Schematic representation of a cross section of a Laue lens based on QM crystals. Gray rectangles represent the crystals. The primary curvature leads to a secondary curvature of the planes affected by quasi-mosaicity. In this configuration the QM diffracting planes are perpendicular to the main surface of the plates. The primary curvature allows focalizing diffracted radiation onto the focal plane, while the QM curvature increases the diffraction efficiency.