Nadège Marchiando

Bio: Nadège Marchiando is an academic researcher from University of Geneva. The author has contributed to research in topics: Rogue wave & Infragravity wave. The author has an hindex of 2, co-authored 3 publications receiving 64 citations.

Triggering filamentation using turbulence

Abstract: We study the triggering of single filaments due to turbulence in the beam path for a laser of power below the filamenting threshold. Turbulence can act as a switch between the beam not filamenting and producing single filaments. This 'positive' effect of turbulence on the filament probability, combined with our observation of off-axis filaments suggests the underlying mechanism is modulation instability caused by transverse perturbations. We hereby experimentally explore the interaction of modulation instability and turbulence, commonly associated with multiple-filaments, in the single-filament regime.

Nonlinear fast growth of surface gravity waves under the action of wind

Abstract: The generation of ocean waves by wind is a highly nonlinear problem where the physical processes at the airwater interface are difficult to measure and to model for the presence of turbulence in both fluids. Direct field measurements of the induced pressure by airflow on waves are rare and difficult to perform, thus the underlying mechanisms leading to wave amplification are still unclear. We consider here the Miles’ mechanism, which is characterised by growth rates, M=f , in the range from 10 3 -10 2 for fast-moving waves and in the range 10 2 -1 for slow-moving waves and waves in laboratory tank experiments. This prompted us to investigate the case with Miles’ growth rates of first order in the wave steepness, M=f = O( ), instead of the usually considered one, M=f = O( 2 ), where is the wave steepness which both in ocean and tank experiments can be of the order of 0.1. We use the method of multiple scales for deriving the nonlinear Schrodinger (NLS) equation with wave growth rate of first order in the wave steepness. We find that a simple coordinate transformation reduces the wind-forced NLS equation into the standard NLS equation with constant coefficients. Thus, we show how the Peregrine, Akhmediev and Kuznetsov-Ma solutions are modified in the presence of this first-order wind. In particular, the lifetime of both the Peregrine and the Akhmediev solitons increases for large growth rates and the maximum amplitude of these solitons slightly increases for growth rates larger than a certain value. The enhancement of both lifetime and maximum amplitude of rogue waves under the action of wind has been observed in tank experiments and numerical simulations of dispersive focusing, thus confirming the relevance in this context of the case M=f = O( ) considered in the present study.

Reports on Progress in Physics

Abstract: WHEN introduced in 1934, “Reports on Progress in Physics’ was intended to be a series of annual reports In 1942, owing to the need for economy in time and material, a change in policy was made, for what was thought would be only for the duration of the War, by publishing one volume every second year Unfortunately this temporary measure had to be continued after the cessation of hostilities ; but it is now hoped that the volume under review will be the last of the two-year volumes Indeed, the welcome news has recently been given that Volume 12 is already in active preparation and should be published later this year Reports on Progress in Physics Vol 11 (1946–47) Pp iv + 462 + 11 plates (London: Physical Society, 1948) 42s net ; to Fellows, 25s net

Short-pulse lasers for weather control.

Abstract: Filamentation of ultra-short TW-class lasers recently opened new perspectives in atmospheric research. Laser filaments are self-sustained light structures of 0.1-1 mm in diameter, spanning over hundreds of meters in length, and producing a low density plasma (1015-1017 cm-3) along their path. They stem from the dynamic balance between Kerr self-focusing and defocusing by the self-generated plasma and/or non-linear polarization saturation. While non-linearly propagating in air, these filamentary structures produce a coherent supercontinuum (from 230 nm to 4 µm, for a 800 nm laser wavelength) by self-phase modulation (SPM), which can be used for remote 3D-monitoring of atmospheric components by Lidar (Light Detection and Ranging). However, due to their high intensity (1013-1014 W cm-2), they also modify the chemical composition of the air via photo-ionization and photo-dissociation of the molecules and aerosols present in the laser path. These unique properties were recently exploited for investigating the capability of modulating some key atmospheric processes, like lightning from thunderclouds, water vapor condensation, fog formation and dissipation, and light scattering (albedo) from high altitude clouds for radiative forcing management. Here we review recent spectacular advances in this context, achieved both in the laboratory and in the field, reveal their underlying mechanisms, and discuss the applicability of using these new non-linear photonic catalysts for real scale weather control.

Progress in Quantum Electronics Vol 3

Abstract: J H Sandars and S Sleenholm (eds) Oxford: Pergamon Press 1974 Part 1 Three Level Gas Systems and Their Interaction with Radiation pp 106 price £2.95 Part 2 Mode Locking of Lasers pp 107–229 price £2.80 Both parts of this volume are valuable. The first is an extensive account of the behaviour of three level systems in the presence of an intense field resonant with one of the transitions.

Dynamics of flexural gravity waves: from sea ice to Hawking radiation and analogue gravity

Abstract: The propagation of flexural gravity waves, routinely used to model wave interaction with sea ice, is studied, including the effect of compression and current. A number of significant and surprising properties are shown to exist. The occurrence of blocking above a critical value of compression is illustrated. This is analogous to propagation of surface gravity waves in the presence of opposing current and light wave propagation in the curved space-time near a black hole, therefore providing a novel system for studying analogue gravity. Between the blocking and buckling limit of the compressive force, the dispersion relation possesses three positive real roots, contrary to an earlier observation of having a single positive real root. Negative energy waves, in which the phase and group velocity point in opposite directions, are also shown to exist. In the presence of an opposing current and certain critical ranges of compressive force, the second blocking point shifts from the positive to the negative branch of the dispersion relation. Such a shift is known as the Hawking effect from the analogous behaviour in the theory of relativity which leads to Hawking radiation. The theory we develop is illustrated with simulations of linear waves in the time domain.