Quadriwave lateral shearing interferometry (QLSI) is well established phase imaging technique. Information about phase distribution within this method is encoded into complex pattern of intensity distribution. So called difference fronts are then extracted via fast Fourier transform (FFT) technique and optimally merged with various integration algorithms, depending on character of measured phase distribution. QLSI experiment is typically build with the use of dedicated shearing device, based on combination of special amplitude grating with phase chessboard. In our experiment, we perform the diffractive shear through phase spatial light modulator (SLM), which also serves as known in advance phase test. In this context, we present a comparison of measurement results with the use of different illumination sources.
In optical lens imaging, the main attention has traditionally been paid to the lateral resolution roughly estimated by a two-dimensional point spread function (PSF) describing sharp image of a point object. In three-dimensional (3D) imaging and methods based on depth information, an axial profile of the PSF becomes of particular importance. In studies on the 3D PSF, the axial image asymmetry and shift of the intensity maximum out of the focal plane were revealed for optical systems characterized by low Fresnel numbers. In this paper, the 3D PSF is examined in terms of digital imaging, where a point object is recorded optically and its image reconstructed numerically. The analysis includes methods of digital holography, in which the axial image asymmetry is examined in relation to different geometries of coherent recording waves. Attention is also devoted to the Fresnel incoherent correlation imaging that enables recording of 3D objects in spatially incoherent light.