Katsuhiro Ajito

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Recent progress in analytical terahertz (THz) spectroscopy is reviewed with illustrative examples showing that it is an effective method for detecting and identifying intermolecular interactions in chemical compounds, such as hydrogen bonds. The unique and characteristic properties of THz waves, their significance to both science and industry, and the bases(More)
We demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the quadrature phase-shift keying (QPSK) modulation format. For the modulating and demodulating signal, we employed half-Gilbert cell mixers, which provide balanced signaling and moderate performance in(More)
The laser trapping technique combined with near-infrared Raman (NIR) spectroscopy was used for the analysis of single cellular organelles in the nanometer range. The samples were synaptosomes, nerve-ending particles (about 500-700 nm in diameter) isolated from a neuron in a rat brain, dispersed in the phosphate buffer solution. The NIR laser Raman trapping(More)
Terahertz (THz) spectroscopic imaging is a promising technique for distinguishing pharmaceuticals of similar molecular composition but differing crystal structures. Physicochemical properties, for instance bioavailability, are manipulated by altering a drug's crystal structure through methods such as cocrystallization. Cocrystals are molecular complexes(More)
Glutamate is the major excitatory neurotransmitter and is of particular interest in light of current models of memory and learning. The paper describes the first in situ detection of glutamate in single nerve terminals (synaptosomes), which is achieved by using laser trapping Raman spectroscopy. The near-infrared laser light captures a single synaptosome(More)
The quantitative analysis of amino acids by terahertz (THz) time-domain absorption spectroscopy is demonstrated. The optical densities of the amino acids were found to be linearly proportional to the concentration. The molar absorption coefficients of L-glutamic acid (L-Glu), L-glutamic acid sodium salt (Na-L-Glu), L-glutamic acid hydrochloric salt(More)
Terahertz time-domain spectroscopy (THz-TDS) is used to study the intra- and intermolecular vibrational modes of aromatic carboxylic acids, for example, o-phthalic acid, benzoic acid, and salicylic acid, which form either intra- or intermolecular hydrogen bond(s) in different ways. Incorporating the target molecules in nano-sized spaces in mesoporous(More)
In situ Raman spectroscopic measurements with 785 nm excitation were carried out in aqueous solutions containing bipyridine derivatives. Intense Raman signals were observed when the Ag dimer structure was optimized. The SERS activity was dependent upon on the structure of the Ag dimer with a distinct gap distance, suggesting that the intense SERS originates(More)
A nanometer-scale optical switch and transistor were fabricated with thioacetyl-end-functionalized poly(para-phenylene ethynylene)s and Au nanogap electrodes by self-assembly. With photoirradiation, the switch can be switched on/off quickly with a switching ratio as high as 1000. Moreover, the device works well as a p-type transistor. With an increase in(More)
Recent studies of saccharides' peculiar anti-freezing and anti-dehydration properties point to a close association with their strong hydration capability and destructuring effect on the hydrogen bond (HB) network of bulk water. The underlying mechanisms are, however, not well understood. In this respect, examination of the complex dielectric constants of(More)