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Ultra-high intensities open a way towards Terawatt and potentially Petawatt gamma-ray pulses in the so called Gamma Flare regime. We performed our first experiment towards this regime with the J-KAREN-P laser operating at intensities close to 10^22 W/cm^2. In this presentation I will overview the experiment, including very bright hard x-ray generation (sub-MeV to a few-MeV spectral range), high-order harmonic generation (30 to 70 eV), and multiple additional diagnostics revealing information on preplasma (properties of reflected 1st, 2nd, and 3rd harmonics and back-reflection). I will compare these results with the integrated HD and PIC simulations., OPTO-2021 Symposium on Photon and Beam Science

We describe our experiment performed with the J-KAREN-P laser at the intensity approaching 10^22 W/cm^2. In particular, we present the results obtained with hard x-ray (0.1-3 MeV) spectrographs comprising 10 scintillators and a method to reconstruct the x-ray spectra., 3rd International Conference on Nuclear Photonics (NP2020)

We present multi-diagnostic results from laser-plasma experiment at ~10^22 W/cm^2, including optical and high-order harmonics, back-reflection, soft x-rays, keV x-rays, and sub-MeV to MeV x-rays, simultaneously with important laser parameters. We discuss methods to find at-focus target position and compare intensity dependences., OPTICS & PHOTONICS International Congress 2021

Generation of bright sources of hard and soft x-rays is one of the most promising applications of high-power lasers. We report on our first experiment on achieving ultra-high on-target intensities, reaching efficient conversion of laser radiation to hard x-rays (towards the "Gamma Flash" regime [1-3]), and generating intense high-order harmonics [4]. Our international team (Japan, Czech Republic, Russia, UK) used the J-KAREN-P laser facility at KPSI QST, Japan [5-8] and irradiated solid targets with intensities close to 1022 W/cm2. We employed a broad range of diagnostics, including laser, plasma, secondary radiation (from NIR to MeV x-rays) and particle (e-, p+) diagnostics, and controlled the preplasma scale length, which is a critical parameter for both hard x-ray [1,3] and harmonic generation [4]. Here we overview the experiment and dedicated simulations, and show first results on hard x-ray and harmonic generation, x-ray spectroscopy, and preplasma analysis. We thank the J-KAREN-P laser operation group. We acknowledge financial support from ELI-Beamlines, High Field Initiative Project (CZ.02.1.01/0.0/0.0/15\_003/0000449) from the European Regional Development Fund, JSPS JP 17F17811 and 19H00669, QST-IRI, and QST Director Funds 創成的研究#16 and #20. [1]T. Nakamura, et al., Phys. Rev. Lett., 2012, 108 195001. [2]C. P. Ridgers, et al., Phys. Rev. Lett. 2012, 108, 165006. [3]K. V. Lezhnin, P. V. Sasorov, G. Korn, and S. V. Bulanov, Phys. Plasmas, 2018, 25, 123105. [4]U. Teubner and P. Gibbon, Rev. Mod. Phys., 2009, 81, 445. [5]A. S. Pirozhkov, et al., Opt. Express, 2017, 25, 20486. [6]H. Kiriyama, et al., Opt. Lett., 2018, 43, 2595. [7]H. Kiriyama, et al., Opt. Lett., 2020, 45, 1100. [8]H. Kiriyama, et al., Crystals., 2020, 10, 783., International Conference on X-Ray Laser 2020

We present an overview of our recent experiment on achieving ultra-high on-target intensities, reaching efficient conversion of laser radiation to hard x-rays ("Gamma Flash"), and generating intense coherent soft x-rays (high-order harmonics). Our international team used the J-KAREN-P laser facility at KPSI QST and irradiated solid targets with intensities close to 1022 W/cm2. We employed a broad range of diagnostics, including laser, plasma, secondary radiation (from NIR to MeV x-rays) and particle (e-, p+) diagnostics, and controlled preplasma using several laser contrast modes and artificial prepulse. In this presentation we overview the experiment and simulations dedicated to it, and show first results on hard x-ray and harmonic generation, x-ray spectroscopy, and preplasma analysis., Opto-2020 Symposium on Photon and Beam Science

We performed our first experiment on achieving ultra-high on-target intensities, reaching efficient conversion of laser radiation to hard x-rays ("Gamma Flash"), and generating intense coherent soft x-rays (high-order harmonics). Our joint team used the J-KAREN-P laser facility inat KPSI QST and irradiated solid targets with intensities close to 1022 W/cm2. We employed a broad range of diagnostics, including laser, plasma, secondary radiation (from NIR to MeV x-rays) and particle (e-, p+) diagnostics, and controlled preplasma using several laser contrast modes and artificial prepulse. In this presentation we overview the experiment and simulations dedicated to it, and show first results on hard x-ray and harmonic generation, x-ray spectroscopy, and preplasma analysis., 2020 Autumn JPS Meeting

