Necklace-structured high-harmonic generation for low-divergence, soft x-ray harmonic combs with tunable line spacing

Area of Science:

• Nonlinear Optics
• Quantum Optics
• Attosecond Science

Background:

• High-harmonic generation (HHG) is an extreme nonlinear optical process converting laser light properties into electron wave functions and X-ray emissions.
• Conventional HHG beams originate from longitudinal phased distributions of atomic emitters.
• Controlling the spatial properties of HHG beams, particularly in the soft X-ray spectrum, remains challenging.

Purpose of the Study:

• To develop a new method for controlling the spatial properties of high-harmonic generation (HHG) beams.
• To engineer extreme ultraviolet (EUV) and soft X-ray harmonic combs with tunable characteristics.
• To enable novel applications in probing ultrafast dynamics.

Main Methods:

• Formation of a transverse necklace-shaped phased array of linearly polarized HHG emitters.
• Utilizing orbital angular momentum conservation to tune beam properties.
• Characterization of the divergence and spectral properties of the generated harmonic combs.

Main Results:

• Demonstrated a transverse phased array configuration for HHG.
• Achieved tunable line spacing and divergence of EUV and soft X-ray harmonic combs.
• Observed extremely low on-axis divergence, decreasing with harmonic order, outperforming Gaussian beams.

Conclusions:

• The transverse phased array approach offers a new degree of freedom for designing harmonic combs, especially in the limited soft X-ray regime.
• The engineered harmonic beams provide enhanced capabilities for sensitive probing of ultrafast charge and spin dynamics.
• This work opens avenues for advanced spectroscopic techniques in condensed matter physics and chemistry.