Laser filamentation is a spectacular phenomenon where the self-focusing of the laser pulse generates ionizing light channels. Many applications of filamentation, such as the laser lightning rod, require the generation of superfilaments, long plasma channels of higher electron density than normal filaments. Using a multifocal phase mask, we demonstrate an extension of the superfilamentation length of a focused terawatt laser beam. Optimized superfilaments show increased energy deposition compared to a normal gaussian beam and an extension of their length by at least a factor two. When put in contact with a high voltage electrode, the guiding of a single plasma column with a length of ∼1 m is observed. The length of an air waveguide generated by a vortex laser pulse is also increased by a factor 2 in the presence of the phase mask.

We study the use of Laguerre-Gaussian (LG) femtosecond laser filament with multi GW peak power to guide electric sparks in the atmosphere. We demonstrate that an LG beam with a vortex phase or with 6 azimuthal phase steps generates a filamentation regime, where a longer and more uniform energy deposition is produced compared to a normal beam with a flat phase. Such filaments can guide electric discharges over much longer distances. This technique could significantly extend the guiding range of laser filaments for lightning control and other long-range atmospheric experiments involving filamentation. (c) 2024 Optica Publishing Group

We study the influence of the gravitational force on the generation of low-density channels of air left in the path of femtosecond laser filaments at high repetition rate. We observe a more important density variation along the filament longitudinal axis in the case of a vertically created filament as compared to a horizontal one. This leads to a more important reduction of the electrical breakdown field using vertical filament. This geometry induced difference is only observed at high repetition rate because it is directly related to the cumulative effect appearing above 100 Hz.

We study the creation and evolution of meter-scale long-lived laser-guided electric discharges and the interaction between consecutive guided discharges. The lifetime of guided discharges from a Tesla high voltage generator is first increased up to several milliseconds by the injection of additional current. The subsequent discharge evolution is measured by recording the electric current and by Schlieren and fluorescence imaging. A thermodynamic model of the gas evolution is developed to explain the discharge evolution. Finally, we analyze the succession of laser-guided discharges generated at 10 Hz.

Femtosecond laser filamentation in air creates long columns of weakly ionized plasma that result in a low-density channel over μs timescale [1]. These channels can trigger and guide electric discharges [2]–[3]. Applications have been proposed for this effect, such as the laser lightning rod [4], or the plasma antenna [5]. The main limitation for the later one is the discharge lifetime limited to microseconds [6], since a plasma antenna would require the existence of a permanent conductive channel. To overcome this limitation, we investigate a regime using consecutive guided discharges with prolonged lifetime that could create a quasi-permanent conductive channel.

We study the influence of the laser repetition rate on the generation of low-density channels of air left in the path of femtosecond laser filament. At high repetition rates, we observe the formation of a permanent millimeter-wide low-density channel that exceeds the depth and width of the transient depletion due to a single filament. We also show that this permanent cumulative effect decreases the breakdown voltage between two electrodes and can alter the path of the discharge. By comparing this effect in air and in pure nitrogen, we show that an accumulation of O-2 ions contributes to the reduction in the breakdown voltage. (C) 2021 Author(s).

In this study, Linear Discriminant Analysis ( LDA ) is applied to investigate the electron beam effects on the X -pinch produced K -shell Aluminum plasma. The radiating plasma is produced by the explosion of two 25-μm Al wires on a compact L-C (40 kV, 200 kA and 200 ns) generator, and the time integrated spectra are recorded using de Broglie spectrographs. The ion and electron oscillations of K-shell Al plasma are extracted using LDA of spectral database of non-LTE K-shell Al model. A three dimensional representation of LDA shows that the presence of electron beam exhibits outward spirals of Langmuir turbulence and the center region of the spirals recieves lower electron temperatures of 50–100 eV. These spirals then are modeled by logistic growth of predator-prey model. This modeling suggests that the ions (LD1: most dominant eigenvector of LDA) and electrons (LD2: second most dominant eigenvector of LDA) represent the predators and preys, respectively. Besides, addition of electron beams transforms evanescent oscillations to the standing ones.

Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy.

