Attosecond chirp compensation in water window by plasma dispersion.

Compensating attosecond chirp (atto-chirp) of broadband high-order harmonic pulses in the water window region (282 to 533 eV) is a major challenge, due to the lack of natural materials that exhibit negative group velocity dispersion and low loss. Analysis shows that the amount of dispersion of fully ionized hydrogen plasma with suitable density-length product is sufficient to compensate the chirp of attosecond pulses with center photon energy above 300 eV. This is confirmed by numerical simulations based on the Strong Field Approximation.