Acousto-optic component technology and instrumentation continue to mature, and interest in practical applications has accelerated during the past year. Following our symposium in San Diego in August 1976 and publication of the Proceedings (SPI E Volume 90), it was decided to review recent progress and to report in a special issue of Optical Engineering the current state-of-the-art. Thus, this edition of the journal features a series of nine articles dealing with the theory and reduction-to-practice aspects of acoustic imaging and holography, bulk wave and surface wave devices, and other systems such as optical correlators and integrated optical radio frequency spectrum analyzers.
In a holographic imaging system, the limitations on relative motion between the object and the recording plane are usually more restrictive than the limitations in a conventional incoherent imaging system. This paper considers the motion limitations for a scanning acoustic holographic system. The system consists of a cylindrical insonifying antenna and a linear array of receivers perpendicular to the antenna. The reference signal for the system is electronic. Degradation in image quality results from a distortion of the holographic fringe pattern, rather than from blurring of the fringes, as is the case in optical holography. Uniform motion of a point source both parallel and perpendicular to the recording plane is treated first. The analysis and experiments are then extended to include insonified reflecting objects. The results show that in the special case of uniform translational motion, motion limitations are less restrictive than those encountered in conventional imaging systems with lenses. Non-uniformity of motion in a direction perpendicular to the receiving plane and rotation are shown to put stricter limitations on object motion.
The most inherently sensitive type of ultrasonic system for real-time imaging is one that operates in a manner similar to that of a scanning electron-beam microscope. In the acoustic system, an ultrasonic beam is focused at a plane within an object. The focal spot is rapidly scanned in a raster pattern over this plane and the transmitted (or scattered) sound energy is collected by a piezo-electric receiver. The receiver output is displayed on a synchronously-scanned television monitor, yielding a visual image of the spatial pattern of acoustic opacity (or reflectivity) in the object plane. This paper describes an embodiment of this type of system for operation at megahertz frequencies in which the key element is an opto-acoustic transducer (OAT) whose function is to convert an impinging optical intensity pattern into a corresponding spatial pattern of generated acoustic amplitude. An incident optical pattern can be formed and scanned by optical equipment, which will generate, scan and focus a corresponding acoustic beam. This approach does not require the use of high-density transducer arrays with individualized electronics or acoustic lenses and therefore, inherently possesses the potential advan-tages of simplicity and versatility over existing or other proposed scanning-focused beam systems.
Advances in state-of-the-art of surface acoustic wave (SAW) device technology will require better substrate materials than those currently available. Calculations of the surface acoustic wave properties of several materials including the quartz derivatives berlinite (A1PO4 ) and 0-eucryptite (0-Li Al SiO4), certain sulfosalts, and a composite structure, have produced several temperature-compensated crystallographic orientations with greater piezoelectric coupling than that of ST cut quartz. These materials make possible the development of improved broadband, low insertion loss devices with temperature-independent performance characteristics. Methods of growing improved aluminum nitride (A1N) are being studied. Because the SAW velocity of this material is about twice that of currently used materials, A1N promises to extend the upper frequency limit of SAW devices beyond 2 GHz.
A new approach to the theory of light scattering by surface acoustic waves on y-z lithium niobate is presented. The polarization driven wave equation is solved exactly and electromagnetic fields are found so that all the electromagnetic boundary conditions are satisfied across the interface. Both "s" and "p" polarization incidence is treated.
In this paper, we give the design equations and a procedure for the complete specification of the design parameters for a wide bandwidth acousto-optic modulator (AOM). Although the modulating medium, transducer material, and bonding agents determine the modulator performance, we concentrate here on the question of how to design an AOM, given specifications on its minimum modulation bandwidth, diffraction efficiency, and the maximum ellipticity of the output beam.
The theory and practice of tunable acousto-optic filters are reviewed. Topics discussed include the basic principle of operation, filter characteristics and configurations. Experimental results of a noncollinear Te02 filter are also presented.
A tutorial review is presented covering the real-time optical Fourier spectrum analysis of a wide band of electrical signals by means of acousto-optic diffraction. Topics include frequency dispersion, spatial modulation, weighting functions, frequency resolution, sidelobe level, optical background level, acousto-optic bandshapes, normal and birefringent acousto-optic diffraction, figures of merit, diffraction efficiency, nonlinearities and spurious responses, dynamic range and output characteristics.
Many techniques have been proposed in the past for using acousto-optic devices to perform signal correlation. This paper reviews these techniques and discusses the design tradeoffs involved in choosing a particular configuration for a given application. Configurations are classed as two major types. The first type, spatial integrating correlators, perform correlation by integrating light diffracted by all parts of the signal(s) which are simultaneously present in the acoustic device. This type of correlator has a large range window, but the time bandwidth product is limited by device parameters. The second type, time integrating correlators, use a detector array or vidicon to perform an integration in time for each point within the cell. This provides a limited range window but a large time bandwidth product. Results obtained with both types of systems are shown, along with pictures of fabricated hardware. Acousto-optic device parameters are also summarized for comparison with competitive technologies.
A concept for performing RF spectrum analysis using the tech-nology of Integrated Optics is described. Such devices could achieve frequency resolution of about 1 MHz over bandwidths up to 1 GHz in a very small and potentially low cost package. The principles of operation, design constraints, and possible circuit configurations are discussed. The state-of-the-art of key component technologies is also reviewed. The performance levels of the key components are nearing the point which would permit their integration in a complete circuit for a feasibility demonstration.
