Diffraction of light by ultrasonic waves—part II

Summary

With sound of wave-lengths 0·0651 and 0·0501 mm. in liquid, light is found to get reflected in accordance with Brillouin’s formulamλ = 2 λ* sin θ. The formula is satisfied with different values form, λ and λ*. Further, confirmation is obtained by the verification of the relation between the incident and the reflected angles, when the reflected beam moves through twice the angle of rotation of the reflecting surface. Photographs of reflection of the first, second and third orders for some prominent mercury lines are reproduced. It is made out clearly that transmission (Raman-Nath’s theory) and reflection (Brillouin’s theory) are two separate phenomena, superposed on each other, in the case of diffraction of light by high-frequency sound waves. Remarkably enough, the treatment for diffraction by both the methods leads to the same formula, which enhances the difficulty of separating out the intensities due to each cause.