
Creator: Goldstein, J.C.; McVey, B.D.; Tokar, R.L.; Elliott, C.J.; Schmitt, M.J.; Carlsten, B.E. et al.
Partner: UNT Libraries Government Documents Department

Numerical simulations of free-electron laser oscillators

Description: A numerical simulation capability has been developed to model the physics and realistic design constraints of free electron laser oscillators driven by rf linear accelerators. Two computer codes have been written FELEX and FELP. The code FELP is a one spatial dimension code with essentially unlimited time or spectral resolution. The codes are complementary and their use is dependent upon the problem being addressed. The code FELP is used to model optical and electron micropulse structure, broadband noise, and the sideband instability. The code FELEX models accelerator generated electron beam distributions, the transport of these distributions through wigglers with misalignments and field errors, self-consistent interaction with the optical field, and propagation of the optical field through resonators with realistically modelled components. FELEX is routinely used to match resonator designs to the optical parameters of the electron beam, and used to investigate the physics of 3-D micropulse effects. Some details of the codes will be presented along with various examples of simulation results. 22 refs., 10 figs., 1 tab.
Date: January 1, 1988
Creator: McVey, B.D.; Goldstein, J.C.; Tokar, R.L.; Elliott, C.J.; Gitomer, S.J.; Schmitt, M.J. et al.
Partner: UNT Libraries Government Documents Department

Huygens-Fresnel wave-optics simulation of atmospheric optical turbulence and reflective speckle in CO{sub 2} differential absorption lidar (DIAL)

Description: The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. The authors have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these processes: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements. The limitations of the model are also discussed. In addition, studies have been performed to determine the importance of key parameters in the simulation. The results of these studies and their impact on the overall results will be presented.
Date: April 1, 1999
Creator: Nelson, D.; Petrin, R.; MacKerrow, E.; Schmitt, M.; Foy, B.; Koskelo, A. et al.
Partner: UNT Libraries Government Documents Department