The phase differences of the focal points shown in Fig. 3. (a)–(p) The phase patterns of Figs. 3(a)–3(p) minus Fig. 3(a). The independently controlled number of segments of the spatial light modulator is 64 × 64 = 4096. The number of fringes in (a)–(l) is 0 , 1 , 2 , 3 , … , 11 , respectively. We decrease the magnitude of noise levels through averaging the vertical phases of the gradient patterns. (m)–(p) The phase difference patterns outside the range of memory effect.