Producing polarization-modulating optical element for microlithography system

A method of producing a polarization-modulating element that modulates a polarization state of incident light into a predetermined polarization state, the polarization-modulating element being used with an illumination optical apparatus, the method comprising:

• preparing an optical material having optical activity;
• and
• providing the optical material with a circumferentially varying thickness profile and a central region that is an aperture having no optical activity,
• wherein the optical material rotates a plane of oscillation of linearly polarized light traveling through the optical material along a crystallographic axis of the optical material by an angle with a magnitude proportional to a distance travelled by the linearly polarized light inside the optical material, and the thickness profile is set so that light in a linearly polarized state having a direction of polarization substantially along a single direction, is transformed into light in an azimuthal polarization state having a direction of polarization substantially along a circumferential direction or into light in a radially polarized state having a direction of polarization substantially along the radial direction.