Frequency-sheared, time-delayed extreme-ultraviolet pulses produced by high-harmonic generation in argon

Area of Science:

• Quantum optics
• Laser physics
• Atomic physics

Background:

• High-harmonic generation (HHG) is a crucial nonlinear process for producing extreme ultraviolet and X-ray photons.
• Understanding the relationship between driving laser parameters and harmonic properties is essential for controlling HHG output.
• Previous studies have explored various methods to manipulate HHG, but precise control over frequency-sheared harmonics remains an active area of research.

Purpose of the Study:

• To demonstrate the production of frequency-sheared high harmonics in argon.
• To establish a direct correlation between the driving femtosecond laser pulse's envelope and chirp and the resulting harmonic properties.
• To validate experimental findings using theoretical models.

Main Methods:

• Utilizing a femtosecond laser system to generate driving pulses with controlled envelope and chirp.
• Performing high-harmonic generation experiments in an argon gas medium.
• Analyzing the generated high harmonics to characterize their spectral properties.
• Employing the three-step model of high-harmonic generation for theoretical analysis.
• Conducting simulations of the single-atom response within the strong-field approximation framework.

Main Results:

• Successfully produced frequency-sheared high harmonics in argon.
• Established a clear link between the laser pulse's temporal characteristics (envelope and chirp) and the spectral features of the generated harmonics.
• Experimental results were found to be in good agreement with the predictions of the three-step model and single-atom simulations.
• Demonstrated that controlling the driving pulse allows for tailoring the properties of the emitted high harmonics.

Conclusions:

• The envelope and chirp of the femtosecond driving laser pulse are critical parameters for controlling frequency-sheared high harmonics.
• The three-step model provides a reliable framework for understanding and predicting HHG in this regime.
• This work offers a pathway for generating tailored high-harmonic radiation for various applications.