Electron Vortices in Femtosecond Multiphoton Ionization

Area of Science:

• Atomic and molecular physics
• Quantum optics
• Ultrafast laser science

Background:

• Multiphoton ionization is a fundamental process in atomic physics.
• Femtosecond laser pulses enable the study of ultrafast electron dynamics.
• Electron vortex momentum distributions offer insights into ionization mechanisms.

Purpose of the Study:

• To investigate electron vortex formation in potassium atoms using shaped femtosecond laser pulses.
• To analyze the influence of pulse polarization on photoelectron momentum distributions.
• To explore the relationship between ionization regime and vortex symmetry.

Main Methods:

• Utilizing a sequence of two counter-rotating circularly polarized femtosecond laser pulses.
• Employing polarization shaping to generate specific pulse sequences.
• Reconstructing three-dimensional photoelectron momentum distributions via velocity map imaging.

Main Results:

• Observed vortex-shaped photoelectron momentum distributions forming Archimedean spirals.
• Demonstrated c_{6} rotational symmetry for electron vortices under perturbative ionization.
• Showcased a transition from c_{6} to c_{4} rotational symmetry in the nonperturbative regime.

Conclusions:

• Shaped femtosecond laser pulses can precisely control electron vortex formation.
• The rotational symmetry of electron vortices is sensitive to the ionization regime.
• This work provides a new pathway to study light-matter interactions with tailored electron beams.