Communication technology has shown trends towards wireless systems (for improved mobility) and broader bandwidths (for high data rates). This has led to growing interest in terahertz (THz) wireless communication systems—for which there are great benefits and equally great challenges. Arguably, the single greatest challenge for THz wireless communication systems is the susceptibility of the THz spectrum to water vapour absorption in the free-space/air environment. Our study recognizes this challenge and introduces a physical model through which the water vapour characteristics can be fit and then removed from measured signal characteristics. We show the physical foundations of our model and demonstrate its effectiveness in fitting the water vapour characteristics in measured signals from a THz time-domain spectroscopy system. The theoretical and experimental results show strong agreement, suggesting that the model can be an effective tool for characterizing and mitigating the effects of water vapour absorption in future THz wireless communication systems.
Nonlinear dynamics of free-carriers in direct bandgap semiconductors at terahertz (THz) frequencies is studied using
intense few-cycle pulses. Techniques as Z-scan, THz-pump / THz-probe, and optical-pump/ THz-probe are employed to
explore nonlinear interactions in both n-doped and photoexcited systems. The physical mechanism that gives rise to such
interactions is found to be intervalley scattering.
Terahertz emission from n-type (100), (110) and (111) InAs crystals have been measured as a function of the sample orientation. Emission was excited using 120 fs Ti:Sapphire laser pulses at an incident angle of 45° with fluences of approximately 1-2mJ/cm2. The data is shown to match the behavior expected for optical rectification at the surface, with small contributions from bulk optical rectification and photo-carrier diffusion. Thus, at fluences employed in the present study, it appears that the dominant mechanism for generating THz radiation is optical rectification at the surface.
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