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Skobelev, I. Yu.*; Ryazantsev, S. N.*; Kulikov, R. K.*; Sedov, M. V.*; Filippov, E. D.*; Pikuz, S. A.*; Asai, Takafumi*; Kanasaki, Masato*; Yamauchi, Tomoya*; Jinno, Satoshi; et al.
Photonics (Internet), 10(11), p.1250_1 - 1250_11, 2023/11
Times Cited Count：0 Percentile：0(Optics)It is challenging to clearly distinguish the impacts of the optical field and collisional ionization in the evolution of the charge state of a plasma produced when matter interacts with high-intensity laser pulses. In this work, time-dependent calculations of plasma kinetics are used to show that it is possible only when low-density gaseous targets with sufficiently small clusters are used. In the case of Ar plasma, the upper limit of the cluster radius was estimated to be 
m.
Nishiuchi, Mamiko; Choi, I. W.*; Daido, Hiroyuki; Nakamura, Tatsufumi*; Pirozhkov, A. S.; Yogo, Akifumi*; Ogura, Koichi; Sagisaka, Akito; Orimo, Satoshi; Daito, Izuru*; et al.
Plasma Physics and Controlled Fusion, 57(2), p.025001_1 - 025001_9, 2015/02
Times Cited Count：3 Percentile：13.75(Physics, Fluids & Plasmas)Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of 
20 micron meter and 10 micron meter diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration.
Kiriyama, Hiromitsu; Mori, Michiaki; Pirozhkov, A. S.; Ogura, Koichi; Sagisaka, Akito; Kon, Akira; Esirkepov, T. Z.; Hayashi, Yukio; Kotaki, Hideyuki; Kanasaki, Masato*; et al.
IEEE Journal of Selected Topics in Quantum Electronics, 21(1), p.1601118_1 - 1601118_18, 2015/01
Times Cited Count：60 Percentile：95.3(Engineering, Electrical & Electronic)This paper reviews the development of a high-contrast high-intensity petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser for research on high field science. We discuss in detail the design, performance and characterization of the laser. We also describe the on-going upgrade of the laser system and some applications for the laser in relativistic dominated laser-matter interactions.
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Faenov, A. Y.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; Koga, J. K.; Mori, Michiaki; Kawase, Keigo*; et al.
RAL-TR-2015-025, P. 22, 2015/00
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; et al.
New Journal of Physics (Internet), 16(9), p.093003_1 - 093003_30, 2014/09
Times Cited Count：30 Percentile：81.06(Physics, Multidisciplinary)Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
AIP Conference Proceedings 1465, p.167 - 171, 2012/07
Times Cited Count：1 Percentile：46.45(Physics, Applied)Esirkepov, T. Z.; Pirozhkov, A. S.; Kando, Masaki; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A.*; Pikuz, T.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
AIP Conference Proceedings 1465, p.172 - 180, 2012/07
Times Cited Count：0 Percentile：0.13(Physics, Applied)The bow wave induced mechanism of high-order harmonics generation was discovered using simulations and catastrophe theory. This mechanism feasibility was successfully demonstrated in 3D and 2D PIC simulations. The mechanism and the simulations explained high-order harmonics in the XUV spectral region seen in recent experiments with terawatt lasers. Development of new XUV light and X-ray source based on the high-order harmonics generation mechanism is proposed.
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T.; Kawachi, Tetsuya; Sagisaka, Akito; et al.
Physical Review Letters, 108(13), p.135004_1 - 135004_5, 2012/03
Times Cited Count：69 Percentile：90.73(Physics, Multidisciplinary)We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multi-terawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving 
J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.
Choi, I. W.*; Kim, I. J.*; Pae, K. H.*; Nam, K. H.*; Lee, C.-L.*; Yun, H.*; Kim, H. T.*; Lee, S. K.*; Yu, T. J.*; Sung, J. H.*; et al.
Applied Physics Letters, 99(18), p.181501_1 - 181501_3, 2011/11
Times Cited Count：17 Percentile：57.65(Physics, Applied)We report the manufacturing of a thin foil target made of conjugated polymer, and the simultaneous observation of laser accelerated ions and second harmonic radiation, when irradiated with ultrahigh-contrast laser pulse at a maximum intensity of 410
W/cm. Maximum proton energy of 8 MeV is achieved along the target normal direction. Strong second harmonic with over 6% energy ratio compared to fundamental is emitted along the specular direction. Two-dimensional particle-in-cell simulations confirm the simultaneous generation of protons and high-order harmonics, which demonstrates the feasibility of applications requiring particle and radiation sources at once, effectively using the same laser and target.
