We experimentally demonstrated that the microsphere can discern the details of the object whose sizes are below the conventional diffractive limit and such super-resolution capability can be reinforced if semi-immersing the corresponding microspheres in liquid droplet, producing a sharper contrast and a comparatively smaller magnification factor. The microsphere is considered as a channel that connects the near-field evanescent wave and the transmission one in far field. A conjecture based on this is proposed to explain the mechanism of super-resolution and the corresponding phenomenon.

We demonstrate that a sharper focal spot area can be generated (0.147λ(2)) by using an azimuthally polarized beam propagating through a vortex 0-2π phase plate than for radial polarization (0.17λ(2)) or for linear polarization (0.26λ(2)) under the same condition. Further research illustrates that such optimistic results can still be expected when condition limitations are liberalized. This will facilitate new approaches to get superresolution in confocal systems.

The size of the dark focal spot directly determines the resolution and stability of stimulated emission depletion (STED) microscopy. This paper investigates the relationship between the size of the dark focal spot and the polarization of the input light beam. The types of fundamental polarization are discussed, their effects on the dark focal spot are compared and the optimized mode for each kind of polarization is proposed. The results of the analysis provide the theoretical basis and reference for designing a STED system.

We propose a novel physical mechanism for breaking the diffraction barrier in the far field. Termed fluorescence emission difference microscopy (FED), our approach is based on the intensity difference between two differently acquired images. When fluorescence saturation is applied, the resolving ability of FED can be further enhanced. A detailed theoretical analysis and a series of simulation tests are performed. The validity of FED in practical use is demonstrated by experiments on fluorescent nanoparticles and biological cells in which a spatial resolution of <λ/4 is achieved. Featuring the potential to realize a high imaging speed, this approach may be widely applied in nanoscale investigations.

Sensitivity of the amplitude and phase measurements in interferometric microscopy is influenced by factors such as instrument design and environmental interferences. Through development of a theoretical framework followed by experimental validation, we show photon shot noise is often the limiting factor in interferometric microscopy measurements. Thereafter, we demonstrate how a state-of-the-art camera with million-level electrons full well capacity can significantly reduce shot noise contribution resulting in a stability of optical path length down to a few picometers even in a near-common-path interferometer.