Laser Plasma Accelerators (LPAs), reaching gigavolt-per-centimeter accelerating fields, can generate high peak current, low emittance and GeV class electron beams that can be qualified by a Free Electron Laser (FEL) application. We report here on the commissioning of the COXINEL beamline driven by the HZDR plasma accelerator and experimental demonstration of FEL lasing at 270 nm in a seeded configuration. We also present the transport and characterization of LPA based beams using different imaging systems along the beamline. The use of a streak camera and a UV spectrometer enable to align the seed and the electron beam in the temporal, spectral and transverse domains. Furthermore, the appearance of interference fringes, resulting from the interaction between the phase-locked emitted radiation and the seed, confirms longitudinal coherence, representing an essential feature of seeded FELs. These results are comforted by ELEGANT and GENESIS simulations.
While synchrotron light facilities and Free Electron Lasers (FELs) are widely used for matter investigation, Laser Plasma Acceleration (LPA), delivering nowadays GeV electron beams in few centimeter accelerating distance, can be considered to drive undulator radiation and FEL. We report on the generation of undulator radiation on the COXINEL dedicated manipulation line designed for an FEL application. The LPA large divergence is handled with variable gradient permanent magnet quadrupoles and the high energy spread is reduced via a magnetic chicane. We evidence the undulator spatio-spectral signature on the first and second harmonics while measuring the radiation focused onto the entrance slit of a spectrometer equipped with a CDD camera. A good agreement is found between measurements and SRW simulations, using electron beam parameters in the undulator deduced from the measured initial electron beam parameters transported along the beamline. In addition, ray optics approach is compared to Fourier optics for the radiation propagation through optical elements.
The photonic time-stretch technique allows electric field pulse shapes to be recorded with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could directly record spatial patterns that spontaneously appear in relativistic electron bunches, and follow their dynamical evolution over time. We present recent results obtained using two strategies. At SOLEIL, we present the shapes of the THz pulses which are emitted by the structures, and detected far from the emission point, at the end of a beamline. At ANKA, we present how it has been possible to monitor directly the electron bunch near-field. These new types of single-shot recordings allow direct and stringent tests to be performed on electron bunch dynamical models in synchrotron radiation facilities.
E. Roussel, C. Evain, M. Le Parquier, C. Szwaj, S. Bielawski, L. Manceron, J.-B. Brubach, M.-A. Tordeux, J.-P. Ricaud, L. Cassinari, M. Labat, M.-E. Couprie, P. Roy
We consider the problem of shot-by-shot acquisition of pulse shapes at high repetition rate in accelerator-based systems. More specifically, we examine the two-step strategy consisting in (i) encoding the pulse information onto a laser pulse, and (ii) use the so-called time-stretch strategy to “slow-down” the information before recording. We thus show that the repetition rate of already existing electro-optic sampling setups can be straightforwardly increased up to the 100 ×106 pulses/s range, and make a demonstration for the detection of coherent THz pulses. The strategy is however not limited to electro-optic sampling of THz pulses or electron bunches. It can be applied to other types of wavelengths, provided the desired information (as e.g., FEL pulses or electron bunches shapes) can be imprinted onto a laser pulse.
Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, i.e. that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. As an example, the lack of longitudinal coherence, that is shot-to-shot fluctuations, of Free-Electron Lasers (FEL) has prevented so far their full amplitude and phase temporal characterization. To sort out this issue, we have adapted Frequency-Resolved Optical Gating (FROG), the first and one of the most widespread techniques for pulse characterization, to enable the measurement of partially coherent XUV pulses even down to the attosecond timescale. Especially, this technique allows one to overcome the sources of decoherence that normally prevent a pulse measurement, such as the spectrometer resolution or the presence of XUV/laser arrival time jitter.
