Figure 4
(a) Focus is diffraction-limited [\sigma_{\rm{F}}] = [\sigma_{\rm{dl}}] if the beam size [\Sigma_{\rm{L}}] and transverse coherence length [\Xi_{\rm{L}}] are larger than the lens aperture [Omega]. (bc) Focus size is larger than the diffraction limit if the coherence length (b) or beam size (c) incident on the lens is smaller than the aperture. (d) For a very large aperture the focus is a demagnified image of the source.  [article HTML]