Some characteristics of four principal types of display holograms are outlined in order to permit accurate identification and comparison by observers in the field. Several well-known non-holograms are also discussed.
The major use of holography in optical pattern recognition systems has been in matched spatial filter correlators. We discuss new uses of holographic techniques in optical pattern recognition applications. These include: optical pattern recoanition architectures of reduced size, weight and volume; optical pattern recognition architectures with reduced component tolerances; new nonlinear local optical preprocessing architectures; and optical pat-tern recognition systems that operate when geometrical and other differences are present in the input image.
This paper discusses ways in which laser speckles may be used to determine strain on the surface of an object. This may be done either by measuring variations in speckle displacement across a specklegram, or by measuring the slewing of the speckle field relative to the object surface. The latter method requires the use of tandemly recorded specklegrams, and, although data processing is time consuming, it yields a complete solution for the surface strain rotation matrix. The first method is effective when the surface is observed in focus, along the surface normal, but it suffers serious problems when a significantly contoured surface is considered. Equations are derived that relate the derivatives of observed speckle displacements to surface strains and rotations as a function of illumination and observation direction and variations in defocusing.
Speckle Metrology has transitioned from a laboratory curiosity to a useful engineering tool. It is now in a stage where some means is required to process the enormous amount of data it is capable of generating. This paper explores the requirements and characteristics for an automated data reduction system. Examples are given of current operational systems and what direction future system developments may take.
The high sensitivity combined with the externally controlled spatial frequency response of photoconductive electrooptic Bi12 Si 020 crystals (B.S.0.) allow real-time non destruc-tive testing either by phase conjugation in the four-wave mixing configuration (FWM) or by energy transfer in two-wave mixing experiments (TWM). Applications to image amplification and mode pattern visualisation of a vibrating 3-D diffuse object is demonstrated.
Through a combination of lectures and 'hands-on' opportunities in a workshop format, we have taught an extensive and low-cost investigation into the field of holography that is offered to anyone, regardless of their academic background. Over the past 10 years, 23 have also written a book entitled "A Guide to Practical Holography" and also produced a 1-hour video tape, "Practical Holography I", which details many of our in-class experiments. The rational to our teaching format, the activities that are covered in the class sessions, and the equipment we use to convey the relative simplicity of the medium are described.
Several applications of holographic testing are described together with the holographic methods used. Test subjects include components of gas turbine engines, cooling turbines, as well as statically loaded structures. Several typical examples are shown.
This paper describes a new opportunity in holographic industrial use with a large aperture thermoplastic film recording system. This system is computer-driven and can be synchronized with other stages in the holographic control. The system is designed and tested for use in an industrial context.
Two major applications of holographic scanners are considered, the first is the code reader scanner now in use in supermarkets and soon to be used in automated warehousing. The second is the multipurpose line scanner currently used in line printers and soon to be included in automated inspection systems. Code reader facets perform multiple functions, each one deflects and focuses laser light at a unique angle and scans a short arc, the return light from a bar code is collimated by the same facet and is subsequently focused through a small aperture. Ambient light is diffracted at other angles and focused at points all around the aperture giving a high signal to noise ratio and the large high efficiency facets gather sufficient return light so that photo diodes and low power lasers can be used in the system. Line scanners can be made in a large variety of sizes and configurations inexpensively and with perfect fidelity, each one being a holographic replica of a master hologram. Focused arcs as well as parallel straight lines and even arbitrary computer generated scans are possible. The limitations and considerations of such devices are discussed along with design criteria related to fabrication problems and actual production line results.
The necessity of perfect stability of the object during the holographic recording step is one of the chief problems which limits the use and the development of such an optical coding technique. In this communication, it is shown that the quality of the reconstructed image depends upon several parameters, first of all the object motion, the structure of the object, the type of recording set-up, the nature of the coding and finally the linearity of the transfer intensity → density in the hologram. Taking into account such different parameters, it is then possible to design holographic set-ups characterized by a relative insensitivity to motion and more generally to perturbations of the object during the recording step. The adopted device is based on imagery which ensures optical paths of equal lengths and on the use of holographic optical elements as beamsplitters. Thanks to holographic beamsplitters it is possible to modify the distribution of the object information in the hologram plane. Two holographic codings are studied : i) a small hologram area codes one object point (point to point coding), ii) a small hologram area codes the whole object information (object to point coding). Although the second coding gives a better result than the first in the case of a fixed object, the first one enables us to retrieve images of good quality even for object displacements of a few millimeters. The developed technique should be carried out in holographic microscopy of living cells.
This communication presents a preliminary study and a prototype of a holographic solar concentrator where both focusing and dispersive properties of holographic optical elements are exploited. In such a concentrator, the image of the sun is chromatically dispersed and projected on a photovoltaic cell array ; each cell corresponds to a specific band of the solar spectrum. This configuration insures the matching between the spectral response of the cells and the solar spectrum. Due to this matching, the photovoltaic cells can work in optimal conditions, that is, with maximum energy efficiency. The aim of this work is to underline the different problems and perspectives of such a realization. The problems are connected to chromatic aberrations, amplitude of dispersion, diffraction efficiency, stability in time, etc.
