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Yamakawa, Koichiro
Shototsu, 17(5), p.86 - 101, 2020/09
no abstracts in English
Yamakawa, Koichiro; Ishibashi, Atsuki*; Namiyoshi, Toshinobu*; Azuma, Yuichi*; Arakawa, Ichiro*
Physical Review B, 102(4), p.041401_1 - 041401_5, 2020/07
Times Cited Count:1 Percentile:9.13(Materials Science, Multidisciplinary)Yamakawa, Koichiro; Nasu, Hirokazu*; Shimizu, Genki*
Bunko Kenkyu, 69(3), p.105 - 106, 2020/06
Terahertz and infrared spectroscopy is one of the powerful ways to elucidate the structures and vibrational modes of molecular clusters. We review an experimental apparatus for absorption spectroscopy in an ultra-high vacuum covering the wavenumber range of 60-7000 cm, from the viewpoints of vacuum-, low-temperature-, and spectroscopy-techniques. We also introduce the terahertz and infrared spectrum of D
O clusters isolated in an Ar matrix measured with this apparatus.
Yamakawa, Koichiro; Nasu, Hirokazu*; Suzuki, Natsumi*; Shimizu, Genki*; Arakawa, Ichiro*
Journal of Chemical Physics, 152(17), p.174310_1 - 174310_13, 2020/05
Times Cited Count:0 Percentile:0.01(Chemistry, Physical)We have established an apparatus for terahertz and mid-infrared spectroscopy in an ultrahigh vacuum and have measured absorption spectra of DO clusters trapped in solid Ar. To assign terahertz absorption peaks due to the D
O dimer, trimer, and tetramer, the dependence of the spectrum on the annealing temperature and D
O dilution was analyzed. The assignment was also examined by ab initio calculations with use of the ONIOM method, where flexibility of surrounding Ar atoms was systematically incorporated. We identified all of the intermolecular fundamentals of the dimer and those with significant intensities of the trimer and tetramer, whose structural symmetries were revealed to be broken down. After isolating the D
O clusters in solid Ar, we sublimated only Ar atoms to leave behind matrix-sublimation ice, which was found to be amorphous- or crystal-like depending on the formation conditions: the dilution and sublimation-temperature. Since the crystallinity got higher with raising the dilution and sublimation-temperature, the diffusion of the D
O monomer on the surface of sublimating solid Ar was found to be crucial to the crystallization of the sublimation ice.
Tomizawa, Hiromitsu*; Sato, Takahiro*; Ogawa, Kanade*; Togawa, Kazuaki*; Tanaka, Takatsugu*; Hara, Toru*; Yabashi, Makina*; Tanaka, Hitoshi*; Ishikawa, Tetsuya*; Togashi, Tadashi*; et al.
High Power Laser Science and Engineering, 3, p.e14_1 - e14_10, 2015/04
Times Cited Count:6 Percentile:36.7(Optics)no abstracts in English
Akagi, Takashi*; Yagi, Masashi*; Yamashita, Tomohiro*; Murakami, Masao*; Yamakawa, Yoshiyuki*; Kitamura, Keiji*; Ogura, Koichi; Kondo, Kiminori; Kawanishi, Shunichi*
Radiation Measurements, 59, p.262 - 269, 2013/12
Times Cited Count:12 Percentile:69.87(Nuclear Science & Technology)In proton therapy, positron emitters are induced from C and
O nuclei by protons on the beam path in the patient. Many studies for monitoring positron emitters with beam-induced PET technique have been performed by various groups to verify the proton beam range and the dose in the patient for quality assurance. The aim of this study was to develop a method for measuring the production cross sections of positron emitters using standard equipment for proton therapy. The time-activity curve was then obtained with a high-sensitivity PET scanner to extract the number of positron emitters produced in the target. The production cross sections for four reaction channels:
O(p,pn)
O,
O(p,3p3n)
C,
O(p,2p2n)
N, and
C(p,pn)
C were then measured. The cross sections for the
O(p,pn)
O reaction channel were consistent with data of previous experiments within the uncertainties, while those of
C(p,pn)
C were generally lower than data of previous experiments.
Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Togashi, Tadashi*; Fukami, Kenji*; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164006_1 - 164006_6, 2013/08
Times Cited Count:3 Percentile:19.96(Optics)By introducing 13th- (61.7 nm) and 15th-order harmonics (53.4 nm) of femtosecond laser pulses at 800 nm into an undulator of SCSS (SPring-8 Compact SASE Source) test accelerator at RIKEN, these harmonic pulses were amplified by a factor of more than 10 with a high contrast ratio through the interaction between accelerated electron bunches and the harmonic pulses. From numerical simulations of the amplification processes of high-order harmonic pulses in the undulator, optimum conditions of the electron bunch duration interacting with the high-order harmonic pulses were investigated for generating full-coherent and intense pulses in the extreme ultraviolet wavelength region.
Ogawa, Kanade*; Sato, Takahiro*; Matsubara, Shinichi*; Okayasu, Yuichi*; Togashi, Tadashi*; Watanabe, Takahiro*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; et al.
