Research
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Sub-Attosecond Pulses from Plasma Surfaces We observe in our numerical experiments the train of zeptosecond pulses produced by reflection of an relativistically intense intense femtosecond laser pulse from the oscillating boundary of an overdense plasma because of the Doppler effect.  The plasma-generated sub-attosecond pulses promise to become a unique experimental and technological tool since their length is of the order of the Bohr radius and the intensity is extremely high ~1019 W/cm2. The physical mechanism, analytical theory, and direct particle-in-cell simulations are presented in the publication We show that the harmonic spectrum is universal: the intensity of n-th harmonic scales as n-8/3for n<8g3 , where g is the largest relativistic g-factor of the electron fluid boundary. The subattosecond pulses originate from this universal spectrum. Coherent Harmonics Focusing Focusing of high harmonics produced by the reflection of a few femtosecond laser pulse from a concave plasma surface opens a new way towards unprecedentally high intensities. The key features allowing for boosting the focal intensity is the harmonic coherency and the small exponent of the power-law decay of the harmonic spectrum. Using the similarity theory and direct particle-in-cell simulations we find that the intensity at the Coherent Harmonic Focus (CHF) scales as ICHF ~ a03 I0, where a0 and I0~a02 are the dimensionless relativistic amplitude and intensity of the incident laser pulse.
The scaling suggests that due to the CHF, the Schwinger intensity limit can be achieved using lasers with I0 = 1022 W/cm2. The pulse duration at the focus scales as tCHF~a0-2 and reaches the subattosecond range.
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