The capability of analyzing hologram lenses recorded with arbitrary wavefronts has been added to a holographic raytracing design program. The recording wavefronts are defined by analytical phase functions, for example, a two-dimensional polynominal expansion. The coefficients of the functional representations of the recording wavefronts are used as parameters to optimize the performance of an optical system containing the hologram lens. The optimum recording wavefronts are then produced with the help of computer-generated holo-grams. Several useful arbitrary wavefront phase functions are discussed. Design predictions and experimental results will be shown for a holographic Fourier transform lens recorded with the aid of a computer-generated hologram.
A thin lens analogy between holographic optical elements, including transmission, reflection, flat, and curved holographic optical elements, and conventional optical elements is discussed. Examples show that a thin lens model of a holographic optical element can be used with a conventional optical design program such as ACCOS V for designing holographic optical elements.
Dichromated Gelatin is the most versatile material presently available for recording reflection holograms for image display. Aside from its well known properties of low scatter and high diffraction efficiency, its peak reconstruction wavelength and reconstruction bandwidth can be controlled independently over the entire visible spectrum. Observed relationships between reconstruction color, exposure wavelength, exposure energy, and processing parameters suggest a new model for the mechanisms of hologram formation in dichromated gelatin.
The production of cylindrical holographic stereograms, or multiplex holograms, requires the use of a large, low f/number cylindrical lens to form a line image on the holographic film. To have an image of reasonable size for display purposes, the f/number of the lens must be quite small, on the order of f/1, and the dimensions of the lens must be reasonably large, on the order of eight inches in width and height. The optical quality of the lens must also be quite good to prevent interference fringes in the image and to minimize the number of multiple exposures in the multiplexing process. For economic reasons, adjustable, oil-filled plastic lenses are commonly used for this purpose instead of conventional optics. Considerable difficulty is usually encountered, however, in adjusting the oil lens to minimize aberrations. Making the oil lens adequately adjustable, while at the same time maintaining the oil seal, also presents mechanical difficulties. We have eliminated these problems with the use of an off-axis, holographic cylindrical lens. The lens is easy to make, requires no adjustment, and has excellent optical quality. Techniques for producing this lens and its use in making multiplex holograms are described.
The image width in cylindrical holographic stereograms has been limited to about one-third the diameter of the display drum. An analysis of the optical system shows that producing an image which fills two-thirds of the drum diameter or more requires a cylindrical lens with an f/number of 0.5 or smaller. Cylindrical lenses of such small f/number and adequate optical quality are not commonly available. These optical characteristics can be achieved readily, however, with a holographic element on a curved surface. A system designed for increasing image width making use of such a holographic lens is described. The requirement for an extremely low f/number cylindrical lens can be eliminated by another technique which involves curving the holographic film over a short radius platen. This technique is also described. It is shown that both these techniques compensate the nonlinear horizontal magnification distortion in cylindrical holographic stereograms.
A simple, single-element, holographic ally formed device for use as a multiplexer/demultiplexer in wave-length division multiplexing in optical fiber systems is described. The single holographic element performs all the required functions of collection, separation, and focusing. Experimental results for a thick dichromated gelatin HOE are described. Efficiencies of 70% over a bandwidth of 30% have been measured in the visible. Methods of extending the operation to the near IR are discussed.
Recently developed techniques for making binary computer-generated holograms (CGH) are reviewed. These include a method of using fringes to record the phase information and three methods for recording the amplitude information. Practical considerations for producing CGH's with high optical efficiency are also discussed. The applications of CGH's as beam splitters, aberration compensation plates and as optical elements for infrared wavelength are briefly mentioned.
A computer-generated hologram is a geometric pattern that can be used as a precise reference in an optical test. Computer-generated holograms can be used to make reference wavefronts that would be very difficult and expensive to make by other methods. This paper reviews the development of computer-generated holograms for optical testing. Various encoding methods are discussed. Examples are given to demonstrate some of the properties of such holograms. A review of interferometer design leads to a discussion of how the hologram functions as a part of the interferometer and of the limitations to the computer-generated hologram as used in optical testing.
