Phase differences of focal points measured experimentally. Each time the focal point on the screen moves by 24 μ m . The independently controlled number of segments of the spatial light modulator is 64 × 64 = 4096. (a)–(h) The phase mask of the focal point moves by 0 × 24 μ m , 1 × 24 μ m , … , 7 × 24 μ m , respectively, and the images show the phase patterns of the moved focal points minus the original focal point. The red curves denote the phase gradient patterns to guide eyes for observation, while the fuzzy fringe patterns show the experimental values. (i)–(j) The phase masks of the focal points move by 16 × 24 μ m , 17 × 24 μ m , 18 × 24 μ m , and 19 × 24 μ m , respectively, and the images show the phase patterns of the moved focal points minus the original focal point.