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1. Introduction Burst Intensification by Singularity Emitting Radiation (BISER) [1] is the emission of coherent traveling waves by multi-stream flow singularities. Such singularities can be produced in relativistic plasma by high-power lasers, resulting in very bright coherent x-ray emission [2],[3]. 2. Experimental We have recently performed an experiment on BISER coherent x-ray generation with the Astra Laser at the CLF RAL, UK. We extensively optimized the experimental conditions, namely the plasma density and profile, and laser spot [4] and pulse, making use of substantial beam time. This resulted in a ~2 orders of magnitude higher BISER brightness compared to earlier experiments with 10 TW lasers. 3. Results In this presentation we discuss results from two soft x-ray spectrographs: a three-channel flat field spectrograph [5] in the forward direction (channels at −0.6, 0, and 0.8°) operating in the 17-34 nm range and a normal-incidence imaging spectrograph [6] in a 10° off-axis direction operating in the 12.4-20 nm range. Under optimum conditions, both spectrographs showed μJ and higher BISER pulse energies per shot in the corresponding spectral ranges and within their acceptance angles. This implies multi-100 μJ BISER pulses in the entire spectral range and within the full angular width. Acknowledgement We acknowledge support from the Astra Laser Group and the CLF Target Fab, Mechanical, and Electrical. Financial support: JSPS Kakenhi JP 19KK0355 and 19H00669, CLF, Russian Science Foundation (20-62-46050), IAP RAS, ELI-Beamlines, MŠMT by the project "Advanced Research Using High Intensity Laser Produced Photons and Particles" (CZ.02.1.01/0.0/0.0/16_019/0000789), High Field Initiative (CZ.02.1.01/0.0/0.0/15_003/0000449) from the European Regional Development Fund, and the QST Director Fund 創成的研究 #20. References [1]A. S. Pirozhkov, T. Zh. 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" PRL 108, 135004 (2012). [3]A. S. Pirozhkov, et al., "High order harmonics from relativistic electron spikes" NJP 16, 093003 (2014). [4]A. S. Pirozhkov, et al. "Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities," Quantum Beam Sci. 2, 7 (2018). [5]D. Neely, et al., "A multi-channel soft X-ray flat-field spectrometer," AIP Conf. Proc. 426, 479 (1998). [6]A. N. Shatokhin, et al., "High-resolution stigmatic spectrograph for a wavelength range of 12.5-30 nm," Opt. Express 26, 19009 (2018)., OPIC-2022 (ALPS-2022)

Burst Intensification by Singularity Emitting Radiation (BISER) [1] is the phenomenon of extremely bright coherent wave emission (constructive interference, N^2 effect) by singularities of multi-stream flows. High-power femtosecond lasers can produce such flows and corresponding relativistic plasma singularities in underdense plasma; these singularities emit very bright coherent x-rays [2]-[3]. We have recently performed an experiment on BISER coherent x-ray generation with the Astra Laser in the CLF RAL, UK. We observed BISER coherent soft x-rays with two spectrographs: a three-channel flat field spectrograph [4] in the forward direction (channels at -0.6, 0, and 0.8°) operating in the 17-34 nm range and a normal-incidence imaging spectrograph [5] in a 10° off-axis direction operating in the 12.4-20 nm range. Both spectrographs, in addition, provided data on the angular distribution of the BISER radiation. We took advantage of an extensive experiment term and long daily laser operation hours to optimize the laser (in particular, focal spot, which is a necessary prerequisite for BISER [6], and pulse width) and the experimental conditions (in particular, the density profile). These resulted in ~2 orders of magnitude enhancement in BISER photon number, providing >10^11 photons and >μJ energies per pulse in each channel at 7 TW laser power, the result which could previously be obtained at >100 TW laser power only. We acknowledge support from the Astra Laser Group and the CLF Target Fab, Mechanical, and Electrical. Financial support: JSPS Kakenhi JP 19KK0355 and 19H00669, CLF, Russian Science Foundation (20-62-46050), IAP RAS, ELI-Beamlines, the Ministry of Education, Youth and Sports of the Czech Republic by the project "Advanced Research Using High Intensity Laser Produced Photons and Particles" (CZ.02.1.01/0.0/0.0/16_019/0000789), and the QST Director Fund 創成的研究 #20. [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" PRL 108 135004 (2012) [3] A. S. Pirozhkov et al., "High order harmonics from relativistic electron spikes" New J. Phys. 16, 093003 (2014). [4] D. Neely et al., "A multi-channel soft X-ray flat-field spectrometer," AIP Conf. Proc. 426, 479 (1998). [5] A. Shatokhin et al., "High-resolution stigmatic spectrograph for a wavelength range of 12.5-30 nm," Opt. Express 26 19009 (2018). [6] A. S. Pirozhkov, et al. "Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities," Quantum Beam Sci. 2, 7 (2018)., Annual meeting of the JSAP

