A system which may be used to generate a plurality of spots on a surface is provided. The spots may be aligned with the incident plane of oblique illumination. The system may include a diffractive optical element configured to split a beam into a plurality of beams by generating a plurality of diffraction orders. The system may also include a focusing lens configured to focus at least some of the plurality of beams on the surface in the plurality of spots. At least some of the plurality of beams may be focused on the surface at an oblique illumination angle. The system may also include an illumination source positioned off-axis relative to an optical axis of the diffractive optical element. Using the system, a plurality of spots may be generated on an inclined surface.