Speaker
Description
The propagation of intense, ultrashort laser pulses in gases is characterized by complex, highly nonlinear processes such as strong-field ionization and multiphoton excitation. Strong field ionization using UV (260 nm) light is of particular interest for new applications such as in-situ injection of spin-polarized electron beams in plasma-accelerators by ionization of Xe atoms. We have used interferometric measurements of plasma densities of argon (Ar), krypton (Kr), and xenon (Xe) ionized by ultrashort linearly and circularly polarized laser pulses to validate strong-field ionization theories and numerical simulations. However, the UV laser pulses can also create excited atoms, which are difficult to distinguish from plasma using interferometry. Measured ionization rates match theory and simulation for long wavelengths (800 nm and 400 nm) but at shorter wavelengths (around ~260 nm), significant discrepancies are observed due to resonant multiphoton processes involving specific atomic excited states. The largest discrepancy is observed for argon and can be explained using theory and simulations which take into account individual multi-photon resonances. We use a combination of interferometry and absorption measurements to quantify the populations of free electrons and excited atoms and determine the role played by multiphoton-resonant bound states in the strong-field ionization process.
| Working group | WG3 |
|---|