@misc{oai:repo.qst.go.jp:00066554,
 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 A., Pikuz Tatiana and Ya., Faenov Anatoly and 小倉, 浩一 and 林, 由紀雄 and 小瀧, 秀行 and N., Ragozin Eugene and Neely, David and 桐山, 博光 and コーガ, ジェームズ and 福田, 祐仁 and 匂坂, 明人 and 錦野, 将元 and 今園, 孝志 and 長谷川, 登 and 河内, 哲哉 and ボルトン, ポール and 大道, 博行 and 加藤, 義章 and 近藤, 公伯 and ブラノフ, セルゲイ 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 小倉 浩一 and 林 由紀雄 and 小瀧 秀行 and 桐山 博光 and コーガ ジェームズ and 福田 祐仁 and 匂坂 明人 and 錦野 将元 and 今園 孝志 and 長谷川 登 and 河内 哲哉 and ボルトン ポール and 大道 博行 and 加藤 義章 and 近藤 公伯 and ブラノフ セルゲイ and 神門 正城},
 month = {Apr},
 note = {In our experiments and simulations [1, 2] we discovered a bright source of high-order harmonics and revealed the mechanism of their generation in relativistic plasma driven by multi-terawatt femtosecond lasers focused onto gas jet targets with typical electron densities of ~10^19 cm^-3. The harmonics extended up to the 'water window'; the energy within the 60 to 100 eV bandwidth was up to 100 nJ per shot. Simulations showed that the emission consisted of several attosecond pulses. In our subsequent experiments we confirmed the predictions and observed the soft x-ray emission originated from point-like sources.
\nHere we generalize this mechanism and introduce the concept of BISER, Burst Intensification by Singularity Emitting Radiation. In this concept, we consider an emitting medium with multi-stream flows. Elementary components participating in such flows eventually form structurally stable density singularities explained by catastrophe theory. The wave emission from such singularities can be coherent due to tight localization of elementary emitters. In addition, if the singularities move with relativistic speed towards an observer, the apparent frequency increases and emission becomes more intense and directional. In our previous work the emitting medium was relativistic plasma, the elementary components were electrons, and the emitting waves were high-frequency electromagnetic waves, i.e. soft x-rays. In general, BISER can be applicable to any type of traveling waves, not necessarily electromagnetic.
\n[1] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, et al., "Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes," Phys. Rev. Lett. 108, 135004-5 (2012).
[2] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, et al., "High order harmonics from relativistic electron spikes," New J. Phys. 16, 093003-30 (2014)., The Optics & Photonics International Congress OPIC-2017, International Conference on High-Energy Density Sciences HEDS-2017},
 title = {BISER: Burst Intensification by Singularity Emitting Radiation},
 year = {2017}
}