Ionization by relativistically intense short laser pulses is studied in theframework of strong-field quantum electrodynamics. Distinctive patterns arefound in the energy probability distributions of photoelectrons. Except of thealready observed patterns, which were studied in Phys. Rev. A {\bf 94}, 013402(2016), we discover an additional interference-free smooth supercontinuum inthe high-energy portion of the spectrum, reaching tens of kiloelectronovolts.As we show, the latter is sensitive to the driving field intensity and it canbe detected in a narrow polar-angular window. Once these high-energy electronsare collected, they can form solitary attosecond pulses. This is particularlyimportant in light of various applications of attosecond electron beams such asin ultrafast electron diffraction and crystallography, or in time-resolvedelectron microscopy of physical, chemical, and biological processes.
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机译：在强场量子电动力学的框架内研究了相对论强短激光脉冲的电离。在光电子的能量概率分布中发现了独特的模式。除了已经观察到的模式以外，在Phys。 Rev. A {\ bf 94}，013402（2016），我们在光谱的高能部分发现了一个额外的无干扰的平滑超连续谱，达到数十千电子伏特。如我们所示，后者对驱动场强度敏感并且可以在狭窄的极角窗口中检测到它。一旦收集了这些高能电子，它们就可以形成孤立的阿秒脉冲。鉴于超音速电子束的各种应用，例如超快电子衍射和晶体学，或物理，化学和生物学过程的时间分辨电子显微镜，这尤其重要。
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