Before elaborating on the principles of acousto-optics let me give you my personal impression on how this field has developed. It is now roughly fifty years ago that Brillouin predicted certain effects that should occur when a beam of light interacts with a beam of high frequency sound. (Refs.1,2). In particular he predicted that in such an interaction, if the light were incident at a certain critical angle, it would be split into various orders propagating into different directions. This can be under-stood intuitively if one considers the planes of compression and rarefaction caused by the sound wavefronts to act somewhat like the layers of atoms in a crystal. The effect should then be closely analogous to that of X-ray diffraction. Because, however, in the case of a sound wave the "atomic planes" are moving with sound velocity, the diffracted orders of light should not only propagate in different directions but also have slightly different frequencies caused by Doppler shift. Effects like this were indeed observed in 1932 by Debye and Sears(Ref. 3) and also by Lucas and Biquard. (Ref. 4) .
Birefringence of circularly polarized light induced by the external magnetic field or internal magnetization in a material medium can be described phenomenologically by a skew symmetric permittivity tensor. The origin of this effect can be understood on the basis of magnetic field interacting on orbital electrons for the case of diamagnetic media, or the spin-orbit interaction for oriented spins in the case of ferromagnetic or low-temperature paramagnetic media. Faraday transmission and Kerr reflection effects are the dominant magneto-optic effects and are proportional to the field or magnetization contained in the off-diagonal term of the permittivity tensor, whereas the Voigt and Cotton-Mouton effects are second order effects and are usually difficult to observe. Using this permittivity tensor in the Max-well's equation, the detailed beam propaga-tion characteristics can be analyzed for arbitrary orientation between the magnetization or field, the polarization and the direction of beam propagation. Progress made in recent years in the preparation and refinement of magneto-optic media such as insulating magnetic materials, metallic films, glasses, and semiconductors has led to many new magneto-optic technologies and applications. These include laser mode control, optical mass memory, mode conversion in integrated optics, modulation and deflection, and tunable lasers. Both the magneto-optic materials and applications will be reviewed.
Before the laser, if you wanted light at a particular optical frequency there were only two practical possibilities: you could either get lucky and find a spectral lamp which happened to have an emission line at the right frequency, or you would have to resort to using a broadband light source and filtering its output. The filter could take the form of an absorbing glass, a monochromator, or an interference filter -- depending on how narrow you wanted the spectrum and how little light you were prepared to put up with. Since all conventional incoherent light sources are approximately in thermal equilibrium at some well-defined temperature, their spectral radiance can never exceed that of a blackbody at the same temperature.
Liquid crystal devices have become popular in a variety of display and optical data processing applications. These voltage-driven devices can control a beam of light in one of two ways: by induced optical scattering, or by induced optical phase retardation. This paper will review light-modulation effects in liquid crystals, with particular emphasis upon phase modulation effects.
The purpose of this paper is to exam-ine some of the advantages and limitations of hot-pressed materials for optical applications. Several examples which illustrate the effect of a polycrystalline microstructure on optical properties are given, and a few devices based on hot-pressed materials are discussed.
With the increased applications of television imaging systems in the Department of Defense and Aerospace industries, requirements for recording this information have increased accordingly. Development of television tape recorders usable in airborne applications has essentially paralleled development of these imaging systems and has suffered similar inconsistencies. Because of the typically complex and fragile nature of television recorders, the industry has directed most of its efforts toward commercial and consumer markets and very few equipments are oriented to high environment applications. As high performance airborne video recorder technology is in its infancy, so is an in-depth understanding of these devices by most users. The text philosophy of this paper is to provide a better understanding of rotary head video recorders in a relatively simple but comprehensive manner and to present Echo Science's approach to solving traditional problems common to these devices.
