Experimental multiphoton ionization of cesium atoms through the 9D 3/2 resonant level

In this letter we report the results of an experiment concerning the multiphoton ionization of cesium atoms through the 9D3/2 resonant level, using a ruby laser. The experimental dispersion curve of the resonance obtained is compared to the theoretical shape of the resonant multiphoton ionization profile for cesium deduced from the calculations of B. L. Beers and L. Armstrong [1].Nous présentons dans cette lettre une expérience d'ionisation multiphotonique d'atomes de césium à partir du niveau résonnant 9D3/2, à l'aide d'un laser à rubis. La courbe de dispersion de la résonance est comparée à l'allure de la courbe théorique d'ionisation multiphotonique résonnante déduite des calculs de B. L. Beers et L. Armstrong [1] pour le césium

Remarques sur la structure des couches métalliques minces déterminée par microscopie électronique

The authors indicate a direct method for the determination of the structural parameters affecting the optical properties of very thin metallic layers, the starting-point being the direct counting of the crystallites by electron microscopy. They have been led to suspect the determinations of thickness (determined by weighing in air).Les auteurs indiquent une méthode directe de détermination des paramètres structuraux influençant les propriétés optiques des couches métalliques très minces, à partir du dénombrement direct des cristallites par microscopie électronique. Ils sont amenés à suspecter les déterminations d'épaisseur massique effectuées dans l'air

Création d'atomes d'argon excités dans des états de Rydberg en vue de l'étude de l'autodétachement électronique d'ions moléculaires SF6 -6 dans un piège quadrupolaire radiofréquence

In this work, we describe experimental conditions to obtain argon atoms excited in Rydberg states by an electron gun. Precisions are given about some of their properties it is necessary to know with a view to the study of electronic autodetachment of SF6- molecular ions in a radiofrequency quadrupole trap. These ions are created by nearly-zero energy interaction of SF6 molecules with excited atoms in Rydberg states. In our experimental conditions, the excitation of argon atoms by electronic bombardment in such states has led us to bring to light a deflection angle of the excited atoms, an evaluation of the energy of the electrons which lead to electronic attachment, the number of created excited atoms, and an estimation of their related mean lifetime.Nous décrivons dans ce travail les conditions expérimentales d'obtention d'atomes d'argon excités dans des états de Rydberg par bombardement électronique. Nous précisons certaines de leurs propriétés qu'il est nécessaire de connaître dans la perspective de l'étude de l'auto-détachement électronique d'ions moléculaires SF6-dans un piège quadrupolaire radiofréquence. Ces ions sont créés par interaction, à énergie quasi-nulle, de molécules SF6 avec des atomes excités dans des états de Rydberg. Dans nos conditions expérimentales, l'excitation d'atomes d'argon dans de tels états par bombardement électronique nous a conduits, en particulier, à la mise en évidence d'un angle de déflection des atomes excités, à l'évaluation de l'énergie de l'électron donnant lieu à l'attachement électronique, au nombre d'atomes excités créés, ainsi qu'à une estimation de leur durée de vie moyenne correspondante

Rydberg electron capture mass spectrometry of some environmental pollutants

International audienceThis work relates a coupling between a Rydberg electron capture (REC) source and a mass spectrometer (MS) using a quadrupole ion trap within a special operating mode. The MS instrument is only briefly described as it has already been published. The advantages of the REC are shown, i.e. no fragmentation of the molecule occurs during charge exchange with the Rydberg xenon atoms. The molecular ion lifetime seems to be sufficient to perform mass spectrometry by Fourier analysis. The experiments concern certain molecules of interest in the field of the environment having a positive electron affinity to insure Rydberg electron capture, i.e. certain polyaromatic hydrocarbons, certain polychloro-biphenyls, and one dioxin. (Int J Mass Spectrom 189 (1999) 181–188

Probing radial and axial secular frequencies in a quadrupole ion trap

International audienceWe simulate an operating mode in which the ions are introduced inside a quadrupole trap and slowed down to be confined; after a given confinement time, they are ejected out of the trap towards the detector through the upper end-cap. This elementary experiment is repeated for a set of increasing confinement times. The temporal ion signal obtained is an image of the confined ions' motion. This signal, which is periodical, contains the radial and/or axial secular frequencies of all the confined ionic species depending on the mode of detection. In previous papers, we have shown that with a large circular exit hole centred on the z axis of the trap and with a numerical treatment of the ion time-of-flight (TOF) histogram recorded for each confinement time, we obtain only the z secular frequency. In this paper, we show that the exit position of an ion in the radial plane depends principally on its radial position at the end of the confinement. For this, simply by reducing the dimension of the centred exit hole or by decentring it and counting only the number of ions passing through the hole, we can obtain evidence on the radial secular frequencies. Also, this simulation work allows one to clarify the best operating conditions to measure the x-secular frequencies, that is a decentred exit hole tangential to the oz axis and an ion cloud the excursion of which along the ox axis is limited to the radial position of the exterior edge of the hole and with an ox dimension about three times lower than the hole diameter. In this case, the amplitude calibration is possible as the frequency peak amplitude is proportional to the square value of the mean number of created ions. Moreover, we give the signal over noise ratio under usual values of the operating parameters. This operating mode and its two associated modes of detection could be an useful tool to measure ion motion secular frequencies along the oz axis and along any radial directions. Besides mass spectrometry, the determination of the frequencies shifts and couplings related to the ion motion can lead to other important applications. © 1997 Elsevier Science B.V

A dual quadrupole ion trap mass spectrometer

International audienceTwo quadrupole ion traps are used to carry out a mass spectrometer. The first concerns ion preparation with possible mass selection functions. The second is used as a mass analysis cell to obtain the secular frequency of simultaneously confined ions. After ion ejection, the secular frequencies are computed from the evolution of time-of-flight (TOF) histograms. Comments and results concerning the ion preparation are given. Then, the metrological parameters of the mass spectrometer prototype are examined: amplitude calibration, visibility, resolution, and mass range. (Int J Mass Spectrom 190/191 (1999) 59 – 68) © 1999 Elsevier Science B.V

New operating mode of a quadrupole ion trap in mass spectrometry 4. Simulation studies

International audienceThe purpose of this simulation is to understand the contribution of the parameters of the new protocol of ion mass analysis which we have developed in previous papers and to improve the data treatment in order to predict the experimental results. In this first simulation paper, we limit the study to an ion cloud of the same species. The first part describes the formalism chosen to simulate the ion creation, the ion trajectory during confinement, the ion detection by time of flight measurements and the associated treatments. The second part shows the results and explains the influence of the principal parameters. Experimentally, the initial conditions of ion confinement (position and velocity in the axial and radial directions) are not fully controlled and are estimated for the simulation. For the chosen conditions, the results agree with the experimental ones. We show the influence of the different parameters on the intensity of the signal and the uniqueness of the spectral peak, and we confirm the theoretical expressions given in previous papers for the amplitude of the peaks, the signal-to-noise ratio and the resolution. The limit of sensitivity (defined for a signal-to-noise ratio equal to 6), is obtained with statistically 0.35 ion in the trap for 1024 confinement times. © 1997 Elsevier Science B.V