  Magneto-terahertz phenomena are the main focus of the thesis. This work
started as supporting research for the science of an X-ray laser (SwissFEL).
X-ray lasers have recently drawn great attention as an unprecedented tool for
scientific research on the ultrafast scale..... To answer this fundamental
question, we performed original numerical simulations using a coupled Landau-
Lifshitz-Gilbert Maxwell model. ... Those requirements were the motivations for
the experiments performed in the second part of the thesis. To shape the
terahertz pulses, .... Regarding the field intensities, we followed two
approaches. The first deals with field enhancement in nanoslits arrays. We
designed a subwavelength structure characterized by simultaneous high field
enhancement and high transmission at terahertz frequencies to suit nonlinear
sources. The second approach depended on up-scaling the generation from
laser-induced plasma by increasing the pump wavelengths. Numerical calculations
have also brought to our attention the importance of linear magnetoterahertz
effects. In particular, the simulations showed that the ultrafast dynamics
could lead to significant rotation of the polarization plane of the triggering
terahertz pulse. Motivated by this finding, we focused in the last part of the
thesis on the linear effects. We performed three original studies coming out
with first demonstrations of broadband non-reciprocal terahertz phase
retarders, terahertz magnetic modulators, and the non-reciprocal terahertz
isolators. In the first two experiments, we extended the unique properties of
the magnetic liquids (Ferrofluids) to the terahertz regime. In the latter
experiment, we used a permanent magnet (Ferrite) to experimentally show
complete isolation (unidirectional transmission) of the terahertz waves.
