THz nonlinearity is reported in actively tunable integrated graphene/metamaterial arrays by using an ultrafast tabletop powerful time domain spectroscopic system with incident E-field energy pulses between 1 kV/cm and 100 kV/cm. The nonlinear interaction between the main metamaterial resonance and the sub-ps THz pulses produced a few distinct nonlinear phenomena, such as harmonic generation, optical Kerr effect. The complex dispersive properties of these devices pave the way for a plethora of novel functionalities, ranging from frequency generation to saturable absorbers.
We report on the THz harmonic generation in a graphene/metamaterial device by using ultrafast table top powerful THz-TDS systems. A complex nonlinear transmission spectra, which includes a peak at the third harmonic signal is detected on top of the main resonant features at 0.65 THz, for E-field pulses in the range 1-30 kV/cm. Whilst these results are consistent with acquainted literature, they offer a novel perspective for the exploitation of graphene nonlinearity in integrated devices.
The dynamic increase in terahertz photoconductivity resulting from energetic intraband relaxation was used to track the formation of highly mobile charges in thin films of the tin iodide perovskite Cs1-xRbxSnI3 and compared to the lead based Cs0:05(FA0:83MA0:17)0:95Pb(I0:83Br0:17)3. Energy relaxation times were found to be around 500 fs, comparable to those in GaAs and longer than the ones of the lead-based perovskite (around 300 fs). At low excess energies the efficient intraband relaxation can be understood within the context of the Frohlich electron-phonon interaction. For higher excess energies the photoconductivity rise time lengthens in accordance with carrier injection higher in the bands, or into multiple bands. The findings contribute to the development of design rules for photovoltaic devices capable of extracting hot carriers from perovskite semiconductors.
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