Fig. 1. Flow chart of improved G-S algorithm

Fig. 2. Resulting CPP distribution of two different algorithms. (a) Traditional algorithm; (b) improved algorithm

Fig. 3. Focal spots and one-dimensional distributions obtained by two different algorithms. (a)(b) Traditional algorithm; (c)(d) improved algorithm

Fig. 4. FOPAI of focal spot with two different algorithms

Fig. 5. PSD of far field intensity distribution with and without spectrum control

Fig. 6. Comparison of experimental and designed results. (a) Experimental focal spot; (b) 1-D distribution chart; (c) 1-D filtering results of design focal spot

Fig. 7. 1-D distribution of initial phase and final CPP

Fig. 8. Variations of RMS in the same iterative times with different algorithms

Fig. 9. Results of asymmetric focal spot. (a) CPP distribution; (b) far field intensity distribution with CPP