Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of a broad range of materials, including semiconductors and biomolecules.

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Terahertz radiation from InSb and InAS, which are typical narrow band-gap semiconductors, was investigated using time-resolved THz emission measurements. When we compared between the polarity of the THz waveforms of these narrow band-gap semiconductors with that of InP, which is a wide bandgap semiconductor, we concluded that the ultrafast buildup of the photo-Dember field is the main mechanism for the emission of THz radiation in both InAs and InSb. The emission efficiency of InSb is approximately one-hundredth of that of InAs, although the electron mobility in InSb is higher than in InAs. Wavelength-dependent measurements implied that the anomalously low THz emission efficiency of InSb might be due to a reduction in transient mobility resulting from the scattering of electrons into the low-mobility L valley.

We have investigated the absorption spectra of seventeen explosives and related compounds (ERCs) by using terahertz time-domain spectroscopy in the 0.1-2.8 THz region. Most of these substances show characteristic absorption features in this frequency range. The measured absorption coefficients of these ERCs form a database, which is of great importance for biochemical, defense and security related applications.

We report our recent study of ultrafast electro-optic field sensors for the coherent measurement of freely propagating subpicosecond pulsed electromagnetic waves (THz beams). The sensitivity and bandwidth of these electro-optic sensors are comparable with the conventional ultrafast photoconductive dipole antennas. The simplicity of the detection geometry and capability of optical parallel processing make these sensors suitable for real-time 2D subpicosecond far-infrared imaging.

We report a broadband coherent terahertz detection system using GaP as a free-space electro-optic field sensor with a demonstrated 3 dB bandwidth of 3.6 THz, useful bandwidth of 7 THz, and a pulse width of 185 fs. These figures represent new records in the coherent detection of free-space THz radiation. Sensor response as a function of crystal thickness and copropagation velocity mismatch dispersion in the THz regime is studied.

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Abstract. Let d 1 and α ∈ (0, 2). Consider the following non-local and non-symmetric Lévy-type operator on R d :