New terahertz (THz) optical devices which can control the optical properties of THz waves are needed to broaden the
application area of THz technology. Liquid crystals (LCs) are very attractive materials for developing such devices
because they have outstanding properties such as sensitivity to applied electric fields, chemical stability, relatively large
birefringence and moderate absorption in the THz range. LCs need to be optimized to have a large birefringence and
small absorption in the THz range. In this paper, we have investigated optical properties of a set of LCs in the THz range:
E7, BL037, and RDP-97304. Optical parameters for the ordinary and extraordinary axis of LCs were acquired using THz
time-domain spectroscopy and THz air-biased coherent detection system. We found that RDP-97304 has the largest
birefringence and smallest absorption compared to E7 and BL037 in the THz range. It is thus a good candidate to design
fast and efficient THz optical devices.
Optically pumped terahertz emission has been observed in a wide range of semiconductors. We show that InAs quantum dots on GaAs can be used to significantly enhance terahertz emission compared with a bare GaAs surface.
Two-dimensional (2D) photonic quasicrystals (PQCs) were fabricated by a holographic nanolithography technique. Using two laser beams with different angles incident on the sample, microcavities with 2D internal nanostructures are patterned with a few micrometer periods.
Air guided single mode propagation of THz radiation in a photonic crystal waveguide has been experimentally demonstrated. The photonic crystal waveguide has been fabricated by introducing an air defect at the center of the air/Si 1D photonic crystal.
Guided-wave propagation of sub-ps terahertz (THz) pulses in a highly birefringent plastic photonic crystal fiber has been experimentally demonstrated. The fabricated fibers have exhibited an extremely high birefringence of ~ 0.021 at 0.3 THz.
A scanning near-field microscope provides nano-scale imaging capability of field induced THz wave emission spectra from semiconductor surfaces and interfaces. Combined with a scanning probe tip and femtosecond optical pulse excitation, THz wave emission with sub-100 nm spatial resolution has been demonstrated. The scanning probe tip modulates semiconductor surface field with nano-scale accuracy through the imaging charge dipole, the tunneling current, or the contact current. The modulated THz wave from the highly localized area under the scanning tip is detected in time-domain. This aperture-less imaging method leads the way to study nano-scale to atomic level emission spectroscopy at THz frequency range.
Intermixing effects of MOCVD (metal organic chemical vapor deposition) grown InGaAs SAQDs (self-assembled quantum dots) covered with SiO2 and SiNx-SiO2 dielectric capping layers were investigated. The intermixing of SAQDs was isothermally performed at 700°C by varying annealing time under the N2-gas ambient. It was confirmed from the PL measurement after the thermal annealing that, the emission energy of SAQDs was blue-shifted by 190 meV, the FWHM (full width at half maximum) was narrowed from 76 meV to 47 meV and the PL intensity was increased. SiNx-SiO2 double capping layer have been found to induce larger PL intensity after the thermal annealing of SAQDs compared to SiO2 single capping layer. The results can be implemented for increasing quantum efficiency and tuning the detection wavelength in quantum dot infrared photodetector (QDIP).