Holographic microscopy

As mentioned in Chapter 1, holographic imaging was originally developed in an attempt to obtain higher resolution in microscopy. Equations (3.20) and (3.21) show that it is possible to obtain a magnified image if different wavelengths are used to record a hologram and reconstruct the image, or if the hologram is illuminated with a wave having a different curvature from the reference wave used to record it. However, neither of these techniques has found much use, in the first instance because of the limited range of coherent laser wavelengths available, and, in the second, because of problems with image aberrations [Leith & Upatnieks, 1965; Leith, Upatnieks & Haines, 1965].

The most successful applications of holography to microscopy have been with systems in which holography is combined with conventional microscopy. In one approach, a hologram is recorded of the magnified real image of the specimen formed by the objective of a microscope, and the reconstructed image is viewed through the eyepiece [van Ligten & Osterberg, 1966]. While this technique offers no advantages for ordinary subjects, it is extremely useful for phase and interference microscopy [Snow & Vandewarker, 1968]. In another, a hologram is recorded of the object, and the reconstructed real image is examined with a conventional microscope. This technique is particularly well adapted to the study of dynamic three-dimensional particle fields, as described in the next section.