We report on the first experiments of high-order harmonic generation done with the 100 Hz high-energy optical
parametric amplifier (OPA) of the Advanced Laser Light Source. Using krypton and argon as targets, we show that the
OPA's signal beam − with a wavelength range from 1200 nm to 1600 nm, 1.3 mJ to 0.8 mJ of pulse energy and 100 fs
pulse duration − can generate fully tunable XUV radiation down to a wavelength of 15 nm. We have also started to
investigate the use of the OPA pulses for molecular imaging. Inducing molecular alignment with 800 nm, 70 fs pulses,
we have measured the high harmonics spectra generated with 1300 nm pulses from nitrogen molecules oriented at
various angles with respect to the ionizing field, in order to study for the first time the technique of molecular orbital
tomography with a laser wavelength different than 800 nm.
This paper presents result form a systematic study of the feasibility of triggering lightning in a controlled fashion, using ultrashort pulse lasers. We show the importance of producing a plasma with local gradients of electron density by focusing the laser beam in order to trigger streamers, which are the first condition required for the initiation of large-scale spark discharges. We present evidence of the ability of laser filaments to guide streamer discharges, which are akin to the final jump phase of a lightning discharge. We also demonstrate that the leader propagation can be considerably modified by the presence of a laser- produced plasma channel, in a rod-plane electrode geometry. Finally, we have developed numerical models for the ultrashort pulse laser beam propagation through air, plasma production and streamer inception.