Fig. 9From: Coaxial superposition of Bessel beams by discretized spiral axiconsCalculated phase gradients from spot displacement in Cartesian coordinates at z=18 mm: (left column) or (a)+(c) \(\frac {\partial \phi (x,y)}{\partial x}\); (right column) or (b)+(d) \(\frac {\partial \phi (x,y)}{\partial y}\); (top row) or (a)+(b) on-axis vortex; (bottom row) or (c)+(d) off-axis vortexBack to article page