Controlling laser-dressed resonance line shape using attosecond extreme-ultraviolet pulse with a spectral minimum

Area of Science:

• Quantum optics
• Attosecond science
• Atomic physics

Background:

• High-harmonic generation produces extreme-ultraviolet (XUV) light with sharp spectral features.
• Shaped XUV pulses can be generated by spectral filtering, leading to attosecond pulse splitting.
• Cooper minima in atomic spectra are characterized by rapid phase variations.

Purpose of the Study:

• To theoretically investigate attosecond transient absorption (ATA) spectra of helium autoionizing states using shaped XUV pulses.
• To demonstrate the control of Fano line shapes using time-delayed infrared laser fields.
• To explore the potential for attosecond timescale control of atomic resonances.

Main Methods:

• Theoretical simulation of ATA spectra.
• Application of spectrally filtered, shaped isolated attosecond XUV pulses.
• Resonant excitation of helium autoionizing states coupled to dark states by infrared lasers.

Main Results:

• Asymmetric Fano line shapes were rapidly tuned into symmetric Lorentzian shapes within tens of attoseconds.
• Destructive interference during the excitation of the autoionizing state by shaped XUV pulses enabled this control.
• The simulated ATA spectral line shapes are predicted to be experimentally observable after propagation in a gas medium.

Conclusions:

• Shaped attosecond XUV pulses provide a powerful tool for controlling and probing narrow resonances on the few-ten attosecond timescale.
• This method offers significantly faster control over Fano resonance line shapes compared to previous femtosecond-scale techniques.
• The findings open new avenues for attosecond spectroscopy and the study of ultrafast dynamics in atomic systems.