11 - Special techniques

Summary

Polarization recording

With normal holographic techniques, the amplitude and phase of the object wavefront are recorded accurately, but information on its state of polarization is lost. The polarization of the reconstructed wave is determined by the polarization of the light used to illuminate the hologram.

Orthogonally polarized reference beams

Two basic methods for recording the state of polarization of the object wave have been described. The first method was proposed by Lohmann [1965a] and subsequently demonstrated by Bryngdahl [1967]. The experimental arrangement for this method, which is shown in fig. 11.1, uses two orthogonally polarized reference waves which interfere with the corresponding polarized component of the light from the object, so that two holograms are recorded on the same plate. After processing, when the plate is illuminated once again with the same reference beams, it yields two superimposed images that reproduce the polarization of the object wave. Care must be taken to adjust the angles of incidence of the beams so that the cross-talk images formed by diffraction of each of the reference beams at the hologram formed with the orthogonally polarized component do not overlap the desired image.

Coded reference beams

The other method, which is due to Kurtz [1969], uses a single reference beam in which, as shown in fig. 11.2, an opal glass diffuser is inserted. The light transmitted by this diffuser is depolarized, and the complex amplitudes of the two orthogonally polarized components of the reference beam at any point exhibit little or no correlation.