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.     

Analyse qualitative et quantitative de melanges complexes de chlorures de lanthanides,en utilisant la dispersion rotatoire magnetique

The general features of a new physical process for the qualitative and quantitative routine analysis of rare earth mixtures are given. The characteristic sharp lines in the magneto-optical rotation spectra of these elements are utilized. The recording photoelectric spectropolarimeter used is described briefly. A comparison is made with two other physical processes-absorption and X-ray fluorescence spectrometry. The proposed method appears to be the best when a mixture with more than 3 or 4 elements must be analysed. The sensitivity and accuracy are given for 9 rare earths. Improvements of the process are suggested.     

Utilisation de la magnetooptique en spectroscopie cristalline (effets faraday et cotton-mouton)

Sans résumé     

Electron-lattice coupling of F centers: Particular case of NaI: F

Absorption and magnetic circular dichroism studies of the F centers in NaI reveal a strong electron-lattice coupling with the vibration modes of Γ₁⁺ symmetry in comparison with those of Γ₃⁺ and Γ₅⁺ symmetry. On the other hand, the F electron exhibits in its first excited state a large spin-orbit coupling, in agreement with the value previously calculated. These results are confirmed by the Raman spectra which show a predominant intensity for the Γ₁⁺ modes, particularly for the resonant mode at 113 cm^?1.First and second-order Raman spectra have been calculated using a “quasi-resonant” theory in which the vibrations of the ions up to the fifth shell have been taken into consideration. We have been able to determine from these calculations absolute values for the contributions of the different types of vibration modes to the broadening of the F-absorption band.     

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.     

Optical absorption spectrum of the U centre in SrCl2

Studies of the correlation between i.r. and u.v. absorption spectra show that the u.v. absorption band of U centres is peaked at 212.3 nm. The weak peak observed at 233 nm is probably due to an impurity and some of the experimental results allow us to assume that it can be O^2-.The absorption band shape of U centres is very similar to that of F centres in SrCl₂. The second moment variations of these bands vs temperature can be interpreted in terms of an effective phonon frequency of 93 cm^-1.