Nonparaxial iterative calculation of diffractive optical elements focusing in a subwave light spot

The main efforts in overcoming the diffraction limit have been recently concentrated on the use of damped waves. The implementation, however, is connected with a serious drawback: superresolution is attained only in the immediate vicinity of the device, namely, at a distance of less than the wavelength. It is, therefore, impossible to use the available results, in particular, to reduce information on optical media. The aim of the paper is calculation of optical elements for subwave focusing of a monochromatic wave at a distance of several dozens of wave lengths. The problem of overcoming the diffraction limit expressed in accordance with the Abby theory and the Raleigh criterion dealt with in multiple fundamental and applied investigations is discussed in the paper. The analysis of subwavelength localization of radiation based on the interference effect that makes it possible to reduce the sizes of a light spot due to redistribution of energy in the peripheral area holds a prominent place in the paper. Calculations are performed using the iterative algorithm based on the method of plane wave expansion and the method of main directions. The problem is considered for the cylindrical and radial cases. Special attention is given to the search of solutions that would be more convenient for practical implementation. Prospective viability of developing the solution of the problem for data storage, contactless probing and nanolithography is demonstrated.