Fukuda, Yuji; Faenov, A.*; Tampo, Motonobu; Pikuz, T.*; Nakamura, Tatsufumi; Kando, Masaki; Hayashi, Yukio; Yogo, Akifumi; Sakaki, Hironao; Kameshima, Takashi*; et al.
Progress in Ultrafast Intense Laser Science VII, p.225 - 240, 2011/05
http://www.springer.com/physics/atomic,+molecular,+optical+%26+plasma+physics/book/978-3-642-18326-3We present substantial enhancement of the accelerated ion energies up to 10-20 MeV per nucleon by utilizing the unique properties of the cluster-gas target irradiated with 40-fs laser pulses of only 150 mJ energy, corresponding to approximately tenfold increase in the ion energies compared to previous experiments using thin foil targets. A particle-in-cell simulation infers that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in sub-critical density plasmas. The demonstrated method can be important in the development of efficient laser ion accelerators for hadron therapy and other applications.
Sagisaka, Akito; Pirozhkov, A. S.; Mori, Michiaki; Yogo, Akifumi; Ogura, Koichi; Orimo, Satoshi; Nishiuchi, Mamiko; Ma, J.*; Kiriyama, Hiromitsu; Kanazawa, Shuhei; et al.
NIFS-PROC-85, p.30 - 33, 2011/02
The experiment of proton generation is performed for developing the laser-driven ion source. We observe proton signals in the laser-plasma interaction by using a thin-foil target. To get higher energy protons the size of the preformed plasma is reduced by changing the laser contrast level. In the high-contrast laser pulse case the maximum energy of the protons generated at rear side of the target increases.
Sagisaka, Akito; Pirozhkov, A. S.; Mori, Michiaki; Yogo, Akifumi; Ogura, Koichi; Orimo, Satoshi; Nishiuchi, Mamiko; Ma, J.*; Kiriyama, Hiromitsu; Kanazawa, Shuhei; et al.
Reza Kenkyu, 38(9), p.702 - 705, 2010/09
High-intensity laser and thin-foil interactions produce high-energy particles, hard X-ray, high-order harmonics, and terahertz (THz) radiation. A proton beam driven by a high-intensity laser has received attention as a compact ion source for medical applications. In this study we have tested simultaneous generation of protons and THz radiation from a thin-foil target. We use a Ti:sapphire laser system (J-KAREN) at JAEA. A laser beam is focused by an off-axis parabolic mirror at the thin-foil target. We observed the high-energy proton in the rear side of the target and THz radiation in the reflected direction. Next, high energy protons are observed by reducing the size of preformed plasma.
Koga, J. K.; Moribayashi, Kengo; Fukuda, Yuji; Bulanov, S. V.; Sagisaka, Akito; Ogura, Koichi; Daido, Hiroyuki; Yamagiwa, Mitsuru; Kimura, Toyoaki*; Fujikawa, Taketoshi*; et al.
Journal of Physics D; Applied Physics, 43(2), p.025204_1 - 025204_15, 2010/01
Times Cited Count：17 Percentile：56.56(Physics, Applied)Fukuda, Yuji; Faenov, A. Y.; Tampo, Motonobu; Pikuz, T. A.*; Nakamura, Tatsufumi; Kando, Masaki; Hayashi, Yukio; Yogo, Akifumi; Sakaki, Hironao; Kameshima, Takashi*; et al.
Physical Review Letters, 103(16), p.165002_1 - 165002_4, 2009/10
Times Cited Count：162 Percentile：96.67(Physics, Multidisciplinary)A new approach for accelerating ions, based on the use of a cluster-gas target and a compact ultrashort pulse laser, is presented. It is shown that ions with energy 10-20 MeV per nucleon having a small divergence (full angle) of 3.4
are generated, corresponding to an approximately tenfold increase in the ion energies compared to previous experiments using solid targets. It is inferred from a particle-in-cell code simulation that the high energy ions are generated at the rear side of the target due to the formation of a strong dipole vortex structure in near-critical density plasmas.
