The diffraction of light by high frequency sound waves: Part I.

4. Summary

(a) A theory of the phenomenon of the diffraction of light by sound-waves of high frequency in a medium, discovered by Debye and Sears and Lucas and Biquard, is developed.

(b) The formula

$$\sin \theta = \pm {{n\lambda } \over {\lambda * }} n (an integer) \ge 0$$

which gives the directions of the diffracted beams from the direction of the incident beam and whereλ andλ* are the wave-lengths of the incident light and the sound wave in the medium, is established. It has been found that the relative intensity of themth component to thenth component is given by

$$J_m ^2 (2\pi \mu L/\lambda ) / J_n ^2 (2\pi \mu L/\lambda )$$

were the functions are the Bessel functions of themth order and thenth order,μ is the maximum variation of the refractive index and L is the path traversed by light. These theoretical results interpret the experimental results of Bär in a very gratifying manner.