Resonance enhanced high-order harmonic generation in H2+ by two sequential laser pulses

Area of Science:

• Quantum Optics
• Attosecond Science
• Molecular Physics

Background:

• High-order harmonic generation (HHG) is a fundamental process for producing coherent extreme ultraviolet and X-ray radiation.
• Optimizing HHG efficiency and controlling the harmonic spectrum are crucial for advanced applications.
• Molecular hydrogen ions (H2+) offer unique properties for studying HHG dynamics.

Purpose of the Study:

• To investigate the enhancement of high-order harmonic generation in H2+ using a two-sequential-laser-pulse scheme.
• To explore the extension of the harmonic cutoff and the increase in harmonic efficiency.
• To assess the feasibility of generating water window radiation via this method.

Main Methods:

• Solving the time-dependent Schrödinger equation for H2+ under the influence of two laser pulses.
• Employing a pump-probe configuration with an 800-nm pulse and a time-delayed 1600-nm pulse.
• Analyzing the effects of pulse intensity, wavelength, and time delay on HHG

Main Results:

• The two-pulse scheme significantly extends the harmonic cutoff compared to a single 1600-nm pulse.
• Harmonic efficiency is enhanced by 2-3 orders of magnitude.
• Charge-resonance-enhanced ionization, steered by the 800-nm pump pulse, is identified as the key mechanism for enhancement.
• The scheme shows potential for efficient HHG in the water window region by using longer wavelength probe pulses.

Conclusions:

• The presented two-color laser pulse scheme offers a powerful method for optimizing high-order harmonic generation in H2+.
• This approach enables significant control over harmonic cutoff extension and efficiency enhancement.
• The findings pave the way for generating specific wavelength ranges, such as the water window, for advanced spectroscopic applications.