Digital recording and numerical reconstruction of holograms

Abstract

This article describes the principles and major applications of digital recordingand numerical reconstruction of holograms (digital holography). Digitalholography became feasible since charged coupled devices (CCDs) with suitablenumbers and sizes of pixels and computers with sufficient speed became available.The Fresnel or Fourier holograms are recorded directly by the CCD and storeddigitally. No film material involving wet-chemical or other processing isnecessary. The reconstruction of the wavefield, which is done optically byillumination of a hologram, is performed by numerical methods. The numericalreconstruction process is based on the Fresnel–Kirchhoff integral, whichdescribes the diffraction of the reconstructing wave at the micro-structureof the hologram. In the numerical reconstruction process not only theintensity, but also the phase distribution of the stored wavefield can becomputed from the digital hologram. This offers new possibilities for avariety of applications. Digital holography is applied to measure shape andsurface deformation of opaque bodies and refractive index fields withintransparent media. Further applications are imaging and microscopy, where it isadvantageous to refocus the area under investigation by numerical methods.