Kando, Masaki; Pirozhkov, A. S.; Fukuda, Yuji; Esirkepov, T. Z.; Daito, Izuru; Kawase, Keigo; Ma, J. L.*; Chen, L. M.*; Hayashi, Yukio; Mori, Michiaki; et al.
European Physical Journal D, 55(2), p.465 - 474, 2009/09
Times Cited Count：18 Percentile：64.01(Optics)Nonlinear interaction of intense laser beams with plasma causes a number of different regimes of generation of high energy particle beams and of strong radiation with the emitted photon energy from the X-ray to THz frequency range. The review of the first proof-of-principle experiment and the latest progress on the flying mirror is presented. A low frequency EM radiation emission has also been observed in our experiments. The interpretation invokes the relativistic electromagnetic solitons. The solitons are formed in an underdense plasma in the process of the laser pulse frequency downshift. They store a portion of EM wave energy with the polarization inherited from the laser and emit it at the plasma-vacuum interface in a form of the low frequency EM bursts. We present the results of the polarization-resolved measurements.
Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Fukuda, Yuji; Chen, L.-M.*; Daito, Izuru; Ogura, Koichi; Homma, Takayuki; Hayashi, Yukio; Kotaki, Hideyuki; et al.
AIP Conference Proceedings 1153, p.274 - 284, 2009/07
Kando, Masaki; Pirozhkov, A. S.; Fukuda, Yuji; Esirkepov, T. Z.; Daito, Izuru; Kawase, Keigo; Ma, J.-L.; Chen, L.-M.; Hayashi, Yukio; Mori, Michiaki; et al.
Harnessing Relativistic Plasma Waves as Novel Radiation Sources from Terahertz to X-Rays and Beyond (Proceedings of SPIE Vol.7359), p.73590K_1 - 73590K_11, 2009/05
Times Cited Count：0 Percentile：0.07(Optics)Mori, Michiaki; Yogo, Akifumi; Kiriyama, Hiromitsu; Nishiuchi, Mamiko; Ogura, Koichi; Orimo, Satoshi; Ma, J.*; Sagisaka, Akito; Kanazawa, Shuhei; Kondo, Shuji; et al.
IEEE Transactions on Plasma Science, 36(4), p.1872 - 1877, 2008/08
Times Cited Count：7 Percentile：28.47(Physics, Fluids & Plasmas)A dependence of cut-off proton kinetic energy on laser prepulse duration has been observed. ASE pedestal duration is controlled by a fast electro-optic pulse slicer where the risetime is estimated to be 130 ps. We demonstrate a new correlated spectral technique for determining this risetime using a stretched, frequency chirped pulse.
Nishiuchi, Mamiko; Daido, Hiroyuki; Yogo, Akifumi; Orimo, Satoshi; Ogura, Koichi; Ma, J.-L.; Sagisaka, Akito; Mori, Michiaki; Pirozhkov, A. S.; Kiriyama, Hiromitsu; et al.
Physics of Plasmas, 15(5), p.053104_1 - 053104_10, 2008/05
Times Cited Count：45 Percentile：83.73(Physics, Fluids & Plasmas)High-flux energetic protons whose maximum energies are up to 4 MeV are generated by an intense femtosecond Titanium Sapphire laser pulse interacting with a 7.5, 12.5, and 25m thick Polyimide tape targets. The laser pulse energy is 1.7 J, duration is 34 fs, and intensity is 310Wcm
. The amplified spontaneous emission (ASE) has the intensity contrast ratio of 410
. The conversion efficiency from laser energy into proton kinetic energies of 3% is achieved, which is comparable or even higher than those achieved in the previous works with nanometer-thick targets and the ultrahigh contrast laser pulses (10
).
Pirozhkov, A. S.; Ma, J.-L.; Kando, Masaki; Esirkepov, T. Z.; Fukuda, Yuji; Chen, L. M.; Daito, Izuru; Ogura, Koichi; Homma, Takayuki; Hayashi, Yukio; et al.
Physics of Plasmas, 14(12), p.123106_1 - 123106_22, 2007/12
Times Cited Count：92 Percentile：47.37(Physics, Fluids & Plasmas)