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

Efficient Optical Modulation of Terahertz Transmission in Organic and Inorganic Semiconductor Hybrid System for Printed Terahertz Electronics and Photonics

Highly efficient optical modulation of terahertz (THz) transmission through Si substrate coated with thin layer of organic π-conjugated materials was investigated under various laser light irradiation conditions using THz time-domain spectroscopy. As in the pioneering work by Yoo et al. [Yoo et al., Applied Physics Letters. 2013;103:151116-1–151116-3.], we also used copper phthalocyanine (CuPc). It was perceived that the charge carrier transfer from Si to CuPc is crucial for the photo-induced metallization and efficient optical modulation of THz transmission. We found that the thickness of CuPc layer is a critical parameter to realize high charge carrier density for efficient THz transmission modulation. We also fabricated a split-ring resonator (SRR) array metamaterial on CuPc-coated Si utilizing superfine inkjet printer and succeeded in obtaining efficient modulation of resonant responses of SRR array metamaterials by laser light irradiation. We have further investigated THz transmission modulation through Si substrates coated with another four solution-processable π-conjugated materials. Two of them are π-conjugated low molecules such as the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene), and another two are the π-conjugated polymer materials such as poly[5-(2-ethylhexyloxy)-2-methoxycyanoterephthalyliden] (MEH-CN-PPV) and poly(benzimidazobenzophenanthroline) (BBL). Among these four π-conjugated materials, PCBM- and TIPS-pentacene showed better modulation efficiencies even higher than CuPc. Our findings may open the way to fabricating various types of THz active devices utilizing printing technologies

Terahertz absorption spectra of L-, D-, and DL-alanine and their application to determination of enantiometric composition

Absorption spectra of polycrystalline L-, D-, and DL-alanine have been measured by the terahertz time domain spectroscopy (THz-TDS)in the frequency range from 10 to 90 cm−1 at room temperature. We observed several absorption bands, which have the large difference between enantiomers (L- and D-alanine)and the racemic compound (DL-alanine)in their peak frequencies. This obvious difference shows that the THz absorption bands are strikingly sensitive to the crystal structures. This result indicates that the THz-TDS can be used for distinguishing between the enantiomers and the racemic compound. We propose and demonstrate a method to determine the enantiometric composition of amino acids from the THz absorption spectra

Three-dimensional bulk metamaterials operating in the terahertz range

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 96(8):081105 (2010) and may be found at https://doi.org/10.1063/1.3327830 .Three-dimensional bulk metamaterials that operate in the terahertz (THz) frequency range were fabricated by stacking 100 two-dimensional sheets containing metallic split-ring resonators (SRR) on thin polyethylene terephthalate film substrates. The THz magnetic resonance for the incident magnetic field perpendicular to the plane of the SRR structure was measured. We also investigated the dependence of the magnetic resonant strength on the metal thickness.ArticleAPPLIED PHYSICS LETTERS. 96(8):081105 (2010)journal articl

Characteristics and generation process of surface waves excited on a perfect conductor surface

This paper was published in OPTICS EXPRESS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: https://doi.org/10.1364/OE.18.017576 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.We investigate characteristics and generation process of surface waves excited on a structured perfect conductor surface in order to clarify the mechanism of resonant transmission in metal hole arrays made of the perfect conductor. By using a metal hole array of kagome lattice, we can separate two modes excited on the perfect conductor surface; a surface wave and an edge mode. Our calculation based on finite-difference time-domain method provides a generation process of the edge mode and the surface wave that is responsible for the resonant transmission in metal hole arrays. (C) 2010 Optical Society of AmericaArticleOPTICS EXPRESS. 18(16):17576-17583 (2010)journal articl

Three-dimensional bulk metamaterials operating in the terahertz range

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 96(8):081105 (2010) and may be found at https://doi.org/10.1063/1.3327830 .Three-dimensional bulk metamaterials that operate in the terahertz (THz) frequency range were fabricated by stacking 100 two-dimensional sheets containing metallic split-ring resonators (SRR) on thin polyethylene terephthalate film substrates. The THz magnetic resonance for the incident magnetic field perpendicular to the plane of the SRR structure was measured. We also investigated the dependence of the magnetic resonant strength on the metal thickness.ArticleAPPLIED PHYSICS LETTERS. 96(8):081105 (2010)journal articl

Optical transmittance investigation of 1-keV ion-irradiated sapphire crystals as potential VUV to NIR window materials of fusion reactors

We investigate the optical transmittances of ion-irradiated sapphire crystals as potential vacuum ultraviolet (VUV) to near-infrared (NIR) window materials of fusion reactors. Under potential conditions in fusion reactors, sapphire crystals are irradiated with hydrogen (H), deuterium (D), and helium (He) ions with 1-keV energy and ∼ 1020-m-2 s-1 flux. Ion irradiation decreases the transmittances from 140 to 260 nm but hardly affects the transmittances from 300 to 1500 nm. H-ion and D-ion irradiation causes optical absorptions near 210 and 260 nm associated with an F-center and an F+-center, respectively. These F-type centers are classified as Schottky defects that can be removed through annealing above 1000 K. In contrast, He-ion irradiation does not cause optical absorptions above 200 nm because He-ions cannot be incorporated in the crystal lattice due to the large ionic radius of He-ions. Moreover, the significant decrease in transmittance of the ion-irradiated sapphire crystals from 140 to 180 nm is related to the light scattering on the crystal surface. Similar to diamond polishing, ion irradiation modifies the crystal surface thereby affecting the optical properties especially at shorter wavelengths. Although the transmittances in the VUV wavelengths decrease after ion irradiation, the transmittances can be improved through annealing above 1000 K. With an optical transmittance in the VUV region that can recover through simple annealing and with a high transparency from the ultraviolet (UV) to the NIR region, sapphire crystals can therefore be used as good optical windows inside modern fusion power reactors in terms of light particle loadings of hydrogen isotopes and helium.Iwano K., Yamanoi K., Iwasa Y., et al. Optical transmittance investigation of 1-keV ion-irradiated sapphire crystals as potential VUV to NIR window materials of fusion reactors. AIP Advances 6, 105108 (2016); https://doi.org/10.1063/1.4965927