This paper discusses recent progress in producing computer-generated holograms (CGH) of low spatial distoration and high space-bandwidth product. The CGH are drawn directly on electron-resist using an electron beam pattern generator which is intended for use in the production of integrated circuits with sub-micron feature sizes. This approach not only reduces plotting errors below those introduced by indirect writing methods, but also provides more than 106 distortion-free resolution points in a hologram of correct size. The quality of the CGH made by this process will be illustrated by an example in the testing of an aspheric surface.
A holographic recording system will be flown on the NASA Space Shuttle (SL-3 mission) to record fluid phenomena under low-zero gravity conditions; namely, solution growth of crystals and fluid convection. A 25 milliwatt helium neon laser will be the illuminator for two orthogonal hologram recorders and a real time schlieren monitor. The holograms will be re-recorded on S0-253 films vacuum clamped to optical flats. Processing and analysis of the holographic records will all be after the Shuttle's return.
New possibilities for engineering uses of hologram interferometry are shown by two experiments. 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 re-construction. Fringes caused by in-plane rigid body motion can be compensated for, and local displacements evaluated. It is shown that an in-plane 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. An object, 1 m long was placed in a fixture and a recording of the object was performed on one of the plates in the sandwich pair. Then the object was removed from the fixture as well as the holographic laboratory and holes were drilled in one wall of the object in a workshop. Then the object was put back in the fixture and the second plate in the sandwich pair was recorded. At reconstruction the influence caused by a slight reposition error was compensated for by tilting the sandwich hologram and then the deformation around the drilled holes could be studied.
The principle of Electronic Speckle Pattern Interferometry - ESPI - is explained by comparing it to image holography where recording and reconstruction are performed by videotechniques. As such, ESPI can be used for different interferometric measurements, but it is especially suitable for vibration testing and measurement of movements. Our work on extending the measuring range and general use of ESPI for those purposes is described and illustrated by some practical applications.
The current status of far-field holography is reviewed with particular attention to the work reported since the previous reviews of 1974 and 1975. The basic techniques continue to be improved and very good resolution can now be achieved. Automatic readout is a current problem that still requires further attention. Application of single and multiple pulse methods continue to be developed in a variety of important fields including agricultural pest control, cavitation studies, and evaluation of fuel droplet size and burning in engines.
The lens-assisted holomicroscopic technique has been described at an earlier SPIE conference. Continuing research has led to further improvements of the lense assisted technique. In order to accommodate a larger scene volume, a scaled-up version of the lens assisted holocamera (LAH) was made. Unlike the small LAH, coherence considerations imposed greater care in spacially and temporally matching the recombined reference and scene beams. A description of the modified holocamera and the rationale for the introduction of a novel beam-splitting element is discussed. The improved holocamera has recorded a droplet spray volume of approximately one liter at a mean distance of 38 cm. The Raleigh resolutions achieved are 144 line pairs per mm or droplet diameters of 3.4 microns.
In recent years, there has been a slow but steady advance in the use and the technology of acoustical holography. The major use for this imaging method is in the non-destructive evaluation of thick materials used in the nuclear industry. The most recent advances in-volve the use of linear transducer arrays and computer reconstruction. The former enables the data to be gathered at high speeds and the latter provides aberration-free imaging, as well as pre-and post-processing of the data. In this paper, we describe these advances and show some experimental results.
By making and testing matched filters representative of the various classes we wish to recognize, we can compute sums of those filters which are superior to the individual matched filters in terms of joint between-class separation and within-class insensitivity. Those new filters (composite matched filters) can be constructed by either multiple exposure holography or computer holography.
