 PATTERNS OF SOUND IN A CRYSTAL E&MP 98.001 Piezoelectricity October 25, 1965 These photographs taken at intervals of one millionth of a second show how the structure of a crystal changed when it was made to oscillate by an ultrasonic sound wave at a frequency of 100 kilocycles per second. The technique of photographing sounds in a crystal was developed by Dr. G. E. Peterson and Mr. P. M. Bridenbaugh of Bell Telephone Laboratories. The crystal used in this experiment was potassium dihydrogen phosphate (KDP). November 26, 1965 INSTANTANEOUS PATTERNS OF ACOUSTIC STRAIN PHOTOGRAPHED Scientists can NOW ACTUALLY SEE HOW A CRYSTAL CHANGES at each moment as a sound wave passes through it or when it is made to oscillate at high frequencies. Dr. G. E. Peterson and Mr. p. M. bridenbaugh of Bell Telephone Laboratories have devised a way of observing the instantaneous strain in the transparent piezoelectric crystal, potassium dihydrogen phosphate (KDP). The KDP crystal was sandwiched between to glass electrodes. While the crystal was vibrating, bursts of polarized light, synchronized with the acoustic vibrations, were directed through the crystal and focused onto a camera. This technique provides an almost continuous picture of the crystal's acoustic strain at intervals as short as a fraction of a microsecond. Previous methods of observing acoustic strain, such as sprinkling powder on the crystal surface or using x-ray diffraction, did not provide the time-resolved patterns or the detail now possible. The new technique, reported in the December issue of the Journal of Applied Optics , is useful in the visual analysis of instantaneous strain in transparent material, and can help in developing improved transducers, filters and frequency control devices. The time-resolved acoustic method may also help in understanding the scattering of an acoustic beam as it moves through a crystal.
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