Attosecond pulse walk-off in high-order harmonic generation.

Area of Science:

• Quantum optics
• Attosecond science
• Nonlinear optics

Background:

• High-order harmonic generation (HHG) is a key process for producing ultrashort light pulses.
• Understanding factors influencing pulse characteristics, like group delay, is crucial for advanced applications.
• Gas dispersion significantly impacts light propagation and pulse dynamics in HHG.

Purpose of the Study:

• To investigate how generation conditions influence the group delay of attosecond pulses.
• To elucidate the role of gas pressure and medium dispersion in shaping attosecond pulse timing.
• To validate theoretical models against experimental observations of group delay.

Main Methods:

• Experimental generation of attosecond pulses via high-order harmonic generation in gases.
• Systematic variation of gas pressure within the generation cell.
• Theoretical modeling using an on-axis phase-matching approach for HHG in absorbing media.

Main Results:

• Group delay of attosecond pulses relative to the fundamental field decreases as gas pressure increases.
• This decrease is attributed to temporal walk-off caused by the nonlinear medium's dispersive properties.
• The observed trend in group delay is accurately reproduced by the phase-matching model.

Conclusions:

• Gas pressure is a critical generation condition affecting attosecond pulse group delay.
• The dispersive properties of the nonlinear medium play a dominant role in temporal walk-off.
• The on-axis phase-matching model provides a reliable framework for predicting HHG dynamics, including group delay.