Showing papers by "Aix-Marseille University published in 1980"

X-ray topographic analysis of a particular dislocation-dislocation interaction inducing cross-slip

Abstract: Bending experiments have been performed on thin Cu plates with special orientation. Repusive half-loops were developed from sources at both the free surfaces. The mutual interaction of such expanding loops is strong enough to cause the cross-slip of their screw segments. It results in a particular configuration which has been analysed.

60, 90 and 250 MHz 1H NMR spectra of sultams and sultones†‡

Abstract: The high-field 1H NMR spectra of 1,3-propanesultams (2), 2,4-butanesultams (3) and 2,4-dimethyl-1,3-butadienesultams (6) are reported. Comparison of 2,3 and 6 with 1,3-propanesultone (1) and 2,4-dimethyl-1,3-butadienesultone (5) reveals that the paramagnetic shift induced by the NH group is smaller than that induced by oxygen. NMR spectra at lower temperature show coupling effects with the NH proton. A half-chair conformation was deduced for 2,4-butanesultam from coupling constants and from a conformational analysis based on the R values, but a chair-chair interconversion could not be detected in the temperature range between 210 and 330 K. An unambiguous assignment was carried out for the methyl signals in the spectrum of 5 by homodecoupling experiments.

Supersonic flow low temperature electronic transition excimer lasers

Abstract: High power pulsed ultraviolet excimer laser emissions have been achieved with the high density and very low temperature supersonic flow-electron beam excitation and supersonic flow electron beam stabilized discharge excitation devices developped at I.M.F.M. (p s 2 amagats, T 70 150 K). Experimental results are given for effects of strong cooling and very high speed and high density flow on lasing characteristics of several U.V. and visible laser s y s t e m s ( ~ e F q ~ e ~ l * , N e + , ~ ~ p f fects of strong cooling on other excimer sysiems and*noticeally strong enhancement of fluorescence efficiency for several trimers (Kr2F , Xe2C1 , Kr2C1 ) , very attractive as potential visible high efficiency lasers, are described. Experimental results on fluid dynamics of these supersonic flow U.V. and visible lasers, noticeally discharge stability, and flowing medium behavior following excitation, as recorded by interferometry, are presented. Possibilities of very high speed flow, high density systems are discussed with the aim to consider development of future high average power excimer lasers. INTRODUCTION and to maintain a good medium homogeneity in the. Excimer lasers promise the availability of high average power ooherent sources in the ultraviolet and visible regions of the spectrum. Potential applications of such laser systems are important in particular in the energetic field (1)'(2). However in scalling these lasers to high average power, challenging problems are encountered in source of excitation, molecular kinetics and active medium homogeneity.The difficulty of this last problem is increased by the high gas den~it~(~')(~')(~) and short wavelength(6) of these systems. Fluid mechanic techniques associated to elecsame way as the well known infrared vibrational flow lasers (3)j(8)'(9). Very recently up to 220 Watts average power has thus been extracted in the U.V. from a high repetition rate subsonic flow excimer laser at GTE -Sylvania by Fahlen(l0) and possibility of very high repetition rate has been demonstrated by R.C. Sze at Los Alamos (11) and C.P. Wang at Aerospace Corporation(12) and J.L. Miller at Lawrence Livermore ~aboratories'~). In the case of electronic transition molecular lasers and more particularly with high density active medium, strong cooling of the working medium may tend on the one hand to lower the excited species quenching and absorption lostrical excitation are of high interest to achieve ses and, on the other hand to increase the rate such high average power U.V. and visible lasers and the branching ratio of usefull specific reacthrough electronic transitions of molecules (7) tions and more generally the gain of the laser Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980962 C9-456 JOURNAL DE PHYSIQUE Cooling t h e gas by means of a supe r son ic channe 1 expansion could moreover l ead t o C.W. o r ve ry high r e p e t i t i o n r a t e l a s e r systems as t he h e a t and waste products a r e ve ry r a p i d l y c a r r i e d away by t h e supe r son ic flow t o g e t h e r w i t h t h e aerodynamic d i s tu rbances induced by energy d e p o s i t i o n . Associa ted wi th supe r son ic f low and a d i a b a t i c expansion which permits t o r each tempera tures n o t e a s i l y ach ievab le w i th thermal exchangers , t h e u se of a high energy e l e c t r o n beam s t a b i l i z e d d i s c h a r g e t o e x c i t e t h e gas mix tu re could a l l ow development of h igh average power h igh e f f i c i e n c y excimer l a s e r sys tems. The aim o f t h i s paper i s t o p re sen t t h e c h a r a c t e r i s t i c s of s e v e r a l quasi-continuous l a s e r emiss ions achieved on s e v e r a l excimer systems i n t h e u l t r a v i o l e t range wi th supe r son ic flow e l e c t r o n beam e x c i t a t i o n and supe r son ic flow e l e c t r o n beam s t a b i l i z e d d i scha rge e x c i t a t i o n devices developped a t I.M.F.M. Some r e s u l t s on excimer f l uo re scence enhancement fo l lowing s t r o n g cool ing and f l u i d dynamics of excimer l a s e r s a c t i v e medium a r e a l s o p re sen ted .

Sur une interprétation des propriétés optiques anormales des couches metalliques minces.

Abstract: Some thin metallic films show anomalous optical properties, namely, that both energetic position and magnitude of the absorption bands depend on the film thickness. An interpretation, usually accepted, is based on a direct excitation of surface plasmons by means of the granular structure or the roughnesses of the films. The existence of these anomalous bands are explained, independently of the surface irregularities, if we assume a localized absorption.

Influence of grain boundaries and recrystallization on the thermal desorption of the oxide film on aluminium samples

Abstract: A study of thermal desorption of oxide films on single-crystal and polycrystalline aluminium is described and the influence of grain boundaries and recrystallization in the latter is discussed.