Compensation of Aberration of Inclined X-ray Monochromators.

Inclined double-crystal monochromator for synchrotron radiation suffer from aberration that is connected with the horizontal divergence of the synchrotron radiation beam. Two different methods are proposed to compensate for this aberration. The first method introduces slightly different angles of inclination for the first and the second monochromator crystals. The condition for the difference of the angles of inclination is Bragg angle dependent and also depends on the projection of the distance of both crystals onto the direction of the normal to the diffracting planes. The second method uses an additional inclined double-crystal monochromator cut such that the aberration introduced by the first pair of crystals is nearly completely compensated by the second pair of crystals. This method is independent of wavelength. Both methods are illustrated by ray tracing.