Order of diffraction

Figure 3.5 Various orders of diffraction tfom a plane reflection grating G R indicates the red end of the spectrum V indicates the violet end of the spectrum the central number is the order of diffraction...

What wavelength will be observed at a detector that is placed at 23.5° when the light source strikes the reflection grating at an angle of 45.3° and the grating has 1250 lines per mm. Assume that the order of diffraction is first order. What is the second order wavelength observed ... 

So far we have used the scattering factor, /, to take account of the effect of structure within the unit cell. It is instructive to make use of Equation (2.5) instead. At one extreme the case of all the scattering power in a unit cell being located at one point leads to Equation (2.9) with /being a constant. In this extreme case, all orders of diffraction have the same amplitude. As the electron density within the unit cell is represented by more spread out and realistic functions, so the higher order terms in Equation (2.9) decrease more rapidly with increasing values of Q. Thus in the extreme case represented by... 

It is interesting to compare this result with (2.14) which assumes long range order whereas (2.24) does not. One cannot expect 2.25 with a=0 to correspond to (2.14) with u=0 as we have employed an approximation to obtain (2.15). For finite values of a and u, the most obvious difference in behaviour between the functions in (2.14) and (2.25) is the fact that all orders of diffraction defined by the latter equation are widened as well as being decreased in magnitude by the exponential factor and that this widening increases rapidly as one proceeds to higher orders of diffraction. 

It is worth pointing out that, even without the effects of disorder, there will be a fairly rapid, though not monotonic, decrease of intensity with progressively higher order of diffraction maxima except in the artificial case of point atoms. The extreme case of this effect is illustrated by the argument associated with Equations (2.10) and (2.11). 

Figure 3.2-8 Beam diffraction on a grating with constant g in transmission and reflection a angle of incidence,, 3 - angle of diffraction, m - order of diffraction.

Figure 8 Scattering curve from human SC after heating to various temperatures followed by cooling to room temperature. The temperatures to which the SC was heated are indicated, n = 1, 2, etc. refer to the orders of diffraction peaks from a lamellar structure with a Bragg spacing of 134 A. n = I, II refer to peaks corresponding to a lamellar structure with Bragg spacing of 64 A. (Data from Bouwstra et al., 1991.)...

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