Paraxial models for the surface plasmon self- interference at off-axis excitation

Area of Science:

• Optics and Photonics
• Surface Science
• Nanotechnology

Background:

• Surface plasmon polaritons (SPPs) are essential for nanoscale optical phenomena.
• Self-interference of SPPs can enhance or degrade optical signals.
• Vortex beams offer unique polarization and phase properties for excitation.

Purpose of the Study:

• To analytically investigate surface plasmon self-interference excited by focused vortex beams.
• To understand the impact of off-axis illumination on SPP excitation and interference.
• To characterize the degradation of self-interference in paraxial regimes.

Main Methods:

• Analytical study of surface plasmon self-interference using a geometrical model.
• Application of angular spectrum representation and homogeneous transformation.
• Derivation of integral expressions for SPP fields with off-axis convergence angle.

Main Results:

• Self-interference degradation observed even in ideal Gaussian microscopic imaging systems.
• Surface plasmon excitation quantified by longitudinal field peak intensity.
• Standing wave characteristics determined by transmitted field intensity profile's FWHM.
• Interference disappears and resonance detunes as off-axis angle increases.

Conclusions:

• Off-axis illumination significantly impacts surface plasmon self-interference.
• Degradation of interference is an inherent issue in paraxial systems.
• Control over off-axis angle is critical for maintaining surface plasmon resonance.