Determination of the elastic and piezoelectric constants for crystals in class (3m) is complicated by the large number of independent constants and the many possible ways in which they may be combined. An experimental and analytical procedure has been developed to determine all the constants using primarily thickness-mode measurements made on small, plate-shaped samples of various crystallographic orientations, and results using this procedure have been obtained for lithium tantalate and lithium niobate, two recently developed synthetic crystals. The resonant and antiresonant frequency constants for thickness modes have been calculated as functions of a plate's rotation angle. Information in this form makes possible the selection of plate orientations that might be useful as resonators and transducers.

All of the elastic and photoelastic constants of crystalline lead molybdate (PbMoO4) and various optical and thermal properties of the material have been measured. This information has been used to evaluate the material for a number of practical acousto-optic device applications. The high figure of merit found in earlier preliminary studies is only 10% smaller than the maximum figure of merit of the material. Thus the material is well suited for acousto-optic modulator and deflector applications. However, the material is not particularly useful for tunable acousto-optic filters because the relevant elasto-optic coefficient is small. Acoustic and optical losses, and changes in sound velocity and index of refraction with temperature, can cause operating limitations in practical devices, and these are discussed.

Crystalline lead molybdate PbMoO4 has been found to be well suited for acousto-optical device applications. This material has desirable properties similar to the previously reported α-iodic acid α-HIO3. However, PbMoO4, unlike α-HIO3, is insoluble in water and can therefore be readily fabricated into devices and its optical surfaces do not require protection from the atmosphere. The elastic, photoelastic, optical, and thermal properties of PbMoO4 have been measured. These data have been used in the design of several acousto-optic devices. An example consisting of a two stage (horizontal and vertical) acoustically driven light deflector is described. Each stage of this deflector has an 80-MHz bandwidth and can deflect over 50% of an incident laser beam (5145 Å) with less than 1 W of electrical drive power.

Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto-optic figure of merit in single-crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this material's birefringence to circularly polarized light. Dixon's equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound-to-light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a capacity of 500 linearly resolvable spots with a random access time of 10 μsec, with 50% of the incident light being deflected at 35-mW acoustic power.

A 2.5-mc crystal unit has been developed for use in a new, extremelu stable frequrncy standard oscillator. A well-balanced design was achieved by using a 30-mm-diameter, plano-conoex, polished quartz plate, coated with gold and operated on its fifth ooertone. The quartz plate is mounted on its quiescent edge in an eoacuaied bulb, and achieoes a Q of five to six million, represeniaiioe of the Q of the quartz itself. The temperature coefficient, current coefficient, frequency adjustmen: tolerance and frequency aging oj the crystal unit are all consistent with a frequency stability in the order of one part in 1010. It was necessary to deoelop polishing methods that would not disturb the crystal structure of the quartz plate and new methods of orienting the crystallographic a.res to achiere better temperature coefficient control. New methods of mounting the quartz plate werc found that aroid strain and reduce the e,{fects oj shock and cioralion. The new crystal unit makes possible oscillators characterized by excellent frequency stability, small and uniform aging and straightforward design. For periods up to one month, the frequency stability of such. standards compares Javorably with that of atomic [requenci) standards. I. I NTHODFCTIO:-\The quality of a quartz crystal frequency standard is determined by the crystal-controlled oscillator, and particularly by the mechanically vibrating, piezoelectrically excited quartz plate. Special quartz crystal resonators, characterized by high Q, excellent frequency stability under shock and vibration, and small change with time, have been developed for use in a new general-purpose, extremely stable frequency standard.The development of improved oven and oscillator circuits has contributed substantially to this improved standard, and will be reported in a separate urticle. Over-all performance of an experimental oscillator has heen reported briefly,' and similar oseillutors are in operation at the Xu-1193