There is a method and hence a set of criteria that chairmen use to select speakers for opening or keynote addresses. The process operates in the following way: 1. Look for the clearly acknowledged leader in the field and get that person. If successful, allow 30-40 minutes for the talk. If that person is not available or there is no clearly identifiable person, proceed to step 2. Do not be tempted to choose someone else in the field. 2. Select an eminent person who is somewhat familiar with the field but is well known in some other area. This person will clearly not be controversial and will have no personal axe to grind. If successful, allow 20 minutes for the talk. If this is not possible, proceed to step 3. 3. Select the President of the sponsoring organization for the meeting and indicate to him that it is his unavoidable responsibility to present this particular address. Allow the minimum time possible for the talk. Do not be tempted to use any other argument other than 'unavoidable responsibility'. Method 3 cannot fail, since the only other recourse is for the Program Chairman to do it himself.
A well-developed technology of depositing ZnO piezoelectric transducers on crystals for bulk-wave acoustic delay devices has been applied to the manufacture of microwave acousto-optic devices. Unlike the basic difficulties encountered when attempting high frequency operation of bonding thin-plate piezoelectric transducers, sputtered ZnO transducers operate well at high frequencies but encounter difficulty with thick films (> lOmicrons), The ZnO films for longitudinal bulk^wave propagation work best when confined to the frequency band of 200 MHz to 18 GHz, ZnO transducer depositions are not suitable for some materials, including PbMoO4, and TeO2, which have very high acousto-optic figures of merit, but do work well with LiNbO3, LiTaO3, TiO2, Ba2NaNb5O15 fused silica, YAG, single-crystal quartz and sapphire. Broad bandwidths can be achieved using ZnO transducers. Acousto-optic units with more than 1 GHz (3 dB) bandwidth have been built with LiNb03 and LiTaO3 as the acousto-optic material, with center frequencies ranging from 2.6 GHz to 6.5 GHz. Transducer conversion loss (total loss encountered from incident RF signal to acoustic signal including matching network losses) for the 1 GHz bandwidth units is less than 10 dB. Examples of broadband microwave acousto-optic devices (presently in production) for use with cavity dumpers are given.
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.
The performance of an acoustooptic beam deflector depends on its bandwidth and diffraction efficiency with its acoustic delay time providing a trade-off possibility between resolvable spots and access time. Transducer power density considerations with present fabrication techniques place a limit on acoustooptic beam deflectors at 100 MHz bandwidth with 50% efficiency. It has been known for some time that the deflector efficiency bandwidth product can be improved with acoustic beam steering by stepped-array-transducers. However, a simple practical fabrication technique for the step-array-transducer in the UHF region is yet to be developed, due to miniature step dimensions. Employing a wedged intermediate medium to make up the precise steps, we have successfully constructed a number of wideband step-array acoustooptic beam deflectors with total flexibility in interaction medium selection. Typical parameters on our deflectors are 50% diffraction efficiency at 750 mW rf drive power, up to 250 MHz 3 db bandwidth (200 MHz 1.5 db), and 2mm by 30 mm optical aperture with PbMoO4 deflector body. That is a deflector of 2000 spots at 8.5 microsecond access time. Ultimate deflector bandwidth limit with this fabrication technique is estimated to be about 350 MHz.
In this paper we wish to discuss the applications of acousto-optic modulation and the recent advances in device technology. We will also present medium volume device fabrication processes and projections on modulator costs in OEM quantities.
Analytical models are presented which quantitatively relate the efficiency/bandwidth per-formance of A-0 modulators to the transverse mode structure and polarization states of the incident laser beam. The cases treated include plane and elliptically polarized, He-NE (632.8 nm) and He-Cd (441.6 nm) laser radiation in either a TEM00, TEM01 or TEM10 transverse mode. For modes higher than TEM00 a significant decrease in efficiency/bandwidth occurs. The effect of power fluctuations associated with the principal polarization components of internal mirror gas laser output beams is also evaluated. Such effects present severe problems in the case of He-Ne laser beam modulation, but are less serious for He-Cd lasers. Several experimental measurements which confirm the general validity of the analyses are also described.
This paper describes recent advances in the area of acoustic-traveling-wave-lens technology as applied to optical beam deflection. Test data from a breadboard, beam deflector system will be presented. This system rapidly scans a focused laser beam across a recording medium (for recorder applications) or across an existing image (for readout applications). The scanner uses a Bragg-effect, acousto-optic beam deflector (AOBD) working in series with an acoustic-traveling-wave-lens (ATWL) device to produce an extremely fast, high resolution laser scanner that uses no moving parts. The breadboard system has achieved a resolution of approximately 5000 single-Rayleigh spots per scan line and a bandwidth of 100 MHz. A further advantage of this approach is its excellent linearity. A linearity of one part in 104 has been achieved and a goal of 2 parts in 105 has been established for experiments currently underway. This technology appears to possess excellent growth potential with resolutions of 20,000 spots and bandwidths of 200 MHz being clearly in the realm of possibility.
A detector consisting of a piezoelectric substrate with periodically spaced, thin-film absorber strips on its surface for generation of a surface acoustic wave (SAW) is described. Various modes of operation of the absorber of the incident radiation are considered. Use of the detector for detection of wavelength and angle of arrival of the incident radiation is discussed. Results are given of tests of a detector (25 MHz) with a CO2 , a Nd:YAG, and a ruby laser. A qualitative analysis of the detector is made, explaining the observed variation of the detector response to laser pulses of identical energy. The rise time, tr , is found to be an important parameter. For good performance the periodicity of the absorber must be selected so the frequency of the SAW is considerably less than 1/tr . On the basis of an experimental comparison with pyroelectric detectors, and theoretical predictions of improved performance by changes in the detector design, it is predicted that the detector will provide better detection of nanosecond CO2 laser pulses than that provided by other room-temperature thermal detectors.