A. Loulergue, M. Labat, C. Evain, N. Hubert, F. Briquez, F. Marteau, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, L. Cassinari, L. Chapuis, M. El Ajjouri, C. Herbeaux, M. Khojoyan, D. Dennetiere, N. Leclercq, JP. Duval, A. Lestrade, O. Marcouillé, P. Rommeluère, J.-L. Marlats, P. Morin, F. Polack, K. Tavakoli, M. Valleau, D. Zerbib, W. Yang, X. Davoine, I. Andriyash, G. Lambert, V. Malka, C. Thaury, S. Bielawski, C. Szwaj, M.-E. Couprie
KEYWORDS: Free electron lasers, Electron beams, Diagnostics, Plasma, Magnetism, Colorimetry, Synchrotrons, Spectroscopy, Optical testing, Electron transport
One direction towards compact Free Electron Laser is to replace the conventional linac by a laser plasma driven beam, provided proper electron beam manipulation to handle the large values of the energy spread and of the divergence. Applying seeding techniques enable also to reduce the required undulator length. The rapidly developing LWFA are already able to generate synchrotron radiation. With an electron divergence of typically 1 mrad and an energy spread of the order of 1 % (or few), an adequate beam manipulation through the transport to the undulator is needed for FEL amplification. Electron beam transfer follows different steps with strong focusing variable strength permanent magnet quadrupoles, an energy demixing chicane with conventional dipoles, a second set of quadrupoles for further dedicated focusing in the undulator. A test experiment for the demonstration of FEL amplification with a LWFA is under preparation and progress on the equipment preparation and expected performance are described.
Insertion devices are key components for high brightness third and fourth generation synchrotron facilities, and even for compact light sources where new acceleration concepts are envisioned. Different technological developments carried out worldwide lead to improved undulator performance. In-vacuum permanent magnet undulators demonstrate to be quite useful and adequate devices for present storage ring and Free Electron Lasers (FELs). Pushing towards higher fields with shorter undulator period becomes possible in operating at cryogenic temperature with Nd2Fe14B or Pr2Fe14B magnets. The development of Cryogenic Permanent Magnet Undulators (CPMU) is reported, including the issues in terms of magnet choice, thermal handling, magnetic measurements, radiation properties. Prospects for pushing the CPMU performances are given, with variable gap undulator or a combination with superconducting coils.
In storage rings, short electron bunches can produce an intense THz radiation called Coherent Synchrotron Radiation (CSR). The flux of this emission between 250 and 750 GHz is very advantageous for spectroscopy, but intensity fluctuations lead to artifacts in the FTIR spectra and, until now, prevented the use of CSR for high-resolution measurements. At SOLEIL, we found stable CSR conditions for which the signal-to-noise ratio (S/N) allows for measurements at high resolution. Moreover, we developed an artifact correction system, based on a simultaneous detection of the input and the output signals of the interferometer, which allows improving further the signal-to-noise ratio. The stable CSR combined with this ingenious technique allowed us to record for the first time high-resolution FTIR spectra in the sub-THz range, with an exceptional S/N of 100 in a few hours.
L. Poletto, G. Tondello, S. De Silvestri, M. Nisoli, G. Sansone, S. Stagira, P. Musumeci, M. Petrarca, M. Mattioli, M. Labat, O. Tcherbakoff, M. Bougeard, B. Carré, D. Garzella, G. Lambert, H. Merdji, P. Salières, M. Couprie, D. Alesini, M. Biagini, R. Boni, M. Castellano, A. Clozza, A. Drago, M. Ferrario, V. Fusco, A. Gallo, A. Ghigo, M. Migliorati, L. Palumbo, C. Sanelli, F. Sgamma, B. Spataro, S. Tomassini, C. Vaccarezza, C. Vicario, L. Serafini, S. Ambrogio, F. Ciocci, G. Dattoli, A. Doria, G. Gallerano, M. Germano, L. Giannessi, E. Giovenale, I. Spassovsky, M. Quattromini, A. Renieri, C. Ronsivalle, V. Surrenti, P. Ottaviani, S. Pagnutti, M. Rosetti, A. Dipace, E. Sabia
This communication describes the research work plan that is under implementation at the SPARC FEL facility in the
framework of the DS4 EUROFEL programme. The main goal of the collaboration is to study and test the amplification
and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in
crystals (400 nm and 266 nm) and in gases (266 nm, 160 nm, 114 nm). The SPARC FEL can be con-figured to test
several cascaded FEL layouts that will be briefly analysed.
We propose an accelerator based 4th generation source to provide coherent femtosecond light pulses down to the soft X
ray range to the user community. The project is based on a CW 700 MeV to 1 GeV superconducting linear accelerator
delivering high charge, subpicosecond, low emittance electron bunches with high repetition rate. This facility allows for
providing High Gain Harmonic Generation seeded with high harmonics in gases, covering a spectral range down to
0.8 nm. In addition, two beam loops are foreseen to increase the beam current in using the energy recovery technique.
They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges together with a FEL oscillator
in the 10 nm range. A particular emphasis is put on the synergy between accelerator and laser communities. In particular,
electron plasma acceleration will be tested. Hard X ray femtosecond radiation will be produced by Thomson Scattering.
The first phase of the project, ARC-EN-CIEL phase 1, is now under study. A general overview is given.
