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We report optical coherent control of the emission direction of THz radiation by excitation of bulk GaAs with femtosecond laser pulses. Changing the phase of the optical excitation, steering angles of ∼8 degrees are realized. A simple model is introduced to analyze the underlying parameters.
The photoconductive properties of graphene nanoribbons and carbon nanotubes were studied using optical pump-THz probe spectroscopy. A reduction in conductivity of GNRs compared to CNTs was observed.
We demonstrate all-optically induced real-space charge transfer in semiconductors, which reverses its direction upon a change of the temporal order of two excitation fields. Such charge transfer leads to a new type of photocurrent and only appears for certain polarization-shaped optical pulses while it ceases for continuous-wave excitation.
Laser driven terahertz radiation sources have been developed to enable energy modulation of relativistic electron bunches on a sub-picosecond timescale. Photoconductive and nonlinear optical generation schemes capable of providing the required > 1MV cm−1 field strengths, and longitudinal polarisation components, are discussed.
Using optical pump - THz probe spectroscopy we reveal complex ultrafast photoconductivity dynamics in InGaN/GaN quantum wells under dynamical screening conditions, where, at sufficiently high excitation densities, the photo-generated carriers fully screen the initial internal field of 3 MV/cm. The THz photoconductivity spectra contain features of both localized and free charges.
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