Fig. 1. Schematic diagram of the designed system for generating the enhanced superchiral needle. HP, half-wave plate; PBS, polarizing beam splitter; SP, S-wave plate; SPP, spiral phase plate; BS, beam splitter; TP, thin plate; RA, ring aperture; Obj, objective.

Fig. 2. (a) Distribution of the enhancement factor gr at the focal plane. (b) Distribution of the enhancement factor gr at the x−z plane (y=0). (c) Lateral distribution in the x-direction of the enhancement factor gr at the focal plane. tanη=2(η=63°), β0=1.5, NA=1.32, ni=1.518, nt=1, δ=0, and α=0.99.

Fig. 3. Comparison of the distributions for the electromagnetic components at the focal plane between the combined field (columns 1 and 3, tanη=2) and the RPVBGB alone (columns 2 and 4, tanη=0). The parameters are the same as Fig. 2.

Fig. 4. Comparison of the distributions for Cρ/|E|2, Cϕ/|E|2, and Cz/|E|2 at the focal plane between the combined field (upper row, tanη=2) and the RPVBGB alone (bottom row, tanη=0). The parameters are the same as Fig. 2.

Fig. 5. Comparison of the parameters for the superchiral needle at the focal plane for various values of α between the combined field (tanη=2) and the RPVBGB alone (tanη=0). (a) The maximum of the enhancement factor gr. (b) The FWHM in the x-direction. (c) The deviation of the superchiral needle from the z-axis (Δx). The parameters are the same as Fig. 2.

Fig. 6. (a)–(d) Distribution of the enhancement factor gr at the focal plane for different phase differences δ. The parameters are the same as Fig. 2. (e) The maximum of gr as a function of δ (blue line, left ordinate). The azimuthal orientation (ψ) of the distribution for gr as a function of δ (green line, right ordinate).

Fig. 7. (a) Lateral maximum of the enhancement factor [represented as max(gr,m)] as a function of η. Solid line: resulting from the simplified model [Eq. (1)]. Dashed line: resulting from the reformulated model [Eq. (2)]. (b), (c) The lateral distribution in the x- (b) and y- (c) directions of the modified enhancement factor gm when max(gm) reaches the maximum in (a) for different values of γ. The parameters are the same as Fig. 2.