Intra-oscillator high harmonic source reaching 100-eV photon energy.

Area of Science:

• Nonlinear Optics
• Laser Physics
• Attosecond Science

Background:

• Optical cavities enhance nonlinear optical conversion, crucial for X-ray generation.
• Passive enhancement cavities have enabled high repetition rate XUV sources for spectroscopy and nuclear clock development.
• Mode-locked lasers offer a single-stage alternative to passive cavities, potentially improving efficiency.

Purpose of the Study:

• To investigate the potential of an intra-oscillator approach for high harmonic generation (HHG) X-ray sources.
• To compare the performance of intra-oscillator HHG with passive enhancement cavities and single-pass systems.
• To demonstrate high XUV flux generation at a relevant repetition rate and wavelength for industrial applications.

Main Methods:

• Utilizing a mode-locked thin-disk laser oscillator for intra-cavity high harmonic generation.
• Operating the system at a 17 MHz repetition rate to generate photon energies between 60 eV and 100 eV.
• Characterizing the generated XUV flux and average power at specific harmonic orders, including 13.5 nm.

Main Results:

• The intra-oscillator approach surpassed passive enhancement cavities in XUV flux.
• Achieved XUV flux comparable to single-pass systems using chirped-pulse fiber amplifiers.
• Generated 60 nW of average power per harmonic order at the 13.5 nm wavelength (60-100 eV photon energy range).

Conclusions:

• The intra-oscillator HHG approach offers a simplified and highly efficient single-stage alternative to passive cavities.
• This method demonstrates superior performance in terms of XUV flux, making it suitable for demanding applications.
• The generated XUV radiation at 13.5 nm is highly relevant for the silicon industry and advanced scientific research.