Two applications of the diffraction of light by surface acoustic waves (SAW) on reflection from, and transmission through a propagation surface are discussed. In the first half of this paper it is shown that the properties of the diffracted light make this scattering technique an ideal diagnostic tool for investigating surface waves and surface wave devices. Measurements of a number of surface wave propagation parameters both on a free surface and inside interdigital transducers are presented. Also discussed are device applications of this acoustooptic interaction. It is demonstrated that an image can be scanned at Megabit/ sec rates using light scattering from SAW. A versatile signal processor which utilizes the double diffraction of light by surface waves is discussed and examples of convolution, time compression and time inversion are shown.
In this paper a review of recent progress on wideband guided-wave acoustooptic Bragg deflectors is made. The engineering aspects of guided-wave acoustooptic Bragg deflectors such as materials, design considerations and fabrication techniques are first reviewed. Design, evaluation and performance characteristics of several wideband deflectors which employ multiple surface acoustic waves in Y-cut LiNb03 substrate are then described. Finally, a number of potential applications using such wideband deflectors are discussed together with some performance figures.
In this paper, thin film acousto-optic devices are discussed in terms of (1) the unique features in theoretical calculations which arise from the use of guided wave structures, (2) the possible device configurations which may improve efficiency and speed, (3) the thin film material and fabrication problems, (4) the transducer efficiency bandwidth trade-off, and (5) a comparison with bulk acousto-optic devices and thin film electro-optic devices. Recent experimental results for thin film acousto-optic modulators and convolvers are included.
This paper reviews the results of research in imaging reported in the last two years approximately. The emphasis is placed on the high frequency applications of this subject and very little reference is made to sonar and none to geological applications. The subject is discussed under three main divisions, direct (pulse echo) imaging, holography and finally particular devices. Emphasis has been placed on the physical principles used. It is assumed the reader is conversant with the outlines of earlier work in the field.
Image modulation of an acoustic wave produces refractive effects in a volume of elasto-optic material. A plate having the thickness of half the acoustic wave length generates refractive patterns corresponding to the phase and amplitude modulation of the acoustic carrier. From this a method is proposed to obtain realtime images from sonar echoes. A laser interferometer is described by which the phase undulation of the echo wave front may be encoded in video format. Realtime image reconstruction techniques are presented. Applications and limitations of acoustic imaging are discussed.
It is well known that during the recording of an optical hologram the relative distances among object, holographic plate and light source must remain constant to within half a wavelength, otherwise the interference fringe will be completely blurred and not recorded. This blurring is due to the time integration of the received wavefront which takes place in the photographic emulsion. In acoustical holography, on the other hand, the situation is different, because the output of the piezoelectric transducers which are normally used as detectors follows the acoustic input without any integration. As a result, object motions cause a distortion of the fringes and frequently a shift of the holdgraphic pattern takes place. It should be pointed out, however, that in practice there could always be a small amount of time integration in the processing electronics which will cause a small amount of blurring of the holographic fringes.
Although ultrasound has been used in medicine since the 1930's, it is only recently that this technology has been widely used and its potential fully recognized. Medical ultrasonics is now in a period of rapid growth and is on the verge of making a significant impact on clinical medicine. The field provides challenging and important engineering problems, which are unique to medicine and biology. This review describes ultrasonic techniques presently used in the clinic, discusses several new techniques presently under development in the laboratory, and notes several promising procedures for processing ultrasonic data. The review is limited to pulse-echo techniques or parameter mapping systems which produce pictorial representations of the location of reflectors and scattering sites but which do not "image" in the generally accepted optical sense.
Several existing real-time systems for ultrasonic imaging are capable of producing impressive orthorgraphic images. However, analysis of their ideal performance shows that these systems are still not as sensitive as desirable for practical diagnostic use when it comes to imaging targets through thick regions. An imaging approach utilizing a scanning-focused-beam and piezoelectric detection possesses the best inherent sensitivity, and thus the potential to produce an effective image with the least tissue exposure to ultra-sound. A possible embodiment of a system based on this highly-desirable approach is being worked on. The key element is an opto-acoustic transducer (OAT) addressed by light carrying a focus-inducing pattern. The OAT must be carefully designed and evaluated before construction. Two basic types of OAT structures have been investigated by means of equivalent-circuit models and computer simulation, which takes into consideration the dependence of OAT performance on device geometry, amplitude and phase distortions, material properties and operating conditions. The simulations indicate that certain configurations with available materials have the proper characteristics to qualify as candidates for OAT construction. Designs for prototype OATs have been made. The construction and testing of the prototypes are underway.
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 simulataneously 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 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 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.
A wideband photorecording technique has been developed which will coherently record signals of 1 GHz bandwidth. Strobe illumination of the travelling acoustic wave pattern inside a wideband acousto-optic Bragg cell with sub-nanosecond laser pulses allows recording of the signal waveform by imaging the diffracted light onto photographic film. Coherent readout of a one millisecond record has demonstrated a signal to noise ratio of 25 dB (Speak/Navg).