INELASTIC COLLISIONS OF DRESSED ATOMS

Des atomes à deux niveaux soumis à un rayonnement laser monochromatique peuvent être décrits à l'aide d'états "habillés", qui sont des superpositions cohérentes, dépendant du temps, de ces deux niveaux. Nous établissons que les collisions peuvent coupler directement ces atomes habillés à un troisième niveau, bien séparé en énergie des deux niveaux couplés par le rayonnement, et nous montrons comment exprimer le taux de telles collisions en fonction de taux de collisions relatifs aux niveaux de l'atome nu. Des données expérimentales vérifiant ces prédictions sont présentées pour des collisions Na-He.Two level atoms which are subject to monochromatic laser radiation may be described using dressed states, which are time-varying coherent superpositions of these two levels. We argue that collisions can take these dressed atoms directly to a third level which is well separated in energy from the two radiatively coupled levels and we show how to express the rate for such collisions in terms of collision rates for the bare atomic levels. Data which verify these predictions are presented for Na-He collisions

LASER-INDUCED FLUORESCENCE STUDY OF C2 FROM LASER SPUTTERING OF GRAPHITE AND POLYMERS

Pulsed laser irradiation of graphite surfaces has been known for some time to lead to the ejection of C, C2, C3, etc. neutrals as well as related ions. Since most relevant thermodynamic quantities are known, graphite represents an ideal system for further study. The objectives of this work are two-fold : (1) to compare graphite laser etching results to simple thermal vaporization concepts, and (2) to compare the UV etching of polymers to the results from graphite. We observe that surface morphology and etching rates for graphite indicate a peak surface temperature of ~ 4000K and, hence, can be viewed as a classical vaporization process. The first objective then becomes a question of understanding the energies of molecules, e.g. C2, in the etch plume in terms of an ~ 4000K surface temperature. The second investigation addresses the question of the specific mechanism facilitating far UV etching of polymers. Both photochemical (electronic rearrangement) and thermal degradation have been suggested in various studies

Carbon nanotubes: nanomechanics, manipulation, and electronic devices

Carbon nanotubes are novel materials with unique electrical and mechanical properties. Here we present results on their atomic structure and mechanical properties in the adsorbed state, on ways to manipulate individual nanotubes, on their electrical properties and, finally, on the fabrication and characteristics of nanotube-based electron devices. Specifically, atomic force microscopy (AFM) and molecular mechanics simulations are used to investigate the effects of van der Waals interactions on the atomic structure of adsorbed nanotubes. Both radial and axial structural deformations are identified and the interaction energy itself is obtained from the observed deformations. The conditions under which the structure of a nanotube will adjust to the topography of the substrate are defined. We show that the strong substrate–nanotube interaction allows the manipulation of both the position and shape of individual nanotubes at inert surfaces using the AFM. AFM manipulation is then utilized to position individual nanotubes on electrical pads so that their electrical characteristics can be evaluated. We demonstrate the operation of a field-effect transistor based on a single semiconducting nanotube and of a single-electron transistor using a nanotube bundle as Coulomb island. Finally, conducting nanotubes are employed as tips for AFM lithography

Laser evaporation as a source of small free-radicals

Contains fulltext : 99062.pdf (publisher's version ) (Open Access

Quantitative laser-induced fluorescence: some recent developments in combustion diagnostics

Kohse-Höinghaus K. Quantitative laser-induced fluorescence: some recent developments in combustion diagnostics. Applied Physics, B. 1990;50(6):455-461.This report summarizes several recent applications of quantitative laser-induced fluorescence techniques for the determination of species concentrations and temperature in combustion processes. Several lines of further development are discusse