High-resolution surface plasmon resonance microscopy based on spatial frequency domain filtering

Conventional surface plasmon resonance microscopy (SPRM) suffers from coherent interference-induced point spread functions (PSFs) with asymmetric parabolic tails, limiting spatial resolution in dense imaging. We demonstrate a spatial frequency-domain modulated SPRM method by selectively blocking zero-order reflected light at the Fourier plane to suppress interference and enable an interference-to-scattering imaging transition. This converts a single-particle response into a donut-shaped scattering profile, avoiding the complex background subtraction process required in conventional SPRM. When combined with deconvolution, this method reduces the full width at half maximum (FWHM) of the PSF to nearly one-third of its original value. Numerical simulations and experimental results verified the mechanism behind the generation of the "donut" PSF, which has potential applications in high-density plasmonic imaging and single-particle analysis.