Wavefront measurement of vortex beam using ptychographic phase retrieval

Abstract

For vortex beams, characterization and optimization of the optical system are important. However, wavefront measurements on focused vortex beams are difficult because they have complex phase and intensity distributions. As a measurement method, we proposed the use of ptychography, in which the intensity and phase of the beams are retrieved using several far-field diffraction patterns. We constructed an optical system with a He-Ne laser light source to clarify the usefulness of ptychography. Test vortex beams were produced by a spatial light modulator (SLM) and focused by a plano-convex lens. A pinhole was scanned on the focal plane for collection of the diffraction intensity profiles. The phase and intensity of the vortex beams on the focal plane were retrieved so that the calculated beams were consistent with the intensity data. The retrieved intensity and phase distributions were compared with distributions predicted using the inputs for the SLM. They agreed well, indicating that the ptychographic phase retrieval method can be used for precise characterization of vortex beams. This method is valuable for improving the performance of applications using vortex beams.