Modal decomposition of laser beams for wavefront reconstruction

Modal decomposition is a powerful and yet easily implemented tool to characterize laser beams. We present a novel technique to reconstruct the wavefront of a beam by decomposing it into basis functions, which can be of any kind, provided they are orthogonal. The decomposition is done using a computer-generated hologram (CGH), which performs a correlation of the incident beam with the implemented modes all-optically. As a result, the optical field is reconstructed, including intensity and phase, and the Poynting vector and wavefront are inferred. The technique is applied to different kind of laser beams: beams emerging from multimode optical fibers and aberrated free space Gaussian beams, for both, scalar (linearly polarized) and vector beams. The accuracy of the results is proved by comparison with those of a Shack-Hartmann wavefront sensor and with theoretical predictions, yielding very good agreement.