@misc{oai:repo.qst.go.jp:00073349,
 author = {ピロジコフ, アレキサンダー and エシロケポフ, ティムル and 匂坂, 明人 and 小倉, 浩一 and ゴンザレスイスケルド, ブルーノ and 中新, 信彦 and 黄, 開 and A, Pikuz T and 難波, 愼一 and 福田, 祐仁 and コーガ, ジェームズ and 桐山, 博光 and 近藤, 公伯 and 河内, 哲哉 and 神門, 正城 and ピロジコフ アレキサンダー and エシロケポフ ティムル and 匂坂 明人 and 小倉 浩一 and ゴンザレスイスケルド ブルーノ and 中新 信彦 and 黄 開 and 難波 愼一 and 福田 祐仁 and コーガ ジェームズ and 桐山 博光 and 近藤 公伯 and 河内 哲哉 and 神門 正城},
 month = {Oct},
 note = {We have discovered a new regime of bright coherent x-ray generation by relativistic plasma singularities driven by a multi-terawatt femtosecond laser focused onto a gas jet target [1]-[3]. In this regime, the driving laser pulse propagates through the plasma, pushes electrons producing an electron-free cavity, and generates a bow wave [4]. The singularities are produced at the joining of the cavity wall and the bow wave and represent relativistically moving point-like coherent x-ray emitters. We have generalized this coherent radiation emission mechanism and discovered Burst Intensification by Singularity Emitting Radiation (BISER) [5].
\nIn previous experiments, BISER resulted from relativistic self-focusing, which is a laser beam instability. This spontaneous regime exhibited relatively large shot-to-shot fluctuations of the x-ray source position and low overall stability. However, stability is desirable for prospective applications of the new coherent x-ray source.
\nBasing on simulations with the Particle-In-Cell code REMP [6], we proposed to control the BISER with a tailored plasma density profile. We demonstrated this control for the first time in experiments with the J-KAREN-P laser [7]-[9] using a sharp density jump created by a blade in the supersonic gas flow. This resulted in controllable, low-jitter x-ray source position and higher x-ray yield.
\nOur results, on the one hand, represent an important step towards implementation of a next-generation bright compact coherent x-ray source, and on the other hand, demonstrate the new technique of relativistic self-focusing control and its diagnostics.
\nWe thank the J-KAREN-P laser operation group. We acknowledge the financial support from JSPS Kakenhi JP 25390135, JP 26707031, and the QST Director Fund.
\n[1]A. S. Pirozhkov, et al. "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes," Phys. Rev. Lett. 108, 135004 (2012).
[2]A. S. Pirozhkov, et al., "High order harmonics from relativistic electron spikes," New J. Phys. 16, 093003 (2014).
[3]T. Pikuz et al "High performance imaging of relativistic soft X-ray harmonics by sub-micron resolution LiF film detectors" Phys. Status Solidi C 9 2331 (2012)
[4]T. Zh. Esirkepov, et al., "Bow Wave from Ultraintense Electromagnetic Pulses in Plasmas," Phys. Rev. Lett. 101, 265001 (2008).
[5]A. Pirozhkov, T. Esirkepov et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Sci. Rep. 7, 17968 (2017).
[6]T. Esirkepov, "Exact charge conservation scheme for PIC simulation with an arbitrary form-factor," CPC 135, 144 (2001).
[7]H. Kiriyama, et al., "High-Contrast, High-Intensity Petawatt-Class Laser and Applications," IEEE JSTQE 21, 1601118 (2015).
[8]A. S. Pirozhkov, et al. "Approaching the diffraction-limited, bandwidth-limited Petawatt," Opt. Express 25, 20486 (2017).
[9]H. Kiriyama, et al., "High-contrast high-intensity repetitive petawatt laser," Opt. Lett. 43, 2595 (2018)., ICXRL 2018},
 title = {Control of Burst Intensification by Singularity Emitting Radiation},
 year = {2018}
}