Cascaded harmonic generation from a fiber laser: a milliwatt XUV source

Area of Science:

• Strong field physics
• Attosecond science
• Laser physics

Background:

• Femtosecond ytterbium-doped fiber lasers offer advancements in strong field physics.
• High-order harmonic generation (HHG) produces high-flux ultrashort extreme ultraviolet (XUV) radiation.
• Optimizing macroscopic parameters is crucial for efficient HHG.

Purpose of the Study:

• Investigate enhancing the single-atom response in HHG.
• Explore HHG driven by multiple harmonics of a femtosecond Yb-fiber laser.
• Determine optimal driving harmonic for efficient XUV generation.

Main Methods:

• Utilized a 50 W, 166 kHz femtosecond Yb-fiber laser system.
• Generated high-order harmonics from the second, third, and fourth harmonics of the fundamental laser output.
• Measured photon flux and average power of generated XUV radiation in argon.

Main Results:

• Harmonic efficiency was found to be optimal when driven by the third harmonic.
• Achieved 6.6 ± 1.3 × 10¹⁴ photons/s at 18 eV in argon.
• This corresponds to an average power of 1.9 ± 0.4 mW.

Conclusions:

• The third harmonic of the Yb-fiber laser provides optimal driving conditions for HHG.
• This method enhances the single-atom response for efficient XUV generation.
• Demonstrated a viable pathway for producing high-flux ultrashort XUV radiation.