Disclosed is an apparatus for illuminating a sample. In one embodiment, this apparatus includes a laser for outputting an incident laser beam towards a sample and a first diffractive element having a plurality of diffraction pattern portions. The first diffractive element is movable so that each of its diffraction pattern portions can be selectively positioned in the incident beam's path and the diffraction pattern portions of the first diffractive element are designed to cause the incident beam to have different spatial illumination profiles at a pupil plane of the incident beam while reducing effects caused by the incident beam's coherence. The apparatus further includes an illumination profile element configured to spatially distribute light at an illumination plane of the incident beam and a plurality of illumination optical elements for directing the incident beam towards the sample.