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

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

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

The Institutional Design and Effectiveness of Timber Benefit Sharing under Joint Forest Management in Madhya Pradesh, India

This paper explores the institutional design of timber benefit sharing under the Joint Forest Management (JFM) policy and its effectiveness as an incentive for forest protection in Madhya Pradesh, India. Institutional analysis and case studies including household surveys for five committees were carried out. Except for plantations newly created under JFM, the places and times of timber harvesting were determined solely by the state forest department according to the division-level working plan. The sharing of the monetary benefits was determined by the state government and paid in equal amounts to committees in a lump sum, without taking the committees’ differing degrees of performance into consideration. Except in one committee, only a few respondents knew about the benefit sharing. In a committee where the shared benefits had been paid, even though little collective action had taken place, the money was used without communal decisions. It was confirmed that benefit sharing from timber production in Madhya Pradesh had not been implemented with flexible calculation and payment systems based on local people’s involvement in the decision-making process. Information provided by the concerned forest officers was the only way to motivate local people, and yet the appropriate information provisions were not likely to be in place. At the very least, improvements in the information provision with a change in the forest officers’ perceptions and attitudes are desirable

Dependence of emission of terahertz radiation on geometrical parameters of dipole photoconductive antennas

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(21):211104 (2010) and may be found at https://doi.org/10.1063/1.3436724 .The dependence of the emission spectrum of terahertz (THz) radiation on the geometrical parameters of the dipole antenna, and the relationship between these parameters and the temporal characteristics of the transient current that generate THz radiation, is reported. The emission intensity and the peak frequency strongly depend on these geometrical parameters. This dependence varies significantly with changes in the temporal characteristics of the transient current. We have also found that the emission efficiency can be increased by increasing the aspect ratio for the dipole.ArticleAPPLIED PHYSICS LETTERS. 96(21):211104 (2010)journal articl

Terahertz emission from transient currents and coherent phonons in layered MoSe2_2 and WSe2_2

Terahertz (THz) time-domain emission spectroscopy was performed on layered 2H-MoSe2 and 2H-WSe2. The THz emission shows an initial cycle attributed to surge currents and is followed by oscillations attributed to coherent interlayer phonon modes. To obtain the frequencies of the interlayer vibrations, analysis of the THz emission waveforms were performed, separating the two contributions to the total waveform. Results of the fitting show several vibrational modes in the range of 5.87 to 32.75 cm-1 for the samples, attributed to infrared-active interlayer shear and breathing modes. This study demonstrates that THz emission spectroscopy provides a means of observing these low frequency vibrational modes in layered materials

Phase Equilibrium Relations of Semiclathrate Hydrates Based on Tetra- n-butylphosphonium Formate, Acetate, and Lactate

Phase equilibrium (temperature-composition) relations of tetra-n-butylphosphonium formate (TBP-For), acetate (TBP-Ace), and lactate (TBP-Lac) semiclathrate hydrate systems have been measured. The highest equilibrium temperatures of TBP-For, TBP-Ace, and TBP-Lac semiclathrate hydrates were 280.9, 284.6, and 283.8 K at the atmospheric pressure, respectively, where the composition of tetra-n-butylphosphonium carboxylate was approximately 0.035 ± 0.001 (mole fraction) in every system. The dissociation enthalpies of tetra-n-butylphosphonium carboxylate semiclathrate hydrates were measured by differential scanning calorimetry. The dissociation enthalpies of TBP-For, TBP-Ace, and TBP-Lac semiclathrate hydrates were (187 ± 3), (193 ± 3), and (177 ± 3) J·g-1, respectively.Jin Shimada, Masami Shimada, Takeshi Sugahara, et al. Phase Equilibrium Relations of Semiclathrate Hydrates Based on Tetra-n-butylphosphonium Formate, Acetate, and Lactate. Journal of Chemical & Engineering Data, 63 (9), 3615-3620, September 13, © 2018 American Chemical Society. https://doi.org/10.1021/acs.jced.8b0048

A Fatal Aortoesophageal Fistula Caused by Critical Combination of Double Aortic Arch and Nasogastric Tube Insertion for Superior Mesenteric Artery Syndrome

Double aortic arch (DAA) is a rare vascular congenital abnormality. Since a vascular ring surrounds bronchus and esophagus, any oral or nasal intubation can physically cause fatal aortoesophageal fistula (AEF). We report herein the first case of association of DAA and superior mesenteric artery (SMA) syndrome and the second case of AEF caused by nasogastric intubation in an adult with DAA. A 19-year-old woman visited our hospital for nausea and vomiting. She was diagnosed with SMA syndrome by computed tomography (CT). Nasogastric intubation relieved her symptoms in 4 days. Extramural compression with top ulceration was found in esophagogastroduodenoscopy on the 5th hospital day. She suddenly showed massive hematemesis on the 12th hospital day. AEF was found by CT. Soon, she died despite of intensive care. Retrospective interview disclosed the fact that DAA was pointed out in her childhood. We conclude that intubation must be avoided in DAA and a detailed clinical interview about DAA is mandatory to avoid AEF