We have improved the efficiency of photoconductive antennas (PCAs) using low-temperature-grown GaAs (LT-GaAs). We found that the physical properties of LT-GaAs photoconductive layers greatly affect the generation and detection characteristics of terahertz (THz) waves. In THz generation, high photoexcited carrier mobility and the presence of a few As clusters in the LT-GaAs are two important factors. In detection, short carrier lifetime and the absence of a polycrystalline structure in the LT-GaAs are significant factors. By optimizing these physical properties, we improved the total dynamic range of THz generation and detection by 15 dB over that obtained by conventional commercially available PCAs. In addition, we replaced the semi-insulating GaAs (SI-GaAs) substrate with a Si substrate, which has a low absorption in the THz region. We proposed a new idea of including a highly insulating Al0.5Ga0.5As buffer layer on the Si substrate. Finally, we confirmed the feasibility of manufacturing PCAs using Si substrates.

We study precision electroweak constraints within a RS1 model with gauge fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to SU(2) L × SU(2) R × U(1) B−L , thereby providing a custodial isospin symmetry sufficient to suppress excessive contributions to the T parameter. We then construct complete models, complying with all electroweak constraints, for solving the hierarchy problem, without supersymmetry or large hierarchies in the fundamental couplings. Using the AdS/CFT correspondence our models can be interpreted as dual to a strongly coupled conformal Higgs sector with global custodial isospin symmetry, gauge and fermionic matter being fundamental fields external to the CFT. This scenario has interesting collider signals, distinct from other RS models in the literature.

Thermal recording using a dielectric as a recording material was examined to make a high-density optical disc master. We confirmed that a pit of 53 nm length was able to be recorded with a laser of 405 nm wavelength. As a result we could make a master with a 200 gigabyte (GB) data capacity with a conventional laser beam recorder (LBR). A 100 GB disc made by the same method was able to be read with a tester equipped with a solid immersion lens (SIL) and the measured jitter value was 9.9%. #

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