We report here preliminary work done on possible applications of mixtures of nematic and cholesteric liquid crystals to the optical conversion of ultrasonic images and holograms. We discuss of an original method by which very small changes of pitch of the helical cholesteric structure can be easily measured a s a function of temperature or pressure. Somme experimental results are given and we expose the principles of an experimental system which is being realized and that should permit direct conversion, in real time, of acoustical images and holograms.
Ferroelectric ceramic material lanthanum-modified lead zirconate titanate (PLZT) has the unusual property that thin plates of fine grained material are transparent. PLZT offers a variety of properties of interest, including electrically controlled birefringence (Ref. 1) and electrically controlled scattering of light (Ref. 2), and ferroelectric, pyroelectric and piezoelectric properties. The first two properties are of particular interest as the basis for constructing light switches, insulators, displays, and optical memories. Parameters entering into the material preparation process, such as impurities, modifiers, dopants, conditions of hot pressing, and the grain size of the ceramic influence the device performance characteristics (Ref. 3). Materials in the PLZT family can exhibit an electro-optic memory effect (related to variations of ceramic birefringence with remanent polarization), a quadratic (Kerr) electro-optic effect, or a linear (Pockels) electro-optic effect depending on the lanthanum content and the Zr/Ti ratio. Land (Ref. 4) indicates that electro-optic memory effects are found in low coercivity rhombohedral and tetragonal PLZT compositions. The Kerr quad-ratic electro-optic effect occurs in slim-loop ferroelectric PLZT compositions for electric fields in the range 0 s lE 1 <Es , where ES is the value of electric field at which the ferroelectric polarization begins to saturate. The linear electro-optic effect is found in high-coercivity tetragonal PLZT compositions.
Two thermal quantities, namely specific heat and thermal conductivity, of hot-pressed cadmium sulfide (a semiconductor) and hot-pressed magnesium fluoride (an insulator) have been measured at low temperatures; such characteristics of these materials as have been determined from analyses of the specific heat data and the thermal conductivity data will be discussed, and will be compared with similar results on single crystal samples of the same materials. The particular hot-pressed samples on which our measurements were made were purchased from the Eastman Kodak Co. (CdS) and the Harshaw Chemical Co. (MgF). Our single crystal CdS was an ultrt high-purity sample purchased from the Eagle-Picher Co. In studying the thermal properties of hot-pressed materials one finds that the hot pressing temperature is probably significant (although detailed information is not available), that impurities and defects are introduced into the material in the preparation process (but not to the extent of measurably altering the density), and that the composite material consists of small crystallites with hexagonal structure in the case of CdS and rutile structure for These structures have been verified in our laboratory by X-ray powder patterns. The grain sizes in our specimens were determined from scanning electron micrographs to be about 2.1 microns and 0.4 microns for CdS and MgF, respectively. It is reasonable to ekpect that grain size might also play an important role in the thermal properties but, as will be shown later, the presence of defects formed in hot-pressing apparently dominates the effects of the small grains.
Measurements of sound velocity and of ultrasonic attenuation have been made on samples of hot-pressed cadmium sul-fide and of hot-pressed magnesium fluoride in the megahertz range and in a temperature range from cryogenic temperatures to room temperature. Both longitudinal and transverse pho-nons have been introduceds and in figures 1 and 2 the sound velocity for each of these polarizations is given as a function of temperature.
Laser communication systems may be divided into four classes: (a) terrestrial short-range systems through the atmosphere, (b) closed-pipe systems for sending high data rate between and within major metropolitan centers, (c) near-space communications for relaying high data rates, and (d) deep space communications.
Optical storage of information offers the potential advantages of high packing density, fast access and low cost. Present research and development on optical memories is divided into two main approaches: those employing bit by bit direct imaging and those employing page organized holograph coding. Each of these categories can be further subdivided on the basis of whether the storage medium is reversible or irreversible. In this paper we will review all four types with emphasis given to the present state of the art and possible future developments. A further class of optical systems which involve the storage of information in non-digital form, i.e. as either direct or holographic images of pictures or documents, is beyond the scope of the present discussion.
