Naslov
Surface self-organization into coherent structures of string-like objects in laser-matter interaction

Autori
Lugomer, Stjepan

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
NCSS-5, "Fifth Nordic Confwerence on Surface Science" / Valden, Mika - Tampere : Tampere University of Technology, 2004, 34-35

Skup
Fifth Nordic Conference on Surface Science

Mjesto i datum
Tampere, Finska, 22.09.2004. - 25.09.2004

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Surface selforganization; Vortex filaments; Strings

Sažetak
Surface selforganization (SO) into coherent structures of various levels of topological complexity caused by nanosecond laser-matter interaction (ns-LMI) is a nonliner and nonequilibrium process. The scenario for the SO structure formation is based on the turbulent field which is the two component fluid: the first, high vorticity component, forms the long living coherent SO structures ; the second, low vorticity component, forms the short living structureless fluctuating background fluid, in which the coherent structures are embeded. (1-6) Coherent structures stay frozen permanently at the end of laser pulse becouse of ultrafast cooling at the rate of ~ 109 K/s, thus enabling a posteriori study. The ns-LMI driven by excimer XeCl laser on Co-coated steel surface, causes the formation of a shear layer of the fluid velocity U ~ 6000 m/s, of the kinematic viscposity n ~10-4 m2/s , of the Reynolds number Re ~ 2 x 103 - 5 x 103, and the of the circulation G ~ 2pdU ~ 0.2 m2/s, which results in a paralel set of micron-scale vortex filaments(2-5) as the string-like objects of the core size d ~ 5mm, and of the length L ~ 500 mm.Exposed to torsion, vortex filaments form the loop solitons (the Hasimoto soiltons). Transversal perturbation of filaments results in the formation of helically paired and braided structures. Complex braids of 5 vortex filaments can be represented as the Wolfram's cellular automata generated on three space-time latices, the periods of which can be expressed as the integers of the "smallest natural period" of Wu. In the regions of dense filament population the filaments organize into bundles, and then into helicallly paired, braided, or tangled complexes. These bundle-structures are associated with a "multiloop" ie., the common loop soliton, as a result of collective response to torsion. The type of organization depends on the filament-filament distance, and on the single-mode or the multimode undulations, thus making difference between dynamics of the "subcritical", "critical" and a "supercritical" bundle. The novel approach is introduced in the topological analysis of selforganized structures in which the graph of a tangled structure of bundles, is substituted by the topologicaly closest regular braid graph, as its "regular representation".

Izvorni jezik
Engleski

POVEZANOST RADA