Wavelength-encoded multi-wavevector excitation for filling the spatial frequency gap in label-free plasmonic...

Optical super-resolution microscopy under surface plasmon illumination has been proven to realize an ultra-high imaging resolution based on the deep Spatial Frequency Shift (SFS) effect. However, SFS super-resolution imaging always suffers from loss of spatial frequencies (SFs) between the cutoff frequency and the modulated high SF, which leads to image distortion. Here, a wavelength-encoded multi-wavevector excitation (WEME) method is proposed for filling the SF gap under plasmonic illumination in label-free super-resolution imaging. The dispersion properties of the multilayer film enable surface plasmon polariton (SPP) illumination modes with various lateral wavevectors (k_x), making it possible to obtain different depths of SFS supported by the same multilayer structure at designed wavelengths. We experimentally demonstrated that a large SF span of 4NA/λ (NA/λ∼5/λ) can be detected, which supports the reconstruction of real-size super-resolution images using only three frames. WEME experimentally provides a universal approach for efficient ultra-high resolution imaging under high-k_x SPP illumination to detect the nanostructures with a scale varying from sub-100 nm to sub-1 µm.