@misc{oai:repo.qst.go.jp:00066714,
 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 中新, 信彦 and 黄, 開 and A., Pikuz T. and Ya., Faenov A. and Namba, S. and 大東, 出 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 中新 信彦 and 黄 開 and 大東 出 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 = {Mar},
 note = {We have discovered Burst Intensification by Singularity Emitting Radiation (BISER) [1], a new phenomenon which in particular results in bright coherent x-ray generation by relativistic plasma singularities driven by a multi-terawatt femtosecond laser focused onto a gas jet target [2], [3]. Singularities are produced in plasma by the laser pulse which pushes electrons creating an electron-free cavity and bow wave [4]. The singularities at the joining of the cavity wall and bow wave manifest themselves as point-like coherent x-ray emitters. A spontaneous BISER regime realized in previous experiments exhibits relatively large shot-to-shot fluctuations of the x-ray source position and low overall stability because the emission occurs after the relativistic self-focusing. However, stability is desirable for prospective applications of the new coherent x-ray source.
\nA tailored plasma density profile can help to control the BISER, as shown by our simulations with the PIC REMP code [5]. Here, we present an experiment with the plasma profile tailoring, where a shock in supersonic gas flow generates a sharp density up-jump. We demonstrate the BISER control using this density jump scheme and the J-KAREN-P laser [6]-[7]. In contrast to the spontaneous regime, here we obtain low-jitter x-ray source position and higher x-ray yield. Moreover, these advantages are achieved simultaneously in an optimized case. Our results represent a crucial step towards implementation of the next-generation bright compact coherent x-ray source. Further, they 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 and JP 26707031.
\n[1]A. S. Pirozhkov, T. Zh. Esirkepov, et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Scientific Reports 7, 17968 (2017).
[2]A.S.Pirozhkov, et al. "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes" Phys. Rev. Lett. 108, 135004 (2012).
[3]A.S.Pirozhkov et al., "High order harmonics from relativistic electron spikes" New J. Phys. 16, 093003-30 (2014).
[4]T. Zh. Esirkepov, Y. Kato, and S. V. Bulanov, "Bow Wave from Ultraintense Electromagnetic Pulses in Plasmas," Phys. Rev. Lett. 101, 265001-4 (2008).
[5]T. Zh. Esirkepov, "Exact charge conservation scheme for Particle-in-Cell simulation with an arbitrary form-factor," Comput. Phys. Comm. 135, 144-153 (2001).
[6]H. Kiriyama, et al., "High-Contrast, High-Intensity Petawatt-Class Laser and Applications," IEEE J.S.T.Quantum Electron. 21, 1601118-18 (2015).
[7]A.S.Pirozhkov, et al. "Approaching the diffraction-limited, bandwidth-limited Petawatt" Opt. Express 25, 20486 (2017)., JSAP Spring Meeting},
 title = {Plasma density jump for the control of coherent x-ray emission via BISER mechanism},
 year = {2018}
}