Direct Experimental Access to the Nonadiabatic Initial Momentum Offset upon Tunnel Ionization

Area of Science:

• Strong field physics
• Quantum mechanics
• Atomic, molecular, and optical physics

Background:

• Strong field tunneling ionization is a fundamental process in atomic physics.
• Understanding initial electron momentum distribution is crucial for probing ionization dynamics.
• Nonadiabatic effects play a significant role in strong field interactions.

Purpose of the Study:

• To investigate and experimentally control the nonadiabatic offset in electron momentum distribution.
• To explore the influence of laser field temporal evolution on nonadiabaticity.
• To establish a link between experimental observations and theoretical approximations.

Main Methods:

• Single ionization of argon using strong laser fields.
• Employing two-color counter- and corotating laser fields (390 and 780 nm).
• Utilizing single-color circularly polarized fields for comparison.
• Applying the strong-field approximation for theoretical analysis.

Main Results:

• The nonadiabatic offset is highly sensitive to the temporal evolution of the laser electric field.
• A straightforward experimental method for accessing the nonadiabatic offset using two-color fields is introduced.
• A donutlike electron momentum distribution shows an increasing radius with momentum in the light propagation direction for circularly polarized fields.
• Experimental results are accurately reproduced by the strong-field approximation.

Conclusions:

• The nonadiabatic offset in strong field ionization can be experimentally controlled.
• The temporal evolution of the laser field is a key factor determining the degree of nonadiabaticity.
• A mechanistic model connects the nonadiabatic offset to the magnetic quantum number of intermediate states.