Simple phase optical elements for narrowing of a focal spot in high-numerical-aperture conditions

It is shown that a decrease in the size of the focal spot produced by a high numerical aperture focusing system comes as the result of the spatial redistribution of different electric field components in the focal region. The focal distribution of electric field components can be controlled using vortex or binary phase diffractive elements. Situations for differently polarized incident laser beams are discussed and illustrated. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)