We investigate experimentally the plasma dynamics of a centimeter-scale, laser filamentation-guided spark discharge. Using electrical and optical diagnostics to study monopolar discharges with varying current pulses, we show that plasma decay is dominated by free electron recombination if the current decay time is shorter than the recombination characteristic time. In the opposite case, the plasma electron density closely follows the current evolution. We demonstrate that this criterion holds true in the case of damped alternating current sparks, and that alternative current is the best option to achieve a long plasma lifetime for a given peak current.

The triggering and guiding of electric discharges produced in atmospheric air by a compact 100 kV Marx generator is realized in laboratory using an intense femtosecond laser pulse undergoing filamentation. We describe here an approach allowing extending the lifetime of the discharges by injecting a current with an additional circuit. Laser guiding discharges with a length of 8.5 cm and duration of 130 μs were obtained.

Summary form only given. Laser filamentation guided electric discharges have many interesting applications, among which are the laser lightning rod, plasma aerodynamic control, high-power closing switches and plasma antennas. The latter cases rely on a precise control of the discharge plasma lifetime, either to adapt the switch or antenna on-state time to the current situation. In this work, we study the link between the temporal evolution of a laser filamentation triggered discharge plasma column and the discharge current waveform. The centimeter long plasma is generated by the discharge of a 2 nF capacitor charged to 15 kV, yielding a constant electric energy of 200 mJ. Various ballast resistances ranging from 400 to 10 Ω allow modifying the current waveform in the monopolar regime. A 29 μH coil can also be used to bring the circuit in the oscillatory regime. Plasma is characterized by means of two-color interferometry, enabling us to extract space and time-resolved electron density and neutral density radial profiles. We found that, in the monopolar regime, as the current pulse amplifies and shortens, electron density decay becomes dominated by electron-ion recombination, while low-current impulses result in a plasma decay closely related to the current waveform. Longer plasma lifetime is achieved using strong and short current pulses. As for the oscillatory regime, we show that in this case the plasma has a very slow decay, resulting in more favorable conditions for the generation of long lived plasma columns.

We developed a compact Marx generator triggered in atmospheric air by a single femtosecond laser beam undergoing filamentation. Voltage pulses of 180 kV could be generated with a subnanosecond jitter. The same laser beam was also used to initiate simultaneously guided discharges up to 21 cm long at the output of the generator.

Summary form only given. Laser filamentation triggered electric discharges are very promising in view of their numerous applications such as the laser lightning rod, plasma aerodynamic control, high-power closing switches and plasma antennas. However, the development and maturation of these technologies rely on a good knowledge of the plasma parameters. To this purpose, we developed an interferometric diagnostic for electron density. However, as the discharge heats the medium, strong hydrodynamic effects emerge and lead to a non-negligible contribution of bound electrons to the plasma refractive index. We consequently record this index simultaneously at two different wavelengths to discriminate between the free and bound electron contributions, so-called two-color interferometry. The interferometer is built in a standard Mach-Zehnder configuration. We use a 8 ns-full width at half maximum Nd:YAG laser to probe the plasma at both 532 and 1064 nm in a transverse geometry. CCD cameras with a 10 μm pixel size are used to record both interferograms at the same time. Phase recovery from interferograms is done using a 1D continuous wavelet transform algorithm coupled to a cost function routine. Phase unwrapping is done following a noncontinuous path of decreasing reliability. Finally, a Fourier-Hankel Abel inversion algorithm allows recovering electron and neutral radial density profiles. The interferometer is demonstrated on ~40 A sparks triggered by femtosecond filamentation. The limiting phase noise of the interferometer is estimated to be 30 mrad RMS at 532 nm.

The guiding of meter scale electric discharges produced in air by a Tesla coil is realized in laboratory using a focused terawatt laser pulse undergoing filamentation. The influence of the focus position, the laser arrival time, or the gap length is studied to determine the best conditions for efficient laser guiding. Discharge parameters such as delay, jitter, and resistance are characterized. An increase of the discharge length by a factor 5 has been achieved with the laser filaments, corresponding to a mean breakdown field of 2 kV/cm for a 1.8 m gap length. Consecutive guided discharges at a repetition rate of 10 Hz are also reported.

We study the guiding effect of femtosecond laser filaments on high-voltage electric discharges generated by a compact Tesla coil. Meter scale repetitive discharges are demonstrated.