Date&Time: July 12, 12:00-12:35
Place: UVSOR Build. #304 (User's room)

1) Speaker: Ms. Marie Labat
Affiliation: CEA, France
Title: FEL saturation in case of UVSOR-II

2) Speaker: Mr. Guillaume Lambert
Affiliation: CEA, France
Title: Seeding a free electron laser in "High Gain Harmonic Generation"
configuration with laser harmonics produced in gases.


*** Abstracts ***
Marie Labat
"FEL saturation in case of UVSOR2"

In a storage ring Free Electron Laser (FEL), the bunching of the electrons is
generally performed in an optical klystron. The spatial modulation turns the
synchrotron radiations into a coherent emission of light, leading an intense
and monochromatic FEL light. The saturation of the FEL comes from the so-called
"bunch heating" phenomenon. The periodic interaction between the electron bunch
and the laser pulse within the cavity is responsible of the enhancement of the
energy spread of the bunch correlated with a bunch lengthening.
The new operating point of UVSOR2, using a distributed dispersion function
allowed the facility to achieve an emittance of 18 nm.rad and a higher
brightness for synchrotron radiation users. The introduction of achromatic
optics modifies FEL's dynamics, and processes of saturation. In addition of the
energy spread, the enhancement of the transverse sizes has to be considered.
The obtained experimental results, and the modifications to the simulation
model will be presented.
Free-Electron Laser dynamics can also be explored versus the detuning, i.e. a
small difference between the frequencies of revolution of the electron bunches,
and of the optical pulse circulating into the optical cavity. In fact, it
provides situations ranging from the maximum initial gain over losses
conditions to threshold ones. Systematic measurements of the UVSOR2 detuning
curves have been realized. The analysis of the FEL behaviour versus detuning is
compared with simulations performed with LAS, and illustrated under different
cases (current, control of the pulsed zone, chromatic or achromatic electron-
beam optics).

2) Guillaume Lambert
"Seeding a free electron laser in "High Gain Harmonic Generation"
configuration with laser harmonics produced in gases."

In order to reach very short wavelengths in systems based on Free Electrons
Laser (FEL), and to have more compact sources, a High Gain Harmonics Generation
(HGHG) configuration is studied here, in which an external laser source is
seeded into an undulator, used as a modulator, thus allowing a strong
prebunching of the e-beam. Then, a second undulator amplifies a harmonic of the
seeding source while reproducing its longitudinal and transverse coherence,
while common Self Amplified Spontaneous Emission (SASE) schemes have a limited
longitudinal coherence. Seeding straightfully in the XUV range, provided by the
harmonics of the Ti:Sa femtosecond laser generated in gas and tunable in the
266-10 nm spectral range is very promising. Intense, ultra-short laser
harmonics can be now generated. High Harmonics (HH) provide the fundamental
seed leading to radiations on its harmonics (first, third or fifth) via the
high gain FEL amplifier. Finally, we propose to extract the third and fifth non
linear harmonics of these radiations down to the 25th of the fundamental seed
radiation (5th non linear harmonic of the 5th radiated harmonic). These studies
have been made for the SCSS phase 1 and SPARC projects.
Using state-of-the-art High Order Harmonics in gas for seeding High Gain FEL
amplifiers appears very interesting, because the seed radiation is fully
coherent and tunable in the VUV-XUV range. Such a seeding can reduce the
saturation lengths, thus giving a more compact source. Estimations carried out
have shown that high peak power could be obtained with this scheme.
Finally, these experiments will provide key results for ARC-EN-CIEL proposal,
which is based on seeding with harmonics in gases.