Albert Einstein has in his memoires written that he as a young boy pondered about what a light wave would look like to an observer riding along with it. One hundred years after his birth in 1879 it has now become possible to make observations that to a surprisingly high degree correspond to that proposed method. A flat object surface and a hologram plate are both illuminated at an oblique angle by laser light of short pulse duration or short coherence length. Only those parts of the object surface are holographically recorded that correspond to small pathlength differences between object beam and reference beam. The hologram plate therefore corresponds to an infinite set of gated viewing systems triggered by the traversing reference beam. Scanning along the processed plate produces a continuous motion picture of the light in flight.
Multi-channel stereophonic systems that can create images of acoustic sources are introduced. The systems are analyzed in conjunction with optical holographic recording and reconstruction methods. The diffraction problem from the multi-channel system, generation of the primary image and the conjugate image are dis-cussed.
Holography is a Nobel Prize winning invention. It incorporates many basic scientific principles as well as artistic and technical applications. As such, it needs to be brought to the attention, understanding, and appreciation of the general public in a coordinated manner. In particular, we believe that one of the greatest contributions made by holography to date have been its educational values in promoting and motivating interest in science. Herein we describe a nationwide effort over the last decade to bring holography to the public in general, and to the classrooms in particular.
Although the two-step holographic technique for producing white-light-transmission, or "rainbow", holograms has proven the most practical for producing display images, one-step apertured-lens techniques can also be useful in producing such holograms. Typically, the diameter of the lens limits the field of view, but not the image size, for pseudoscopic image presentation, or imposes an intermediate vignetting aperture in the orthoscopic case. Here we describe how the combination of conjugate wavefront illumination and conjugate diffraction can be used to produce a large-area, undistorted, orthoscopic image, with only the field of view limited by the lens size. The resulting holograms enjoy very high image contrast, and rival the results of the two-step process in many respects.
We have introduced a one-step process that greatly simplifies the procedure in making rainbow holograms. With the newly developed astigmatic process, we have demonstrated that a wide field orthoscopic image can be generated. by the one-step rainbow technique. Impartment applications, such as the archival storage of color images and the rainbow holographic interferometry are also discussed.
In time, holography will have a major impact on all types of displays. Priceless, one of a kind artifacts can be copied and disseminated for esthetic and education purposes. Additionally, holography interferometry can safely test artifacts for incipient faults or damage, allowing corrective measures to be applied at an early stage.
Volume phase holograms, whose holographic characteristics are similar to those of conventional dichromated gelatin holograms, can be formed employing commercial silver-halide films. Major advantages of silver-halide gelatin holograms are wide spectral response and lower exposure requirement.
Phase conjugate wavefront generation has recently received much attention because of its potential applications to real-time adaptive optics, information processing and imaging trough phase disturbing media or optical fibres .1:2,3,4 The object of the lecture is to demonstrate an alternative approach to phase conjugation by using real-time holography and degenerated four wave mixing in photorefractive Bi12 Si020 crystals (B.S.0.).5,6
Reflective holographic optical elements offer a number of advantages over conventional optical elements at the 10.6 μm wavelength of the CO2 laser. One proposed application is to irradiate the appropriate infrared hologram with a high power CO2 laser and use the projected real image for laser materials processing. The required holograms can be ob-tained using computer generation, direct recording at 10.6 μm, or by recording holograms in the visible and converting them to phase reflection holograms. An analysis of the aberrations introduced when holograms are recorded in the visible and the image reconstructed at 10.6 μm shows that aberrations can be made acceptably small even for extended images. A statistical analysis of the diffraction efficiency of computer generated holograms for extended objects with a uniform phase distribution shows that a realistic value for diffraction efficiency is about 28% as compared to about 40% for a simple point object. Phase reflection holograms fabricated using a copper electroplating method have good surface quality and a diffraction efficiency of about 30%.
We report in this paper the development of an automated thermoplastic holographic camera which produces reproducible results from cycle-to-cycle and from sample to sample. Design innovations and performance characterization of the camera are described; its use in holographic interferometry is also illustrated.