  High-precision measurements implemented by means of light is desired in all
fields of science. However, light is a wave and Rayleigh criterion gives us a
diffraction limitation in classical optics which restricts to get arbitrary
high resolution. Sub-wavelength interference has a potential application in
lithography to beat the classical Rayleigh limit of resolution. We carefully
study the second-order correlation theory to get the physics behind
sub-wavelength interference in photon coincidence detection. A Young's
double-slit experiment with pseudo-thermal light is carried out to test the
second-order correlation pattern. The result shows that when different scanning
ways of two point detectors are chosen, one can get super sub-wavelength
interference patterns. We then give a theoretical explanation to this
surprising result, and find this explanation is also suitable for the result by
using entangled light. Furthermore, we discuss the limitation of this kind of
super sub-wavelength interference patterns in quantum lithography.
