Extreme Ultraviolet Beam Enhancement by Relativistic Surface Plasmons

Area of Science:

• Plasma Physics
• Laser-Matter Interaction
• Nanophotonics

Background:

• High-order harmonic generation (HHG) is a key process for producing extreme ultraviolet (XUV) and soft X-ray radiation.
• Surface plasmons offer unique pathways to enhance light-matter interactions at the nanoscale.
• Controlling HHG requires precise manipulation of laser-plasma interactions.

Purpose of the Study:

• To investigate the experimental generation of high-order harmonics in the extreme ultraviolet (XUV) range.
• To explore the role of surface plasmon excitation in enhancing harmonic emission from grating targets.
• To demonstrate the possibility of nanometric-scale control over target profiles for HHG.

Main Methods:

• Experimental investigation of high-order harmonic emission using intense, short laser pulses interacting with grating targets.
• Resonant excitation of surface plasmons to enhance harmonic intensity and order.
• Preforming density gradients at the target surface for nanometric profile control.
• Spatiotemporal correlation measurements of harmonic emission and multi-MeV electron bunch acceleration.
• Particle-in-cell (PIC) simulations to interpret experimental results and elucidate mechanisms.

Main Results:

• Surface plasmon excitation significantly increases both the intensity and the highest observed order of harmonic emission compared to flat targets.
• Harmonic emission is achieved with preformed nanometric density gradients on the grating surface, enabling profile manipulation.
• Harmonic emission is spatiotemporally correlated with the acceleration of multi-MeV electron bunches along the grating surface.
• PIC simulations successfully reproduce experimental findings and provide insights into the HHG mechanism.

Conclusions:

• Resonant excitation of surface plasmons on grating targets is an effective method for enhancing high-order harmonic generation in the XUV range.
• Nanometric control over target surface profiles is achievable without hindering surface plasmon excitation, offering a new route for HHG manipulation.
• The observed correlation between harmonic emission and electron acceleration highlights the underlying plasma dynamics in this process.