Parametric attosecond pulse amplification far from the ionization threshold from high order harmonic generation in He

Area of Science:

• Atomic Physics
• Quantum Optics
• Attosecond Science

Background:

• High-harmonic generation (HHG) is a key process for producing ultrashort X-ray pulses.
• Parametric amplification offers a route to enhance the intensity and control properties of these pulses.
• Previous studies have not achieved single-atom-level parametric amplification of attosecond pulses.

Purpose of the Study:

• To demonstrate parametric amplification of attosecond coherent pulses at the single-atom level.
• To investigate the underlying physics and attosecond dynamics of this amplification process.
• To explore methods for controlling the amplified photon energy.

Main Methods:

• Utilizing the 3D time-dependent Schrödinger equation for simulations.
• Modeling high-harmonic generation from excited states of Helium ions (He+).
• Analyzing the synchronization requirements between seed XUV pulses and the driving laser field.

Main Results:

• First demonstration of parametric amplification of attosecond coherent pulses at the single-atom level in He+.
• Identification of precise temporal synchronization for stimulated recombination as crucial for amplification.
• Observation that amplified photon energy is controllable by adjusting the laser field intensity.

Conclusions:

• Parametric amplification at the single-atom level is achievable for attosecond X-ray pulses.
• The process is highly sensitive to laser-electron synchronization, occurring in specific laser cycles.
• This work lays the foundation for developing compact, intense attosecond X-ray lasers.