The mechanism of ultrasonic amplification in piezoelectric semiconductors has been investigated by a good many scientists since this phenomenon was first observed by Hutson et al. in 1961. At the same time, current saturation and oscillation associated with the ultrasonic amplifica-tion have also been examined and many valuable results have been obtained. The investigation of these associated phenomena is very necessary to develop the ultrasonic amplifiers because the ultrasonic noise arises from these phenomena. The mechanism of ultrasonic amplification can be interpreted sufficiently by the classical theory based on the electron bunching model. On the other hand, the quantum treatments are needed to interprete current saturation and oscillation since these phenomena are quite complicated. The application of the ultrasonic amplifiers will soon become practical in various fields, for examples, electronic industry, medicine, research of physics etc. with the development of suitable materials and ultrasonic transducers of a high efficiency.
A proposal is made to define the OTF (optical transfer function) of a screen-film combination which can be treated as linear, as the Fourier transform of a linear combination of effective exposure distributions of line images on each of two emulsion layers one over the other. This composite OTF is given as a product of OTFs of a single coated emulsion film optical scattering between film and screen, and two intensifying screens. The customary OTF which is somewhat ambiguous and non-linear is but an approximation of OTF of the new definition excepting the case of low contrast or low spatial frequency in which the two become the same. The OTFs obtained by experiment made on two different screen-film combinations differ considerably, but the OTFs of multiple scattering in these two combinations are almost the same, which justifies the theoretical presumption. The obtained value of OTF of multiple scattering calculated as a func-tion of film base thickness by using an approximate model corresponds well with the value found by experiment.
Thomson scattering of Q-switched ruby laser by plasma is a very important diagnostic tech-nique for high density and high temperature plasma. It is measured when caunsed by a shock produced plasma. Spurious scattering is reduced to a tolerable level by using a special chamber. In order to determine the electron density from the Thomson scattering, Rayleigh scattering in one atmospheric pressure air is used as the measuring standard. By experiment, the electron density behind the reflected shock wave at initial pressure of 1 mmHg of Ar and for mach number of 10_??_13 is determined to be about 1016 cm-3, which is in good agreement with the value calculated by shock theory or obtained by optical interferometry measurement.
Oscillatory decay of photocurrent in silicon single crystal is observed when the crystal is locally illuminated at room temperature by a Xenon lamp and the bias current is increased. By measure-ment, the decaying wave form is found characterized by the interaction between injected carriers and localized high electric field in the vicinity of electrode where the cariers gathered. This seems to be a kind of plasma instability and its essential physical mechanism is not fully understood. Utilization of this effect may provide new semiconductor devices with memory and delay characte-ristics.
The laser oscillation in high current region is studied by the use of quasi-cw excitation supplied by L-C discharge. In such transient excitation the laser had a hysteresis character. In the decaying period of current, the laser power output had I6_??_J2 dependence, which corresponds to the multi-step process in do exciation as reported before. In the increasing period, however, the power output in-creased in the same manner as the light intensity of spontaneous emission, therefore as the excitation rate, did.