Diffraction of light by high-frequency ultrasonic waves

Bhagavantam, S. ; Ramachandra Rao, B. (1947) Diffraction of light by high-frequency ultrasonic waves Nature, 159 . p. 267. ISSN 0028-0836

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Official URL: http://www.nature.com/nature/journal/v159/n4034/ab...

Related URL: http://dx.doi.org/10.1038/159267a0


Recently diffraction patterns have been produced in this laboratory by using ultrasonic waves of frequencies higher than 100 Mc./sec. At such high frequencies, the patterns show some interesting features. Progressive waves of frequency 102.6 Mc./sec. and maintained in water have been employed. When the sound wave is exactly normal to the incident light, the diffraction pattern disappears altogether. On tilting the crystal holder to one side or the other, so that the light rays meet the sound wave-front at an angle of 52', the first-order diffraction line alone on the appropriate side is obtained. This angle agrees closely with the value derived from the equation λ/λ =2μ sinθ, where λ and λ are the wave-lengths employed and μ is the refractive index of water. In no position of the sound wave-front has it been possible to get the first-order line on both sides at the same time. The value of the above angle for which the first-order line attains the maximum intensity is quite critical. Even a slight variation of about 2' has been found to reduce its intensity to half. Thus the diffraction effect at such high frequencies (λ= 0.00148 cm.) appears to be very much like reflexion in the Bragg sense.

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