Isotropic superresolution imaging for fluorescence emission difference microscopy.

Fluorescence emission diffraction microscopy (FED) has proven to be an effective sub-diffraction-limited imaging method. In this paper, we theoretically propose a method to further enhance the resolving capability of FED. Using a coated mirror and only one objective lens, this method achieves not only the same axial resolution as 4Pi microscopy but also a higher lateral resolution. The point spread function (PSF) of our method is isotropic. According to calculations, the full width at half-maximum (FWHM) of the isotropic FED's PSF is 0.17λ along all three spatial directions. Compared with confocal microscopy, the lateral resolution is improved 0.7-fold, and the axial resolution is improved 3.1-fold. Simulation tests also demonstrate this method's advantage over traditional microscopy techniques.