Bulk and surface phonon–polaritons in anistropic crystals

In recent years the properties both of bulk and surface phonon-polaritons in anisotropic crystals became more and more important. We owe a long line of pioneering work on phonen-polaritons to Sergio Porto and his co-workers. Of all complex anisotropic crystals α-quartz was investigated most extensively with regards to bulk and surface phonon-polaritons. Therefore α-quartz in the following is treated as a model crystal for polaritons in anisotropic crystals. Both theoretical and experimental results on phonon–polaritons in α-quartz are discussed in detail. Most of the experimental results are in quantitative agreement with theory and numerical calculations.