Figure 9

COMSOL numerical simulation results of optical hollow needle performance in air and water. Color maps of the optical hollow needle intensity in the propagation XZ plane (a) with the entire needle in air, (b) with half the needle in water, and (c) with the entire needle in water, where the dashed lines indicate the air-water interface at z = 305λ for (b) and z = 299λ for (c). The peak intensity (d), sidelobe ratio (e), and transverse FWHM (f) are plotted along the propagation direction for the three different cases of the entire needle in air (red), half the needle in water (green), and the entire needle in water (blue). The optical intensity, sidelobe ratio, and FWHM are given in arbitrary unit, ratio value, and λ respectively. And, the black and wine-colored dashed-dotted lines indicate the diffraction limit and super-oscillatory criterion, respectively.