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Np and 
Am gamma ray regionsFukuda, Tatsuo; Kobata, Masaaki; Shobu, Takahisa; Yoshii, Kenji; Kamiya, Junichiro; Iwamoto, Yosuke; Makino, Takahiro*; Yamazaki, Yuichi*; Oshima, Takeshi*; Shirai, Yasuhiro*; et al.
Journal of Applied Physics, 132(24), p.245102_1 - 245102_8, 2022/12
Times Cited Count：1 Percentile：15.88(Physics, Applied)Direct energy conversion has been investigated using Ni/SiC Schottky junctions with the irradiation of monochromatized synchrotron X-rays simulating the gamma rays of Np (30 keV) and Am (60 keV). From current-voltage measurements, electrical energies were obtained for both kinds of gamma rays. The energy conversion efficiencies were found to reach up to 
1.6%, which is comparable to those of a few other semiconducting systems reported thus far. This result shows a possibility of energy recovery from nuclear wastes using the present system, judging from the radiation tolerant nature of SiC. Also, we found different conversion efficiencies between the two samples. This could be understandable from hard X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements, suggesting the formation of Ni-Si compounds at the interface in the sample with a poor performance. Hence, such combined measurements are useful to provide information that cannot be obtained by electrical measurements alone.
Akagi, Hiroshi*; Kumada, Takayuki; Otobe, Tomohito*; Itakura, Ryuji*; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Chemistry Letters, 49(4), p.416 - 418, 2020/04
Times Cited Count：1 Percentile：4.73(Chemistry, Multidisciplinary)Akagi, Hiroshi*; Kumada, Takayuki; Otobe, Tomohito*; Itakura, Ryuji*; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Applied Physics B, 124(1), p.14_1 - 14_8, 2018/01
Times Cited Count：2 Percentile：14.58(Optics)We propose and numerically simulate a method of laser isotope separation based on field-free alignment of isotopologues, utilizing an intense switched nanosecond (ns) laser field which is slowly turned on and rapidly turned off at the peak with the falling time of 200 fs. The femtosecond (fs) laser induced alignment of molecules including a heavy atom is severely disturbed by ionization because of their small ionization potential. Our simulations for I
Br and I
Br isotopologues demonstrate that the switched ns laser field can make isotopologues well-aligned with the reduced ionization probability at the laser intensity which is an order-of-magnitude lower than a typical intensity for field-free alignment induced by a fs laser field.
Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Physical Review A, 91(6), p.063416_1 - 063416_7, 2015/06
Times Cited Count：7 Percentile：38.69(Optics)We propose a strategy of isotope-selective ionization for a binary mixture of isotopologues of homonuclear diatomic molecules, utilizing field-free alignment with a train of femtosecond laser pulses. Field-free alignment can be achieved simultaneously for two isotopologues consisting of two atoms with the same atomic mass number 
or 
, utilizing a pulse train with their time interval of T
= T() = T(), where T() and T() are the rotational revival times of the isotopologues. We demonstrate experimentally that a train of four alignment pulses with their interval of T ( = 14, = 15) creates transiently aligned 
N
and anti-aligned 
N just before T/2 after the last pulse, and vice versa just after T/2. Highly isotope-selective N ionization is achieved at these timings with another femtosecond laser pulse, which induces the non-resonant multiphoton ionization with the cross section remarkably depending on the angle between the molecular axis and the laser electric field direction. The ion yield ratio I(N
)/I(N) ranges from 0.49 to 2.00, which is wider than the range obtained with single alignment pulse.
Akagi, Hiroshi; Kasajima, Tatsuya; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
Applied Physics B, 109(1), p.75 - 80, 2012/10
Times Cited Count：16 Percentile：61.23(Optics)We demonstrate a laser nitrogen isotope separation, which is based on field-free alignment and angular dependent ionization of N and N isotopomers. A linearly-polarized short laser pulse (
795 nm, 
60 fs) creates rotational wave packets in the isotopomers, which periodically revive with different revival times as a result of different moments of inertia. Another linearly-polarized short laser pulse (795 nm, 60 fs) ionizes one of the isotopomers selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio 
[= 
(N)/(N)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
Optics Letters, 37(17), p.3528 - 3530, 2012/09
Times Cited Count：18 Percentile：64.82(Optics)A novel technique for the terahertz (THz) tomography of a photo-induced carrier that is based on optical-pump THz-probe time-resolved reflection spectroscopy using counter-propagation geometry of the pump and probe pulses has been proposed. Transient reflection due to the photo-induced carrier provides information about the physical properties and spatial distribution separately. We have experimentally demonstrated this method using a silicon wafer. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations, assuming an exponential distribution of the photo-induced carrier density.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
Journal of Physical Chemistry A, 114(42), p.11202 - 11209, 2010/07
Times Cited Count：12 Percentile：38.05(Chemistry, Physical)When neutral NO molecules are partly ionized in intense laser fields (
35 TW/cm
), a hole in the rotational wave packet of the remaining neutral NO is created by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed and then the characteristic feature that the population at higher 
levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schrodinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
no journal, ,
Nonadiabatic rotational excitation of molecules proceeds in intense laser fields. As the laser intensity increases, not only rotational excitation, but also tunnel ionization occurs. In the present study, rotational excitation dynamics accompanied by ionization is investigated through the resonant two-photon ionization measurement with a weak ns dye laser. Additionally, numerical simulations are performed introducing an imaginary potential into the time-dependent Schrodinger equation for describing ionization processes properly.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
no journal, ,
Molecules in intense laser fields are rotationally excited through the non-adiabatic interaction between the induced dipole moment and the laser field. As the intensity of the laser fields increases, the ionization proceeds significantly. In this study, we observed the rotational state distribution of NO irradiated with intense laser pulses using a spectroscopic approach. We also calculated a time-dependent Schrodinger equation for the rotational excitation taking into account of the ionization.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
no journal, ,
When neutral molecules are partly ionized in intense laser fields (I 35 TW/cm), a hole in the rotational wave packet of the remaining neutral NO is created by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed and then the characteristic feature that the population at higher J levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schr
dinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of I = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.
