PhD thesis defense: Silin FU (F-ILM)

Tailoring femtosecond laser filamentation in the atmosphere

When an intense femtosecond laser pulse propagates in a transparent medium, the filamentation phenomenon enables the laser beam to self-focus and to maintain a high laser intensity sufficient to ionize the medium over very long distances. By optimizing the laser parameters, plasma filaments have been obtained up to kilometer distances. The properties of the filaments open up a wide range of applications, particularly in the air: they can guide lightning, create optical waveguide structures, reduce the drag of supersonic craft, guide terahertz and microwave radiation, and serve as UV laser sources or terahertz radiation sources for remote sensing.

This thesis focuses on the spatio-temporal shaping of femtosecond filaments in air, and their optimization for atmospheric applications. In particular, I will present several studies based on the use of Laguerre-Gauss beams to produce optical waveguides in the air or to guide electric discharges. Another method developed involves organizing filaments along the propagation axis with multifocal diffractive plates to extend the length of superfilamentation, thus doubling the length of laser guided discharges. Finally, I will show that using the flying focus method, we’ve been able to modify the direction and velocity of the ionization front of a plasma filament, making it an adjustable THz radiation source in all directions.