Carrier-envelope phase-dependent molecular high-order harmonic generation from H2+ in a multi-cycle regime

Area of Science:

• Quantum Dynamics
• Attosecond Science
• Molecular Physics

Background:

• High-order harmonic generation (HHG) is a key process in strong-field physics.
• Understanding the influence of laser parameters like carrier-envelope phase (CEP) is crucial for controlling HHG.
• Investigating molecular systems like H2+ offers insights into correlated electron-nuclear dynamics.

Purpose of the Study:

• To investigate the carrier-envelope phase (CEP) dependence of high-order harmonic generation (HHG) in H2+.
• To elucidate the underlying mechanism of CEP-dependent frequency modulation (FM) in multi-cycle laser pulses.
• To explore the potential of CEP-dependent FM for probing ultrafast molecular dynamics.

Main Methods:

• Solving the non-Born-Oppenheimer time-dependent Schrödinger equation (TDSE).
• Analyzing classical electron trajectories.
• Performing time-frequency analysis of HHG spectra.
• Utilizing a simplified time-domain algorithm for confirmation.

Main Results:

• High harmonics in the plateau show counterintuitive frequency modulation (FM) with varying CEP.
• CEP-dependent FM arises from the interference of half-cycle HHG radiations.
• Laser-driven nuclear motion modulates this interference pattern.
• A simplified algorithm successfully reproduces TDSE results, confirming the mechanism.

Conclusions:

• The carrier-envelope phase (CEP) dependence of HHG in H2+ is governed by laser-driven nuclear motion.
• CEP-dependent FM provides a novel pathway to study electron-nuclear dynamics.
• This phenomenon enables probing nuclear motion with attosecond resolution.