The spatial resolution of a conventional wide-field as well as a confocal microscope is influenced by the numerical aperture (NA) of the objective and the excitation wavelength λ. Furthermore the spatial resolution can be evaluated in terms of the lateral (x-y-direction) resolution and the depth (z-direction) resolution.
The theoretical lateral resolution of a microscope system can be estimated by the Rayleigh criterion.
For confocal microscopes with high NA, the lateral resolution is proportional to λ/NA. A confocal Raman imaging microscope can reach 250 – 300 nm lateral resolution.
The depth resolution of a confocal microscope is proportional to λ/ NA2. A confocal Raman imaging microscope can achieve a depth resolution of 1 µm or less.