Acousto-optic Light Pulse Shaper for Measuring the Parameters of Photo-detectors

The paper emphasizes that intensive utilization of the optical range increases the need for the development of new optoelectronic devices. Accordingly, there is a growth in the need for effective methods and tools to study photoelectric properties of semiconductor materials, including photo-detectors.In the paper we have analyzed the well-known methods and tools for measuring the photo-detector parameters, defined the restrictions in their applications, and proved that it is relevant to create a measuring system, the parameters of which are easily adapted to the study of photoelectric characteristics of a wide range of semiconductor materials, including photo-detectors.The scheme and principle of operation of the acousto-optic processor and the features of the photo-elastic effect are discussed, and it is proved that they can be used to form a light pulse of required duration and power. The expressions obtained for calculating the response at the acousto-optic processor output enable us to estimate separately the effects of time of crossing the optical beam by the elastic wave packet and the photo-detector inertia.The capability to determine the time of crossing the optical beam by the elastic wave packet and taking it into account as a device error has been substantiated. The proposed formulas have been tested and by numerical analysis based on the datasheet specifications of the FD-24K photodiode, the effectiveness of the obtained expressions has been convincingly proven.The inertia parameters of a particular sample of the FD-24K photodiode are experimentally studied. The emphasis is upon measuring the rise time of the transient response of the object under study. The exact rise time value of the transient response of the experimental FD-24K sample was approximately 7 μs, which is less than that indicated (≤10 μs) in the product certificate. In real life, such a measurement is necessary when selecting the photodiode pairs with identical parameters.By comparing the results of numerical analysis and experimental studies, it has been convincingly proven that the features of the photo-elastic effect can be used to construct a light pulse shaper with the required parameters.

Photo-elastic Effect Features Used for Measuring Laser Radiation Parameters

The article discusses the photo-elastic effect features in acousto-optic processors for processing pulse signals on the time axis. The photo-elastic interaction in these devices is divided into two areas. In the first area, the input pulse duration is longer than the time of intersecting the optical beam by the elastic wave packet. This particular area is widely used in the practical applications of these processors, where it is a priori assumed that the input pulse duration is longer than the time for the elastic wave packet to intersect the optical beam.In the second area, the input pulse duration is less than the time for the optical beam to be intersected by the elastic wave packet. The objective of this work is to study the photo-elastic effect features in this area. It was established that in this area the pulse duration at the processor output is equal to the time for the optical beam to be intersected by the elastic wave packet and does not depend on the input pulse duration, which is permissible in some cases (for example, in radar pulse existence rather than its duration is recorded). It is shown that in the second area, the output pulse is formed as the sum of three terms. The first term corresponds to the elastic wave packet entering the optical beam. The second term corresponds to the elastic wave packet advancement in the optical beam aperture, and the third one keeps with the elastic wave packet leaving the aperture of the optical beam. The corresponding equations for calculating the pulse at the device output are obtained. The numerical calculations have proved the provisions and patterns established. The numerical modeling results were tested experimentally using a prototype of an acousto-optic processor with direct detection. The analysed results of theoretical and experimental studies unequivocally confirmed that the obtained formulas, formulated statements, and established provisions can be used to expand the functionality of acousto-optic processors, both with direct detection and of heterodyne type. It is shown that with a significant decrease in the input pulse duration relative to the time during which the optical beam is intersected by the elastic wave packet, the latter is converted into a scanning line and can be used to measure the geometric and energy characteristics of the quasi-coherent light.

Experimental Study of Slamming Effects on Wedge and Cylindrical Surfaces

Slamming is a very significant phenomenon that occurs in marine structures operating under extreme conditions. Slamming significantly reduces the design life of floating offshore wind turbines, as well as marine structures, and causes structural damage. Thus, the slamming load should be considered sufficiently during the design phase of the structure, and the results of experiments of good quality should be incorporated. The phenomenon of slamming should be analyzed using peak pressure, width, duration, and dynamic loads that depend on the design and natural frequency of the structure. In the case of a slamming experiment, the deadrise angle shows the greatest pressure between 3° to 10°. In this study, pressure values were compared using a model with a deadrise angle of 10° and a cylinder model most commonly used for the fabrication and installation of offshore structures. The peak pressure of the cylindrical model is greater than those of the flat model and the wedge model with a 10° deadrise angle. Pressure and strain were measured using free drops from heights of 1.0 and 1.7 m from the water surface, and the elastic effects were studied accordingly. Also, the peak pressure due to a slamming impact occurs several times depending on the natural frequency of the structure. In order to understand the behavior of the structure against the elastic effect, the second peak in the experimental results was theoretically and experimentally analyzed. The second pressure peak is greater than the first pressure peak due to the elastic behavior effects based on the natural frequency of models used in the slamming test. Also, a single slamming results in several peak pressures and it greatly deteriorates the fatigue strength. Experiments and simulations were carried out to derive the effects of repeated slamming loads on the structure. In the structural design considering the slamming loads, information on the elastic effect of the structure and accumulated loads is very important. This can be an important variable in the design of the floater and can play an important role in assessing the impact on the floater. These results raise questions as to the extent that slamming pressures are replaced with equivalent hydrostatic pressures in most design rules of the recognized certification society.