Application axicons in a large-aperture focusing system

Abstract

We consider the application of axicons in large-aperture focusing systems with different polarization. The aim is to increase the longitudinal extent of the focal spot and decrease its transversal size. Unlike conventional circular diaphragms, supplementing a high-aperture lens with an axicon is more efficient from the energetic point of view. The gain is proportional to the area of the masked part of the lens. Using an axicon we reduce the size of the central light spot from 0.51? to 0.3? for radial polarization. When we deal with linear polarization, which is the case for most laser beams, it is possible to produce a light spot narrowed in one direction to 0.32?. For circular and azimuthal polarization it is efficient to use spiral axicons for producing compact distributions. When a large-aperture lens is supplemented even with a "weak" converging axicon, the focal area gets the conic form whose vertex has a smaller transverse dimension than the focal spot of a single lens. By choosing the axicon parameters we can vary the extent and "sharpness" of the cone. Moreover, by adding vortex phase we can control the contribution of different components of the electromagnetic field in the core and vertex of the cone. It can be useful in interaction of the electromagnetic field with the materials that have selective sensitivity to either longitudinal or transverse components of the field.