Unveiling Under-the-Barrier Electron Dynamics in Strong Field Tunneling

Area of Science:

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

Background:

• Quantum tunneling is a fundamental phenomenon extensively studied since quantum mechanics.
• Strong-field ionization is a key process in attosecond physics and laser spectroscopy.
• Freeman resonances (FR) are observed in strong-field ionization but require further theoretical explanation.

Purpose of the Study:

• To investigate nonadiabatic tunneling dynamics in strong-field ionization.
• To unravel the under-the-barrier-recollision mechanism leading to Freeman resonances.
• To experimentally validate predictions of the under-the-barrier-recollision model for FR phenomena.

Main Methods:

• Theoretical investigation of nonadiabatic tunneling in strong-field ionization.
• Experimental studies across a wide range of laser intensities.
• Analysis of photoelectron energy spectra to identify FR features.

Main Results:

• The under-the-barrier-recollision model explains distinct FR features beyond the direct multiphoton transition scenario.
• High-order FR dominance over above-threshold ionization was observed in photoelectron spectra.
• A flat dependence of the FR signal on laser intensity was confirmed in the nonadiabatic tunneling regime.

Conclusions:

• The experimental results corroborate the under-the-barrier-recollision model for Freeman resonances.
• This work provides deeper insights into the control of tunneling dynamics in laser-driven atomic processes.
• The findings contribute to advancements in laser spectroscopy and attosecond physics.