Streamerless guided electric discharges triggered by femtosecond laser filaments

Abstract

The time evolution of electrical discharges induced and guided between the cathode of a Van de Graf generator and a ground sphere was studied using a 100 fs Ti:Sapphire laser. Nonlinear focusing and ionization effects produce optical and plasma filaments in the discharge region. Streak camera images often exhibit streamers that propagate towards the cathode, but sudden discharge triggering is frequently observed with no streamer precursors. The typical discharge triggering delay time was measured to be 150 ns. Similar time delays were obtained from an air chemistry code used to model the long time behavior of the plasma induced by the short laser pulse. The model shows that ohmic heating of the filament plasma persists over long time scales and inhibits the decay of electron density due to recombination and attachment processes. Eventually the rise in electron temperature causes the avalanche rate to increase to the point where breakdown occurs. The hydrodynamic density reduction process reported by Tzortzakis et al. [Phys. Rev. E 64, 057401 (2001)] is also taken into consideration. Its main effect is found to be a hastening of the breakdown process.

Extended lifetime of high density plasma filament generated by a dual femtosecond–nanosecond laser pulse in air

“…In our earlier work [12] it was proposed that a combination of a high-intensity short pulse Ti-Sapphire laser and a low-intensity 100 nsduration CO 2 laser pulse can be used to remotely produce a plasma-based source with its lifetime on the microsecond timescale. Numerical studies of femtosecond laser-generated plasma channels in an external electric field and irradiated by an additional laser pulse were also reported [13,14]. Experiments aimed at increasing the lifetime of low-density plasma channels by detaching electrons from negatively charged oxygen molecules (produced by electron attachment) with a delayed ns laser pulse were reported [15,16].…”

Shockwave-assisted laser filament conductivity

“…In the shorter gap (4 cm, Figure 4b), the laser-generated conducting channel is not sufficient to let the voltage drop below the breakdown threshold. Therefore, discharges are not suppressed, but rather guided by the conducting filaments that offer a more favorable way to the discharges [6,[12][13][14][15][16][17][18]. Almost all discharges are guided for repetition rates above 100 Hz, most probably related to the ability of the high-repetition rate beam to timely intercept streamer discharges before they develop into free-propagating sparks.…”

“…Ultrashort laser filaments [9][10][11] can trigger (with breakdown threshold reduction by typically 30 %) and guide high-voltage discharges both in the near-infrared [12][13][14][15] and in the ultraviolet [6,[16][17][18]. Laser filaments have also been used as a probe to investigate the dynamics of high-voltage discharges [19,20], streamers [21] and leaders [22,23].…”

The importance of corona generation and leader formation during laser filament guided discharges in air

“…6,7 In the literature, it has also been noted that corona discharges and associated space charge build up can play a role. 3,[8][9][10][11] Here, we present results from our filament guided HV discharge experiments that show corona generation by the filament, which then leads to leader formation. The electrons act as a seed from where discharge leaders nucleate and start propagating in the filament path across the gap.…”