G. Lambert, B. Carre, M. Couprie, M. Desmons, O. Chubar, B. Gilquin, D. Garzella, M. Jablonka, M. Labat, A. Loulergue, J. Marques, J. Ortega, F. Meot, P. Monot, A. Mosnier, L. Nahon, A. Rousse
The French project of a fourth generation light source, ARC-EN-CIEL (Accelerator-Radiation for Enhanced Coherent Intense Extended Light), is a unique facility providing the user community with coherent femtosecond light pulses covering the UV, VUV and soft X ray spectral range. It is based on a CW 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches with high repetition rate (1 kHz), and adjustable polarisation until 1 keV. In addition to the High Gain Harmonic Generation (HGHG) experiment seeded with High Harmonics in Gases (HHG), allowing radiation down to 0.8 nm to be produced, two beam loops are foreseen to increase the beam current in using the energy recovery technique. They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges together with a FEL oscillator in the 10 nm range. Moreover, an important synergy is expected between accelerator and laser communities. Indeed, electron plasma acceleration will be tested and hard X ray femtosecond radiations will be produced by Thomson Scattering. The first phase of the project, ARC-EN-CIEL phase 1, is now under study. A general overview will be given.
The first applications of a storage ring Free Electron Laser started in 1993 on the Super-ACO FEL with the study of the anisotropy decay of a coenzyme, NADH, allowing to understand the thermodynamical equilibrium of the different conformational states of the molecule and their hydrodynamical volume in solution. After this first one- color experiment using the time-resolved fluorescence technique, a transient absorption experiment was developed in which the system is excited with the UV FEL and is probed by Visible-UV absorption using synchrotron radiation. First results on the dynamical behavior were obtained for the acrinide molecule.
Storage Ring Free Electron Laser (FEL) are attractive, full of promise, tuneable and powerful laser sources for the UV range. High reflectivity dielectric mirrors should be produced in order to allow lasing at very short wavelength, with a long stability in a strongly harsh environment and to optimize the extracted FEL power required for most of the newest applications. The front mirror of the laser cavity receives all the synchrotron radiation (SR) emitted by the wiggler, which is responsible for the mirror degradation, combined with the contamination by the vacuum residuals. We are tackling the problem of tests and manufactures of reliable robust mirrors and explore themes such as resistance analysis of UV mirrors to FEL multiscale power, broadband (X-UV) mirror robustness. Under drastic SR conditions, multiscale wavelength damages could be observed. Specific measurement techniques, able to investigate localized spatial modification induced by the non-uniform synchrotron radiation are presented. A local crystalline structure modification of the high index material appears together with a severe increase of the roughness.
Storage Ring Free Electron Laser are attractive and full of promise tunable and powerful laser sources for the UV range. Concerning the optical cavity, the relatively small gain obtained in the UV calls for the necessity to use high reflectivity multilayer mirrors with reliable longevity in synchrotron environment. It is also crucial to limit their absorption in order to optimize the extracted power required for most of the applications. Indeed, the front mirror of the laser cavity receives not only the first harmonic where the lasers operates but all the synchrotron radiation emitted by the undulator: a wide spectrum extending towards X rays. These short wavelengths are responsible for the mirror degradation which results from changes in the coating materials (high induced absorption, color centers, heating...) as well as from carbon contamination due to cracked hydrocarbons originating from the residual vacuum atmosphere. Deposition technologies which allow the manufacture of very dense oxide coatings with low absorption and high reflectivity in UV spectral region were optimized and characterized for this purpose. We report here degradation studies performed on UV mirrors for Storage Ring Free Electron Lasers down to wavelengths as short as 200 nm.
The Super-ACO storage ring FEL is operating with a high average power in the UV range (300 mW at 350 nm), and recently at wavelengths down to 300 nm. In addition this source exhibits high stability and long lifetime which makes it a unique tool for user applications. The coupling of the FEL with other synchrotron based sources (bending magnet and undulator) opens many unexplored possibilities for various types of two-color time-resolved spectroscopies. Presently, we are developing a two-color experiment where we study the sub-nanosecond time-resolved absorption of different chromophoric compounds. In this type of pump-probe experiments, the intense UV pulse of the Super-ACO FEL is used to prepare a high initial concentration of chromophores in their first singlet electronic excited state. The nearby bending magnet synchrotron radiation provides on the other hand a pulsed, white light continuum ranging from UV to IR, which is naturally synchronized with the FEL pulses and can be used to probe the photochemical subsequent events and the transient species. With a dye molecule (POPOP), we have obtained a two-color effect which demonstrates the feasibility of the experiment in terms of flux. Applications on various chromophores of biological interest are planned.
