Tetsuo Sasaki

Spectral measurement of terahertz vibrations of biomolecules using a GaP terahertz-wave generator with automatic scanning control

Having previously generated frequency-tunable terahertz (THz) waves from GaP, we constructed a THz spectral measurement system with an automatic scanning control. We demonstrate the use of this THz spectrometer for measuring the transmittance spectra of D-(+)-glucose, 2-deoxy-D-glucose, D-(−)-fructose, and D-(+)-sucrose in the 0.8 to 5.5 THz (25 to 185 cm−1) frequency region with a spectral resolution of 3.2 GHz (0.1 cm−1), using a pyroelectric detector operated at room temperature. Each crystalline saccharide had different spectral features.

GaP THz wave generator and THz spectrometer using Cr:Forsterite lasers

We have developed a type of THz wave generator that uses Cr:Forsterite lasers as the pump and signal sources for difference frequency generation in GaP (Cr:F source system). We confirmed the generation of THz waves in the frequency range from 0.3to7.5THz, which is just similar to that obtained using the THz wave generator previously developed utilizing yttrium aluminum garnet and optical parametric oscillator (OPO) lasers (OPO source system). A peak output power of 100mW was obtained from 1.2to5THz when the power of the two input beams was 3mJ each, similar to the OPO source system. A wide measurable frequency range from below 0.6THz to over 6THz was obtained by using the Cr:F source system as the light source of a spectrometer, which has the merits of simple structure, easy maintenance, and low cost compared with the OPO source system. Although the linewidth of the Cr:F source system is greater than that of the OPO source system, the THz spectrometer still has sufficient resolution for measuring solids o...

Continuous-Wave Frequency-Tunable Terahertz-Wave Generation From GaP

Continuous-wave (CW) single-frequency terahertz (THz) waves were generated using difference-frequency generation via excitation of phonon-polaritons in GaP. The two pump sources were an external cavity laser diode (LD) and an LD-pumped Nd : YAG laser. The power density of the latter beam was enhanced by using a ytterbium-doped fiber amplifier. The two incident beams were focused to near the wavelength of THz waves. This optical alignment enabled us to generate frequency-tunable CW THz waves in the 0.69-2.74 THz range. With a fixed angle between the pump beams, we obtained a frequency bandwidth as large as 600 GHz

Characteristics of terahertz-wave generation from GaSe crystals

Terahertz (THz) waves from 0.3 to 4.9 THz were generated from GaSe by difference-wave generation using a YAG laser and an optical parametric oscillator. The spectral THz intensity distribution matched the spectrum of the THz absorption coefficient well, which suggested the effect of imperfections in the crystal. The fairly narrow beam profile and narrow line width, together with the simplicity of the collinear configuration, make GaSe an effective THz-wave generator. It is compared with a GaP THz-wave generator.

Analysis of vibrational spectra of solid-state adenine and adenosine in the terahertz region

The low-frequency vibrations of crystalline adenine and adenosine were studied by 5 K terahertz (THz) spectroscopy and solid-state density functional theory (DFT) based on a harmonic model. The accuracy of the calculations was assessed from aspects of frequencies and isotope shifts. The anharmonicity of the potential surface was discussed by observing the thermal shift of the sequence bands. An analytical method was proposed for quantifying the contributions of the intermolecular and intramolecular motions to the normal modes. Adenine exhibited weak coupling between the intermolecular and intramolecular vibrations. The adenine and ribose moieties of adenosine, which are linked through a glycosidic bond, showed intense relative vibrations strongly coupled with the intermolecular vibrations. This finding reveals that adenosine has high flexibility, which arises from the glycosidic bond. An experimental method was further proposed to identify the intermolecular or intramolecular modes.

Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: effect of dispersion force on the vibrational modes.

The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D(*) have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D(*) simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D(*) data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D(*) produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D(*).

Two-step growth of InP on GaAs substrates by metalorganic vapor phase epitaxy

Layers of InP grown on GaAs substrates by a two-step growth using metalorganic vapor phase epitaxy have been investigated. We have succeeded in improving the crystallinity of InP epilayers on GaAs substrates by employing a low V/III ratio for initial layer growth. The initial layers of InP were characterized by transmission electron microscopy. By lowering the V/III ratio to 20 during the growth of initial layers at 400°C, the surface became smooth and the X-ray diffraction peak intensity increased. The full width at half maximum of X-ray rocking curve is as small as 163 arcsec for a 3 μm InP layer. Using a low V/III ratio for initial layer growth is effective in improving the crystallinity of InP epilayers.

Purification and partial characterization of the muscle LDH-A4 and -B4 isozymes and the respective subunits of the fish, Oryzias latipes

Abstract 1. 1. The muscle LDH-A 4 and -B 4 isozymes of the inbred and outbred fish of a Japanese cyprinodont, Oryzias latipes , were purified and some of the protein chemical as well as enzymological characteristics were examined. 2. 2. The molecular weights of the A and B subunits were about 36.0 kD and 36.5 kD, respectively. There was a marked similarity in amino acid composition between the corresponding subunits of this fish and the salmon, Oncorhynchus tshawytscha . 3. 3. The optimal pHs of both A 4 and B 4 isozymes were almost the same, being about 6.5 for pyruvate reduction and about 10.0 for lactate oxidation. 4. 4. The B 4 enzyme was markedly more heat-stable and of higher affinity to the substrates in the reciprocal reactions than the A 4 enzyme.

Hormone-Dependent Expression of γ-Casein mRNA in Mouse Mammary Epithelial Cells Cultured on Floating Collagen Gels

Abstract Mammary epithelial cells isolated from pregnant mice were plated on a collagen gel matrix and cultured in a serum-free medium supplemented with combinations of insulin, dexamethasone and prolactin (PRL). After the cells formed a monolayer, the collagen gel was detached from the culture dish and allowed to float in the medium. Quantification of &ggr;-casein mRNA by a competitive PCR method revealed that the cells on the floating gel accumulated considerably larger amounts of &ggr;-casein mRNA than the cells on the gel remained attached to the dish. Under these floating collagen gel culture conditions, addition of both dexamethasone and PRL to the insulin-supplemented basal medium maximally stimulated the accumulation of &ggr;-casein mRNA. These observations strongly suggest that the status of the extracellular matrix as well as hormones controls the differentiation of mouse mammary epithelial cells at the mRNA level.

Single-frequency coherent terahertz-wave generation using two Cr:forsterite lasers pumped using one Nd:YAG laser

We have developed a compact terahertz-wave generator using two small Cr:forsterite lasers with single Nd:YAG laser pumping based on difference frequency generation in a GaP crystal. A Cr:forsterite laser was constructed with diffraction gratings, by which the pulse duration and delay time of the Cr:forsterite laser depend on the Cr:forsterite laser energy and the cavity length. The Cr:forsterite laser energy was tuned using the optical alignment and pumping energy. Temporal overlap of two Cr:forsterite laser pulses was realized at the GaP crystal. A single-frequency terahertz wave was generated at energy of 4.7 pJ around 2.95 THz using a 30-cm-long Cr:forsterite laser system.