Nonzero Fourier component

Nonzero higher order Fourier components (/ > 1) give the deviation from a purely sinusoidal density distribution along z, that is, represent a sharpening of the layer structure, and the coefficients are then direct measures of the higher smectic order parameters T . In the limit of perfect smec-... 

If A] is phase-free, as discussed in Section III, and in Ref. 15, there are no longitudinal electric field components. This also occurs if A,-3"1 is zero [17]. The B(3) field is then a Fourier sum over modes with operators a qaq and is perpendicular to the plane defined by A and /1<2>. The four-dimensional dual to this term is defined on a time-like surface, following Crowell [17], which can be interpreted as E under dyad vector duality in three dimensions. The ( field vanishes because of the nonexistence of the raising and lowering operators l3 , . The BM is nonzero because of the occurrence of raising and lowering... 

As any normal component Ak = gi is allowed, the full reciprocal lattice (as defined by the values Ak to produce a nonzero lattice factor) consists of structureless parallel rods normal to the surface whose lateral periodicity is given by gy = ghk as illustrated in Figure 3.2.1.6c. In a formal sense and as evident from Eq. (3.2.1.5), the reciprocal lattice is equivalent to the modulus square of the discrete Fourier transform of the two-dimensional lattice of the real-space unit-cell arrangement. 

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