Nonlinear Atomic Response to Intense Ultrashort X Rays
Abstract
The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of Ne9+ is observed at x-ray frequencies below the Ne8+, 1s2 absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of Ne8+ ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations.
- Publication:
-
Physical Review Letters
- Pub Date:
- February 2011
- DOI:
- 10.1103/PhysRevLett.106.083002
- Bibcode:
- 2011PhRvL.106h3002D
- Keywords:
-
- 32.80.Rm;
- 42.55.Vc;
- 42.65.Re;
- 52.59.-f;
- Multiphoton ionization and excitation to highly excited states;
- X- and gamma-ray lasers;
- Ultrafast processes;
- optical pulse generation and pulse compression;
- Intense particle beams and radiation sources