Spin Polarization in Strong-Field Ionization as Sensor of Trapped Electron Orbits

Area of Science:

• Atomic Physics
• Quantum Mechanics
• Strong-Field Physics

Background:

• Strong-field ionization of noble gases typically results in photoelectrons rapidly escaping the ionic core.
• The spin-orbit interaction is expected to be short-range, leading to frozen spin polarization of escaping photoelectrons.
• Previous simulations with frozen spin polarization did not fully align with experimental measurements.

Purpose of the Study:

• To investigate the cause of discrepancies between experimental spin polarization measurements and theoretical simulations.
• To identify and characterize unexpected electron dynamics during strong-field ionization.
• To demonstrate the utility of photoelectron spin polarization as a probe for electron behavior.

Main Methods:

• Analysis of photoelectron spectra from strong-field ionization of noble-gas atoms using circularly polarized near-infrared fields.
• Detection of spin polarization of photoelectrons.
• Comparison of experimental results with theoretical models incorporating electron trapping near the ionic core.

Main Results:

• Clear evidence of electron spin flips observed in photoelectron spectra at low energies.
• Identification of highly unexpected electron orbits where photoelectrons are temporarily trapped near the ionic core.
• Explanation for the deviations between experimental spin polarization data and frozen-spin simulations.

Conclusions:

• Electron trapping near the ionic core leads to spin flips, challenging the frozen-spin approximation.
• Photoelectron spin polarization is a sensitive indicator of complex electron dynamics, including transient trapping.
• The findings necessitate revised theoretical models for strong-field ionization to account for electron-core interactions and unexpected orbits.