SOLEIL, Gif-sur-Yvette
LOA, Palaiseau
ELETTRA, Basovizza
ENEA C.R. Frascati, Frascati (Roma)
In the quest for compact FEL ultra-compact sources, a test experiment is under preparation, to couple an electron beam from a laser driven plasma accelerator, stable and tunable in energy, to an undulator. The electron beam is generated in the colliding laser pulses scheme, by focusing two short and intense laser pulse in an underdense plasma plume. The electron bunch has an energy tunable in up to a few hundreds MeV with 1% energy spread, a length 10 fs, a charge in the 10 pC range, while its radius and divergence are respectively 1μm and 3 mrad. As a first step toward a FEL experiment, the transport and radiation through an undulator of this short and compact electron beam is studied. The spontaneous emission through a 60 cm undulator in the 40-120 nm range is presented, and criteria to reach the threshold of Self-Amplified Spontaneous Emission are discussed.
LOA, Palaiseau
GoLP, Lisbon
PSI, Villigen
Free-electron lasers have been recently evolving very fast in the extreme-ultraviolet to soft X-ray region. Once seeded with high harmonics, these schemes are considered as next generation soft X-ray light sources delivering ultrashort pulses with high temporal and spatial coherence. Here we present a detailed experimental study of a kHz two-colour (fundamental + second harmonic) high harmonic generation and investigate its potential as a suitable evolution of the actual seeding sources. It turns out that this source (both odd and even harmonics) is highly tuneable, and delivers intense radiations with only one order of magnitude difference in the photon yield from 65 nm to 13 nm. We also observed an astonishing aberration-free character of these harmonics (aberration below λ/17 rms at 44 nm). Finally, the variable linear polarization of the harmonics was revealed to be easily controllable with the generation conditions. Then, the implementation of this technique on seeded FELs would allow amplifications, with perfect beam quality, to be achieved at wavelengths shorter than previously accessible.
SOLEIL, Gif-sur-Yvette
Imagine Optic, Orsay
BNL, Upton, Long Island, New York
LOA, Palaiseau
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
The VUV Self-Amplified Spontaneous Emission of the SPring-8 Compact SASE Source (SCSS) Test Accelerator is characterized at different stages of amplification up to saturation [1]. Experimental measurements are performed by use of a VUV Hartmann wavefront sensor. This kind of sensor gives access to both intensity and phase profiles of the incoming beam. We characterize the mode selection when approaching the saturation regime of the FEL. Optical quality of the saturated SASE radiation is measured to be better than Lambda/5 PV and Lambda/22 rms (Lambda = 61.5 nm) depending on the machine optimization. Moreover, pointing of the beam as well as spatial structure, size and position of the source are retrieved and their shot-to-shot fluctuations investigated. Analytical [2] and numerical calculations [3], using SRW and GENESIS codes, show good agreement with the experimental measurements. All these elements are of crucial importance for a better understanding and optimization of the FEL and of course for user applications requiring a stable focused beam on their samples. We are grateful to the SCSS Test Accelerator Operation Group at RIKEN for continuous support in the course of the studies
[1] R. Bachelard et al., "Wavefront and Transverse Structure of the FEL Self-Amplified Spontaneous Emission", to be submitted
[2] M. Xie, NIMA 445, 59(2000)
[3] O. Chubar et al., Proc. EPAC-98, 1177(1998)