Practical configuration for wave-front sensing with two-beam phase retrieval

A wave-front sensing approach based on two-beam phase retrieval is described. Light from an aberrated beam is split into two paths. A random phase and amplitude perturbation is applied to the beam in one path, and the interference patterns of the resultant two beams are measured in two planes along the axis of propagation. By modulation of one of the two beams, the intensity of each beam and the phase difference between the two beams are recovered in each plane. A rapidly convergent phase-retrieval algorithm is formulated by the method of sequential projections onto constraint sets. Examples are given illustrating the convergence properties of the approach.