Субволновая фокусировка с помощью зонной пластинки Френеля с фокусным расстоянием 532 нм

Using a near-field scanning optical microscope we measure a focal spot resulting from the illumination the phase zone plate with focal length 532 nm, radius 7,7 um and etch depth 510 nm by linearly polarized Gaussian beam with wavelength 53 2 nm. The diameter of focal spot equals to 0,44 of wavelength. The root3mean3square deviation of the focal spot intensity from the calculated value is 5%.