It becomes harder and harder to judge a paper by its title. This paper is about Displays. But what does that really define? Not very much, I'm afraid - because Displays mean different things to different people. Right now for example, because of the wide spread interest in elec-tronic watches and hand-held calcula-tors, Displays often conjures up visions of Liquid Crystals and LED's (Light Emitting Diodes). On the other hand, a recent book entitled "Data Display Systems", by W. Gray Horton, turned out to be about various wall charts. Several years ago, a Display paper may have been discussing NIXIE tubes, or projection digit displays, or el?ctroluminescent panel displays, or light valves, or SOLARI "flapper" displays. However, many times when Displays are mentioned, one is really thinking about cathode ray tube systems, and that's what this paper is about.
Optical spatial filtering techniques have been applied to character recognition; several papers have been written which illustTae the basic principles of these techniques. The primary difficulty is that the similarity between certain sets of characters and the variations in a given character due to noise sources make it difficult to make adequate discrimination and to achieve sufficiently low error rates.
Light from a projector lamp is passed through condenser optics and a polarising beam splitter/ analyser, and illuminates uniformly an electron beam actuated Pockels modulator. The modulator rotates the plane of polarisation of the light which is reflected back to the analyser. The output of the analyser can be projected to a large screen. The electro-optic target consists of an A1203 - ZnS layer structure biased with a d. c. voltage. A charge pattern correspond-ing to a T.V. image is produced at the interface by electron beam induced conductivity in the .A1203 layer. Current gain in the EBIC layer enables low beam currents to be used. By controlling the amount of uv in the light, the electro-optic ZnS is rendered sufficiently conductive for the interface charge to decay in a frame time. Calculations show contrast ratios > 100:1 could be obtained using a 4 cm diameter target and a brightness of 60 ft lamberts could be achieved on a 12ft by 9ft screen, from commercially available arc lamp.
A photoelectric scanning system has been constructed to determine line positions on the 65-centimeter diameter divided circle of a meridian circle telescope. The system consists of six scanning micrometers attached to microscopes which are aimed at different portions of the circle. Each micrometer has a field of view of 0.35 degrees. Six different quasi-linear segments on the circumference of the divided circle are scanned simultaneously. Profiles of divided circle lines and reference lines are obtained in digital form and analyzed by a data acquisition computer. On repeated scans (n=30) the system achieved a resolu-tion of 0.04 arcsec with a standard devia tion of 0.05 arcsec. The operational characteristics and reliability of the system indicate that it can be used as a real -time primary angular readout method for the accurate determination of the zenith distances of stars.
Storage oscilloscopes are largely used as output instruments of analog and digital computer. The large diffusion of this type of display is due to its high resolution versus its limited cost. For comparison, a standard CRT display used for graphical application requires either a large special purpose memory or continuous image refreshing by computer; other applications of storage oscilloscopes are the analysis of non periodic events and the monitoring of slow signals. The main disadvantage of such oscilloscopes has been up to now the difficulty of interacting with the image, while for standard CRT display several light pen systems are available for image interaction. The light pen operates by correlating the time phase of the light, as detected by a photodetector, with the period of the image refreshing, as performed by a flying spot of light on the CRT screen. This time phase is strictly related with the position of a pen holding the photodetector optically oriented toward the screen.
In this paper experimental results of He-Ne laser light diffraction by ultrasound in a liquid waveguide are pre-sented. The 45 MHz ultrasound (also known as layer waves) in the liquid waveguide, which consists of water sandwiched between two parallel plates of LiNbO3 and fused quartz, is generated by interdigital transducers at one end of the LiNbO, plate. The diffracted light is used to obtain inforMation about the properties of these layer waves, such as the velocity dispersion for different mode of propagation. This optical probing also enables one to directly observe the evanescent ultrasound in the guiding solids and measure the decay parameter. Possible applications in the field of integrated optics and signal processing are discussed.
