Narrow Results

We solve analytically the out-of-equilibrium initial stage that follows the injection of a radially finite electron beam into a plasma at rest and test it against particle-in-cell simulations. For initial large beam edge gradients and not too large beam radius, compared to the electron skin depth, the electron beam is shown to evolve into a ring structure. For low enough transverse temperatures, filamentation instability eventually proceeds and saturates when transverse isotropy is reached. The analysis accounts for the variety of very recent experimental beam transverse observations.

The paper presents the ring formation during the course of filamentation in laser and weak inhomogeneous plasma interaction. Due to the combined influence of off-axial component and plasma density ripple, normal single ring changed into abnormal splitted ring during the course of filamentation. With increase in off-axial component and plasma density ripple, the abnormal splitted ring became stronger.

We present an experimental study on the interaction between femtosecond laser and water. When a beam of femtosecond laser is focused at a single point inside water, nonlinear interaction between the laser and water molecules gives rise to several interesting optical phenomena, starting with filamentation, supercontinuum white light generation and then the formation of cavitation microbubbles near the laser focus region. We observe drifting of the laser focus region and cavitation bubbles against the direction of laser propagation with increasing laser power. Due to conical emission, geometric scattering of white light on the bubble surface manifests itself as multicolored sparkling at the edge of the bubbles. Careful analysis of the video footage of the geometric scattering event reveals a unique color-changing property which occurs only within a tiny fraction of a second. This property can be explained as due to the hydrodynamical flow of the laser-induced plasma strings that leads to instability in the frequency of the emitted light.

This paper presents the experimental investigation of the changes in the geometrical shape of femtosecond laser-induced plasma in air under different laser power, and its effects on supercontinuum white light generation and conical emission. When a femtosecond laser is focused into a tiny spot in air, optical breakdown of air molecules occurs and this leads to the generation of plasma filament whose geometrical size and shape depend on laser power. This process is then followed by two light-emitting processes, namely supercontinuum white light generation and conical emission, both of which scatter light that reveals the characteristics of the plasma filament. Our experiment shows that the laser-induced plasma becomes thinner and longer at high average laser power but appears thick and round at lower laser power. At higher laser power, conical emission which scatters laser light in the forward direction dominates the scattering process while at lower laser power, it is the scattering of supercontinuum white light in all directions that plays a bigger role. The intricate rainbow-like pattern formed on a white screen located far away in the forward direction reveals sophisticated nonlinear optical processes that take place in conical emission which slowly diminishes as the laser power is gradually reduced.

In 2002, Hrencecin and Kauffman defined a filamentation invariant on oriented chord diagrams that may determine whether the corresponding flat virtual knot diagrams are non-trivial. A virtual knot diagram is non-classical if its related flat virtual knot diagram is non-trivial. Hence filamentations can be used to detect non-classical virtual knots. We extend these filamentation techniques to virtual links with more than one component. We also give examples of virtual links that they can detect as non-classical.