Patent ID: 7292393

Claim:
An apparatus for illuminating a sample, comprising: a laser for outputting an incident laser beam towards the sample; a first diffractive element having a plurality of diffraction pattern portions, wherein the first diffractive element is movable so that each of its diffraction pattern portions is 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, wherein the diffractive pattern portions are different annular sections of the first diffractive element and each annular section has a plurality of cells thereon and the annular sections are selectively positionable in the incident beam's path so as to provide the different spatial illumination profiles and the first diffractive element is rotatable so as to sequentially position different cells of its selected annular section into the incident beam's path during illumination of the sample to thereby introduce phase variations into the incident beam and reduce effects caused by the incident beam's coherence; 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.