Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part I. Transmission holographic optical elements.

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOE's). The drawback of DCG is its low sensitivity and limited spectral response. Silver halide materials can be processed in such a way that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-high-resolution silver halide emulsions. An optimized processing technique for transmission HOE's recorded in these materials is introduced. Diffraction efficiencies over 90% can be obtained for transmissive diffraction gratings. Understanding the importance of the selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOE's.

Holographic interferometry with multiple wavelengths.

One of the unsolved problems in the well-established field of holographic interferometry is identification of zeroth-order fringes in cases in which the locations of zero displacement are unknown. We offer a simple solution: By making the double-exposure hologram of a white object in full color by using three or more wavelengths, the zeroth-order fringes will be indentified by their white color.

High-resolution contact Denisyuk holography.

The configurations, to assure high resolution in contact Denisyuk holography, are investigated by varying the construction and the viewing angles in the recording and the reconstruction setups, respectively. A range of optimized angles, obtained with Agfa 8E75 HD plates is given. These results are compared with another holographic material. To introduce this holographic technique in medical diagnostics, we made holograms of various stained-tissue samples. These holograms have been improved by the selection of tissue-staining dyes and their concentrations.

Chrono-coherent imaging for medicine.

We describe a new method for imaging with visible and near visible light inside media, such as tissues, which have strong light scattering. The chrono-coherent imaging (CCI) method is demonstrated in this paper for a transmission geometry where an absorbing object is completely hidden from normal visual observation by light scattering of the media. The resultant images are most similar to X rays, with cumulative transmission showing absorption features and refractive index differences in the media. We discuss laser coherence properties, coherence measurements, the relation of CCI to light-inflight holography, holographic film properties relevant to CCI, a particular optical setup for CCI, the results of a demonstration experiment imaging an absorbing object hidden by light scattering, and an experiment to estimate the clinical applicability of CCI.

Chrono-coherent imaging for medicine.

Imaging inside the body with optical wavelengths encounters problems due to light scattering of tissues and other optical distortions. A description is given of chrono-coherent imaging (CCI), a new method for imaging with visible and near-infrared light that uses coherent image formation and subpicosecond timing to remove the time-delayed scattered light. With CCI it is possible to form images in the presence of the overwhelming amount of scattered light that blocks conventional image formation. The coherent image formation process allows the use of long-duration, high-total-energy, and modest-peak-power pulses to overcome scattering losses. CCI is an extension of light-in-flight holography, which combines the properties of short-duration pulses and hologaphy for various measurements of objects and optical wavefronts.

Movements of healthy and periodontally involved teeth measured with laser reflection technique.

The laser reflection method of remote measurement was used to register small tooth movements of upper central incisors from a group of subjects with healthy teeth and another group with periodontally involved teeth. The mobility of the healthy maxillary incisors over a period of 24 hours was well within normal limits. Among orthodontically treated and periodontally involved maxillary incisors relapse was larger sagittally than laterally and largest buccally. This tendency was greatest during the first 5 hours and almost reached its maximum after 1 day. These movements were within the limits of mobility but were not always correlated with mobility or the loss of marginal bone. Furthermore, the relapse was not correlated with the magnitude of orthodontic correction. In this respect, the mean buccal relapse was low, however, individual variations were large. The extent of relapse may be related to the varying intensity of parafunctional habits.

Tooth position measurements on dental casts using holographic images.

A new accurate method for comparing tooth positions on dental casts at different stages is described. Holograms of casts were prepared with a helium-neon gas laser. For evaluation of tooth movements, a cast and hologram representing different time points were superimposed by means of an adjustable x-y stage. Occlusal surface detail was used as a reference for the superimposition. Positional changes of the upper incisors were detected as discrepancies between the cast and the hologram image.

A laser instrument for measuring tooth movements.

An improved apparatus has been constructed which is based upon the laser reflexion method and is used in a highly accurate direct technique of measuring tooth movement without contact. The possibility of making clinical investigations of tooth movements with the equipment has been investigated by testing its various components. The most critical part of the system is the repositioning of the patient, which has been done with an accuracy of +/- 20 micron. The reflected pattern used during 3 months of experiments was the same. The instrument can be used for measurements down to 50 micron.

Sandwich holography for storing information interferometrically with a high degree of security.

An entirely new method of storing confidential data is presented. The method is based on sandwich holography, and its-main principle is the following: The basic state of a surface is recorded in one plate of a sandwich pair; in the other plate the same surface is recorded slightly deformed. When the two holograms are combined an interference fringe pattern is formed. By controlling the deformation of the surface it is possible to obtain exactly the interference pattern wainted. This controlled pattern can be used to create information that is either directly readable digital information or a binary coded information, suitable to automatic readout. The data stored in the holograms are not possible to read out from one hologram alone, but the two holograms must be put together to make the information available. The system is primarily meant to be applied on ID cards but can also be used for other applications where data have to be stored securely.

Sandwich hologram interferometry. 5: Measurement of in-plane displacement and compensation for rigid body motion.

Sandwich holography has been used for measurements of in-plane displacement of an object. The sign of the displacement is found by tilting the sandwich hologram during reconstruction. Fringes caused by inplane rigid body motion can be compensated for, and local displacements evaluated. It is shown that an inplane motion of more than 1 mm of the object placed at a distance of about 1 m from the plates can be compensated for and a local tilt of 1.5 x 10(-3) degrees evaluated. A comparision between conventional evaluation and evaluation of sandwich holograms by measuring the tilt angle of the plates to calculate an object's displacement is shown with a series of experiments.

Pulsed sandwich holography. 2: Practical application.

The vibration of a small electric drilling machine was studied holographically. The machine was held by hand, and drilling was done on a steel plate during two exposures from a double pulsed ruby laser. The recording was made on a rotating sandwich hologram. The influence of rigid motion was eliminated, and the local vibration evaluated. The phase relation between different areas was studied using three methods, all based on the simple idea that interference fringes are formed when a modified object surface is intersected by interference planes which tilt in the same direction as the observer tilts the sandwich hologram during the reconstruction.

Pulsed sandwich holography.

A new method is introduced which utilizes sandwich holography combined with a pulsed laser. In a special rotating hologram holder two plates sandwiched together are exposed through a slit during the double pulse operation of a laser. The two pulses are separated by less than 1 msec. Afterward, in an evaluating holder, one plate is rotated in relation to the other so that the images from the two pulses are overlapped. Then the two plates are glued together. If the emulsions are separated, fringes caused by object tilt between the two pulses can be eliminated by an analogous, but much larger, tilt of the sandwich hologram during reconstruction. Even the direction of tilt, forward or backward, is found this way.

The use of laser beams for measuring tooth mobility and tooth movements.

The laser reflexion method, a direct contactless measuring technique with a high accuracy, has been applied for clinical purposes. A prototype has been tested using a laser beam to illuminate a patient's tooth fixed to the equipment by an impression plate. The reflected patterns were thrown onto a screen with a coordinate system and photographically recorded, and the movement of the tooth has been geometrically calculated. The relapse tendency after orthodontic treatment of a patient with periodontal disease and parafunctions was studied by repeated measurements of the left medial upper incisor. By use of the method, it was possible to observe that the velocity of the studied tooth was highest during the 1st day and, besides the horizontal movement, a rotation of the tooth began at the end of the measuring period.