# Characterization of attosecond pulses in the soft x-ray regime

## TL;DR

This paper discusses the challenges of characterizing attosecond x-ray pulses, focusing on inner-shell ionization effects, and proposes adaptations to existing methods for reliable pulse reconstruction in the soft x-ray regime.

## Contribution

It introduces modifications to a pulse characterization method to account for inner-shell ionization and secondary processes in the x-ray regime.

## Key findings

- Inner-shell ionization causes delay-dependent modulations.
- Secondary processes affect pulse reconstruction accuracy.
- Modified method improves reliability of x-ray pulse characterization.

## Abstract

Attosecond x-ray pulses offer unprecedented opportunities for probing and triggering new types of ultrafast motion. At the same time, pulse characterization of x-rays presents new challenges that do not exist in the UV regime. Inner-shell ionization is the dominant ionization mechanism for x-rays and it is followed by secondary processes like fluorescence, Auger decay, and shake-up.In general, we find that inner-shell ionization and secondary processes can create additional delay-dependent modulations that will affect pulse reconstruction schemes. Our recently proposed pulse characterization method [Pabst and Dahlstr\"om, PRA 94, 013411 (2016)], where a bound electron wavepacket is sequentially photoionized by the attosecond pulse, can be adapted to mitigate the impact of these effects, thus opening up an avenue for reliable pulse reconstruction in the x-ray regime.