Fig. 1. Schematic of multi-focus distribution under large numerical aperture

Fig. 2. Nonlinear mapping diagram

Fig. 3. Flow chart of iterative loop for solving objective function

Fig. 4. Simulation results of equivalent energy three-focus with axial focus interval of 80 μm. (a) Phase hologram；(b) axial intensity distribution

Fig. 5. Simulation results of equivalent energy five-focus with axial focus interval of 160 μm. (a) Phase hologram; (b) axial intensity distribution

Fig. 6. Simulation results of five-focus with axial focus interval of 160 μm and energy ratio of 1∶2∶3∶2∶1. (a) Phase hologram; (b) axial intensity distribution

Fig. 7. Schematic of experimental multi-focus stealth dicing setup

Fig. 8. Cross-section of wafers after cutting