Proceedings of 10th Conference on Lasers and Electro-Optics Pacific Rim and 18th OptoElectronics and Communications Conference and Photonics in Switching 2013 (CLEO-PR & OECC/PS 2013) (USB Flash Drive), 2 Pages, 2013/06
no abstracts in English
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Hara, Toru*; et al.
Proceedings of Ultrafast Optics IX (CD-ROM), 2 Pages, 2013/03
We have demonstrated free-electron laser radiation seeded by high-order harmonics in the extreme-ultraviolet region. Strong enhancement of the radiation intensity by a factor of 104 was observed with timing control of an electro-optical sampling technique.
Iwasaki, Atsushi*; Sato, Takahiro*; Owada, Shigeki*; Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Kannari, Fumihiko*; Yagishita, Akira*; et al.
Reza Kenkyu, 40(9), p.687 - 690, 2012/09
no abstracts in English
Iwasaki, Atsushi*; Sato, Takahiro*; Owada, Shigeki*; Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Matsubara, Shinichi*; Okayasu, Yuichi*; et al.
Proceedings of International Conference on Ultrafast Phenomena 2012 (UP 2012) (Internet), 3 Pages, 2012/07
Times Cited Count:0 Percentile:0.03no abstracts in English
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Hara, Toru*; et al.
Proceedings of 11th International School and Symposium on Synchrotron Radiation in Natural Science (ISSRNS 2012), p.1 - 21, 2012/05
The 13th harmonic of a Ti:sapphire laser has been significantly amplified with the SCSS test accelerator. The temporal and spatial overlap of the electron beam and the high harmonic radiation were precisely tuned for achieving the seeded free electron laser operation. With numerical simulation the present HH-seeded FEL scheme could readily be applied to the wavelength region down to 10 nm.
Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.
Europhysics News, 42(5), P. 10, 2011/09
The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.
Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.
Journal of Physics B; Atomic, Molecular and Optical Physics, 44(16), p.161001_1 - 161001_5, 2011/08
Times Cited Count:35 Percentile:83.92(Optics)The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Okino, Tomoya*; Yamanouchi, Kaoru*; Hara, Toru*; et al.
Proceedings of 2011 Conference on Lasers and Electro-Optics (CLEO 2011) (CD-ROM), p.1527 - 1528, 2011/05
We succeeded in generating the seeded free electron laser (FEL) with wavelengths of 61 nm at the SCSS test accelerator. The 13th (61 nm) harmonics generated by focusing the high peak power Ti:Sapphire laser to the Xe gas cell was directed to the undulator. This is first realization of the seeded FEL in extreme ultraviolet region.
Takahashi, Eiji*; Togashi, Tadashi*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Hara, Toru*; et al.
Proceedings of European Conference on Lasers and Electro-Optics and the 12th European Quantum Electronics Conference (CLEO/Europe-EQEC 2011) (CD-ROM), 1 Pages, 2011/05
We succeeded in generating the seeded free electron laser (FEL) with wavelengths of 61 nm at the SCSS test accelerator. The 13th (61 nm) harmonics generated by focusing the high peak power Ti:Sapphire laser to the Xe gas cell was directed to the undulator. This is first realization of the seeded FEL in extreme ultraviolet region.
Takahashi, Eiji*; Togashi, Tadashi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Hara, Toru*; Matsubara, Shinichi*; et al.
Proceedings of International Quantum Electronics Conference and the Pacific Rim Conference on Lasers and Electro-Optics (IQEC/CLEO Pacific Rim 2011) (CD-ROM), p.199 - 200, 2011/05
We succeeded in generating the seeded free electron laser (FEL) with wavelengths of 61 nm at the SCSS test accelerator. The 13th (61 nm) harmonics generated by focusing the high peak power Ti:Sapphire laser to the Xe gas cell was directed to the undulator. This is first realization of the seeded FEL in extreme ultraviolet region.
Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Okino, Tomoya*; Yamanouchi, Kaoru*; et al.
Optics Express (Internet), 19(1), p.317 - 324, 2011/01
Times Cited Count:93 Percentile:96.63(Optics)The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.
Ogawa, Kanade; Akahane, Yutaka; Tsuji, Koichi; Yamakawa, Koichi
Reza Kenkyu, 38(10), p.779 - 783, 2010/10
We have newly designed a grism pair compensator for third-order dispersion in a fiber stretched chirped-pulse amplification system. In a numerical calculation, we have obtained a pedestal-free re-compressed pulse close to the transform-limited pulse using the grism pair. We have experimentally demonstrated a two-fold enhancement of peak intensity and pulse shortening of the compressed pulse with this device.
Akahane, Yutaka; Ogawa, Kanade; Tsuji, Koichi; Aoyama, Makoto; Yamakawa, Koichi
Proceedings of SPIE, Vol.7589, p.75890L_1 - 75890L_8, 2010/02
Times Cited Count:0 Percentile:0.01We have proposed and demonstrated a very simple and robust femtosecond optical-parametric chirped-pulse amplification scheme in which an even order dispersion of an idler pulse is compensated by passing through an identical positive dispersive material used for temporal stretching a signal pulse. By compressing the idler pulses having a negatively chirp in this manner, high power sub-100 fs pulses were successfully obtained with only a transparent glass block used for the stretcher and compressor.