The absorption-layer method for inducing pressure shocks is employed to generate finite-amplitude, broadband surface wave pulses in crystalline silicon. Spectral evolution equations are used to compute the wave form distortion from the first to the second measurement location, and the results are shown to be in quantitative agreement with the measured data. The measurements also confirm that a nonlinearity matrix which describes the coupling of harmonics provides a useful tool for characterizing wave form distortion. In the (001) plane, the measurements show that the longitudinal velocity wave forms develop rarefaction shocks along [100] and compression shocks along 26degrees from [100]. In the (110) plane, compression shocks are observed in the longitudinal velocity wave forms in the direction 37degrees from [100], whereas rarefaction shocks are seen along [1(1) over bar 0]. The results in the (001) and (110) planes are consistent with sign changes in the nonlinearity matrix elements. In the (111) plane, the measured wave form distortion is consistent with the phase changes associated with the computed complex-valued matrix elements. In particular, the characteristics of propagation in the [11(2) over bar] and [(11) over bar 2] directions are shown to differ. This specific case is proved to follow from a more general result based on the symmetry properties of surface acoustic waves in this plane. In all the planes, it is demonstrated that, unlike bulk waves, the peak acoustic amplitude of surface waves can increase as they propagate, thereby allowing large stresses to be generated at surfaces. Finally, the power flux and total power of the pulses are shown to be substantially higher than in previous reports.

Solitary acoustic pulses can propagate along the surface of a coated homogeneous and inhomogeneous medium. It is shown how these nonlinear surface acoustic waves evolve out of initial pulselike conditions generated by pulsed laser excitation and how they can be monitored by optical detection. The solitary pulse shapes at the surface are computed on the basis of an evolution equation with nonlocal nonlinearity. They depend on the anisotropy of the substrate. Various approaches for the derivation of the evolution equation from nonlinear elasticity theory are critically compared. The behavior of the solitary pulses in collisions is investigated and is found to strongly depend on the linear dispersion law. The nontrivial depth dependence of these solitary pulses is also analyzed.

Previous numerical and experimental studies of surface acoustic waves (SAWs) in the (111) plane of cubic crystals have shown that linear properties, including the wave speed and the direction of power flow, exhibit sixfold symmetry. However, recent measurements by Lomonosov and Hess of finite-amplitude SAW pulses propagating in opposite directions in the (111) plane of crystalline silicon have demonstrated that the same periodicity does not hold for the nonlinear distortion. Calculations based on a model for nonlinear SAWs in anisotropic media [Hamilton et al., J. Acoust. Soc. Am. 105, 639–651 (1999)] indicate that complex-valued nonlinearity matrix elements, which describe the coupling between harmonics, have sixfold symmetry in magnitude but only threefold symmetry in phase. As a result, pulses traveling in opposite directions exhibit different nonlinear phase shifting between harmonics that give rise to the distinctly different types of observed distortion. Threefold symmetry of nonlinearity is also predicted for other cubic crystals besides silicon. Additional computations show that the complex-valued eigenvalues and eigenvectors of the linearized equations (physically corresponding to the depth decay coefficients and component amplitudes, respectively) also have sixfold symmetry in magnitude but only threefold symmetry in phase. [Discussions with A. P. Mayer are gratefully acknowledged.]

Intense laser radiation was used to generate a Rayleigh wave pulse of finite amplitude in fused quartz. Measurements of the pulse at two locations along the propagation path reveal the formation of well-defined shocks in the horizontal (in-plane) velocity waveform. As the pulse propagates, the different propagation speeds of the head and tail shocks lead to a considerable increase in the duration of the pulse. Theoretical predictions based on nonlinear spectral evolution equations are in close agreement with the observed waveform distortion and shock formation.

Intracavity and extracavity photoacoustic resonance experiments have been performed for C2H4, using a cylindrical acoustic resonator and a 3.39 μm HeNe laser as a light source. The pressure dependence of the photoacoustic signal of the first radial mode excited in the acoustic resonator was studied as a function of C2H4 pressure. It is shown that theory yields a reasonable description of the experimental results taking into account the effective laser power.

Acoustic modes in a spherical resonator are excited with a chopped 3.39-μm He–Ne laser by vibrational excitation of CH4. The recording of resonance curves is completely controlled by a microcomputer. This includes repeated registration of the resonator temperature, stabilization and determination of the modulation frequency, and integration of the acoustic signal detected with an electret microphone. A detailed description of the timing of such an automatic data acquisition for high-precision experiments is given. The accuracy of the resonance method is investigated by fitting the experimental resonance curves to the corresponding line profile and performing an analysis of the errors involved.

Photoacoustic resonance experiments have been performed for CH4 and CH3F. The first radial mode of a cylindrical cavity was excited using the chopped beam of a 3.39 μm He-Ne laser. The pressure dependence of the resonance frequency and half-width of the acoustic resonances was determined. The frequency dispersion and peak broadening due to vibrational relaxation were obtained by calculating the contribution of other dissipation processes and intermolecular forces. The agreement between theory and experiment indicates an accuracy of a few percent in the description of the resonator processes.

A modified Sell-type ultrasonic transducer, utilizing Teflon materials and the hard-anodization process for the aluminum back plates, shows significant improvement in operating characteristics over earlier models. The vibrational self-relaxation times of ClCN ( pτ=29 ns bar) and BrCN ( pτ=15 ns bar) are measured for the first time. The results are discussed in relation to the empirical Lambert–Salter plot for V–R,T energy transfer.

IR laser-induced ionization is investigated in condensed methanol (77 K) using a TEA CO2 laser for resonant vibrational excitation and a quadrupole mass spectrometer to analyse the ion spectra produced by laser irradiation. Ions are already detected at laser fluences below 1 J/cm2, far below dielectric breakdown. The fluence dependence of the ion yield is measured for two groups of ions and the total number of ions. A mechanism is proposed for the photochemical production of protonated molecules. The protonated monomer is the species with the highest abundance; however, protonated dimers and other quasimolecular ions and fragment ions are also found.