Phase retrieval method from multiple-wavelength holograms for in-line holography

We propose two phase retrieval methods based on multiple diffraction intensity patterns recorded at different illumination wavelengths using in-line digital holography in which the appropriate constraints are imposed both on the hologram plane and object plane. A synthetic wavelength is used to retrieve wrap-free phase distributions with a much extended vertical measurement range; thus the reconstructed phase distribution directly provides the height distribution of the surface of the sample after eliminating the twin image. In comparison with previous research, the proposed method requires a fewer number of illumination wavelengths and has a faster rate of convergence, which is demonstrated by the simulation and experimental results.