Mirror reflectivity, and

When one has a planar surface, one can take advantage of X-ray optics to enhance surface sensitivity.61,62 The most important is specular or mirror reflection, and this is due to the fact that at X-ray energies the index of refraction of matter is slightly less than one and is given by ... 

The symbols for plane groups, the Hermann-Mauguin symbol, have been the standard in crystallography. The first place indicates the type of lattice, p indicates primitive, and c indicates centered. The second place indicates the axial symmetry, which has only 5 possible vales, 1-, 2-, 3-, 4-, and 6-fold. For the rest, the letter m indicates a symmetry under a mirror reflection, and the letter g indicates a symmetry with respect to a glide line, that is, one-half of the unit vector translation followed by a mirror reflection. For example, the plane group pAmm means that the surface has fourfold symmetry as well as mirror reflection symmetries through both x and y axes. 

Reflection analysis of a silver mirror surface taken as a reference standard showed that the reflection of light from this surface is mostly mirror reflection and that the degrees of mirror reflection are very close to the ideal reflectance of silver. The structural characteristics of this surface, which provide a high degree of mirror reflection, are flat and mutually parallel parts which are smooth on the atomic level, with adjacent flat parts being separated by several atomic diameters of silver. 

The relation between the overlap of the spontaneous emission spectrum and the cavity length is illustrated in Fig. 1.8, which shows the optical mode density of a short and a long cavity. Both cavities have the same mirror reflectivities and finesse. The natural emission spectrum of the active region is shown in Fig. 1.8(c). The best overlap between the resonant optical mode and the active region emission spectrum is obtained for the shortest cavity. Thus a cavity length of 2/2 provides the largest enhancement. 

The reflection of light from a silver mirror surface is mostly mirror reflection and the degree of diffuse reflection is very small (up to 2 %). The degree of mirror reflection from this surface is also very close to the ideal reflectance of silver [87,91,92], The silver mirror surface consists of parts parallel to the base and flat on the atomic level with low-step heights between them, as is shown in Fig. 2.28. It is clear that bright metal surfaces must be similar to the surface of the mirror. 

Q, mirror reflections, and a glide reflection along both the a and b axes for the centered rectangular lattice... 

The inversion notation has become standard for a number of good reasons. In the Hermann-Mauguin terminology, the center of symmetry is dropped and the inversion axes maintained. In the Schonflies terminology, the center of symmetry is a key element and all the mirror reflections and simple or inversion rotation axes are dropped and replaced by other symbols these are described in Section V, as they are important in relation to site symmetry, group theory, and Raman scattering. 

---