Mid-infrared laser-driven broadband water-window supercontinuum generation from pre-excited medium

Area of Science:

• * Ultrafast laser science
• * Attosecond physics
• * Nonlinear optics

Background:

• * Supercontinuum generation is crucial for various spectroscopic applications.
• * The water window (2.3–4.4 nm) is important for biological imaging.
• * Generating broadband supercontinuum in the water window using mid-infrared pulses is challenging.

Purpose of the Study:

• * To theoretically investigate broadband water-window supercontinuum generation.
• * To understand the influence of pre-excited medium properties on supercontinuum generation.
• * To optimize conditions for generating high-quality attosecond pulses in the water window.

Main Methods:

• * Theoretical investigation using a single-atom model.
• * Simulation of macroscopic effects of intense phase-stabilized few-cycle 1.6 μm laser pulses.
• * Analysis of wavelength scaling of harmonic yield and macroscopic effects.

Main Results:

• * Wavelength scaling of harmonic yield found to be λ(-2.7) from 0.8 μm to 1.8 μm.
• * Broadband water window supercontinuum (approx. 140 eV) generated using a 1.6 μm laser pulse.
• * High initial excited state population leads to detrimental free electron generation, diminishing supercontinuum and degrading attosecond pulse quality.
• * Small initial excited state population enables well phase-matched XUV supercontinuum and a 100-as pulse (2.8 nm, 0.15 nJ).

Conclusions:

• * Controlling the initial excited state population is critical for efficient water-window supercontinuum generation.
• * Optimized conditions yield high-quality attosecond pulses in the water window.
• * This research provides a pathway for advanced applications in X-ray science and imaging.