Dispersion limits for attosecond coherent synchrotron emission

Abstract

Attosecond coherent synchrotron emission from relativistic plasma surfaces is a promising route to intense UV and X-ray bursts that can be transmitted through solid-density targets without external spectral filtering. In this work, we demonstrate that the same overdense plasma responsible for attosecond radiation generation also imposes a strong dispersion limit on the usable target thickness. One- and two-dimensional particle-in-cell simulations combined with a simple wave-propagation model are employed to quantify the dispersion-induced temporal broadening and the chirp of transmitted attosecond pulses. Compact scaling laws are derived as functions of plasma density, target thickness, and effective harmonic order and are formulated as an accumulated-dispersion criterion that determines the conditions under which the attosecond temporal structure is lost. These results provide practical design rules for plasma-based attosecond sources and plasma-optics elements, such as attosecond plasma lenses, by defining the maximum target thickness compatible with sub-femtosecond pulse delivery.