Infrared microspectrometry, using a synchrotron radiation source, has been developed at Super-ACO (LURE-France). In order to accommodate for constrained horizontal (45 mrad) and vertical (18 mrad) collection angles, a particular care has been devoted to the design and making of the extraction optics, in order to achieve the highest brightness as possible, for small area illumination. Experimentally, a net gain of one hundred in Signal to Noise Ratio has been measured for an upper aperture of 3 X 3 micrometers 2. Several applications are currently underway, and some of them, related to Biomedical Science are reported in this paper.
The UV-storage ring Free Electron Laser (FEL) operating at Super-ACO is a tunable, coherent and intense (up to 300 mW) photon source in the near-UV range (300 - 350 nm). Besides, it has the unique feature to be synchronized in a one-to-one shot ratio with the Synchrotron Radiation (SR) at the high repetition rate of 8.32 MHz. This FEL + SR combination appears to be very powerful for the performance of pump- probe time-resolved and/or frequency-resolved experiments on the sub-ns and ns time-scales. In particular, there is a strong scientific case for the combination of the recently- commissioned SA5 Infra-Red Synchrotron Radiation beamline with the UV-FEL, for the performance of transient IR- absorption spectroscopy on FEL-excited samples with a Fourier-transform spectrometer coupled with a microscope allowing high spectral and spatial resolution. The principle and interest of the two-color combination altogether with the description of both the FEL and the SA5 IR beamline are presented. The first synchronization signal between the IR and the UV beams is shown. The correct spatial overlap between the UV (FEL) and the IR (SR) photon beams is demonstrated by monitoring via IR-spectro-microscopy the time evolution of a single mineral particulate (kaolinite) under UV-FEL irradiation.
KEYWORDS: Mirrors, Free electron lasers, Ultraviolet radiation, Electron beams, Synchrotron radiation, Absorption, Magnetism, Optical resonators, Dielectrics, Electron transport
Storage Ring Free Electron Layers (FELs) are brand new laser sources where a relativistic electron beam passing through an undulator emits synchrotron radiation at a wavelength (lambda) which is tunable according to the electron beam energy and the magnetic field intensity. An overview of the SRFELs presently operating in the UV range is presented. The easy tunable FEL operation in the whole UV range is mainly limited by the mirrors losses, which should be maintained low even in the very hostile environment generated by the broadband high power spectrum of the undulator, extending to x-rays, and which action lead to the mirrors degradation. Dedicated mirror measurements have been then developed in LURE, in the visible and in the UV range, for checking the mirrors performances before insertion in the optical cavity and after degradation. In order to insure a wide tunability range and large output power of the FEL, low total losses are crucial for FEL oscillation at shorter wavelength. New FEL sources, for instance at the ELETTRA synchrotron source, could then provide a widely tunable and powerful laser light down to 200 nm.
Storage ring FELs (SRFELs) recently demonstrated to be useful coherent light sources for applications in several branches of scientific research. In particular, the super ACO SRFEL provided UV light at 350 nm for successful operations in a time resolved fluorescence experiment on a biological molecule and in the first two color experiment combining synchrotron radiation and FEL light. Up to now, SRFELs are characterized by a relatively low gain and hence, great care must be invested on the choice of optical cavity mirrors. In this paper we relate the several characterizations performed on different set of mirrors and the obtained results.
Storage ring Free Electron Lasers (FELs) are very promising tunable and powerful laser sources for the UV range. However, the relatively small gain obtained in the UV, requires the use of high reflectivity multidielectric mirrors. In addition, all the synchrotron radiation (not only the first harmonic where the laser operates) emitted by the undulator, consisting of a wide spectrum of the harmonics of the fundamental wavelength extending towards the X rays is received by the front mirror of the laser cavity. These higher harmonics are responsible for the mirror degradation. The reflectivity of the multidielectric mirrors has to remain at a high level even in the presence of synchrotron radiation covering a wide spectral range, leading to specific requirements for FEL optics. The FEL at 350 nm was obtained with Ion Beam Sputtering of Ta2O5/SiO2, with super polished substrates. Extension towards shorter wavelength requires to use another type of material such as HfO2/SiO2. Substrates and mirrors are characterized in roughness, transmission and total losses. The evolution of the mirror degradation is studied versus the deposition technology. The realization of high reflectivity mirrors submitted to the radiation from the undulator remains a challenging issue for the development of tunable short wavelength FELs.
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