10.5. 532 nm laser light is incident in a solid of refractive index 2.1, in which the speed of sound is 5000 m/s. A small fraction of the incident photons undergo Brillouin scattering such that they emerge at a scattering angle 20 = 90° with slightly lower energy. (a) In what direction are the phonons created in this process initially traveling? (b) What energy do these phonons have? (c) By what fraction is the wavelength of the scattered light increased relative to that of the incident light?