In this paper we present a numerical study of terahertz pulses interacting with crystals of cesium iodide. We model the molecular dynamics of the cesium iodide crystals with the Density Functional Theory software CASTEP, where ultrafast terahertz pulses are implemented to the CASTEP software to interact with molecular crystals. We investigate the molecular dynamics of cesium iodide crystals when interacting with realistic terahertz pulses of field strengths from 0 to 50 MV/cm. We find nonlinearities in the response of the CsI crystals at field strengths higher than 10 MV/cm.
We present a spatial characterization of terahertz (THz) beams generated from a two-color air plasma under different
conditions by measuring full 3D beam profiles using a commercial THz camera. We compare two THz beam profiles
emitted from plasmas generated by 35 fs and 100 fs laser pulses, and show that the spatial properties of the two THz
beams do not change significantly. For the THz beam profile generated by the 35 fs pulse, the spatial effect of
eliminating the lower frequencies is investigated by implementing two crossed polarizers working as a high-pass filter.
We show that this reduces the beam waist, and that the beam spot shape changes from Lorentzian to Gaussian. Finally,
we observe a forward-propagating Gaussian THz beam by spatially filtering away the conical off-axis radiation with a
1 cm aperture.
We present a characterization of THz beams generated in both a two-color air plasma and in a LiNbO<sub>3</sub> crystal. Using a commercial THz camera, we record intensity images as a function of distance through the beam waist, from which we
extract 2D beam profiles and visualize our measurements into 3D beam profiles. For the two-color air-plasma, we
measure a conical beam profile that is focused to a bell-shape at the beam waist, whereas we observe a Gaussian beam
profile for the THz beam generated from the LiNbO<sub>3</sub> crystal.