<title>Laser generation and reception of acoustic ultrasonic waves in solids</title>

Abstract

Pulses of longitudinal, shear and surface waves are generated when a powerful laser pulse interacts with a surface of a solid. These waves serve to control strength, structure, and dynamic modulus of elasticity of solids. They are also used for ultrasonic testing.The optical methods and means have been developed in Dalstandart, RSRI of PTM, for generation and reception of ultrasonic waves in the frequency range of 0-30 MHz. Efficient techniques have been devised to determine different parameters of ultrasonic wave propagation, such as propagation velocities, coefficients of sound attenuation, and acoustic dispersion. Based on theoretical and experimental background the devised installations offer the highest accuracy for measurement of parameters of ultrasonic wave propagation in solids.Key words: optical methods, ultrasonic waves, ultrasonic wave velocity, coefficient of sound attenuation, a solid.At present, pulse methods are the most-used ways of measurements in acoustics. The application of short acoustic pulses reduces consumption of power and allows to produce broad frequency bands. It gives convenient means of measurement and provides higher repetitive results and accuracy. In order to decrease errors, it is required that the send transducer should provide high reproducibility of generated wave packets and their minimal duration (10 -12 s). It is also important that they should facilitate the control of types of waves and parameters of packet shape. It is essential that the receivers of acoustic waves should have a low sensitivity threshold (10 -14 m). They must have broad bands and must be easily calibrated. All this reduces errors in an information signal to a minimum.Laser methods of generation and reception of ultrasonic waves meet completely all requirements of acoustic measurements. These methods make it possible to generate acoustic wave packets of duration to 10 -12 s, which corresponds to the frequency values to 10 -12 Hz. They provide means for contactless and remotely controlled measurements and allow a light spot to be formed on the surface of an investigated object of almost any shape and dimension. Optical methods used for the reception of acoustic waves are practically inertialess and they don't require acoustic contact with an object under investigation. These methods make possible to narrow the area of measurement down to a few micrometers and ensure sufficient accuracy. They don't require calibration and yield high reproducibility of results.