Itakura, Ryuji; Hasegawa, Hirokazu*; Kurosaki, Yuzuru; Yokoyama, Atsushi; Oshima, Yasuhiro*
no journal, ,
When neutral molecules are partly ionized in intense laser fields (I 35 TW/cm), a hole in the rotational wave packet of the remaining neutral NO is formed by the ionization, whose rate depends on the alignment angle of the molecular axis with respect to the laser polarization direction. Rotational state distributions of NO are experimentally observed with the spectroscopic technique and then the characteristic feature that the population at higher J levels is increased by the ionization can be identified. Numerical calculation for solving time-dependent rotational Schrdinger equations including the effect of the ionization is carried out. The numerical results suggest that NO molecules aligned perpendicular to the laser polarization direction are dominantly ionized at the peak intensity of I = 42 TW/cm, where the multiphoton ionization is preferred rather than the tunneling ionization.
Akagi, Hiroshi; Kasajima, Tatsuya; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
no abstracts in English
Tsubouchi, Masaaki; Yokoyama, Atsushi; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
no abstracts in English
Akagi, Hiroshi; Kasajima, Tatsuya; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
We have experimentally realized a new laser isotope separation method, utilizing molecular laser alignment and angular dependent ionization. We have introduced gas mixture including N and N isotopomers into a vacuum chamber, and have shined a linearly-polarized laser pulse onto the gas jet to produce molecular alignment state of the isotopomers. We have shined another laser pulse to ionize the isotopomers through the nonresonant multiphoton ionization. Ion yield ratio N/N has varied from 0.85 to 1.22, depending on delay time between the two laser pulses.
Akagi, Hiroshi; Kasajima, Tatsuya; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
We have proposed a laser isotope separation method utilizing molecular alignment and non-resonant multiphoton ionization, and demonstrated isotope-selective ionization of N and N isotopomers. In the present work, we use a train of four identical pulses to create rotational wave packets in the isotopomers. When we set the pulse interval to 125.7 ps, which corresponds to the fifteenth full revival of N and the fourteenth full revival of N, we obtained ca. two-times higher selectivity than that in the one-pulse alignment case.
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
We have proposed a novel technique for the THz tomography of photo-induced carrier based on the optical-pump THz-probe reflection spectroscopy with the counter-propagated pump and probe pulses. We have experimentally demonstrated it with silicon. The obtained complex reflection can be reproduced by the exact solution of the Maxwell equations.
Kondo, Masato; Oshima, Yasuhiro*; Tsubouchi, Masaaki
no journal, ,
no abstracts in English
Kondo, Masato; Oshima, Yasuhiro*; Tsubouchi, Masaaki
no journal, ,
no abstracts in English
Tsubouchi, Masaaki; Nagai, Masaya*; Oshima, Yasuhiro*
no journal, ,
We have proposed a novel technique for the THz tomography of photo-induced carriers based on optical-pump THz-probe reflection spectroscopy with the counter-propagated pump and probe pulses. We have experimentally demonstrated it with silicon. The obtained complex reflection can be reproduced by the exact solution of Maxwell's equations.
Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*
no journal, ,
We demonstrate the isotope selection with molecular alignment and angle-dependent ionization in intense laser fields. The 14-N2 and 15-N2 mixed gas is irradiated with a linearly polarized femtosecond laser pulse for creation of rotational wavepackets. After a certain delay when one of two isotopologues is aligned along the laser polarization direction, another linearly polarized femtosecond laser pulse is shined for ionization. It is confirmed that the ionization yield ratio between the two isotopologues can be changed as a function of the delay between the two laser pulses.