The effect of input source varia-tions during the time of the measurement interval is analyzed in relation to transform spectrometry. Both over-all and relative spectral changes are considered. Hadamard and Fourier transform spectrometry are used as examples. The Fourier spectrometer (interferometer) is shown to be capable, after correction, of generating the mean value of the input spectrum over the measurement interval, while the so-called "Hadamard" spectrometer fails to do so. These conclusions are demonstrated experimentally using synthetic spectra.
Acousto-optic devices are finding increasing application as deflectors, modulators, Q-switches and mode lockers in laser systems. A key element in any such device is the transducer which converts the electrical drive signal to the acoustic wave. Usually the transducer is a piezoelectric plate bonded to a material chosen for its acousto-optic properties. The performance of piezoelectric transducers has been studied extensively since Mason (Ref. 1) developed a convenient equivalent circuit for bonded thickness mode piezoelectric plates. We review here the performance of a variety of transducer -acousto-optic material combinations of current relevance.
The rotatory power of a crystal can be modified in the presence of an external force, due to changes of the optical spatial dispersion tensor. In first order, such changes are linear in the applied force, and they must conform with the force-free crystal symmetry, for weak forces. The behavior of the applied force under time reversal should also be considered, since a time-antisymmetric force will modify the axial character of the gyration tensor. In particular, application of an electric field will lead to the so called electro-optical activity (EOA), i.e., rotation of the plane of polarization linearly with the field. Modulation of the applied field will accordingly lead to modulation of the plane of polarization. It is shown that EOA can be separated from the electro-optic effect, birefringence and natural optical activity, by apprpriate choice of crystal class and optical geometry. Similar effects due to a magnetic field have been identified as magneto-spatial effects or magneto-optical activity (MOA). Their relation to the well-known Faraday effect is discussed. Other possibilities are also presented, including stress effects, pressure and temperature effects. The acoustical analog of these effects is also introduced, as well as the possibility of rotational effects, i.e., effects arising from the antisymmetric (rota-tional) part of a shear elastic wave. By using simple group-theoretical arguments, it is shown that the component array of the higher-rank tensors which describe the above non-linear phenomena can, in most cases, be obtained from well-known tensors of crystal physics by inspection. Specific examples are given.
In order to clearly separate the various systems that are to be discussed in this paper it is necessary to settle some definitions at the outset. We are going to very briefly discuss two different types of remote detection and compare them with the technique known as point sampling. Point samplers require the presence of some part of the instrument at the location where measurement is to occur. Relatively narrow area of coverage is obtained although the instruments are sensitive and can be quite small since sample dilution is minimal. All of the techniques mentioned are usable in point samplers although, in some cases, they are unnecessarily expensive and complex for such straightforward use. Quan-titative detection in terms of point sampling, while valid for a relatively small area or location, can be questioned in terms of how well the point sample characterizes an area in the surrounding vicinity. (Ref. 1)
The test results presented were obtained over a 9 month period at the Naval Electronics Laboratory Center at San Diego. The test objective was to assess the structural and other physical property characteristics of non-coherent, plastic jacketed, glass fiber-optic cable types of current manufacture. Tests were conducted to evaluate the capabilities of these type products to sustain structural integrity and operability after subjection to test exposures simulating Naval shipboard environmental conditions. The guide for these test conditions was either existing Military Standards and Specifications, where appropriate, or assigned test levels believed to be in excess of operational requirements. A total of 29 types of tests were performed utilizing over 200 fiber optic cables. A major part of this task involved the development of diagnostic test techniques for the evaluation of the test-induced cable property modifications. Tests of cable mechanical strength properties included bending radius, tensile, terminal, twist, mandrel, cyclic flexibility, vibration, mechanical shock and jacket abrasion. Test data analysis permitted determination of the limiting cable strength characteristics based upon measured 10 percent fiber breakage levels. Environmental tests performed consisted of thermal cycle and extended high and low temperature regimes, humidity cycle and steady state profiles and salt fog exposures. Chemical bath immersion tests included salt, mineral oil, sodium hydroxide and sulphuric acid as tests reagents. Results obtained from these tests demonstrated the ability of these type products to with-stand a wide range of physical exposures. Generally, it is concluded that the difficulties associated with the present utilization of fiber optic cables for many Naval applications are not as much related to limitations in the physical properties of these cables as they are to the lack of component and system manufacturing technology in this field. A final report detailing the fiber opticcable performance obtained in this test program is available by writing either to the author at Code 4400, or Library, Naval Electronics Laboratory Center, San Diego, California 92152. The report is entitled "Fiber Optic Cable Test Evaluation" and identified as NELC TR-1869.
