Free Electron Laser Applications Research Articles

Femto-seconds kilo-ampere electron beam generation

Generating femtoseconds electron bunches is critical for X-ray free electron laser, laser accelerators and many other applications. Computer simulation of ultra-short (10–100fs, rms) kilo-ampere electron bunch production from a photocathode injector are presented in this report. The electron beam is produced by an 8ps (FWHM) laser from a photocathode RF gun injector operating at the longitudinal emittance compensation mode. The electron beam is compressed continuously in the RF gun, drift space followed the RF gun and energy boost linac operating at 70° off-crest. Simulation shows that, 10fs (rms) kilo-ampere electron beam can be produce at about 40MeV with transverse emittance less than 1mm-mrad.

Status of Infrared Free Electron Laser at Nihon University

A free electron laser (FEL) system has been developed for the experiments of material, life, resource sciences and others at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. The beam from a 125MeV electron linac was first introduced to the FEL system in 1998. We had encountered several difficulties especially in the electron beam stability for the long pulse operation of the linac which was required for a relatively short wavelength FEL system. In 2001 the first lasing of 1.5µm FEL was achieved at the electron energy of 86MeV using an undulator designed for the near infrared FEL. We could suppress the beam current fluctuations quite effectively by improving the stability of the phase of the klystron output RF and have succeeded in lasing. The current important subject is to improve the stability of the FEL lasing for the applications of the LEBRA FEL to various studies.

Sources, instrumentation and detectors for protein crystallography

Some of the requirements for protein crystallography experiments on a synchrotron are described. Although data from different types of crystal are often collected without changing the X-ray beam properties, there are benefits if the incident beam is matched to a particular crystal and its diffraction pattern. These benefits are described with some examples. Radiation damage and other effects impose limits on the dose and dose rate on a protein crystal if the maximum amount of data is to be obtained. These limitations have possible consequences for the X-ray source required. Presently available commercial detector systems provide excellent data for protein crystallography but do not quite reach the specifications of the “ideal” detector. In order to collect the most accurate data (e.g. for very weak anomalous scattering applications) detectors that produce near photon counting statistics over a wide dynamic range are required. It is possible that developments in “pixel” detectors will allow these demanding experiments to be carried out more easily. Finally some possible applications of X-ray free electron lasers for biological applications are discussed.

Evaluation of an attenuation system for an infrared free-electron laser

This study concerns the attenuation of the incident power from a free-electron laser (FEL) in steps of up to two orders of magnitude, while maintaining optical beam geometry. We have developed and evaluated the properties of a FEL attenuation filter system, which can be attached and detached, with the position of the focusing lens and the target sample fixed. As a result, we have established that our FEL attenuation filter system enables two orders of magnitude of power control for infrared wavelengths between 5.5 and 6.5 μm. We conclude that the attenuation system is extremely useful for various FEL applications.

Magneto-plasmon spectrum in a semiconductor under intense laser radiation

We study how a linearly polarised intense laser irradiation affects the magneto-plasmon (MP) modes in a semiconductor. We first evaluate the electron Green's function, the density–density correlation function, and the random-phase approximation (RPA) dielectric function in the (Q,t) representation in the presence of a laser field and a quantizing magnetic field. From these results, we obtain the electron density of states (DOS) and the plasmon spectrum in the (Q,Ω) representation and investigate the dependence of the MP excitations on the frequency and intensity of the laser field in GaAs. The results are pertinent to the application of free-electron lasers developed recently.

Duke FEL storage ring light sources and applications

In this paper we present the status of the Duke UV FEL (Free Electron Laser) storage ring, ring based light sources, and a related multi-disciplinary application program. Using the OK-4 optical klystron system, we have demonstrated tunable spontaneous radiation from the near Infrared (IR) to UV, coherent laser radiation from 345 to 413 nm, and Compton back-scattered linearly polarized γ-ray radiation from 3 to 16 MeV. We report the progress made in developing new light source capabilities. We also report user interface development for a pilot application program organized to utilize various ring driven sources. We discuss future upgrades and additions to the ring based sources.

Industrial applications of the Jefferson Lab high-power free-electron laser

In partnership with the US Navy, high-technology corporations, and research universities, Jefferson Lab is building a superconducting radio-frequency (SRF) accelerator-driven free-electron laser (FEL) and is outfitting an FEL user facility. This first fourth-generation light source – a 1 kW, 3 μm infrared (IR) laser – is the first step in a program to develop high-average-power SRF-based IR and ultraviolet (UV) FELs for multiple manufacturing applications as well as for defense-related applied research and basic scientific research. This initial FEL will be driven by a 42 MeV, 5 mA recirculating SRF linac similar to the much larger SRF linac in Jefferson Lab's 4 GeV, 200 μA Continuous Electron Beam Accelerator Facility (CEBAF). The FEL is expected to demonstrate 75% energy recovery. Its linac will be cooled by the existing CEBAF cryogenic system. At Jefferson Lab, an infrastructure of facilities and people already supports the advance of SRF and closely related technologies in the furtherance of the lab's primary mission of nuclear and particle physics. This paper summarizes the opportunity represented by SRF-driven FELs and reports on the program now underway to develop them.

