Eiji J. Takahashi
Graduate University for Advanced Studies
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Featured researches published by Eiji J. Takahashi.
Optics Letters | 2004
Eiji J. Takahashi; Hirokazu Hasegawa; Yasuo Nabekawa; Katsumi Midorikawa
We demonstrated a high-throughput and high-damage-threshold beam splitter for high-order harmonics using Si, SiC and Mo plates, set at Brewsters angle with respect to the pump wavelength
IEEE Journal of Selected Topics in Quantum Electronics | 2004
Eiji J. Takahashi; Yasuo Nabekawa; Hiroki Mashiko; Hirokazu Hasegawa; Akira Suda; Katsumi Midorikawa
For further development of a variety of applications, one of the most important issues is the improvement of output harmonic energy and conversion efficiency. We review our work on the energy scaling of high-order harmonic generation based on phase-matching using a loosely focused beam. Our harmonic energy scaling method can be universally applied to harmonic generation in the neutral rare gas target. In addition, we demonstrate a new concept for spatial separation between the high-energy pump and harmonic beam to increase the available soft X-ray energy for the applications. This method is very simple and highly useful for not only high-order harmonic generation but also longitudinally pumped X-ray lasers. By combining the high-energy high harmonic source and new spatial separation method, we successfully demonstrate focusing of the soft X-ray beam with a peak intensity of 1/spl times/10/sup 14/ W/cm/sup 2/, which is to our knowledge the highest ever reported in the soft X-ray region.
Journal of Chemical Physics | 2008
Akiyoshi Hishikawa; Akitaka Matsuda; Eiji J. Takahashi; Mizuho Fushitani
The isomerization of acetylene via hydrogen migration in intense laser fields (8 x 10(14) W/cm2) has been investigated by coincidence momentum imaging of the three-body Coulomb explosion process, C2H2 (3+)-->H+ + C+ + CH+. When ultrashort (9 fs) laser pulses are used, the angle between the momenta of C+ and H+ fragments exhibits a sharp distribution peaked at a small angle ( approximately 20 degrees ), showing that the hydrogen atom remains near the original carbon site in the acetylene configuration. On the other hand, a significantly broad distribution extending to larger momentum angles ( approximately 120 degrees ) is observed when the pulse duration is increased to 35 fs, indicating that the ultrafast isomerization to vinylidene is induced in the longer laser pulse.
Physical Chemistry Chemical Physics | 2011
Akitaka Matsuda; Mizuho Fushitani; Eiji J. Takahashi; Akiyoshi Hishikawa
The visualization of ultrafast isomerization of deuterated acetylene dication (C(2)D(2)(2+)) is demonstrated by time-resolved Coulomb explosion imaging with sub-10 fs intense laser pulses (9 fs, 0.13 PW cm(-2), 800 nm). The Coulomb explosion imaging monitoring the three-body explosion process, C(2)D(2)(3+)→ D(+) + C(+) + CD(+), as a function of the delay between the pump and probe pulses revealed that the migration of a deuterium atom proceeds in a recurrent manner; One of the deuterium atoms first shifts from one carbon site to the other in a short timescale (∼90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation. Correlated motion of the two deuterium atoms associated with the hydrogen migration and structural deformation to non-planar geometry are identified by the time-resolved four-body Coulomb explosion imaging, C(2)D(2)(4+)→ D(+) + C(+) + C(+) + D(+).
Journal of Chemical Physics | 2007
Akitaka Matsuda; Eiji J. Takahashi; Akiyoshi Hishikawa
The three-body Coulomb explosion of O3, O3(3+)-->O++O++O+, in ultrashort intense laser fields (2x10(15) W/cm2) is studied with two different pulse durations (9 and 40 fs) by the coincidence momentum imaging method. In addition to a decrease in the total kinetic energy release, a broadening in the Dalitz plot distribution [Philos. Mag. 44, 1068 (1953)] is observed when the pulse duration is increased from 9 to 40 fs. The analysis based on a simple Coulomb explosion model shows that the geometrical structure of O3 remains almost unchanged during the interaction with the few-cycle intense laser fields, while a significant structural deformation along all the three vibrational coordinates, including the antisymmetric stretching coordinate, is identified in the 40 fs intense laser fields. The observed nuclear dynamics are discussed in terms of the population transfer to the excited states of O3.
Journal of Physics: Conference Series | 2009
Mizuho Fushitani; A Matsuda; Eiji J. Takahashi; Akiyoshi Hishikawa
We discuss two novel approaches to visualize ultrafast dynamics of polyatomic molecules using few-cycle intense laser pulses and the high-order harmonics in the soft X-ray region, respectively. First, we present the real-time Coulomb explosion imaging of ultrafast isomerization of C2D22+ by using intense few-cycle laser pulses (<10 fs, ~1 PW/cm2, ~800 nm) to show that the hydrogen migration proceeds recurrently in competition with the molecular dissociation. Secondly, we present a new experimental setup for the real-time inner-core excitation imaging, focusing on the generation and separation of the light source using the 59th order harmonic pulses (~91 eV) and their characteristics.
Journal of Physics: Conference Series | 2007
Akiyoshi Hishikawa; A Matsuda; Mizuho Fushitani; Eiji J. Takahashi
Ultrafast hydrogen migration in deuterated acetylene dication (C2D22+) is studied by the pump-probe Coulomb explosion imaging with few-cycle intense laser pulses (9 fs, 0.13 PW/cm2, 800 nm). The temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C2D23+ → D++ C+ + CD+, shows that the migration proceeds in a recurrent manner: The deuterium atom first shifts from one carbon site to the other in a short time scale (~90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.
Physical Review Letters | 2005
Yasuo Nabekawa; Hirokazu Hasegawa; Eiji J. Takahashi; Katsumi Midorikawa
Physical Review Letters | 2007
Akiyoshi Hishikawa; Akitaka Matsuda; Mizuho Fushitani; Eiji J. Takahashi
Physical Review A | 2005
Hirokazu Hasegawa; Eiji J. Takahashi; Yasuo Nabekawa; Kenichi L. Ishikawa; Katsumi Midorikawa