Classical aspects in above-threshold ionization with a midinfrared strong laser field

Area of Science:

• Atomic Physics
• Quantum Mechanics
• Laser Physics

Background:

• Above-threshold ionization (ATI) is a fundamental process in strong-field physics.
• Existing theoretical models, like the simple-man theory, do not fully explain experimental observations in all regimes.
• Mid-infrared lasers offer unique parameters for exploring ATI phenomena.

Purpose of the Study:

• To investigate high-resolution photoelectron energy spectra of noble gas atoms under high-intensity ATI.
• To explore the influence of mid-infrared wavelengths on ATI spectra.
• To understand unexpected structures observed in the low-energy portion of the spectra.

Main Methods:

• High-resolution photoelectron spectroscopy.
• High-intensity above-threshold ionization (ATI) experiments.
• Semiclassical model calculations.

Main Results:

• High-resolution photoelectron energy spectra of noble gas atoms were obtained using mid-infrared laser wavelengths.
• An unexpected low-energy structure was observed in the spectra, contradicting predictions from the simple-man theory.
• Semiclassical model calculations successfully reproduced the experimental feature.

Conclusions:

• The observed low-energy structure in ATI spectra is attributed to the Coulomb interaction between the outgoing electron and the parent ion.
• This Coulomb interaction plays a significant role in shaping photoelectron spectra at long laser wavelengths.
• The findings necessitate refinements to theoretical models for describing ATI processes, particularly in the long-wavelength regime.