M. Bergher

Optical klystron experiments for the ACO storage ring Free Electron Laser

To improve the gain in the Orsay storage ring Free Electron Laser (FEL) experiment, the 17 period permanent magnet undulator has been modified to form an optical klystron (OK). We report the measurement of spontaneous emission and the effects on it of energy spread and angular spread. Gain and laser induced bunch lengthening measurements with the OK are also reported and are in very good agreement with the FEL classical theory. The spontaneous emission spectrum which is easy to measure with good signal to noise ratio, turns out to be a very good diagnostic tool forenergy spread and angular spread measurements on storage rings. The factor of four increase in the small gain obtained by converting the undulator NOEL into an OK was the critical factor in the recent operation of the ACO storage ring laser above threshold.

Coherent harmonic generation in the vacuum ultraviolet spectral range on the storage ring ACO

Abstract In this paper we summarize the various achievements made at Orsay on the “coherent harmonic generation”, using an external laser focused in an optical klystron. First we observed in 1984 the third harmonic (3547 A) of a Ndue5f8YAG laser, on our storage ring ACO. In a later experiment, performed in 1987 on the same machine, VUV photons (1770 and 1064 A) have been generated by the same method, on the third and fifth harmonic of a doubled Ndue5f8YAG laser. The perspectives offered for VUV production by the new storage ring Super-ACO are discussed, taking into account the parameters recently measured on this ring.

Optical properties of multilayer mirrors exposed to synchrotron radiation

Abstract One main limitation to the future development of free electron lasers towards lower wavelengths is the problem of optical degradation due to spontaneous emission of the undulator. In our case, a high reflectivity is also needed in order to maintain the gain over cavity losses. On the ACO storage ring at Orsay, some dielectric multilayer mirrors for the near UV spectral range have been exposed to synchrotron radiation, and the optical degradation has been studied. With highly degraded mirrors, for which the reflectivity is reduced, optical density curves are generally shifted towards lower wavelengths and sharpened. A theoretical model which explains some of these results has been developed by modifying the real or imaginary part of the optical indices of selected layers constituting the mirror.

Results of the Orsay storage ring free electron laser oscillation

Abstract Recent results obtained with the Orsay free electron laser are summarized in this paper. The laser oscillator was operated at two different wavelengths (6500 and 5800 A) and at energies ranging from 166 MeV to 224 MeV. The main results presented here concern the Q-switched operation, the macro-temporal structure and the saturation mechanism of the storage ring free electron laser.

First Operation Of A Storage Ring Free-Electron Laser

A storage ring free-electron laser oscillator has been operated at a visible wavelength A = 6500 A .

Optical frequency multiplication by an optical klystron on the ACO storage ring

Abstract The optical klystron previously successfully optimized for the realization of an FEL on the ACO storage ring has been used as a non-linear medium aimed at producing harmonics of an external laser. For the first time we have demonstrated experimentally this effect by looking at the third harmonic of a 1.06 μm Nd:YAG laser focused into it. An enhancement of 102 to 103 of the spontaneous emission at 355 nm has been recorded.

Optical klystron experiments at Orsay on Super‐Aco and prospects in the VUV (invited)

This paper consists of a general presentation of the Storage Ring FEL activities at LURE (Orsay). We first summarize the results obtained previously with an optical klystron installed on the ACO storage ring, and then make a presentation of the different projects that have begun on the new storage ring Super‐ACO. The ACO storage ring experiments were of two kinds: the Free Electron Laser oscillator (FEL), and the coherent harmonic generation (CHG). The first allowed us to reach the visible spectral range, between 6500 and 4600 A. In the second, we were able to produce coherent emission in the VUV: it was the shortest wavelengths (1773 and 1064 A) ever obtained with an optical klystron or an undulator acting as a nonlinear medium. In this last configuration, the fundamental wave was an external pulsed and doubled Nd‐Yag laser, focused in the optical klystron. The new Super‐ACO storage ring has been equipped with a new optical klystron. The first ‘‘spontaneous emission’’ spectra have been observed and they ...

Orsay free electron laser activities on the storage rings ACO and super-ACO

Abstract The main results obtained on the free electron laser and on optical harmonic generation with the storage ring ACO at Orsay in France are reviewed. A specific magnetic device, generally called an undulator, allows one to collect coherent light. In the free electron laser case, the undulator radiation is stored and amplified in an optical cavity. Tunable light was obtained in the visible range. For optical harmonic generation, external laser light is emitted in the undulator area, generating coherent harmonic radiation. Experimentally, 350, 177 and 107 nm wavelengths were obtained with a Nd-YAG laser. New experiments are planned with the Super-ACO storage ring, and preliminary experiments with the optical klystron are given.

Characterization of Free-Electron Laser bunch lengthening on the ACO Storage Ring

This paper summarizes the basic low-current, laser-induced bunch-lengthening measurements that have been made on the ACO Storage-Ring Free-Electron Laser (SRFEL). The measurements provide verification of both the functional dependence and absolute magnitude of SRFEL theoretical models. The method of measurement, which is is explained, exploits frequency-domain techniques and is capable of accuracies comparable to those of a streak camara. The measurements are in good agreement with existing SRFEL theory and provide an important base for future work.