Near-Field Subwavelength Focal Spot
This chapter discusses the numerical simulation results obtained via solving the Helmholtz equation by a finite-element method using the COMSOL Multiphysics 4.3 software. When fabricating the surface microrelief by means of the e-beam or photolithography a binary microrelief in the form of a step, or a corner step, with one or two vertical sidewalls can be fabricated most easily and accurately. The focal spot generated close to the corner phase step has different parameters at different distances on the z-axis. Laser vortex beams have been dealt with in quite a number of publications. The diffraction efficiency in the focal plane is defined as the ratio of the focal spot power to the power of the entire focal plane cross-section, amounting to 54%. In the case of a microcylinder with non-resonance radius, both the size and maximum intensity of the focal spot remain almost unchanged in the course of pulse propagation.