[45] C. S. Tsai, Le T. Nguyen. M. A. Alhaider, “Wideband Acoustotwo Tilting Surface Acoustic Waves,” Appl. Phys. Lett. 26, optic Guided-Light  Beam  Deflector  Using Tilting  Surface 140-143, February 15,1975. Acoustic  Waves,” 1974 Ultrasonics  Symposium  Proceedings, [47] C. S. Tsai, M. A. Alhaider, Le T. Nguyen and B. Kim, “WideIEEE Cat.. # 74. C H 0 896-1SU. 768-772. band Guided-Wave Acoustooptic Bragg Devices Using Multiple [46] C. S. Tsai, Le T: Nguyen, 8. K.’Yao and M. A. Alhaider, “HighTilting Surface Acoustic Waves,” Talk-36, Conference on Laier performance  Acousto-optic  Guided-light  Beam  Device  Using Engineering and Applications, Washington, D. C., May 1975

III. Optical Probing of Surface Waves and Surface Wave Devices

The surface restricted transient grating is demonstrated as a sensitive probe of ultrafast surface reaction dynamics. Studies of doped single crystal n‐TiO2 (001) surfaces in air demonstrate linear trapping processes, assigned to crystal defects within the surface deformation layer, that limit carrier lifetimes to 5 ns. Direct in situ grating studies at photochemically active n‐TiO2/H2O interfaces demonstrate that the dominant mechanism of interfacial electron transfer in this system involves thermalized hole carriers at the atomic surface. The dynamics are consistent with adsorbed OH− as the initial hole acceptor. In addition, optical generation of coherent surface acoustic modes is demonstrated. A detailed theory is presented for the grating excitation of the surface acoustics. Acoustic propagation in the H2O half‐space of the TiO2/H2O liquid interface gives evidence for a phase change of the water layer at the polar TiO2 (001) surface to a solid phase.

Picosecond dynamics of surface electron transfer processes: Surface restricted transient grating studies of the n‐TiO2/H2O interface

Surface acoustic waves in nonlinear elastic media

A new type of surface acoustic waves in solids due to nonlinear elasticity

The theory and performance of a two beam differential interferometer for measurement of both surface and bulk waves are described. The system is insensitive to small errors (<1 mm) in focus or in specimen flatness. Both amplitude and phase measurements are demonstrated. The system has been absolutely calibrated and can detect 6 × 10−4 A surface wave displacements on glass.

Ultrasonic wave measurement by differential interferometry.

A theoretical analysis of the diffracting effects produced by ASW on light beams contained on the sagittal plane of the wave is presented. The separate contributions have been explicitly studied, produced by periodical changes of the refractive index and by corrugation of the surface in cases of x‐ and y ‐cut crystalline quartz and y ‐cut LiNbO3 for both states of polarization of the incident light. In all cases analyzed, measurements of light‐deflection efficiency have been performed as a function of the angle of incidence in light‐transmission experiments.

Incidence angle and polarization dependence of light diffracted by acoustic surface waves

The nonlinear electroacoustic effect has been investigated for acoustic Lamb wave propagation in a YZ LiNbO3 plate under a uniform bias electric field. A theoretical model is briefly outlined, which shows how the effect can be interpreted in terms of second and third order material constants. The strength of the nonlinear interaction has been experimentally evaluated through measurements of the change in phase velocity of Lamb modes produced by the bias field. The experiments were performed in the frequency range 8–33 MHz on most of the Lamb modes excited in a 1.25‐mm‐thick plate by an interdigital transducer with a periodicity λ=0.396 mm. The results evidence a strong dependence of the nonlinear effect on the order and symmetry of the analyzed modes.

Acoustic Lamb wave‐electric field nonlinear interaction in YZ LiNbO3 plates

The spread of results obtained by different theoretical approaches in studying acoustic surface wave nonlinear interaction and difficulties in treating strongly piezoelectric materials indicate a need for more experimental data. In the present work the spectral asymmetries of the light diffracted by surface waves are analyzed in order to evaluate the complex coupling coefficient in second harmonic surface‐wave generation. The experimental conditions are such as to keep the acoustic energy mostly confined to within fundamental and second harmonic waves. Amplitude and phase of nonlinear coupling coefficients were separately determined for LiNbO3 and crystalline SiO2 substrates through different geometries of the acousto‐optical interaction, crystal cuts, and propagation directions of the waves.

Phase and amplitude relations between fundamental and second harmonic acoustic surface waves on SiO2 and LiNbO3

The light deflection efficiencies of surface acoustic waves propagating on YZ–LiNbO3 crystal are examined for different geometrical configurations. The optimum one is found to be the back reflection geometry, with S polarization of the impinging light beam, where a figure of ~16% of the total deflected to undeflected light intensity ratio is easily attainable with a surface corrugation amplitude of about 50 A.

Acoustooptic interaction for most effective deflection of unguided light via acoustic surface waves.

The scanning of a transparency is done by letting a collimated light wave front illuminate it and be diffracted by very short pulses of ultrasonic surface waves. Detection of diffracted light follows a time dependence that equals the transparency brightness along each line that is successively scanned. 94−MHz wave trains, about 10 wavelengths long, give a potential number of resolved spots per second almost equal to 107. Interaction geometry by back−surface reflection has been used, which greatly enhances the diffraction efficiency and yet retains the large acousto−optical bandwidth proper to surface waves.

A. Palma

Papers

Incidence angle and polarization dependence of light diffracted by acoustic surface waves

Acoustic Lamb wave‐electric field nonlinear interaction in YZ LiNbO3 plates

Phase and amplitude relations between fundamental and second harmonic acoustic surface waves on SiO2 and LiNbO3

Acoustooptic interaction for most effective deflection of unguided light via acoustic surface waves.

Image scanning through the acousto−optical effect produced by acoustic surface waves