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(*).

Terahertz-wave spectroscopy for precise histopathological imaging of tumor and non-tumor lesions in paraffin sections.

Terahertz (THz; 10(12) Hz) waves have a frequency from 0.1 to 10 THz between the visible light and microwave domains. THz waves are expected to be useful for analysis of the histological features, without any staining procedure that is an indispensable prerequisite for optical microscopy. It has been demonstrated that THz transmittances at cancer and normal tissues are different. However, spectroscopy that is currently used is applicable for imaging only small areas at fixed-wavelength. In this study, we have developed a spectrometer employing a gallium phosphide (GaP) THz-generator and applied it to examine large areas of tissue specimens using a wide range of wavelengths. We thus examined the whole areas of two paraffin sections (metastatic liver cancer and acute myocardial infarction) in a frequency range of 1 to 6 THz, and compared the THz images of ordinary paraffin sections with the histological features detected by microscopy. THz imaging showed striking contrasts between cancerous and non-cancerous regions at 3.7 THz. Likewise, the precise imaging was achieved in the infarct myocardium at 3.6 THz. Images of THz transmittances in optimal wavelength were well matched with HE histological features both in cancer and myocardial tissues. Cancer regions showed higher transmittance than non-cancerous regions in liver. Old scar regions showed low transmittance, and necrotic regions showed relatively higher transmittance than normal myocardial areas. Thus, THz imaging precisely reflects tissue conditions such as tumor, non-tumor tissues, tissue degeneration and fibrosis. The newly established THz spectroscopy would be useful for pathological diagnosis of routinely processed specimens.

Quantitative evaluation of mefenamic acid polymorphs by terahertz-chemometrics.

The purpose of the present study is to measure polymorphic content in a bulk powder, mefenamic acid polymorph of pharmaceuticals, as a model drug by THz-spectrometer using frequency-tunable THz wave generators based on difference-frequency generation in gallium phosphate crystals. Mefenamic acid polymorphic forms I and II were obtained by recrystallisation. Eleven standard samples varying a various polymorphic form I content (0-100%) were prepared by physical mixing. After smoothing and area normalising, the THz-spectra of all standard samples showed an isosbestic point at 3.70 THz. After the THz-spectral data sets were arranged into five frequency ranges, and pretreated using various functions, calibration models were calculated by the partial least square regression method. The effect of spectral data management on the chemometric parameters of the calibration models was investigated. The relationship between predicted and actual form I content was the best linear plot. On the regression vector (RV) that corresponded to absorption THz-spectral data, the peak at 1.45 THz was the highest value, and the peak at 2.25 THz was the lowest on RV. THz-spectroscopy with chemometrics would be useful for the quantitative evaluation of mefenamic acid polymorphs in the pharmaceutical industry. This method is expected to provide a rapid and nondestructive quantitative analysis of polymorphs.

Extension of frequencies from maser to laser. How the laser evolved and was extended to terahertz during my research life: a personal review.

The present review describes the author's involvement and contributions to the development of the semiconductor laser and terahertz oscillators at his laboratory during the period between 1957 and now. The author cites records to show that the idea of a semiconductor laser was documented as a Japanese patent in April 1957 prior to those of G. Gould in 1957 and C.H. Townes in 1958. Terahertz oscillators of high Q values with the use of GaP were developed and applied to areas like investigations of molecular dynamics, cancer diagnosis, etc., thus extending the frontiers of science.

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.

Adaptive optics instrumentation in submillimeter/terahertz spectroscopy with a flexible polyvinylidene fluoride cladding hollow waveguide.

A simple instrument has been developed to carry out temperature dependent submillimeter/terahertz-wave spectroscopy using a polyvinylidene fluoride flexible hollow waveguide and an eggplant-shape launching lens.

GaP Raman Terahertz high accuracy spectrometer and its application to detect organic and inorganic crystalline defects.

One of the most important uses of THz spectrometry is to detect defects in molecular structure or in crystals efficiently. We applied GaP Raman THz (GRT) spectrometer to detect and evaluate defects in inorganic and organic materials. High THz-wave absorption due to high defect density of GaSe crystal lowered the efficiency of THz wave generation, when the crystal is used as nonlinear material for DFG (Difference Frequency Generation). Defects in organic molecules could be observed as changes in frequency, intensities of the absorption, and broadenings of the spectra.