engleski

Nonlinear waves and coherent structures generated by nanosecond laser pulses on metal surface

Nanosecond laser-matter interactions (LMI) cause the spontaneous formation of open-loop and closed-loop vortex filaments of various levels of the organization complexity. The closed-loop filaments appear as vortex rings, Hopf links, trefoil knots, and very complex knotted structures. By varying the laser power density we can operate in the Rayleigh-Taylor (RT) or the Richtmyer-Meskhow (RM) interaction environment. In the RM environment, a shock wave causes wave-like baroclinic vorticity deposition on the density interface which evolve into other types of coherent structres (N: J. Zabusky). That is, once the fluid acceleration in the RT/RM environment reaches a critical Reynolds number 2000 < Re < 5000 a Kelvin-Helmholtz like instability initiates roll-up of nonlinear waves into coherent co-rotating tubes (vortex filaments) of the same circulation polarity: C+C+C+... Also, RM counter-rotating filaments C+C-C+... arise with dipolar and tripolar core deformations. Further deformation and a helical instability leads to the merging of filaments, etc. We also discuss our recent paper (S. Lugomer and N.J. Zabusky) where nonlinear soliton-like structures evolve into breaking waves. References. 1. S. Lugomer and A. Maksimović, &laquo ; ; Solitons on filaments generated by ns laser pulse on metal surface, J. Appl. Phys. 82 (1997) 1374. 2. S. Lugomer &laquo ; ; Braids of vortex filaments generated by laser on metal surface&raquo ; ; Phys. Letters, A259 (1999)479. 3. Y. Fukumoto and S. Lugomer, &laquo ; ; Instability of Vortex filaments in Laser-Matter Interactions&raquo ; ; , Phys. Lett , A308 (2003)375. 4. S. Lugomer and Y. Fukumoto, &laquo ; ; Hierarchical Instability of Vortex Rings Array in Laser-Matter Interactions&raquo ; ; Fluid Dynamics Res., 36 (2005) 277. 5. N. J. Zabusky, S. Lugomer and S. Zhang, &laquo ; ; Micro-Fluid Dyanamics via Laser-surface Interactions&raquo ; ; , Fluid Dynamcs Res. 36 (2005) 291. 6. S. Lugomer and N. J. Zabusky, &laquo ; ; Nonlinear and breaking Micron Waves at the Laser-Liquefied Metal Pool&raquo ; ; Appl. Phys. Letters. 87 (2005) 204101.

Nonlinear waves; Coherent Structures; vortex filaments; Self-organization

The invited seminar was given at the "Department of Complex Physics", Weizmann Institute of Sciences, Rehovot, Israel, April 5th 2006.