Fig. 1. Schematic of 4pi focusing optical system. (a) Tightly focusing optical system; (b) structure of DOE

Fig. 2. Intensity distribution of angularly polarized vortex beam in 4pi focusing system. (a) Intensity distribution of light field in ρ-z plane; (b) radial linear-type distribution of total intensity; (c) longitudinal linear-type distribution of total intensity

Fig. 3. Total intensity. (a) Total intensity distribution in ρ-z plane; (b) linear-type distribution of total intensity along ρ-axis in z=0 plane

Fig. 4. Total intensity distributions along ρ-axis in z=0 plane under different δ₄ values

Fig. 5. Total intensity distribution along ρ-axis in z=0 plane under differentNAvalues

Fig. 6. Total intensity distribution in z=0 plane along ρ-axis with different β

Fig. 7. Total intensity distribution in ρ-z plane when NA=0.95 and β=1.3