Diffraction of light by superposed ultrasonic waves

A method of generating, simultaneously, two sound waves of frequencies in the ratio 1∶n, whose phase difference can be continuously varied, is described. The diffraction of light by such waves is studied, using frequencies in the ratio 1∶2 and 1∶3. Quantitative measurement of the intensities of the various orders is carried out, at phase angles of 0,π/2 and π in case of 1∶2 waves and at phase angles of 0 andρ in case of 1∶3 waves. The measured intensities compared very well with values calculated on the basis of the simple theory worked out by Murty. Photographs, showing the general features of diffraction by superposed waves, have also been reproduced.