X-ray structures with nanometer-spatial resolution in ultraintense laser-plasma interactions

In the last years FELs have confirmed their exceptional capability for generating high-brightness and monochromatic x-ray beams1. Parallel to them new promising x-ray sources have emerged by using ultraintense laser interacting with relativistic plasma. Nowadays, the brightness of the x-ray beams produced by this novel configuration is still a few orders of magnitude lower than those generated by FELs. However, last experiments have demonstrated that high x-ray brightness can also be generated while establishing the basis for approaching values of present FELs in the next few years2,3. These experiments have additionally shown that the produced x-ray sources are in the region from tens to hundreds of nanometers in size and composed of multiple high order harmonics. Conventional reflective (e.g. Kirkpatrick-Baez elliptical mirror4) and refractive optics, used traditionally for focusing and confining x-ray beams into nanometer scale, require relatively long distances in order to achieve measurable magnifications. Besides, diffractive optics (e.g. Fresnel zone plates5) are only optimized for being used with monochromatic x-ray beams, like those produced by FELs. Thus, all these techniques might not be considered suitable due to the broad spectrum exhibited by the x-ray pulses in ultraintense laser-plasma interactions and the relative small-size chamber employed in this particular configuration.\nHere, we present an alternative technique to measure the spatial distribution of x-ray sources in ultraintense laser-plasma interactions with a few hundred nanometer resolution, enabling in addition not only the estimation of the source size but also its brightness. Using ray tracing and physical optics propagation, we optimized a setup for obtaining ~200 nm resolution with a spherical normal-incidence aperiodic (broadband) multilayer reflective mirror [6].\n[1] C. Pellegrini and J. Stohr, “X-ray free-electron lasers—principles, properties and applications,” Nuclear Instruments and Methods in Physics Research A, 500., 33-40 (2003).[2] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, P. Gallegos, H. Ahmed, E. N. Ragozin, A. Y. Faenov, T. A. Pikuz, T. Kawachi, A. Sagisaka, J. K. Koga, M. Coury, J. Green, P. Foster, C. Brenner, B. Dromey, D. R. Symes, M. Mori, K. Kawase, T. Kameshima, Y. Fukuda, L. Chen, I. Daito, K. Ogura, Y. Hayashi, H. Kotaki, H. Kiriyama, H. Okada, N. Nishimori, T. Imazono, K. Kondo, T. Kimura, T. Tajima, H. Daido, P. Rajeev, P. McKenna, M. Borghesi, D. Neely, Y. Kato, and S. V. Bulanov, “High order harmonics from relativistic electron spikes,” New Journal of Physics, 16., 093003 (2014).[3] A. S. Pirozhkov, M. Kando, T. Zh. Esirkepov, P. Gallegos, H. Ahmed, E. N. Ragozin, A. Y. Faenov, T. A. Pikuz, T. Kawachi, A. Sagisaka, J. K. Koga, M. Coury, J. Green, P. Foster, C. Brenner, B. Dromey, D. R. Symes, M. Mori, K. Kawase, T. Kameshima, Y. Fukuda, L. Chen, I. Daito, K. Ogura, Y. Hayashi, H. Kotaki, H. Kiriyama, H. Okada, N. Nishimori, T. Imazono, K. Kondo, T. Kimura, T. Tajima, H. Daido, P. Rajeev, P. McKenna, M. Borghesi, D. Neely, Y. Kato, and S. V. Bulanov, “Soft-X-Ray Harmonic Comb from Relativistic Electron Spikes,” Physical Review Letters, 108., 135004 (2012).[π] A. S. Pirozhkov, T. Zh. Esirkepov, T. A. Pikuz, A. Ya. Faenov, K. Ogura, Y. Hayashi, H. Kotaki, E. N. Ragozin, D. Neely, H. Kiriyama, J. K. Koga, Y. Fukuda, A. Sagisaka, M. Nishikino, T. Imazono, N. Hasegawa, T. Kawachi, P. R. Bolton, H. Daido, Y. Kato, K. Kondo, S. V. Bulanov, and M. Kando, "Burst intensification by singularity emitting radiation in multi-stream flows," Scientific Reports (accepted).[4] H. Mimura, S. Matsuyama, H. Yumoto, H. Hara, K. Yamamura, Y. Sano, M. Shibahara, K. Endo, Y. Mori, Y. Nishino, K. Tamasku, M. Yabashi, T. Ishikawa, and K. Yamauchi, “Hard X-ray Diffraction-Limited Nanofocusing with Kirkpatrick-Baez Mirrors,” Japanese Journal of Applied Physics, 44., L539 (2005).[5] H. M. Quiney, A. G. Peele, Z. Cai, D. Paterson, and K. A. Nugent, “Diffractive imaging of highly focused X-ray fields,” Nature Physics, 2., 101-104 (2006).[6] A. S. Pirozhkov and E. N. Ragozin, "Aperiodic multilayer structures in soft X-ray optics," Phys. Usp. 58, 1095-1105 (2015).OPIC-2018 (HEDS-2018