@misc{oai:repo.qst.go.jp:00067044,
 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 ゴンザレスイスケルド, ブルーノ 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 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 ゴンザレスイスケルド ブルーノ and 匂坂 明人 and 小倉 浩一 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 = {Sep},
 note = {Burst Intensification by Singularity Emitting Radiation (BISER) [1] is a universal phenomenon, which occurs in media emitting travelling waves. If a singularity appears in such medium, e.g., due to multi-stream flow, it produces strongly intensified emission due to constructive interference of waves from elementary emitters. In particular, BISER results in bright coherent x-ray generation by relativistic plasma singularities driven by multi-terawatt femtosecond lasers focused onto gas jet targets [2], [3]. In plasma, density singularities are produced by the laser pulse which pushes electrons aside, creating a multi-stream flow, typically seen as a bow wave [4]. These singularities manifest themselves as point-like coherent x-ray emitters. In 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.
\nA tailored plasma density profile can help to control the BISER, as shown by our simulations with the Particle-In-Cell code REMP [5]. We have recently demonstrated this control for the first time in experiments with the J-KAREN-P laser [6]-[8] using a sharp density jump created by a blade in the supersonic gas flow.
\nHere we present new experimental results on the BISER control. In particular, we discuss the results obtained at different plasma densities and the dependence of the BISER x-ray source position stability on the laser power.
\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. Pirozhkov, T. Esirkepov et al., "Burst intensification by singularity emitting radiation in multi-stream flows," Sci. Rep. 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 et al "Bow Wave from Ultraintense Electromagnetic Pulses in Plasmas," PRL 101 265001 (2008).
[5]T. Esirkepov "Exact charge conservation scheme for PIC simulation with an arbitrary form-factor," CPC 135 144 (2001).
[6]H. Kiriyama et al "High-Contrast, High-Intensity Petawatt-Class Laser and Applications," IEEE JSTQE 21 1601118 (2015).
[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)., JSAP Autumn Meeting},
 title = {Experimental results on BISER control},
 year = {2018}
}