Photonic nanojets formed by square microsteps

It was experimentally shown that square microsteps with width of $0.4$ um, $0.5$ um, $0.6$ um, $0.8$ um and height of $500$ nm illuminated by linearly polarized laser light with wavelength $\lambda = 633$ nm formed near its’ surface focal spots (photonic nanojets) with intensity that is $6$ times higher than the intensity of incident light and diameters of $0.44\lambda$, $0.43\lambda$, $0.39\lambda$ and $0.47\lambda$ (less than the diffraction limit $0.51\lambda$). When the square width was smaller than the wavelength, the focal spot was located inside the step. When the square width was larger than the wavelength, the focal spot was located outside the step and looks like a handle.