Status and Prospects of Free Electron Laser Applications to Scientific and Industrial Researches.

Applications of Free Electron Laser (FEL) performed in Japan are reviewed. The applications are concerning the quantum well, material processing, medical treatment, isotope separation and so on. The prospects of future application of FEL to high gradient accelerator, energy transport, nuclear transmutation are described.

The Selective Processing of Biomolecules by Infrared Free Electron Lasers.

Infrared Free Electron Lasers (FEL) application for selectively removal of targeted biomolecules is described. In advanced atherom atherosclerosis, a large amount of lipids, particularly cholesterol esters, accumulates on the arterial wall. The selective removal of cholesterol esters has clinical significance. In the present work we investigate the removal of cholesterol esters by using FELs in an arteriosclerotic region. Thin films of cholesteryl oleate and albumin, and the cross section of a rabbit artery were placed on a microscope and the changes caused by the FEL irradiation of 5.75μm and 6.1μm with 1.5-3 mW were monitored. FEL irradiation at a wavelength of 5.75μm, which is a stretching bibrational mode of the ester, was able to ablate cholesterol esters without affecting albumin and that it can also remove cholesterol esters from rabbits' arterial walls.

High-brightness photoelectric field-emission cathodes for free-electron laser applications

Field emission from very fine needles in an electric field is characterized by a very small energy spread, less than 1 eV, and emittance of the order of 10 −8π m rad, normalized. In microsecond pulses, total currents in excess of 6 A have been observed, corresponding to normalized brightness of the order of 10 15 A/m 2 str, which is four orders of magnitude higher than conventional sources. Recently, photoemission has been observed from needles operating in fields too small for significant field emission. Total currents as high as 10 A have been observed in nanosecond pulses. The quantum efficiency is of the order of unity. Using e-beams of such high brightness, single-pass FELs can operate at very long and very short wavelengths, with very low total e-beam current. In the FIR, it is possible to construct Cerenkov FELs with enough gain ( e 20) to reach saturation in a single pass using only 10 mA total electron-beam current. In the UV, it is possible to build single-pass Compton-backscatter FELs operating at total current less than 300 mA.

The applications of a short-wavelength FEL (invited, abstract)

The third-generation synchrotron light sources today offer exciting new scientific capabilities due to the high brightness of their hard x-ray beams. Yet further dramatic increases in source brightness are becoming technically feasible, with the advent of free-electron lasers (FELs) operating in the hard x-ray region. The peak brightness of machines under consideration exceeds that of today’s third-generation sources by more than ten orders of magnitude. In addition, an FEL would produce an x-ray beam with very high transverse coherence and subpicosecond pulse length. These characteristics should open up completely new areas of x-ray science, such as nonlinear x-ray optics and femtosecond time-domain spectroscopy. Some areas of current research, such as imaging and interferometry, could be extended to much shorter wavelengths and faster measurements. The intense beam could also be used to modify materials on a nanometer scale. Formidable technical problems in the areas of optics, sample preparation, and data collection will need to be solved before an FEL beam could be effectively utilized. Research in these areas is now beginning to be pursued in the U.S., Germany, and Japan.

Pulpal response to cavity preparation with the Er:YAG and Mark III free electron lasers

The purpose of this investigation was to evaluate the pulp response to class V cavity preparation with the use of the Er:YAG laser and free electron laser. Class V cavities were prepared in 133 teeth of four beagle dogs by one of three methods: (1) Er:YAG laser, (2) free electron laser, (3) high-speed handpiece. Treatment occurred at 1 hour, 1 day, 7 days, and 28 days. The teeth were removed and the pulp evaluated. Histologically, the data were evaluated with Mantel-Haenszel analysis. The Er:YAG laser, free electron laser, and handpiece treatment groups resulted in specimens with normal or mild pulp reactions in 36, 46, and 42 teeth, respectively; moderate or severe reactions were observed in 7, 1, and 1 teeth, respectively. No statistically significant difference in the pulp response to the three treatment modalities was observed. The pulp response to Er:YAG laser and free electron laser application would appear to be similar to the response from high-speed handpiece application.

