Nondispersive Bragg diffraction in the general case of two cylindrically bent crystals

The conventional double crystal setup, employing two flat crystals with equivalent reciprocal lattice vectors generalizes for two crystals with different lattice vectors if the crystals are bent to their appropriate radii. The conditions for nondispersivity are derived in the most general case for two cylindrically bent crystals in reflection geometry with asymmetric cuts using different reflections. The theoretical predictions are verified by experiments.