Leonid Arantchouk

Radiofrequency plasma antenna generated by femtosecond laser filaments in air

We demonstrate tunable radiofrequency emission from a meter-long linear plasma column produced in air at atmospheric pressure. A short-lived plasma column is initially produced by femtosecond filamentation and subsequently converted into a long-lived discharge column by application of an external high voltage field. Radiofrequency excitation is fed to the plasma by induction and detected remotely as electromagnetic radiation by a classical antenna.

A simple high-voltage high current spark gap with subnanosecond jitter triggered by femtosecond laser filamentation

We describe a simple, sturdy, and reliable spark gap operating with air at atmospheric pressure and able to switch currents in excess of 10 kA with sub-nanosecond jitter. The spark gap is remotely triggered by a femtosecond laser filament.

Tesla coil discharges guided by femtosecond laser filaments in air

A Tesla coil generator was designed to produce high voltage pulses oscillating at 100 kHz synchronisable with a nanosecond temporal jitter. Using this compact high voltage generator, we demonstrate reproducible meter long discharges in air at a repetition rate of 1 Hz. Triggering and guiding of the discharges are performed in air by femtosecond laser filaments.

Two-color interferometer for the study of laser filamentation triggered electric discharges in air

We present a space and time resolved interferometric plasma diagnostic for use on plasmas where neutral-bound electron contribution to the refractive index cannot be neglected. By recording simultaneously the plasma optical index at 532 and 1064 nm, we are able to extract independently the neutral and free electron density profiles. We report a phase resolution of 30 mrad , corresponding to a maximum resolution on the order of 4×10(22) m(-3) for the electron density, and of 10(24) m(-3) for the neutral density. The interferometer is demonstrated on centimeter-scale sparks triggered by laser filamentation in air with typical currents of a few tens of A.

Compact 180-kV Marx generator triggered in atmospheric air by femtosecond laser filaments

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.

Large scale Tesla coil guided discharges initiated by femtosecond laser filamentation in air

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.

Plasma dynamics of a laser filamentation-guided spark

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.

Long-lived laser-induced arc discharges for energy channeling applications

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.

Two-color interferometry for the study of laser filamentation triggered discharges in air

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.

Evolution of a laser filamentation triggered electric discharge in air

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.