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.
Circularly polarized high order harmonics in the extreme ultraviolet range (18 - 27 nm) have been obtained
by a two steps process. Harmonics were generated from a linearly polarized infrared laser (40 fs, 0.25 TW)
focused into a neon filled gas cell. The harmonics have then been circularly polarized by a four-reflector phase-shifter.
The polarization of the harmonics have been measured using a rotating multilayer broadband mirror
set at an incidence angle of 45°. Fully circularly polarized radiation has been obtained with an efficiency of
a few percents. This is significantly more efficient than currently demonstrated direct generation of elliptically
polarized harmonics. This demonstration opens up new experimental capabilities based on high order harmonics,
for example, in materials science for time-resolved nanometric magnetic imaging.
We report spatial and spectral characterization an optical-field-ionized high-order harmonic-seeded soft-x-ray laser. We
show that it can be controlled between a regular Gaussian shape and a Bessel profile exhibiting several rings via the IR
laser pump intensity. The temporal coherence and spectral linewidth of both the seeded and unseeded soft-x-ray lasers
were experimentally measured using a varying path difference interferometer. It showed that the high-order harmonic is
subject to a strong spectral narrowing during its propagation in the plasma amplifier without rebroadening at saturation.
Also, we present a new method to generate ultra-short x-ray laser pulses by using the laser-driven betatron source to
photo-pump inner-shell transitions.
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.
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.