Bremen Institute for Applied Beam Technology

About: Bremen Institute for Applied Beam Technology is a facility organization based out in Bremen, Germany. It is known for research contribution in the topics: Holography & Laser. The organization has 326 authors who have published 572 publications receiving 10735 citations.

Direct recording of holograms by a CCD target and numerical reconstruction.

Abstract: The principle of recording holograms directly on a CCD target is described. A real image of the object is reconstructed from the digitally sampled hologram by means of numerical methods.

Digital recording and numerical reconstruction of holograms

Abstract: This article describes the principles and major applications of digital recording and numerical reconstruction of holograms (digital holography). Digital holography became feasible since charged coupled devices (CCDs) with suitable numbers and sizes of pixels and computers with sufficient speed became available. The Fresnel or Fourier holograms are recorded directly by the CCD and stored digitally. No film material involving wet-chemical or other processing is necessary. The reconstruction of the wavefield, which is done optically by illumination of a hologram, is performed by numerical methods. The numerical reconstruction process is based on the Fresnel–Kirchhoff integral, which describes the diffraction of the reconstructing wave at the micro-structure of the hologram. In the numerical reconstruction process not only the intensity, but also the phase distribution of the stored wavefield can be computed from the digital hologram. This offers new possibilities for a variety of applications. Digital holography is applied to measure shape and surface deformation of opaque bodies and refractive index fields within transparent media. Further applications are imaging and microscopy, where it is advantageous to refocus the area under investigation by numerical methods.

Direct phase determination in hologram interferometry with use of digitally recorded holograms

Abstract: A new method of phase determination in hologram interferometry is described. The Fresnel holograms, which represent the undeformed and the deformed states of the object, are generated on a CCD target and stored electronically. No lens or other imaging device is used. The reconstruction is done from the digitally stored holograms with mathematical methods. It is shown that the intensity as well as the phase can be calculated from the digitally sampled holograms. A comparison of the phases of the undeformed and the deformed states permits direct determination of the interference phase.

Digital holographic interference-phase measurement using the Fourier-transform method

Abstract: A method for accurate phase determination in holographic interferometry using a one- or two-dimensional Fourier transform is described. The method calculates the interference phase pointwise, even between fringe extrema, and thus has advantages over conventional fringe-finding and -tracking methods. Only one interference pattern may be used, although the use of two patterns reconstructed with a mutual phase shift permits an easier phase unwrapping and determination of nonmonotonic fringe-order variations. Additionally, the method offers a means for filtering out disturbances such as speckle noise and background variations.