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Ishiyama, Shintaro; Masamune, Ken*; Idehara, Toshitaka*
Nihon Kikai Gakkai Rombunshu (Internet), 82(833), p.15-00449_1 - 15-00449_14, 2016/01
Transmission demonstration experiment of 0.1-0.2 THz beam was performed with transmission system consisted of polymer fibers of 3 mm 
300 mmL coated with gold metal. THz beam was generated by high power compact gyrotron designed output power of 0.25 kW and measured output power at terminal of metallic cladding polymer fibers in the transmission system and the following results were derived. (1) It was demonstrated that maximum output power of the order of 0.84 W through the polymer fibers was observed by SBD detector at input power of the order of 7.5 W.
Ochi, Yoshihiro; Nagashima, Keisuke; Maruyama, Momoko; Tsubouchi, Masaaki; Yoshida, Fumiko; Kono, Nanase; Mori, Michiaki; Sugiyama, Akira
Optics Express (Internet), 23(11), p.15057 - 15064, 2015/06
Times Cited Count：25 Percentile：78.49(Optics)We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 
J of energy were generated by means of optical rectification in an Mg-doped LiNbO
crystal.
Tsubouchi, Masaaki; Nagashima, Keisuke; Yoshida, Fumiko; Ochi, Yoshihiro; Maruyama, Momoko
no journal, ,
The nonlinear interaction between terahertz (THz) light and matter has recently been of interest for its availability to control molecular alignment in space. The pulse train of the intense THz light is one of the candidates to align the molecules efficiently and nondestructively. In this study, we have developed the experimental apparatus to generate the intense THz light. The THz etalon to generate the THz pulse train has been presented in our previous study
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*; Matsumoto, Hideki*
no journal, ,
Superconductivity leads to intriguing and useful devices, owing to its features distinct from the normal electrons. We study terahertz emission from intrinsic Josephson junction stacks in layered High-
cupurate superconductors, with full 3D multi-scale simulations. Typical previous simulations of this issue had the restriction on examining the layer-number dependence of emission spectrum, since a periodic boundary condition along 
-axis inside a superconducting mesa is imposed for brevity. In this article, we develop a method to resolve this theoretical limitation, taking the boundary effects from the electrodes attached to the superconducting mesa into account. The present simulations show an explicit dependence of the emission characteristics on the number of superconducting layers.
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*; Matsumoto, Hideki*
no journal, ,
Observing the teraherz radiation emission from Bi
SrCaCuO
leads to a number of the experimental and theoretical studies of revealing the mechanism of the behaviors in superconducting engineering. We develop a large-scale simulation approach for the teraherz emission from intrinsic Josephson junction stacks with multiple spatial scales. We focus on the effects of the number of the junctions in the system, which is considered to be a key ingredient of determining the emission-power bound. Our simulation method successfully predicts the amplification of the emission peaks corresponding to the fundamental mode, i.e., a primary contribution in low-current-biased region.
Ota, Yukihiro; Machida, Masahiko
no journal, ,
Since the observation of teraherz emission from mesas made of layered high-Tc superconductor Bi
SrCaCuO
, the mechanism of radiation attracts a great deal of attention from theoretical and engineering points of view. Emission has a connection with the dynamical aspects of superconducting phases and electromagnetic wave; constructing a theoretical approach to integrating these degrees of freedom is desirable. A way to resolving the issues is built up by 3D dynamical simulations of intrinsic Josephson junction stacks with outside-vacuum contributions. In this article, we apply our code to characterizing teraherz emission in low-bias-current regions. The highlight is to achieve the change of the junction numbers involved the sample. We successfully reproduce the emergence of 
-kink behaviors. Then, we show the presence of a critical value of the number of junctions for a strong emission.
Sugiyama, Akira
no journal, ,
no abstracts in English
Ochi, Yoshihiro; Nagashima, Keisuke; Maruyama, Momoko; Tsubouchi, Masaaki; Kono, Nanase; Yoshida, Fumiko; Sugiyama, Akira
no journal, ,
We have developed a high average power picosecond laser system, named QUADRA-T, dedicated to intense terahertz (THz) pulse generation. QUADRA-T is a chirped pulse amplification laser equipping Yb:YAG thin-disk amplifier. The Yb:YAG thin-disk regenerative amplifier at room temperature provides 10 mJ pulses at a repetition rate of 1 kHz. Duration of a recompressed pulse is 1.3 ps. By employing this picosecond pulse as a pump source, THz pulse of the center frequency of 0.3 THz with a few micro joules energy has been obtained by the optical rectification in Mg-LiNbO crystal.