Holographic diffraction gratings, when used in a spectroscopic application, produce excellent image quality and stray-light rejection, but sometimes lack optimum efficiency. Ionetching through a sinusoidal photoresist groove into a glass substrate can produce triangular profiles comparable with the groove shape produced by classical diamond burnishing. This can be accomplished in both plano, spherical and aspheric substrates to produce gratings comparable in efficiency to classically ruled gratings.
A holographic non-destructive evaluation (HNDE) system with on-line acquisition and processing of real-time interferograms is presented. The system comprises photoconductor-thermoplastic recording materials, an image acquisiton system based on a photodiode-array line scanner. A microprocessor for controlling acquisition and other system functions and a link to a large computer. The system is capable of fringe detection down to an accuracy of 1/100th of a fringe. Applications for the non-destructive evaluation of an actual industrial specimen, as well as mapping the derivatives of deformation of a 2-D object are presented.
A software package based on symbolic form recognition algorithms has been established for holographic fringe characterization through a video camera. This program also includes sections for separating the inner defects from the outer ones in periodic structures. It has been tested successfully on cylindrical containers made of wired keolar on which all other non-holographic testing methods are inapplicable.
A technique of white-light color encoding of misfocused speckle interferometric fringe patterns is presented. The encoding is performed in the spatial frequency plane with color filters. This technique allows the viewing of a multiset of encoded speckle interferograms simultaneously. Thus it may provide new informational interferometric aspects of the object under stress or vibration. The effect on the speckle fringe pattern due to the spatial filtering is briefly discussed and experimental demonstrations of color encoded fringe patterns are presented. Due to the simplicity and versatility of the processing technique, we feel that the technique may develop into a practical tool for strain, stress and vibrational measurement.
A holographic interferometer system has been installed in the NASA Ames 2- by 2-Foot Transonic Wind Tunnel. The system incorporates a modern 10 pps, Nd:YAG pulsed laser which provides reliable operation and is easy to align. The spatial filtering requirements of the unstable resonator beam are described, as well as the integration of the system into the existing schlieren system. A two-plate holographic interferometer is used to reconstruct flow field data. For static wind tunnel models, the single exposure holograms are recorded in the usual manner; however, for dynamic models such as oscillating airfoils, synchronous laser hologram recording is used.
The presence of particulates, in injectable: solutions, can be medically hazardous depending on their size and shape. Hence, a. mandatory particulate inspection is performed prior to the release of any injectable drug. However, the determination of realistic quality limits, has been hampered by the absence of any physical non-destructive, measurement or comparison technique. This paper describes a far-field holographic' method for the measurement of particulate, contamination in sealed sterile containers. This application of holography provides to the pharmaceutical industry for the first. time, a non-destructive technique to inspect production containers and to classify the size and quantity of contaminants.
A real time holographic interferometer coupled to an automatic fringe analyzing system is presented to evaluate the linearity of the axial displacement of a translation stage. The 'basic holographic set up can separate the lateral from the longitudinal displacements and simplifies the fringe analysis. In plane rotation is identified by observing the nature of the variation of the fringe contrast with change in the viewing aperture stop. Tilt is idendified and measured in the conventional manner that requires a simple modification (a change in the point of illumination) of the basic setup. The automatic fringe analyzing system identifies the'center of a fringe as the midpoint between any two consecutive points of inflexion of the cosine density variation that may be ride on a variable dc bias due to noise and amplitude fluctuation in the recontructed image.
Acoustical holography is rapidly approaching commercial status with applications to nondestructive evaluation, underwater imaging, and underground pipe location being pursued. In this paper we review the techniques involved, show some experimental results, and describe the latest commercial system.
A project was recently completed that irvestigated possible uses cf holography it the nuclear reactor safety program. A portable holographic camera which uses a pulsed ruby laser for illumiratior was constructed and used it various studies, including several desigred to clarify the properties of steam/water mixtures that occur during loss-of-coolant accidents it nuclear reactors. The flexibility of the cameras's optical configuration also enables it to produce holographic interferograms, which have several advantages over conventional interferograms and which can be used to measure very small physical changes in a given environment.
Holographic interferometry offers some essential advantages of over other kinds of testing and measuring methods. Therefore this technology has arrived at such an advanced development stage that it is suited for use in the industrial manufacturing process. In composite materials holographic testing has already provided its worth. In addition to such pure material testing, vibration processes in structures and complete units can be investigated by holography. The methods described will be veryfied by concrete examples.
In 1948,Dr. Dennis Gabor introduced the theory of holography as "the optical recording of the object wave formed by the resulting interference pattern of two mutually coherent, component light beams." Through the studies of enumerous practical applications, the theory of holography was further advanced to be used in conjunction with the laser beam to better serve a more practical minded industry. Such developments were introduced and engineered by Dr. Emmett Leith and Dr. Juris Upatnieks in 1962.