V. M. Ristic

High‐resolution spectroscopy for optical probing of continuously generated surface acoustic waves

Under conditions of continuous acoustic generation, light scattered from oppositely directed surface acoustic waves on y‐cut z‐propagating lithium niobate was frequency analyzed with a high‐resolution Fabry‐Perot interferometer. The following parameters were measured at 105 MHz: acoustic power standing‐wave ratio, reflection coefficient for both sending and receiving transducers, low‐power acoustic damping coefficients, surface wave propagation velocity, and nonlinear harmonic growth. We note that the method used has an advantage over other methods since it is to a large extent independent of the optical quality of the propagation surface.

Rise time and time‐dependent spark‐gap resistance in nitrogen and helium

The rise time and time‐dependent spark‐gap resistance in nitrogen and helium were measured using a novel microwave method. Empirical formulas for spark‐gap resistance and rise time are proposed, with a maximum error, as compared to experimental results, of ±8%.

Nonlinear surface‐wave interactions: Parametric mixing and harmonic generation

The nonlinear interaction of surface acoustic waves propagating in the same direction has been treated from the rigorous theory of thermoelasticity. Exact expressions were derived for the nonlinear volume forces and surface stresses, and the nonlinear cross sections were calculated under two separate assumptions. First, the work done by the nonlinear forces and surface stresses on a normal‐mode surface wave was evaluated and assumed to be totally converted into surface‐wave energy. In the second approach, a linear analytic solution was formulated which simultaneously satisfies the nonlinear wave equation and maintains a stress‐free boundary condition. Numerical values for the strength of second‐harmonic generation were calculated for 24 materials. The characteristics of nonlinear surface‐wave generation were compared with those of nonlinear bulk‐wave generation and significant differences were found. Coupled amplitude equations were derived to treat the case of multiharmonic generation. Finally, a charact...

The evaluation of the input admittance of SAW interdigital transducers

Using the moment‐method technique, the exact charge distribution on a finite interdigital array is obtained. Full account is taken of the coupling to bulk and surface modes. The moment‐method technique greatly simplifies the evaluation of the transducer input admittance. The frequency dependence of the input admittance is computed for a different number of electrode pairs, different metallization ratio, and different sequences. The electrostatic capacitance is proved to be 28% higher than the zero‐coupling capacitance for Y‐Z lithium niobate.

Probing of surface acoustic wave devices with large‐diameter laser beam

The theory of dark field imaging technique as applied to acousto‐optic interactions has been developed and then used in studies of linear and nonlinear surface acoustic waves and volume acoustic waves. The theory is consistently expressed in terms of phase transmittance function. Experimental results show how the technique can be applied in the case of multimode propagation to unfold the complex frequency spectra of spurious modes in surface wave devices, and how to discriminate between different harmonics in the case of nonlinear acoustic propagation.

Surface‐wave harmonic generation on y‐z, x‐z, and 41 1/2‐x lithium niobate

Optical probing was used to evaluate the coefficient for surface‐wave harmonic generation on three high‐coupling cuts of lithium niobate, namely, y‐z, x‐z, and 41 1/2‐x. Surface‐wave attenuation and acoustic beam diffraction profiles of the fundamental and second harmonic were also measured.

Hybrid implementation of a real-time Radon-space image-processing system.

A unique hybrid optical-digital image-processing system that functions at real-time rates and performs analysis in Radon space is presented. This system functions by using the forward Radon transform (a mathematical tomographic transform of image data from two-dimensional image space to onedimensional Radon space), which is achieved by a front-end optical processor followed by a digital processing subsystem operating in Radon space. The system works by optically converting the two-dimensional image data into a series of one-dimensional projections. All further processing is performed digitally in Radon space on the one-dimensional projections. Using the system in transform space, we show that it can perform real-time detection of minimum-resolvable-temperature-difference measurement targets better than a human observer. Also, this paper discusses the potential of real-time object-moment analysis in Radon space. These object moments can be calculated in Radon space with significantly less image data and fewer digital processing operations than in image space. The optical front end is capable of performing 6.04 × 10(10) operations/s on the two-dimensional image data.

Design parameters of Ti:LiNbO/sub 3/ waveguides for optimum acoustooptic interaction efficiency

A computer model of optical and surface acoustic wave modes in titanium indiffused Y-cut LiNbO/sub 3/ guiding structures is used to produce several graphs for the design of guided-wave acoustooptic devices with optimum interaction characteristics. The design concentrates on waveguide fabrication parameters in order to achieve the optimum acoustic frequency and the acoustooptic interaction bandwidth. The optimum acoustic frequency for a given value of Ti film thickness and diffusion depth is defined as the frequency causing the maximum value of the overlap integral. >

Excitation and Detection of Volume Elastic Modes with Surface Conducting Gratings

This paper concerns excitation and detection of volume elastic modes with surface conducting gratings. First, the generation of volume elastic modes is analyzed along degenerate (pure) and nondegenerate mode axes. It is shown under what conditions a strong volume‐wave generation occurs. An experiment aimed at measuring coupling losses, and checking the theory, is described. The paper also includes a brief discussion of the applicability of the results to generation of volume elastic waves in a microwave region.

Study of Anisotropy Effect in Planar Lenses for Integrated Optics

Abstract The extraordinary-ray ray-tracing method for planar waveguides on uniaxial crystals is developed. Using the method and the extended equivalence principle, the effect of anisotropy on the performance of planar lenses is investigated in detail. The agreement between theoretical and experimental results is very good.