By B. P. Hildebrand
Since the 1st papers via E. N. Leith and J. Upatnieks as regards to holography seemed in 1961, there was a digital explosion of analysis job within the box. greater than 500 papers and articles on holo graphy have seemed within the final ten years. Many functions of holo graphy were proposed, and a few of those are commencing to input the world of usefulness. one of many purposes that looks to carry nice promise is acoustic imaging by way of holography. the 1st papers in this topic seemed in 1966, yet already learn job within the box is burgeoning. 3 symposia completely dedicated to acoustical holography were held and the papers released in publication shape. The purposeof this booklet is to compile the result of study in acoustical holography, a few of it as but unpublished, lower than one disguise in order that staff in holography, nondestructive trying out, scientific imaging, underwater imaging, and seismic exploration can come to a decision even if this new method may be necessary to them.
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Additional info for An Introduction to Acoustical Holography
Now, however, a coherent electronic reference is used. Note that the image (b) is now as good as that obtained in Fig. 4 even though no background wave is present. 22 Chapter 2 It is interesting to note that for long wavelength radiation aGabor hologram can be generated with a constant amplitude plane wave component without the aforementioned restriction, as shown by Eq. 15). A hologram of this type, and its reconstruction is shown in Fig. 6. The only remaining disadvantage for Gabor holography at long wavelengths is the interfering effect of the twin image.
This simply means that if one beam is spherical an? the other plane, we obtain a Fresnel pattern. Since the beams are collinear, we have redefined the Gabor hologram with its attendant disadvantages. Images from this type of hologram using different objects were shown in Figs. 5. 2. Fraunhofer Holograms A Fraunhofer hologram is defined as the interference pattern between two collinear radiation beams, where the pattern is recorded in the far field or Fraunhofer zone of the object generating one of the beams .
96) These resolution expressions are identical to those based upon the Rayleigh criterion and are somewhat easier to derive. Hence, this definition will be used in this book. REFERENCES 1. D. Gabor, A new microscope principle, Nature 161 :777 (1948). 2. J. B. DeVelis and G. O. Reynolds, Theory and Applications o[ Holography, AddisonWesley Publishing Co. (1967). Holography 49 3. E. N. Leith, J. Upatnieks, B. P. Hildebrand, and K. A. Haines, Requirements for a wave front reconstruction television facsimile system, J.
An Introduction to Acoustical Holography by B. P. Hildebrand