133 research outputs found
Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water
We analyze numerically and experimentally the effect of the input pulse chirp
on the nonlinear energy deposition from J fs-pulses at nm to
water. Numerical results are also shown for pulses at nm, where linear
losses are minimized, and for different focusing geometries. Input chirp is
found to have a big impact on the deposited energy and on the plasma
distribution around focus, thus providing a simple and effective mechanism to
tune the electron density and energy deposition. We identify three relevant
ways in which plasma features may be tuned.Comment: 9 pages, 7 figure
Self-seeded lasing in ionized air pumped by 800 nm femtosecond laser pulses
We report on the lasing in air and pure nitrogen gas pumped by a single 800
nm femtosecond laser pulse. Depending on gas pressure, incident laser power and
beam convergence, different lasing lines are observed in the forward direction
with rapid change of their relative intensities. The lines are attributed to
transitions between vibrational and rotational levels of the first negative
band of the singly charged nitrogen molecule-ion. We show that self-seeding
plays an important role in the observed intensity changes.Comment: 9 pages, 4 figure
Superfilamentation in air
The interaction between a large number of laser filaments brought together
using weak external focusing leads to the emergence of few filamentary
structures reminiscent of standard filaments, but carrying a higher intensity.
The resulting plasma is measured to be one order of magnitude denser than for
short-scale filaments. This new propagation regime is dubbed
superfilamentation. Numerical simulations of a nonlinear envelope equation
provide good agreement with experiments.Comment: 5 pages, 4 figure
Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses
Acoustic signals generated by filamentation of ultrashort TW laser pulses in
water are characterized experimentally. Measurements reveal a strong influence
of input pulse duration on the shape and intensity of the acoustic wave.
Numerical simulations of the laser pulse nonlinear propagation and the
subsequent water hydrodynamics and acoustic wave generation show that the
strong acoustic emission is related to the mechanism of superfilamention in
water. The elongated shape of the plasma volume where energy is deposited
drives the far-field profile of the acoustic signal, which takes the form of a
radially directed pressure wave with a single oscillation and a very broad
spectrum.Comment: 9 pages, 12 figure
Lasing of ambient air with microjoule pulse energy pumped by a multi terawatt IR femtosecond laser
We report on the lasing action of atmospheric air pumped by an 800 nm
femtosecond laser pulse with peak power up to 4 TW. Lasing emission at 428 nm
increases rapidly over a small range of pump laser power, followed by
saturation above ~ 1.5 TW. The maximum lasing pulse energy is measured to be
2.6 uJ corresponding to an emission power in the MW range, while a maximum
conversion efficiency of is measured at moderate pump pulse energy. The optical
gain inside the filament plasma is estimated to be excess of 0.7/cm. The lasing
emission shows a doughnut profile, reflecting the spatial distribution of the
pump-generated white-light continuum that acts as a seed for the lasing. We
attribute the pronounced saturation to the defocusing of the seed in the plasma
amplifying region and to the saturation of the seed intensity
Laser-induced periodic annular surface structures on fused silica surface
International audienceWe report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse
Two-color interferometer for the study of laser filamentation triggered electric discharges in air
International audienceWe 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
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