Abstract: The present invention discloses a method and an apparatus to compute a complex wavefield, referred to as the object wave o, by means of measuring the intensity signal resulting from the interference of the said object wave with a second wave termed the reference wave. The second wave r is assumed to have some non-vanishing mutual coherence with the said object wave o. The reference wave can be obtained from a source or from the object wave itself. The wave may be emitted from sources of variable degree of coherence and can be scattered waves, but also light-emitting molecules, matter waves such as electron beams or acoustical sources. The disclosed method relates to the said “non-linear method” (NLM). The innovation resides in the fact that the NLM improves considerably the bandwidth of the wavefront reconstructed from off-axis interferograms and holograms obtained in a single shot. The advantage is the significant improvement of the resolution of the images obtained from the reconstructed wavefront, i.e.