Phonons are important for energy harvesting and conversion. How do they behave when radiation illuminates then at changing angle? Researcher have started to investigate this problem. Results have been recently published:
G. Scarel, J.-S. Na, and G.N. Parsons, “Angular behavior of the Berreman effect investigated in uniform Al2O3 layers formed by atomic layer deposition”. J. Phys. Condens. Matter vol. 22, 155401 1-9 (2010).