Recovering image resolution in reconstructing digital off-axis holograms by Fresnel-transform method

The resolution of amplitude and phase reconstruction of images from digital holograms by the Fresnel transformation method is limited by the pixel width in the reconstructed image plane. The reconstruction pixel depends on distance, wavelength, and number of pixels in the hologram. The spatial frequencies, in the reconstructed image, are band limited by the size of the reconstruction pixel. Undersampling can occur, in the image plane, in the reconstructed amplitude and/or wrapped phase maps. Recovery of reconstructed undersampled spatial frequencies, is possible by the fictitious enlargement of the digital hologram. Correct profile reconstruction of a silicon microelectromechanical structure is demonstrated, applying the proposed method.