Holography by shadow casting is a non-interferometric means for recording a hologram. Like ordinary (interferometric) holography, it leads to three-dimensional images of the object. Unlike ordinary holography, it works best at short wavelengths (y-rays and X-rays). The history, techniques, and prospects of shadow holography are reviewed.
X-ray tubes and gamma ray cameras have traditionally involved trade-offs between spatial resolution and radiation flux. Recently we have shown that the use of a Fresnel zone plate as a spatially-coded source or aperture can avoid this trade-off. In radiology, this technique can eliminate the need for a rotating anode and give higher resolution, while in nuclear medicine it can be used either to decrease patient dose or exposure time, or to increase resolution and greatly simplify the apparatus. With a coded source or aperture, the image is also coded, like a hologram and can be reconstructed optically. The system is tomographic with information about all planes contained in a single film.
One of the principal concerns in nuclear medicine is imaging the spatial distribution of tracer amounts of gamma emitting radiopharmaceuticals which have been intravenously administered to patients. These images are customarily formed on a gamma ray detector by means of lead pinholes or multichannel collimators. In practice these apertures yield only 1 cm spatial resolution and geometric efficiencies of 10-4. This paper describes the use of a lead Fresnel zone plate aperture in conjunction with an image intensifier camera to produce coded images of gamma sources. These images possess properties similar to holograms. This method shows promise of a factor of 4 or 5 improvement in resolution, a factor of 10 improvement in efficiency and gives 3 dimensional information about the object.
The inability to observe intraocular pathology behind cataracts is a particularly acute problem to the ophthalmologist from the standpoints of assessment and continuing diagnosis. Moreover, when immediate surgery is required, precise location of the damage and assessment of the pathological necessities are seriously hampered. We have succeeded in demonstrating that image degradation by a cataract is due primarily to random phase aberrations within and on the surface of the cataract. We show that the cataract may be considered to be a quiescent, random phase-distorting medium. The technique of phase aberration balancing is used to cancel the cataract's aberrating power. Our procedure consists of forming a hologram of the phase aberrations. This hologram is then used as a filter, in conjunction with the cataract itself, to correct what would otherwise be highly distorted imagery. In our experiments, using excised cataracts, the average visual acuity of the cataracts before filtering was 20/200, whereas the average acuity after correction was 20/15.
Optical viewing systems have been well designed for specific applications. However, partial coherence evaluation of the optical viewer illustrates potential for control of the frequency response to phase and amplitude components of the photographic image (where the phase component is due to the emulsion relief image). The complex image formed by the partially coherent system contains a separable response to the phase and amplitude components for a low contrast object. Optical frequency response control is applied to the complex image by design of a variable source size condensing system and by inserting an attenuation filter in the pupil of the imaging lens. Illustrations are given to show the adaptability of the system response to low contrast images.
I would like to begin my tenure as editor of Optical Engineering by praising the important role which the previous editor, Professor Douglas C. Sinclair, has played in the development of the Journal. His editorial policy as described in the January-February issue of 1972 lucidly describes the significant contribution which the Optical Engineering Journal can make to the scientific community. It shall be the goal of the present editorial staff to continue to maintain this same policy while at the same time attempting to broaden interest in the Journal, and increasing its usefulness.