Generation of user-defined wavefront using computer-generated holography: a collimated laser beam is incident on a binary amplitude hologram kept at the front focal plane of the lens L1. The diffracted beams from the hologram are focused by the lens L1 and the Fourier transform of the hologram transmittance function is obtained in the back focal plane of L1. The back focal plane thus contains three prominent focal spots comprising ±1 and 0 order beams, as seen in the surface plot (along with the colorbar). The separation between the ±1 orders from the 0 order is dependent upon the τ(x, y) used to construct the binary hologram and is chosen in such a way that an iris diaphragm can separate the +1 order from the rest. The user-defined phase profile ϕ is realized at the back focal plane of the collimating lens L2 (seen as a surface plot with colorbar). In this figure, both L1 and L2 are assumed to have the same focal length f.