Above-Threshold Ionization of Quasiperiodic Structures by Low-Frequency Laser Fields

Area of Science:

• Quantum mechanics
• Atomic, molecular, and optical physics
• Solid-state physics

Background:

• Photoelectron spectroscopy is crucial for understanding electron behavior.
• Laser-induced phenomena in periodic potentials are complex.
• The Kronig-Penney model provides a simplified yet effective framework for studying electron dynamics in periodic structures.

Purpose of the Study:

• To theoretically investigate photoelectron cutoff changes in periodic structures under infrared laser fields.
• To analyze the influence of laser intensity and potential periodicity on electron ionization spectra.
• To elucidate the underlying physics of nonperturbative ionization regimes and energy cutoff increases.

Main Methods:

• Solving the time-dependent Schrödinger equation for a one-dimensional Kronig-Penney potential with a finite number of wells.
• Calculating electron spectra for varying numbers of potential wells and laser intensities.
• Employing an analytical approach based on exact solutions of the full Hamiltonian in a periodic potential.

Main Results:

• A photoelectron energy plateau emerges rapidly as the periodic potential is established, even at moderate laser intensities (10 TW/cm²).
• Increasing laser intensity from 10 to 30 TW/cm² significantly enhances ionization yield and the accessible energy range.
• Efficient population transfer between energy bands occurs when Bloch and laser frequencies are comparable, predicting the nonperturbative ionization regime.

Conclusions:

• The study provides a theoretical model for understanding laser-induced photoelectron cutoff changes in periodic potentials.
• The findings explain the observed increase in photoelectron energy cutoff at moderate laser intensities.
• The research offers quantitative predictions for the intensity ranges governing nonperturbative ionization dynamics.