In 1948,predating lasers by more than a decade,Gabor proposed a "new microscopic principle",which was initially aimed at correcting spherical aberrations in electron microscopy1.While the method has not produced an impact in its originally intended field,it opened a new direction,known as holography,in optics.Gabors technique allows one to store phase information by recording on film the intensity of a field emerging at a certain distance from an object.The image of the object itself can then be reconstructed by shining the same incident light onto the film.Holography created an impact on the lay community,especially because parallax made the imaged objects appear "3D".However,this type of in-line holography suffers from a major limitation:the in-focus image is always overlaid with an out-of-focus version of itself (see Fig.1).The reason for this limitation is as follows:since the recorded signal is real (intensity signal),its Fourier transform is Hermitian,consisting of two complex-conjugated terms,namely,the in-focus and the twin image.This obstacle prevented holography from becoming a practical tool until Lohman,Leith,and Upatnieks reported off-axis holography,which shifts the twin image away from the optical axis2.