Proceedings Article | 6 October 2011
A. Pirozhkov, M. Kando, T. Zh. Esirkepov, P. Gallegos, H. Ahmed, E. Ragozin, A. Ya. Faenov, T. Pikuz, J. Koga, H. Kiriyama, P. McKenna, M. Borghesi, K. Kondo, H. Daido, Y. Kato, D. Neely, S. Bulanov
Proc. SPIE. 8140, X-ray Lasers and Coherent X-ray Sources: Development and Applications IX
KEYWORDS: Diffraction, Mirrors, Spectrographs, Polarization, X-rays, Reflectivity, Extreme ultraviolet, Charge-coupled devices, Pulsed laser operation, Plasma
We present experimental results, theory, and simulations demonstrating two novel sources of coherent X-ray radiation
generated in the relativistic laser (>1018W/cm2) interaction with easily accessible, repetitive, and debris-free gas jet
targets. The first source is based on a relativistic mirror reflecting a counter-propagating laser pulse. A strongly nonlinear
breaking wake wave driven by an intense laser pulse can act as a semi-transparent relativistic flying mirror. Such a
mirror directly converts counter-propagating laser light into a high-frequency (XUV or X-ray) ultrashort pulse due to the
double Doppler effect. In the experimental demonstration with the 9 TW J-KAREN laser, the flying mirror generated in
a He gas jet partially reflected a 1 TW pulse, providing up to ~1010 photons, 60 nJ (~1012 photons/sr) in the XUV range
(12.8-22 nm). The second source is demonstrated with the laser power ranging from 9 to 170 TW in experiments with
the J-KAREN and Astra Gemini lasers. The odd and even order harmonics generated by linearly as well as circularly
polarized pulses are emitted forward out of the gas jet. The 120 TW laser pulses produce harmonics with ~3×1013photons/sr (~600 μJ/sr) in the 120±5 eV spectral range. The observed harmonics cannot be explained by previously
known mechanisms (atomic harmonics, betatron radiation, nonlinear Thomson scattering, etc.). We introduce a novel
mechanism of harmonic generation based on the relativistic laser-plasma phenomena (self-focusing, cavity evacuation,
bow wave generation), mathematical catastrophe theory which explains the formation of structurally stable electron
density singularities, spikes, and collective radiation of a compact charge driven by a relativistic laser.