J.M. Ortega

Free electron laser experiment at Orsay: A review

In this paper we review the results obtained in the last two years with the Orsay free electron laser.

First Production of Vacuum-Ultraviolet Coherent Light by Frequency Multiplication in a Relativistic Electron Beam

We report the first generation of vacuum-ultraviolet harmonics of an external laser focused on an ultrarelativistic electron bunch circulating in a periodic magnetic field. The amplification of the undulator emission at the 3rd (at 1773 A) and 5th harmonics (at 1064 A) of a doubled neodymium-YAG laser (at 5320 A) has been observed in our optical klystron installed on the electron storage ring ACO at Orsay.

Ultraviolet coherent generation from an optical klystron

The optical klystron, previously successfully optimized for the realization of a FEL on the ACO storage ring at Orsay, has been used as a nonlinear medium for producing harmonics of an external 1.06 μm Nd:YAG laser focused into it. Detailed experimental data are reported. A comparison with theoretical calculations shows very good qualitative and quantitative agreement between the experimental data and the theory.

Short–Wave-Length Operation of a Storage Ring Free-Electron Laser

The Orsay storage ring free-electron laser has been operated in the short–wave-length side (blue) of the visible spectral range from 4630 A to 4860 A. General conclusions on storage ring free-electron laser are derived after our successive operations of a tunable laser over almost the entire visible spectral range.

Production of VUV coherent light by harmonic generation with the optical klystron of super-ACO

The aim of the experiment presented was to develop a usable source of coherent light in the vacuum ultraviolet (VUV) range (200-50 nm) using the Super-ACO storage ring. A presentation is made of the most recent results where coherent photons have been produced at the 3rd (177 nm) and 5th (106 nm) harmonics of the incident laser. The better performance of the new machine and the laser, compared to the older ACO, is largely offset by experimental difficulties. The number of photons is, however, larger than that obtained with the ACO, but it is approximately one order of magnitude below the expected rate. This seems to be due to positron beam instabilities. The authors believe that the extremely critical alignment of the whole experiment, from the injection laser to the monochromator, does not appear to be compatible with a user facility. >

Monte Carlo simulation of the harmonic generation in an optical klystron or undulator

Abstract A Monte Carlo numerical simulation code provides spontaneous and coherent emission results, including the effect of electron beam emittance and energy spread and of external laser field properties. Comparisons are made with spectra recently obtained with the ACO optical klystron. Noise characteristics of the spontaneous emission are discussed. Coherent emission is compared with the predictions of analytical models.

The Orsay storage ring free electron laser: New results

A modification of the operating point of the machine is reported. Smaller transverse sizes of the electron beam have been achieved producing a higher optical gain, and a laser tunability ranging from 5700 to 6400 A. The dependence of the temporal and spectral structure of the laser beam versus detuning and Q-switch frequency is discussed.

Enhancement of the free-electron coherent harmonic generation by use of the dispersive function on a storage ring

An alternative to the free electron laser (FEL) oscillator at short wavelengths (λ < 2000 A) is the “coherent harmonic generation” (CHG) process with an external laser. However, this coherent emission is rather weak, particularly on high harmonics (n ⩾ 5). This paper shows that the introduction of an “energy-dispersive function” on a storage ring increases the CHG by several orders of magnitude.

Measurement of stimulated transverse mode mixing in a free electron laser

We report the first measurement of the off-diagonal terms in the transverse gain matrix in a free electron laser. We show that the higher order transverse modes stimulated in the FEL interaction diminish in amplitude as the electron beam size is increased, that the far field and the near field effects of the excited modes are not equivalent, and that in this low divergence case, the mode mixing is insensitive to the resonance parameter. Remarkably close agreement is demonstrated with the theory [1]. The effects of a multiple mode input beam are also observed, and the theoretical expression is derived.