Ochi, Yoshihiro; Nagashima, Keisuke; Maruyama, Momoko; Tsubouchi, Masaaki; Yoshida, Fumiko; Kono, Nanase; Sugiyama, Akira
no journal, ,
We have developed a high average power picosecond laser system dedicated to intense terahertz (THz) pulse generation. The system is a chirped pulse amplification laser equipping with a Yb:YAG thin-disk amplifier. The Yb:YAG thin-disk regenerative amplifier at room temperature provides pulses with energy over 10 mJ and spectral bandwidth of 1.2 nm at a repetition rate of 1 kHz. In a pulse compressor, the laser pulse is compressed to be 1.3 ps. By employing this picosecond pulse as a pump source, THz pulses at the center frequency of 0.3 THz with energy over a few microjoules have been generated at 1 kHz repetition rate by the optical rectification in Mg-LiNbO crystal.
Kono, Nanase; Itakura, Ryuji; Tsubouchi, Masaaki
no journal, ,
We realize a relativistic Doppler reflection of terahertz (THz) light from a counter propagating photo-induced carrier in silicon (Si). We have observed the Doppler reflection of THz light at some different pump light intensity. The up-shift frequency was increasing with pump intensity, and becoming a constant at high pump intensity. We have defined a new parameter, effective carrier thickness, and discussed the interaction between the photo induced carriers and THz light.
Ichihara, Akira
no journal, ,
We explored the pulse shape to excite the vibrational states of diatomic molecules whose rotational states were excited isotope-selectively by a terahertz pulse train. Computer simulations based on the coupled-channel method were performed using the gaseous 
Li
Cl and Li
Cl ensembles in 70 K. The isotope-selective vibrational excitation was investigated using the pulse which has a quasi-rectangle or the Gaussian spectrum. The results indicated that the isotope-selective vibrational excitation can be induced effectively by specifying the spectral frequency range referring to the transition frequencies in the P- and R-branches of molecules. The P-branch transition plays an important role on the excitation in low vibrational states, and both the P- and R-branch transitions contribute to the excitation in high vibrational states.
Yokoyama, Keiichi
no journal, ,
A new isotope-separation scheme using ultrashort terahertz pulses is reported. The principle and mathematical background are also explained. The current status of the development of picosecond high-power THz-wave source in KPSI and apparatus for application study, and future technologies which must be developed for the demonstration of the new scheme are introduced.
Kono, Nanase; Itakura, Ryuji; Tsubouchi, Masaaki
no journal, ,
Plasma is generated when semiconductors are photo-excited, and it reflects a THz light if a density of free electrons is sufficiently high. Plasma acts as a flying mirror with a velocity which is identical to that of pump light because plasma is generated with a proceeding of pump light into a semiconductor. Then, a counter-propagating THz light is up-shifted via relativistic Doppler reflection. In this study, sample semiconductor is silicon, and we investigated a Doppler reflection of THz light by observing an intensity spectrum and waveform of THz light. From the pump energy dependence, phase and frequency shifts of THz light is increased with pump energy. We constructed a model in consideration of phase shift and Doppler reflection.
Yokoyama, Keiichi
no journal, ,
As a potential technique to reduce radioactive waste, we are involved in the study of isotope separation using THz wave. Their background, theoretical consideration, current status of demonstration experiments, and technical challenges are introduced.
Yokoyama, Keiichi; Matsuda, Shohei
no journal, ,
The scheme of cesium isotope separation proposed by us needs low-frequency terahertz wave, which often suffers from significant loss during wave traveling due to the diffraction. To avoid this difficulty, it may be helpful to design an experiment involving interaction between matter and terahertz wave right after the generation. With this regards, we conducted an experiment to measure terahertz waveform right after the generation with the OH1 crystal, which is known to have high efficiency in both THz generation and electro-optic effect. As a result, we found that the waveform can be measured without bother from the pump pulse, by using reflection of terahertz wave inside the OH1 crystal.
Yamakawa, Koichiro; Nasu, Hirokazu*; Suzuki, Natsumi*; Shimizu, Genki*; Arakawa, Ichiro*
no journal, ,
Nano-sized molecular clusters have been intensively investigated in a spectroscopic way to reveal the nature of intermolecular interaction. Compared with the infrared (IR) range, only a few spectral measurements in the terahertz (THz) range have been reported, so that the assignment of the vibrational mode to THz absorption was not established even for the water dimer. In the present study, we constructed an experimental apparatus for THz-IR absorption spectroscopy in an ultrahigh vacuum and measured spectra of deuterated-water clusters formed in solid Ar to identify the THz absorption peaks of the dimer, trimer, and tetramer.
