Core relaxation in atomic ultrastrong laser field ionization

Area of Science:

• Atomic Physics
• Quantum Mechanics
• Laser-Matter Interactions

Background:

• Understanding atomic ionization dynamics is crucial for various fields, including attosecond science and high-harmonic generation.
• The single active electron (SAE) model is often used to describe atomic ionization but requires specific conditions for validity.
• Investigating ionization in the transition from nonrelativistic to relativistic laser intensities probes the limits of theoretical models.

Purpose of the Study:

• To investigate atomic ionization dynamics in Krypton (Kr) at laser intensities ranging from 10^16 to 10^18 W/cm^2.
• To assess the applicability of the single active electron (SAE) description under intense laser fields.
• To examine transient core polarization and alignment effects during inner-shell ionization.

Main Methods:

• Measurement of highly charged ion yields from Kr inner shells.
• Analysis of ionization dynamics in the transition regime from nonrelativistic to relativistic laser intensities.
• Focus on the role of core relaxation and magnetic quantum number dependence in ionization rates.

Main Results:

• Experimental data indicate that internal m-mixing processes are sufficiently fast.
• These rapid m-mixing processes effectively erase transient core polarization.
• The findings are observed for intense laser pulses with a 40 fs pulse width.

Conclusions:

• The single active electron (SAE) description's applicability is limited by transient core effects.
• Fast m-mixing processes in Kr prevent the buildup of core polarization under specific intense laser conditions.
• This research provides insights into the complex dynamics of atomic ionization at extreme laser intensities.