Michel Velghe

The Stanford Mark III infrared free electron laser

Abstract We have built and operated a compact infrared free electron laser using a conventional linear accelerator and a broadband optical cavity. The gain was measured to be 28% and saturation was obtained with a 2.5 μs macropulse. The laser was tuned from 3.1 to 2.6 μm by changing the undulator gap. Coherent spontaneous radiation at the fifth and seventh harmonics was seen.

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.

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.

Laser induced bunch lengthening on the ACO storage ring FEL

Laser induced bunch lengthening has been measured on the ACO storage ring FEL. The experimental data at low current generally confirm the existing theoretical models, while the high-current data is dominated by anomalous effects.

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. >

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.