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Femtosecond laser guiding of a high-voltage discharge and the restoration of dielectric strength in air and nitrogen
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Image of FIG. 1.
FIG. 1.

Experimental schematic. The setup consists of a pair of electrodes, the high-voltage pulse generator, a fast-gated ICCD camera for observation, and the femtosecond laser focus closely aligned with and focused between the electrodes.

Image of FIG. 2.
FIG. 2.

Schematic of high voltage power supply.

Image of FIG. 3.
FIG. 3.

Voltage waveform with parameters of the waveform indicated (left). Typical voltage-current-power characteristics of electrical pulse without laser (right).

Image of FIG. 4.
FIG. 4.

Top images: raw image of guided plasma filament (a); optical scheme for three-projection image acquisition (b). Bottom line: discharge path reconstructed from three projection images. Reconstructions without guiding laser (c), and with fs guiding laser with the approximate laser focus shown in red (d).

Image of FIG. 5.
FIG. 5.

Schlieren (a) and camera (b) images of the streamer phase of the discharge development. The schlieren photo is taken 500 μs after the shot with an exposure of 0.1 μs. The third image (c) is taken after the laser pulse and shows the strong streamer along the laser-designated path. Both images of the streamer development are captured with the high voltage pulse just below the breakdown threshold.

Image of FIG. 6.
FIG. 6.

Voltage waveforms (a) without laser guiding where strong oscillations are the result of streamer branching, and (b) with laser guiding τd = 9.5 μs, where no strong oscillations are evident.

Image of FIG. 7.
FIG. 7.

Images of the first stage of the HV discharge propagation at fs laser guiding. Xf = 10 mm; (a) τd = 1 μs; (b) τd = 3 μs, attached filament; (c) τd = 3 μs, filament a bit aside, (d) τd = 5 μs; (e) τd = 80 μs; (f) τd = 150 μs.

Image of FIG. 8.
FIG. 8.

Breakdown voltage vs delay time between laser pulse and HV pulse maximum. (a) Air at atmospheric pressure, (b) nitrogen of >0.99 purity. “Nearby electrode” indicates that the axial distance from electrode to top end of the laser filament is Xf ≤ 5 mm; “out of electrode” indicates Xf ≥ 10 mm.

Image of FIG. 9.
FIG. 9.

One-dimensional axisymmetric Reynolds-averaged Navier-Stokes simulation of a modeled energy deposition showing (a) Radial density profiles at several fixed times following a modeled energy, and (b) the variation of the centerline density.

Image of FIG. 10.
FIG. 10.

(a) Schlieren image HV spark discharge with a laminar He jet (delay 20 μs); jet nozzle is on bottom, left side. (b) Schlieren image of HV spark discharge interaction with heated air jet; delay time 10 μs, air temperature T ≈ 380 K.

Image of FIG. 11.
FIG. 11.

Time-evolution of plasma components during the initial decay of a femtosecond laser pulse in mixture at P = 1 atm, T0 = 300 K. The initial density of electrons is Ne 0 = 1.5 × 1017 cm−3. (a) Charged particles, (b) neutral components.

Image of FIG. 12.
FIG. 12.

Time-evolution of plasma components on the main stage of plasma decay of a femtosecond laser pulse in N2:O2 = 4:1 mixture at P = 1 atm, T0 = 300 K. The initial density of electrons Ne 0 = 1.5 × 1017 cm−3. Open circles are the experiment data on electron concentration at similar conditions. 18

Image of FIG. 13.
FIG. 13.

Temporal dynamics of the polarization time τpol(t) in nitrogen and air at P = 1 atm, T0 = 300 K.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Femtosecond laser guiding of a high-voltage discharge and the restoration of dielectric strength in air and nitrogen