110 research outputs found
Direct measurement of the electron density of extended femtosecond laser pulse-induced filaments
We present direct time- and space- resolved measurements of the electron
density of femtosecond laser pulse-induced plasma filaments. The dominant
nonlinearity responsible for extended atmospheric filaments is shown to be
field-induced rotation of air molecules.Comment: 12 pages, 5 figure
Optical guiding in meter-scale plasma waveguides
We demonstrate a new highly tunable technique for generating meter-scale low
density plasma waveguides. Such guides can enable electron acceleration to tens
of GeV in a single stage. Plasma waveguides are imprinted in hydrogen gas by
optical field ionization induced by two time-separated Bessel beam pulses: The
first pulse, a J_0 beam, generates the core of the waveguide, while the delayed
second pulse, here a J_8 or J_16 beam, generates the waveguide cladding. We
demonstrate guiding of intense laser pulses over hundreds of Rayleigh lengths
with on axis plasma densities as low as N_e0=5x10^16 cm^-3
Bound electron nonlinearity beyond the ionization threshold
Although high field laser-induced ionization is a fundamental process
underlying many applications, there have been no absolute measurements of the
nonlinear polarizability of atoms and molecules in the presence of ionization.
Such information is crucial, for example, for understanding the propagation of
high intensity ultrashort pulses in matter. Here, we present absolute space-
and time-resolved measurements of the ultrafast laser-driven nonlinear
polarizability in argon, krypton, xenon, nitrogen, and oxygen up to an
ionization fraction of a few percent. These measurements enable determination
of the non-perturbative bound electron nonlinearity well beyond the ionization
threshold, where it is found to be approximately linear in intensity
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