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The problem of the generation of the coherent far ir radiation by a resonant parametric coupling between light waves is taken into consideration in the present paper. The equations of propagation of the interacting waves are given and the effect of the ir activity of the stimulated Raman active resonant mode on the dynamics of the wave interaction is considered. The experimental case of crystals and fluids as suitable media for achieving the effect is taken into account. At last, considerations on the resonant phase matching condition show that the achievement of the effect is not critical in general cases.

Magnetoelastic wave propagation at microwave frequencies in single‐crystal yttrium iron garnet, of various nonellipsoidal geometries, has been intensively investigated experimentally in recent years in connection with delay‐line applications. However, two important features, namely the detailed nature of the energy paths and the magnetic excitation mechanisms, have received scant attention. This paper examines these features from the viewpoint of geometrical ray theory. Attention is first directed to two basic phenomena: magnetoelastic wave anisotropy, which gives rise to deflection of the group velocity from the phase velocity vector, and refraction, which arises from the inhomogeneous internal magnetic field. Consideration is then given to justifiable approximations for the wave behavior and magnetic field, and guidelines which enable a specification of the launching surface to be made. Ray plots are presented for the axially magnetized rod, which is found to be strongly focusing, and for the complement...

Neilson and Benedick have reported an anomalous piezoelectric behavior for negatively‐oriented synthetic alpha‐quartz crystals when subjected to transient stress of about 65 kbar. This paper describes the piezoelectric behavior of negatively‐oriented quartz in the stress region of from 5 to 50 kbar. The first indication of anomalous behavior occurs at 8 kbar. Between 8 and 24 kbar the negative x‐current waveforms show evidence of partial electric breakdown in the quartz. Between 25 and 34 kbar disruptive breakdown occurs. Above 34 kbar disruptive breakdown is followed by gross conduction with positive currents being observed for stress greater than about 50 kbar. The fields associated with the piezoelectric behavior are lower than the field for steady‐state electric breakdown at atmospheric pressure. It is proposed that the anomaly is triggered by stress‐induced dislocation motion resulting in liberated electrons which are accelerated into the stressed region of the specimen by the high negative electric field.

In this paper the macroscopic elastic properties of heterogeneous bodies are studied in terms of the elastic properties of freely orienting microscopic units. Special attention is given to the differences in predicted macroscopic behavior which result from simplifying assumptions regarding stress or strain within a heterogeneous body. By comparison with experimental data, the possibilities and limitations of the concept of freely orienting microscopic elastic units are shown.

This paper describes electro‐optically induced tunable deflection in the plane of a waveguide structure by utilizing the liquid‐crystal property of tunable birefringence together with appropriately designed electrodes. The magnitude of tunable deflection achieved in this experiment (>20°) had only been demonstrated in passive structures in the past. Furthermore, by changing the device parameters slightly, electrically controlled total internal reflection or refraction in the plane of the waveguide structure was demonstrated. This allowed operation of the device as a switch where the guided beam was deflected or ``switched'' through a very large angle (>70°) in the plane of the guide.

The above paper by Kim et al. states that part of the nonlinearity of frequency sweep that we measured in picosecond pulses by dynamic spectroscopy techniques is caused by instrumental effects in a grating pair due to the presence of transverse modes. We would like to make the following comments: (i) The measurements were made with a fast spectrometer rather than with a pair of diffraction gratings. (ii) Transverse modes affect our spectrometer measurements only to the extent of reducing the resolving power by 2%. (iii) The frequency‐dependent group delay in the fast spectrometer has been properly accounted for in our earlier publications. (iv) In deriving their prediction of an instrumental contribution to apparent nonlinearity of frequency sweep, Kim et al. use an incorrect equation that describes a pulse crossing its time‐reversed image, which is not experimentally realizable. (v) The tilted wave packets that we studied with two‐photon fluorescence techniques are unrelated to the tilted wave packets di...

Irradiation of dielectrics with nonpenetrating electron beams has been used for practical purposes, e.g., manufacturing of electrets, and as a research tool, e.g., the investigation of induced conductivity and transport properties. The present paper develops some aspects of the theory of charge transport and storage and radiation‐induced conductivity in irradiated dielectrics. It is assumed that the dielectric is kept in short circuit and that the range of the incident electron beam is smaller than half the sample thickness. The treatment applies only to dielectrics which have a very low dark conductivity and contain a great number of deep traps.