High-repetition-rate optical delay line using a micromirror array and galvanometer mirror for a terahertz system

We developed a high-repetition-rate optical delay line based on a micromirror array and galvanometer mirror for terahertz time-domain spectroscopy. The micromirror array is fabricated by using the x-ray lithographic technology. The measurement of terahertz time-domain waveforms with the new optical delay line is demonstrated successfully up to 25 Hz

Concurrent measurement of sample and reference waveforms in an optical-pump terahertz-probe system using a controlled optical diaphragm shutter

We present concurrent measurement of sample and reference terahertz waveforms for an optical-pump terahertz-probe spectrometer, using a controlled optical diaphragm shutter for the optical pump line. When waveforms are taken consecutively, laser power fluctuations and other experimental conditions can introduce spectral artefacts, thus a concurrent measurement is preferred. Instead of techniques based on double modulation, the use of the diaphragm shutter eliminates the need for a second lock-in amplifier and/or constricted alignment due to the use of a single chopper blade for modulating two signals, simultaneously. Drude fitting of the complex conductivity obtained for GaAs confirms that measurements obtained using our set-up agree with reported scattering times

Generation of monocycle efficient terahertz pulses by optical rectification in LiNBO3 at 800 nm

Generation of efficient terahertz (THz) pulses was experimentally made by tilted pump pulse front scheme with a Mg-doped LiNbO3 crystal. In this study, a spitfire laser (Ti:sapphire laser, 800 nm, 3 mJ, 1 kHz) was used as an optical source for the generation and detection of THz pulses. The electro-optic (EO) detection optics consisting of a ZnTe crystal (1 mm in thickness) and a balanced photodetector was used. To obtain optimum THz characteristics and pump to THz power conversion efficiency, the image of the grating was made coincides with the tilted pump pulse front. The maximum THz electric field of 8.5 kV/cm and the frequency bandwidth of 2.5 THz were achieved by using pump pulse energy of 2.4 mJ and pump pulse width of 100 fs. The THz energy of 4.15 μJ was obtained and pump-to-THz conversion efficiency was estimated to be approximately 1.73 x 10-3

トクシマシ シロヤマ ノ ホルトノキ ノ スイジャク コシ ノ ゲンイン ニツイテ : ホルトノキ イオウビョウ オ ヒキオコス ファイトプラズマ ノ シンコク ナ カンセン ジョウキョウ

Elaeocarpus sylvestris var. ellipticus was a dominant tree species in Mt. Shiroyama (castle mountain) in the Tokushima Central Park until 1970s, however, most of the E. sylvestris trees have died. In this study we investigated whether the death has been caused by Elaeocarpus yellows. Results of nested PCR revealed that DNA of phytoplasma, the pathogen of Elaeocarpus yellows, was found in all E. sylvestris trees in Mt. Shiroyama and about 80% E. sylvestris trees in the Tokushima Central Park. Results of PCR-RFLP showed that the all the trees had the same DNA type of phytoplasma, and it was identical to the one that had been found in Japan. These results indicated that the recent decrease of E. sylvestris in Mt. Shiroyama is due to Elaeocarpus yellows

トクシマシ シロヤマ ノ ホルトノキ ノ スイジャク コシ ノ ゲンイン ニツイテ : ホルトノキ イオウビョウ オ ヒキオコス ファイトプラズマ ノ シンコク ナ カンセン ジョウキョウ

Elaeocarpus sylvestris var. ellipticus was a dominant tree species in Mt. Shiroyama (castle mountain) in the Tokushima Central Park until 1970s, however, most of the E. sylvestris trees have died. In this study we investigated whether the death has been caused by Elaeocarpus yellows. Results of nested PCR revealed that DNA of phytoplasma, the pathogen of Elaeocarpus yellows, was found in all E. sylvestris trees in Mt. Shiroyama and about 80% E. sylvestris trees in the Tokushima Central Park. Results of PCR-RFLP showed that the all the trees had the same DNA type of phytoplasma, and it was identical to the one that had been found in Japan. These results indicated that the recent decrease of E. sylvestris in Mt. Shiroyama is due to Elaeocarpus yellows

Terahertz Radiation from Combined Metallic Slit Arrays

We report an approach to efficiently generate terahertz radiation from a combined periodic structure. The proposed configuration is composed of two metallic slit arrays deliberately designed with different periodic length, slit width and depth. We found that the combination of the two slit arrays could provide special electromagnetic modes, which exhibit nonradiative property above the surface of one slit array and radiative property inside the other one. An electron beam holding proper energy could resonate with those modes to generate strong and directional electromagnetic radiations in the terahertz regime, indicating that the approach has the potential in developing high-performance terahertz radiation sources

Polarization-variable emitter for terahertz time-domain spectroscopy

We report on the progress in the development of linear polarization-variable multielectrode emitters for terahertz time-domain spectroscopy. The results on its microfabrication, the finite element method modeling of appropriate bias distribution between electrodes, the finite-difference time-domain simulated spectral output, and actual experimental testing are presented. The rotation of the emitted terahertz field with linear polarization on an angle multiple of 45° can be achieved by synchronized bias and single polarizer rotations