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We present an easily solvable 1D traveling wave model for laser-guided discharges. By assuming constant propagation speed u, the hydro/electrodynamic/chemistry equations are reduced to ordinary differential equations in retarded time τ. Negative discharges are shown to propagate only if u>μEb, where μ is electron mobility and Eb is the breakdown field; positive discharges propagate only if the channel preconductance exceeds ∼6×10-11 m/Ω. The axial electric field E is shown to spike up to several times Eb and then relax to ∼Eb for as long as the gas remains cold. In this streamer region, the channel conductance, current, and potential all increase linearly with τ. The transition to the leader stage, where E is much smaller, occurs in two steps: excitation of vibrational and low-lying electronic states, then gas heating. The propagation range decreases as a function of initial radius and (for given maximum voltage) of the voltage rise rate. Expansion of the hot channel is shown to increase the range. [ABSTRACT FROM AUTHOR]

Experiments are performed to characterize the electrical properties of plasma filaments that are generated by self-guided femtosecond laser pulses propagating in air. A single plasma filament passes through a high-voltage sphere pulsed at -100 kV to a grounded electrode, which serves as a current monitor. The experiments utilize moderate electric fields to probe the filament conductivity, thereby avoiding the strong perturbations caused by electric discharges. The measured filament current decreases as ∼/R² as the separation R between the electrodes is increased up to 1.5 m. The pulselength of the filament current signal is 2 ns (full-width at half-maximum), but the time resolution is limited by the bandwidth of the oscilloscope. The typical plasma density in the conducting filament is 9 × 1015 cm-3, which is inferred from the conductivity measurements and the size of the optical filaments. Comparisons are made with mobility values derived from electron swarm data, where the mobility depends upon the applied electric field. The conductivity of the filament is measured as the laser pulselength is varied from 50 fs to 1.5 ps. We find that relatively long laser pulses (1 ps) produce filaments with the largest conductivity. A model is used to predict the longitudinal position where the plasma filament forms and is in reasonably good agreement with measurements. [ABSTRACT FROM AUTHOR]

High-energy electrons were generated by the synchronized interaction of a 2-TW laser beam with a nitrogen gas jet and a 10-TW laser beam with helium gas jet. The jets centers are separated by 0.5 mm distance and the propagation of the lasers are collinear. Plasma electrons were trapped and accelerated by the wakefields generated in the gas jet plasmas to above 20 MeV. [ABSTRACT FROM AUTHOR]

The original implementation of the ponderomotive guiding center algorithm is not suitable for modeling the propagation of short laser pulses over long distances. An improved algorithm is given, which improves the accuracy of the calculation, allowing much longer propagation distances to be modeled. [ABSTRACT FROM AUTHOR]