Focusing and imaging in microsphere-based microscopy

Abstract

Microsphere-based microscopy systems have garnered lots of recent interest, mainly due to their capacity in focusing light and imaging beyond the diffraction limit. In this paper, we present theoretical foundations for studying the optical performance of such systems by developing a complete theoretical model encompassing the aspects of illumination, sample interaction and imaging/collection. Using this model, we show that surface waves play a significant role in focusing and imaging with the microsphere. We also show that by designing a radially polarized convergent beam, we can focus to a spot smaller than the diffraction limit. By exploiting surface waves, we are able to resolve two dipoles spaced 98 nm apart in simulation using light at a wavelength of 402.292 nm. Using our model, we also explore the effect of beam geometry and polarization on optical resolution and focal spot size, showing that both geometry and polarization greatly affect the shape of the spot.

Super‐resolution microscopy by movable thin‐films with embedded microspheres: Resolution analysis

“…Based on a solid‐immersion concept ( n o ≈ n s ), the maximal diffraction‐limited resolution available for high‐index ( n s ∼ 2.0) barium titanate glass (BTG) microspheres can be estimated as ∼ λ /4. This estimation is consistent with the calculations of focusing and imaging properties of mesoscale spheres.…”

Super-Resolution Imaging and Microscopy by Dielectric Particle-Lenses

“…Details on SRE are outside the scope of this review and will be presented in a separate publication elsewhere. It is noted that Haong et al also reported super-resonance effect using same experimental parameters as in Fig.1 (a=2.37 um, n=1.46), they found that a ~0.24λ resolution can be achieved at wavelength 402.292 nm, in excess of solid immersion resolution limit of λ/ (2*1.46) =0.34λ) [43]. We believe SRE is vital to microsphere super-resolution imaging.…”

Experimental far-field imaging properties of high refractive index microsphere lens

“…Recent studies have shown that the surface waves play a significant role in focusing and imaging with the microsphere [26]. Therefore, it should be emphasized that, besides the super-strength focus effects discussed in this paper, other mechanisms must be contributing to the microsphere imaging.…”