Kossel cone

Figure 3.15. Continued, (b) Kossel cone of rays such as a and b whose axis is normal to the reflecting plane at P. ...

In our experiment, the immersion objective produces a cone of light illuminating the crystal and receives rays reflected by crystal planes (Figure 2.20). The reflected rays are focused by the objective into a Kossel ring in the focal plane. Due to the finite aperture of the objective, only a part of the Kossel diagram is visible so that in order to compose the whole Kossel diagram it is necessary to combine images obtained with different orientations of the crystal. 

Figure 7.9. Principle of the Kossel diagram technique, (a) From the cone of incident monochromatic light, sets of crystal planes in sample S Bragg scatter light back through the objective lens L to make a Kossel diagram at focal plane FP. (b) Each set of planes is represented by an arc in the Kossel diagram (Kossel diagram courtesy of B. Jerome).

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