@misc{oai:repo.qst.go.jp:00081438,
 author = {Pirozhkov, Alexander and Ogura, Koichi and Armstrong, C. and Neely, D. and Timur, Esirkepov and Sagisaka, Akito and Hayakawa, Takehito and Yan, W. and M. Jeong, T. and Singh, S. and Hadjisolomou, P. and Finke, O. and Kumar, D. and Grittani, G. and Nevrkla, M. and Lazzarini, C. and Nejdl, J. and Velyhan, A. and N. Shatokhin, A. and A. Vishnyakov, E. and O. Kolesnikov, A. and N. Ragozin, E. and A. Pikuz, T. and A. Alkhimova, M. and A. Pikuz, S. and Gonzalez izquierdo, Bruno and Fukuda, Yuuji and Kevin Koga, James and Ishino, Masahiko and Kondo, Kotaro and Miyasaka, Yasuhiro and Kon, Akira and Nishikino, Masaharu and Margarone, D. and Sasorov, P. and Weber, S. and Kando, Masaki and Kiriyama, Hiromitsu and Korn, G. and Kondo, Kiminori and Bulanov, Sergey and Kawachi, Tetsuya and Pirozhkov, Alexander and Ogura, Koichi and Timur, Esirkepov and Sagisaka, Akito and Hayakawa, Takehito and Gonzalez izquierdo, Bruno and Fukuda, Yuuji and Kevin Koga, James and Ishino, Masahiko and Kondo, Kotaro and Miyasaka, Yasuhiro and Kon, Akira and Nishikino, Masaharu and Kando, Masaki and Kiriyama, Hiromitsu and Kondo, Kiminori and Bulanov, Sergey and Kawachi, Tetsuya},
 month = {Apr},
 note = {Efficient generation of ~MeV x-rays in the Gamma Flare regime [1],[2] in
preplasma via the nonlinear Thomson/inverse Compton scattering mechanism
[3] is one of the most promising and expected high-power laser
applications. The hard x-rays are generated by Bremsstrahlung as well,
while the electrons go through the target [4],[5], which also includes
multiple passes (refluxing) [5],[6]. Simulations predict that at high
intensities the preplasma x-rays dominate; however, at intensities
available now, Bremsstrahlung dominates, so that the Gamma Flare
mechanism is not yet demonstrated experimentally.
We describe our experiment performed with the J-KAREN-P laser [7]-[9],
with the emphasis on data from the scintillator-based hard x-ray
spectrographs [10] (0.1 – 1 MeV) and Compton spectrograph [11] (2 – 10
MeV), and our efforts to distinguish the generation mechanism.
We thank the J-KAREN-P laser operation group. We acknowledge financial
support from ELI-Beamlines, JSPS JP 19H00669, and QST Director Funds 創
成的研究 16 and 創成的研究 20.
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165006 (2012).
[3]     K. V. Lezhnin, P. V. Sasorov, G. Korn, and S. V. Bulanov, "High
power gamma flare generation in multi-petawatt laser interaction with
tailored targets," Phys. Plasmas 25, 123105 (2018).
[4]     D. Wu, et al., "Characteristics of X/γ-ray radiations by intense
laser interactions with high-Z solids: The role of bremsstrahlung and
radiation reactions," Matter Rad. Extremes 3, 293-299 (2018).
[5]     J. Vyskočil, O. Klimo, S. Weber, "Simulations of bremsstrahlung
emission in ultra-intense laser interactions with foil targets," Plasma
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[6]     D. R. Rusby, et al., "Effect of rear surface fields on hot,
refluxing and escaping electron populations via numerical simulations,"
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[7]     A.S.Pirozhkov, et al., "Approaching the diffraction-limited,
bandwidth-limited Petawatt," Opt. Express 25, 20486 (2017).
[8]     H. Kiriyama, et al., "High-contrast high-intensity repetitive
petawatt laser," Opt. Lett. 43, 2595 (2018).
[9]     H. Kiriyama, et al., "Experimental investigation on temporal
contrast of pre-pulses by post-pulses in a petawatt laser facility," Opt.
 Lett. (accepted).
[10]    D. R. Rusby, et al., "Novel scintillator-based x-ray spectrometer
for use on high repetition laser plasma interaction experiments," Rev.
Sci. Instr. 89, 073502 (2018).
[11]    S. Singh, et al., "Compact high energy x-ray spectrometer based on
forward Compton scattering for high intensity laser plasma experiments,"
Rev. Sci. Instr. 89, 085118 (2018)., OPTICS & PHOTONICS International Congress 2020},
 title = {Hard x-ray generation at intensity approaching 10^22 W/cm^2},
 year = {2020}
}