量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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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).
Plasma density jump for the control of coherent x-ray emission via BISER mechanism
