Anamorphic Magnification

The ratio b/a is called the anamorphic magnification. For a given wavelength λ, it depends only on the angular configuration in which the grating is used.

For a given wavelength λ, we may consider the ratio of the width of a collimated diffracted beam to that of a collimated incident beam to be a measure of the effective magnification of the grating (see Figure 2-8). From this figure we see that this ratio is

b / a = cosβ / cosα   (2-27)

Since α and β depend on λ through the grating equation, this magnification will vary with wavelength.

Figure 2-8. Anamorphic magnification. The ratio b/a of the beam widths equals the anamorphic magnification; from the grating equation we see that this ratio will not equal unity unless m = 0 (specular reflection) or α = β (the Littrow configuration).
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