Diffraction of light by very high frequency ultrasonic waves

Abstract

In two recent notes, we reported that ultrasonic waves of frequencies as high as 100 Mc./sec. were generated. The diffraction patterns produced by such waves were found to exhibit interesting features. Since then, by using a tourmaline plate and specially designed circuits, We have been able to push up this frequency to nearly 180 Mc./sec, and to study the diffraction effects produced when progressive waves of such high frequencies are maintained in a column of water. Results for the velocity of sound, measured at two different frequencies, are given below. In obtaining these, it has been assumed that the velocity in water is 1,504 metres per second at 15 Mc./sec. and 26.5° C. If the slightly higher temperature of the medium when the highest frequency is used is taken into account, it will be noticed that there is no dispersion of ultrasonic velocity.