Focused field characteristics and focal shift of Laguerre-Gaussian beams passing through an aperture-lens separation system

In this paper, the expression for axial intensity distribution of Laguerre-Gaussian beams passing through an aperture-lens separation system is derived using Collins formula. It is shown that aperture-lens separation affects the focal shift and intensity distribution. T he focal shift may be reversed or eliminated. Furthermore, under certain conditions, the intensity in a large axial range is close to the maximum intensity. Thus a large range of maximum intensity can be obtained.