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Focusing performance of the achromatic flat lens at the wavelength of (a) 600 nm and (b) 700 nm. The focal length is f = 5 μm. The field intensity shown in (a) is multiplied by 2 to obtain a similar contrast as (b). (c) and (d) Corresponding normalized intensity cross-sections at the flat lens’s focal spots along the x axis at the wavelength of 600 nm (c) and 700 nm (d). FWHMs of the focal spots are labelled on the plots.
