Fig. 2: Apochromatic far-field subwavelength focusing.
a, c, e Simulated and b, d, f experimental field patterns (in combined x-z and y-z longitudinal sections) at λB = 488 nm (a, b), λG = 532 nm (c, d), and λR = 640 nm (e, f) by an apochromatic SOL with extended DoF centered at zf ≈ 428 μm. g, j, m Simulated and h, k, n measured intensity profiles in the transverse focal planes for the patterns in (a–f). Exp. experiment, Sim. simulation. i, l, o Comparison of the simulated and measured intensity profiles in the radial direction at zf ≈ 428 μm. p Simulated (solid and dashed lines) and measured (asterisks and stars) FWHM and intensity of the optical needle’s main lobe along the propagation direction at λB= 488 nm. The insets show the measured transverse intensity distribution profiles from z = 426 μm to z = 431 μm at a step size of 1 μm, each exhibiting a bright main lobe at the center and quite weak sidelobes around.