Without any doubt, the dye laser is now out of the experimental stage and is becoming a valuable analytical tool, serving in many applications. Surveys have shown (1) that UV and visible spectrophotometers & GC now dominate the analytical field, accounting for more than half of all analytical instruments being sold. In these instruments, light sources are used which have a relatively low intensity and replacement with dye lasers is quite welcome. Dye laser application areas include: Chemistry, Medicine, Biology (microfluorometry), pollution detection and photochemistry.
Historically, optical activity has been studied by physicists and chemists and found its main contribution in physical chemistry. Optical activity is used in chemistry as a means of studying the structure of organic and inorganic substances. Since most amino acids, which are the building blocks of life, are optical active, scientists have been able to study samples from extraterrestrial sources using the methods of optical activity to predict the existence of life on other planets. (Ref. 9)
Many high quality biocular magnifier eyepieces for two-eye viewing have been designed and fabricated for use with image intensifier direct view systems. These eyepieces provide outstanding imagery across a large exit pupil. The phosphor screen of the image intensifier tube has sufficient brightness (10 to 100 foot lamberts) to allow for very comfortable two-eye viewing. The great advances of the Far Infrared (FIR) technology which detects temperature differences and displays that thermal image in the visible spectrum now provide a new dimension to night vision systems. Those FIR systems that use a cathode ray tube (CRT) display can capitalize on the biocular eyepieces designed for image intensifier systems. However, the majority of FIR systems use Light Emitting Diodes (LED) which are reflected off the back side of the FIR scan mirror so as to avoid the complexity of multiplexing inherent in CRT displays. The scanned LED displays typically use visible relay optics which are slow (approx f/9) and present a real image to an eyepiece lens. One cannot use the afore-mentioned biocular eyepieces since most biocular eyepieces have an f/number less than f/1.0. Therefore, current FIR systems with LED displays use only monocular eyepieces and often cause most observers to "squint" at the thermal picture. This paper proposes a solution to that situation which uses a "diode tube" consist-ing simply of a photo-emitting cathode, proximity focussed on a phosphor screen, which provides a lambertian source of increased brightness located at the reticle plane of the visual optics relay and thereby allows for use of existing image intensifier biocular eyepieces. Measured performance parameters of the biocular eyepiece and diode tube are presented.
Electro-optics, in the broad marketing sense, has more recently come to include the systems dealing with optical phenomena any-where in the electromagnetic spectrum. The electro-optics businesses in the United States, Japan and Western Europe have grown rapidly to a $10 billion a year level as of 1972. Current estimates are that the world electro-optics industry will reach a $35-40 billion level by 1980. A great deal of potential of the electro-optics industry relates to the fact that it is a major segment of and interlink with the knowledge industry, and significant in many types of information and communications advances. A great deal of the work in electro-optics involves handling visual information. This places it in an unusual position as regards the coming "video society." In information handling by computer, electro-optics may be used to provide inputs, processing, communications, and printed or visual output. The continual emergence of new technologies produces new opportunities. Examples are: integrated optical circuitry, charge transfer devices, and other optoelectronic components which make possible major new systems for industry, education, consumer, military, and other markets. This paper briefly touches upon the subjects of major economic import currently estimated for the electro-optics industry.