Efficient generation of ~MeV x-rays in the Gamma Flare regime [1],[2] in preplasma via the nonlinear Thomson/inverse Compton scattering mechanism [3] is one of the most promising and expected high-power laser applications. The hard x-rays are generated by Bremsstrahlung as well, while the electrons go through the target [4],[5], which also includes multiple passes (refluxing) [5],[6]. Simulations predict that at high intensities the preplasma x-rays dominate; however, at intensities available now, Bremsstrahlung dominates, so that the Gamma Flare mechanism is not yet demonstrated experimentally. We describe our experiment performed with the J-KAREN-P laser [7]-[9], with the emphasis on data from the scintillator-based hard x-ray spectrographs [10] (0.1 – 1 MeV) and Compton spectrograph [11] (2 – 10 MeV), and our efforts to distinguish the generation mechanism. We thank the J-KAREN-P laser operation group. We acknowledge financial support from ELI-Beamlines, JSPS JP 19H00669, and QST Director Funds 創 成的研究 16 and 創成的研究 20. [1] T. Nakamura, et al., "High-Power γ-Ray Flash Generation in Ultraintense Laser-Plasma Interactions," Phys. Rev. Lett. 108, 195001 ( 2012). [2] C. P. Ridgers, et al., "Dense Electron-Positron Plasmas and Ultraintense γ rays from Laser-Irradiated Solids," Phys. Rev. Lett. 108, 165006 (2012). [3] K. V. Lezhnin, P. V. Sasorov, G. Korn, and S. V. Bulanov, "High power gamma flare generation in multi-petawatt laser interaction with tailored targets," Phys. Plasmas 25, 123105 (2018). [4] D. Wu, et al., "Characteristics of X/γ-ray radiations by intense laser interactions with high-Z solids: The role of bremsstrahlung and radiation reactions," Matter Rad. Extremes 3, 293-299 (2018). [5] J. Vyskočil, O. Klimo, S. Weber, "Simulations of bremsstrahlung emission in ultra-intense laser interactions with foil targets," Plasma Phys. Control. Fusion 60, 054013 (2018). [6] D. R. Rusby, et al., "Effect of rear surface fields on hot, refluxing and escaping electron populations via numerical simulations," High Pow. Las. Sci. Eng. 7, e45 (2019). [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). [9] H. Kiriyama, et al., "Experimental investigation on temporal contrast of pre-pulses by post-pulses in a petawatt laser facility," Opt. Lett. (accepted). [10] D. R. Rusby, et al., "Novel scintillator-based x-ray spectrometer for use on high repetition laser plasma interaction experiments," Rev. Sci. Instr. 89, 073502 (2018). [11] S. Singh, et al., "Compact high energy x-ray spectrometer based on forward Compton scattering for high intensity laser plasma experiments," Rev. Sci. Instr. 89, 085118 (2018)., OPTICS & PHOTONICS International Congress 2020

New regime of high-order harmonic generation by relativistic-irradiance multi-TW fs lasers focused onto gas jet targets is discussed. The laser induces multi-stream relativistic plasma flow resulting in the formation of density singularities. Here we analyse the dependence of harmonic yield on the focal spot quality and derive the required laser parameters for efficient harmonics generation.

By using of high-resolution X-ray spectroscopic measurements and kinetic simulations, we demonstrate that the energy of femtosecond laser pulses is efficiently converted to X-ray radiation and produces exotic states in solid density plasma regions. It is shown that exotic hollow multicharged ions states can be obtained and studied not only by ultra-intense X-ray radiation of XFEL, but also upon using optical laser technology. We have concluded that observable features of the hollow-ion spectra are sensitive to such plasma parameters as density, temperature, hot-electron fraction, and intensity of X-ray pumping radiation and could be used for effective diagnostics of warm dense matter parameters.

Recent progress made in the development of coherent x-ray sources and their applications in material science and laser processing in the National Institutes for Quantum and Radiological Science and Technology (QST) is presented herein. The upgrade of Ti:Sapphire laser for a grazing incidence pumping (GRIP) scheme was started, to further develop a coherent x-ray source. Investigating the applications of x-ray lasers, we observed temporal evolution of metal surface ablation using an x-ray laser probe, and the damage to an EUV mirror structure by the x-ray pulse irradiation.

