Azimuthal Scanning Excitation Surface Plasmon Resonance Holographic Microscopy

Surface plasmon resonance (SPR) holographic microscopy exploits surface plasmon wave as illumination and acquires both SPR intensity and phase images. It detects extremely tiny variations of weakly interacting objects owing to high sensitivity and has been applied in cell biology, material science, surface chemistry, etc. However, it is very challenging to solve the problem of poor spatial resolution due to the transverse propagation of surface plasmon wave. In this paper, an azimuthal scanning excitation method is proposed in SPR holographic microscopy to improve the spatial resolution by engineering the Fourier spectra of SPR images from dual-arc to circular shape. The study modulates the light field with spatial position, wavevector, and polarization to realize azimuthal scanning excitation of SPR. Systematic experiments of dielectric spheres, nanowires, two-dimension materials, and complex nanostructure are conducted to show the resolution improvement with one order of magnitude, the higher detection sensitivity of SPR phase than that of SPR intensity, and the necessities of both of high-resolution SPR intensity and phase images to retrieve sample information in certain scenarios. Benefiting from the high detection sensitivity and spatial resolution, the proposed microscopy will find wide applications in nanoparticle analysis, low-dimensional material characterization, and imaging extremely thin or transparent samples.