Laguerre-Gaussian laser filamentation for the control of electric discharges in air.

We study the use of Laguerre-Gaussian (LG) femtosecond laser filament with multi GW peak power to guide electric sparks in the atmosphere. We demonstrate that an LG beam with a vortex phase or with 6 azimuthal phase steps generates a filamentation regime, where a longer and more uniform energy deposition is produced compared to a normal beam with a flat phase. Such filaments can guide electric discharges over much longer distances. This technique could significantly extend the guiding range of laser filaments for lightning control and other long-range atmospheric experiments involving filamentation.

Linear discriminant analysis based predator-prey analysis of hot electron effects on the X-pinch plasma produced K-shell Aluminum spectra.

In this study, Linear Discriminant Analysis (LDA) is applied to investigate the electron beam effects on the X-pinch produced K-shell Aluminum plasma. The radiating plasma is produced by the explosion of two 25-µm Al wires on a compact L-C (40 kV, 200 kA and 200 ns) generator, and the time integrated spectra are recorded using de Broglie spectrographs. The ion and electron oscillations of K-shell Al plasma are extracted using LDA of spectral database of non-LTE K-shell Al model. A three dimensional representation of LDA shows that the presence of electron beam exhibits outward spirals of Langmuir turbulence and the center region of the spirals recieves lower electron temperatures of 50-100 eV. These spirals then are modeled by logistic growth of predator-prey model. This modeling suggests that the ions (LD1: most dominant eigenvector of LDA) and electrons (LD2: second most dominant eigenvector of LDA) represent the predators and preys, respectively. Besides, addition of electron beams transforms evanescent oscillations to the standing ones.

Long-lived laser-induced arc discharges for energy channeling applications.

Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy.

Two-color interferometer for the study of laser filamentation triggered electric discharges in air.

We present a space and time resolved interferometric plasma diagnostic for use on plasmas where neutral-bound electron contribution to the refractive index cannot be neglected. By recording simultaneously the plasma optical index at 532 and 1064 nm, we are able to extract independently the neutral and free electron density profiles. We report a phase resolution of 30 mrad , corresponding to a maximum resolution on the order of 4×10(22) m(-3) for the electron density, and of 10(24) m(-3) for the neutral density. The interferometer is demonstrated on centimeter-scale sparks triggered by laser filamentation in air with typical currents of a few tens of A.