関西光化学研究所の J-KAREN-P レーザーを CH または CHCl 薄膜ターゲットに照射し、 無衝突静電衝撃波イオン加速(ECS)の研究を行った。薄膜ターゲット(0.5~4.0μm)をプ レパルスまたはメインパルスの一部を取り出したイオンかパルスによりプラズマ化させる ことで初期プラズマを形成し、そこにメインパルス(プレパルスから数 ns 後)を入射する ことで ECS を生成した。ターゲットの厚さ、レーザーのスポット径、プレパルスとメイン パルスのコントラストなどを変化させることで初期プラズマを変化させて実験を行った。 計測にはトムソンパラボラ(加速イオン)、X 線分光器(プラズマ密度・温度)を使用した。, 第38回 プラズマ・核融合学会 年会

Lithium fluoride (LiF) crystals and thin films have been successfully investigated as X-ray imaging detectors based on optical reading of visible photoluminescence emitted by stable radiation-induced F2 and F3 + colour centres. In this work, the visible photoluminescence response of optically-transparent LiF film detectors of three different thicknesses, grown by thermal evaporation on Si(100) substrates and irradiated with monochromatic 7 keV X-rays at several doses in the range between 13 and 4.5× 103 Gy, was carefully investigated by fluorescence optical microscopy. For all the film thicknesses, the photoluminescence response linearly depends on the irradiation dose in the investigated dose range. The lowest detected dose, delivered to the thinnest LiF film, only 0.5 μm thick, is estimated 13 Gy. Edge-enhancement imaging experiments, conducted by irradiating LiF film detectors at the same energy placing an Au mesh in front of them at a distance of 15 mm, allowed estimating a spatial resolution of (0.38 ± 0.05) μm, which is comparable to the microscope one. This very high spatial resolution in LiF film radiation detectors based on colour centres photoluminescence is combined with the availability of a wide field of view on large areas.

The application of fluorescent crystal media in wide-range X-ray detectors provides an opportunity to directly image the spatial distribution of ultra-intense X-ray beams including investigation of the focal spot of free-electron lasers. Here the capabilities of the micro- and nano-focusing X-ray refractive optics available at the High Energy Density instrument of the European XFEL are reported, as measured in situ by means of a LiF fluorescent detector placed into and around the beam caustic. The intensity distribution of the beam focused down to several hundred nanometers was imaged at 9 keV photon energy. A deviation from the parabolic surface in a stack of nanofocusing Be compound refractive lenses (CRLs) was found to affect the resulting intensity distribution within the beam. Comparison of experimental patterns in the far field with patterns calculated for different CRL lens imperfections allowed the overall inhomogeneity in the CRL stack to be estimated. The precise determination of the focal spot size and shape on a sub-micrometer level is essential for a number of high energy density studies requiring either a pin-size backlighting spot or extreme intensities for X-ray heating.