Diffraction of Gaussian Beam of Light by an Optical Lens and a Small Circular Aperture

Based on the vectorial Rayleigh-Sommerfeid diffraction integrals,analytical expressions of Gaussian beam with unity amplitude propagating through a thin lens followed by one small circular aperture are derived,for the non-paraxial and paraxial approach.Using these expressions,numerical calculations of the transverse distribution of optical intensity and the distribution on the axis have been done.It is found that the non-paraxial approach should be applied if the aperture dimension is comparable with the wavelength,and paraxial approach should be applied if the aperture dimension is larger than the wavelength and Gaussian width is larger.