Image tuning techniques for enhancing the performance of pure permanent magnet undulators with small gap/period ratios

The on-axis field of a small-gap undulator constructed out of pure permanent magnet (PM) blocks arranged in an alternating-dipole (i.e., 2 dipoles/period) array can be substantially varied by positioning monolithic permeable plates above and below the undulator jaws. This simple technique, which can be used to control the fundamental photon energy in conventional synchrotron radiation (SR) or Free Electron Laser (FEL) applications requiring sub-octave tuning, can also be shown to suppress magnetic inhomogeneities that can contribute to the undulator's on-axis field errors. If a standard (4 vector rotations/period) Halbach undulator, composed of PM blocks with square cross sections, is rearranged into an alternating-dipole array with the same period, the peak field that can be generated with superimposed image plates can, for a certain range of magnet dimensions, exceed that of the pure-PM Halbach array. This design technique, which can be viewed as intermediate between the “pure-PM” and standard “hybrid/PM” configurations, provides a potentially cost-effective method of enhancing the performance of small-gap, pure-PM insertion devices. In this paper we report on the analysis and recent characterization of pure-PM undulator with superimposed image plates, and discuss possible applications to FEL research.

Characteristics of the MIT microwiggler for free electron laser applications

Abstract We have designed, constructed, and operated a 70-period microwiggler for free electrons lasers (FELs). The device is a pulsed ferromagnetic-core electromagnet with a period of 8.8 mm, which generates an on-axis peak magnetic field of 4.5 kG. The pulses, of 0.5 ms duration, are generated at a rate of 0.5 Hz. Each field peak is independently tunable. We employed a novel tuning regimen to reduce the rms spread in the peak amplitudes to 0.08%, the lowest value thus far attained in a sub-cm-period periodic magnetic field.

Free-electron lasers: reliability, performance, and beam delivery

The Vanderbilt free-electron laser (FEL) is a continuously tunable source of pulsed, mid-infrared radiation. FEL applications research has been underway for a decade. Recent experimental advances in FEL ablation of soft tissue indicate the potential for FEL-based protocols in surgery and medicine. In anticipation of these medical applications, the Vanderbilt FEL is being upgraded to meet the reliability and performance standards for a medical laser. Facilities for laser surgery have been constructed and equipped and medical delivery systems are being developed for pre-clinical and clinical research.

Cesium telluride photocathodes

Cesium telluride (Cs2Te) photocathodes, with quantum efficiencies (QEs) of 15%–18% at 251 nm, were fabricated by vapor deposition of Te and Cs onto a Mo substrate and used as an electron source for the Los Alamos Advanced Free-Electron Laser. In the fabrication chamber, the spectral response from 251 to 578 nm was measured before and after a controlled exposure of several photocathodes to air. The 251-nm QE dropped by about a factor of 20 when exposed to 2×10−4 Torr of air for 1 h. Heating degraded photocathodes to 150–200 °C partially rejuvenated their QEs to about 60% of the value before air exposure. The performance of Cs2Te as a source of electrons for accelerators was evaluated in the photoinjector stage of the Advanced Free-Electron Laser. The response time, saturation level, and dark current of cesium telluride photocathodes and the emittance and energy spread of the resulting electron beam were determined to be sufficient for free electron laser applications.

Application of a mm-wave free electron laser to the study of high-Tc superconductors

Application of a mm-wave free electron laser to the study of high-Tc superconductors

Generation of low-emittance electron beams in electrostatic accelerators for FEL applications

This paper reports results of transverse emittance studies and beam propagation in electrostatic accelerators for free electron laser applications. In particular, we discuss emittance growth analysis of a low current electron beam system consisting of a miniature thermoionic electron gun and a National Electrostatics Accelerator (NEC) tube. The emittance growth phenomenon is discussed in terms of thermal effects in the electron gun cathode and aberrations produced by field gradient changes occurring inside the electron gun and throughout the accelerator tube. A method of reducing aberrations using a magnetic solenoidal field is described. Analysis of electron beam emittance was done with the EGUN code. Beam propagation along the accelerator tube was studied using a cylindrically symmetric beam envelope equation that included beam self-fields and the external accelerator fields which were derived from POISSON simulations.

Application of a millimetre-wave free-electron laser to study detection processes

Application of a millimetre-wave free-electron laser to study detection processes

Behavior of the positron beam of the super-ACO storage ring in response to a modification of the RF frequency for free-electron laser experiments

The macrotemporal structure of the super-ACO storage ring free-electron laser (FEL) can be either continuous, pulsed, or chaotic, and can present some rapid fluctuations. The temporal evolution of a storage ring FEL involves both the longitudinal motion of the positron beam (especially the synchrotron oscillations) and the FEL dynamics, as in a coupled system. Studies on the dynamics of the positron beam are performed here, in the goal to have a stable source for FEL applications, and to determine the conditions for a stable Q-switching experiment, The employed method is to study the influence of a controlled change of the radio frequency (RF) (modulation or frequency jump) on the beam. A simple theoretical model taking into account the perturbed RF system is presented to help the understanding of the experimental data. The different methods of measurement are described. Then, the results are given for several experimental conditions and the influence of different possible adjustments (synchrotron feedback, RF loop...) is presented. Consequences are derived for the FEL.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>