A selective diffractive optical element includes a first diffractive region having a first design on a first surface of a substrate, and a second diffractive region having a second design on the first surface of the substrate, the first and second designs being different, wherein, by altering a position of a cross-section of an illumination beam, the selective diffractive optical element outputs a desired proportion of the two diffractive patterns aligned along an optical axis of the illumination beam.