Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources

Area of Science:

• Attosecond science
• Quantum optics
• Materials science

Background:

• High-harmonic generation (HHG) produces intense, ultrashort soft X-ray pulses.
• Current HHG sources are limited to linear polarization, hindering certain applications.
• Generating elliptically polarized high harmonics has been challenging due to low yields.

Purpose of the Study:

• To overcome the limitation of linear polarization in high-harmonic generation.
• To develop a simple and efficient method for producing elliptically polarized soft X-ray pulses.
• To demonstrate the utility of this new source for ultrafast magnetic measurements.

Main Methods:

• Utilizing a cross-polarized two-colour laser field for high-harmonic generation.
• Characterizing the polarization state and efficiency of the generated soft X-ray pulses.
• Measuring the X-ray magnetic circular dichroism (XMCD) effect in nickel.

Main Results:

• Achieved high degrees of ellipticity (up to 75%) in soft X-ray pulses.
• Maintained efficiencies comparable to linearly polarized harmonic generation.
• Successfully measured the XMCD effect at the nickel M2,3 absorption edge (67 eV).

Conclusions:

• The cross-polarized two-colour laser field technique efficiently generates elliptically polarized soft X-rays.
• This method enables femtosecond time-resolved XMCD experiments.
• Opens new avenues for investigating ultrafast magnetization dynamics in complex materials.