EXERCISE 2.5-3 Bragg Reflection Light is reflected at an angle from M parallel reflecting planes separated by a distance d as shown in Fig. 2.5-8. Assume that only a small fraction of the light is reflected from each plane, so that the amplitudes of the M reflected waves are approximately equal. Show that the reflected waves have a phase difference Δϕ = k(2d sinθ) and that the angle θ at which the intensity of the total reflected light is maximum satisfies sinθ = mλ/(2d), where m is an integer. Figure 2.5-8: Reflection of a plane wave from M planes separated from each other by a distance d. The reflected waves interfere constructively and yield maximum intensity when the angle θ is the Bragg angle. (2.5-11) Bragg Angle This angle is known as the Bragg angle. Such reflections are encountered when x-ray waves are reflected from atomic planes in crystalline structures. It also occurs when light is reflected from a periodic structure created by an acoustic wave (see Chap. 20).