The choice of the color coordinates for extraction of visually significant edges and boundaries in a color image is discussed. The compass gradient edge detection method developed by the author for monochrome images is extended to color edge detection and a quantitative measure is discussed in choosing the color coordinates for edge extraction.
The development of a very versatile, reliable, and sensitive radiometer has provided a tool for performing a variety of significant infrared measurements from ground-based and aircraft platforms in the .8 to 7 pm spectral region. The development techniques of the radiometer, the capabilities of the developed instrument, and some typical target and atmospheric emission measurements are presented in the paper. The instrument design incorporates various techniques to eliminate the need for cooling of the optics and structural parts which avoid the inconveniences and difficulties associated with the operation of cryogenically cooled instruments without significantly sacrificing sensitivity. The radiometer may be used in a selectable spectral wavelength and bandwidth mode, a limited spectral scanning mode, or a tuneable spectral wavelength mode. The various modes of operation are accomplished through the use of interference filters whose spectral characteristics are somewhat adjustable by properly controlling or setting their angular orientation. The simplicity of operation of the instrument has provided a means of measuring atmospheric airglow emissions and aurorally enhanced emissions in the .8 to 1.75 um region on a routine basis. Also, through the use of a reticle chopper and background suppression technique, the same radiometer has been adapted for measurements of low energy target emissions in the .8 to 7 um region.
A summary is given of several aspects of work required to evaluate the laser for a wide variety of preventive dentistry applications. Results for studies to determine maximum pulpal temperatures following laser absorption indicate that quite high energies can be tolerated by the enamel. Also, measurements of the hemispherical reflectance of tooth enamel show values near 50% in the visible region, diminishing to more desirable values in the near infrared. Initial experimental and theoretical studies for uptake enhancement of topically applied fluorides are also described briefly. Results of the theoretical model indicate that significant enhancement of uptake with heating is due to the increase of the diffusion coefficient with temperature. Experiments indicate an increase of uptake with heating, but some unusual characteristics are yet to be described. Lastly, inorganic materials development for possible durable pit and fissure sealants is touched upon here. While direct apatite sintering on the tooth does not appear promising because of the high temperatures required, thermosetting phosphate bonded sealants and liquid phase sintering may hold the answer.
We describe an approach to the analysis of the optical system of the solar tower concept, which is designed to provide maximum design information. By inputing all quantities in terms of angles or dimensionless ratios the results remain relatively scale independent. First the power redirected from the heliostat field to the central receiver is computed, then solar images are projected from each heliostat to the central receiver and interception factors are obtained. This information allows us to size the central receiver, to enhance performance by redistributing heliostats in the field, and finally to define the rim angle of the field. The procedure for this step-by-step definition of the solar tower optical system results in optimal heliostat fields, receiver flux distributions and diurnal power curves.
The NASA Lewis Research Center has designed and fabricated a closed-cycle, continuous wave (CW), carbon dioxide (CO2) high-power laser to support research for the identification and evaluation of possible high-power laser applications. The device is designed to generate up to 70 kW of laser power in annular-shape beams from 1 to 9 cm in diameter. Electric discharge, either self-sustained or electron-beam-sustained, is used for excitation. This laser facility can be used in two ways. First, it provides a versatile tool on which research can be performed to advance the state-of-the-art technology of high-power CO2 lasers in such areas as electric excitation, laser chemistry, and quality of output beams, all of which are important whether the laser application is government or industry oriented. Second, the facility provides a well-defined, continuous wave beam for various application experiments, such as propulsion, power conversion, and materials processing.
We derive the equations that permit the use of six different periodic analyzers for the frequency-mixing detection (FMD) of polarization-modulated light. The six periodic analyzers are (1) the rotating linear analyzer, (2) rotating half-wave plate and fixed linear analyzer, (3) rotating quarter-wave plate and fixed linear analyzer, (4) rotating linear analyzer and fixed linear analyzer, (5) oscillating-phase retarder and fixed linear analyzer, and (6) oscillating optical rotator and fixed linear analyzer. In all cases, the average polarization and the polarization and intensity modulation parameters of the light beam can be determined easily and explicitly from limited Fourier analysis of the detected signal.
A simple technique is described by which holograms can be made on a single flat plate which, when illuminated with white light, reconstruct very bright images of the front and back of a three-dimensional object. An observer can view the hologram from opposite sides and see both sides of the object imaged in their original spatial relationship.
The use of ultrasound for diagnosis of patient pathology is one of the most rapidly advancing fields of medical imaging. Prior to 1972, ultrasound images were black and white displays with essentially no gray scale variation depicting the amplitude of echoes from interfaces within the body. In 1972, Kossoff introduced the methodology for gray scale display, and improvements over the last four years have yielded ultrasound images with excellent gray scale characteristics and good rendition of anatomic detail. With these improvements, the ability to resolve fine detail is now limited primarily by the frequency and geometrical characteristics of the ultrasound beam, motion of the patient during the scanning interval, and refraction of the ultrasound beam as it travels through the body. Within the constraints imposed by reduced penetration of ultrasound energy with increasing, frequency, limitations introduced by the ultrasound beam can be reduced with the use of higher frequency ultrasound and with careful selection of transducer diameter and focusing characteristics.