Focusing the linearly polarized light using a binary axicon with subwavelength period

Using the finite-difference time domain method it is shown that a binary glass axicon with subwavelength period illuminated by a linearly polarized Gaussian beam forms near the surface an elliptical focal spot with diameters equal to 0.26'lambda' and 0.61'lambda' (the focal spot area equals 0.125'lambda'^2), and the depth of focus equals 0.4'lambda'. The focal spot intensity is 45 times larger than the input beam intensity. This is the smallest focal spot with sidelobes smaller than 30% that can be obtained using a binary axicon.