Burst Intensification by Singularity Emitting Radiation (BISER) is a new mechanism of bright coherent x-ray generation employing high-power femtosecond lasers to drive singularities of multi-stream relativistic plasma flows. We have recently demonstrated that the BISER source can be controlled and stabilized with a tailored plasma density profile (density jump), which is created with a blade inserted into the supersonic gas flow. In this presentation we report on new experimental results obtained with the upgraded J-KAREN-P laser. In particular, we extended the BISER emission up to keV photon energies, and increased the BISER yield in the 60 to 100 eV spectral range up to ~ 1 uJ (10^11 photons) per pulse into the detector acceptance angle of 10^-2 sr., The 11th International Conference of Inertial Fusion Sciences and Applications (IFSA-2019)

我々は、レーザーを “球形”の物質に照射した場合に、球表面に発生した衝撃波が球の 中心に向かって伝播・収束する過程でその強度が増強され、この増強された衝撃波により、 サブ GeV(約 300 MeV、光速の 70 %)の準単色(ΔE/E=10 %)・高指向性(発散角=5°)の 陽子線が生成するという、CSBA(Convergence Shock induced Blow-off Acceleration)と して参照する衝撃波加速の原理に基づく新現象を大型計算機シミュレーションにより発見 した。 また、我々は、この新現象を実験で検証するためのマイクロメートルスケールの水素ク ラスターを生成させる独自技術を確立している。本講演では、量研関西研が所有する J-KAREN-P レーザーを用いて実施した CSBA の原理検証実験で観測された 23 MeV 準単 色陽子加速の詳細について報告する。, 日本物理学会2019年秋季大会

We discovered a new higher order harmonic generation mechanism induced by high power femtosecond laser pulses propagating in underdense plasma. Experimentally it has been shown to be extremely bright, spatially and temporally coherent. Particle-in-cell simulations and Catastrophe theory have explained it as the generation behind the propagating laser pulse of structurally stable oscillating electron spikes at the intersection point between the wake wave and bow wave. Simulations show that the radiation emitted is of attosecond duration. This mechanism has been generalized to explain the emission of waves from a variety of media having multi-stream flows and has been named Burst Intensification by Singularity Emitting Radiation (BISER). It has been proposed that multi-stream space plasmas in relativistic cosmic jets around compact massive objects could produce extremely bright electromagnetic bursts, i.e. GRBs, FRB’s and gravitational radiation. We will present an overview of the BISER mechanism, latest experimental results using the J-KAREN-P laser showing controllability, and brief descriptions of its applications and possible relation to stellar objects., 28th ANNUAL INTERNATIONAL LASER PHYSICS WORKSHOP

Recently we successfully demonstrated controllable BISER in experiments with the J-KAREN-P laser using blade-induced shocks in supersonic gas jets. This resulted in significant improvement of the BISER source stability. Furthermore, the controllable BISER technique made an important breakthrough in the coherent x-ray source performance: the emission extended up to the keV spectral region. Additionally, the soft x-ray and XUV photon yield enhanced by orders of magnitude. In particular, we demonstrated a pulse with up to 1 uJ energy (10^11 photons) in the 60-100 eV spectral range within a 10^-2 sr acceptance angle., VII International Conference "Frontiers of Nonlinear Physics"

We describe new experimental results obtained with the recently upgraded J-KAREN-P laser. The controllable BISER technique enabled us the demonstration of an important breakthrough in the coherent x-ray source performance: the x-ray source position was stabilized, and the emission extended up to the keV spectral region. Additionally, the photon yield enhanced by an order of magnitude resulting in up to 1 µJ pulse (10^11 photons) in the 60-100 eV spectral range within a 10^-2 sr acceptance angle., OPTO-2019

In this study, we have succeeded in observation of the transient surface nano-structures in femto-second laser ablation process of metals by using the laser plasma soft x-ray laser probe., Laser Solutions for Space and the Earth 2019

We overview our research on relativistic optics and BISER discovery and the reasons why it was overlooked for more than four decades, including the required driving laser parameters., International Workshop on Radiation Plasma Diagnostics In memory of Professor Anatoly Ya. Faenov

We describe properties of the BISER coherent attosecond x-ray source derived from our experiments and PIC simulations., International Workshop "Complex Systems of Charged Particles and Their Interactions with Electromagnetic Radiation" CSCPIER-2019

We describe new experimental results obtained with the recently upgraded J-KAREN-P laser, including this BISER control technique. We achieved break-through in the BISER coherent x-ray source performance, detected the BISER emission in the keV spectral region, and obtained an order of magnitude enhancement of the photon yield resulted in up to 1uJ pulse, 10^11 photons in the 60-100 eV spectral range within a 10^-2 sr acceptance angle., The 74th JPS Annual Meeting