Experimental setup for filament characterization. The windowless helium cell was moved in steps of 7.5 cm along the filament propagation from 3 to 12 m. The reflectors in the cell are for laser energy attenuation and wavelength selections.
(a) Two-dimensional image of the USL filament using the windowless helium cell at 10 m for a 50 fs pulse and (b) horizontal line-out of the hot filament shown in (a) showing a peak energy fluence of and a FWHM diameter of 130 μm.
Longitudinal variation of the FWHM diameter of a 450 fs USL filament showed a slight increase from 8 to 12 m.
Longitudinal variation of the energy fluence of a 450 fs USL filament showed a slight decrease from 8 to 12 m.
Longitudinal variation of the integrated energy ( of peak fluence) of a 450 fs USL filament appears to hold relatively constant from 8 to 12 m.
Measured current (voltage across a 50 Ω termination resistor) conducting through a 480 fs USL filament that passed through a high voltage globe as a function of the position of the current collector from the globe. Open triangle indicates the theoretical prediction of a dependence.
An extended electrical discharge over 1.7 m induced by a 500 fs USL pulse between two oppositely charged Van de Graaff generators.
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