Methods for reducing polarization aberration in optical systems

A method of reducing the retardance caused by intrinsic birefringence in an optical system comprising a plurality of [111] cubic crystalline optical elements with respective [111] crystal axes aligned along an optical axis, said method comprising:

• clocking at least one said [111] cubic crystalline optical element to provide a more circularly symmetric retardance pattern over a pupil centered about said optical axis at least for on-axis field points;
• and
• introducing one or more uniaxial birefringent elements comprising media having a single birefringence axis into said optical system, said one or more uniaxial birefringent elements having a substantially circularly symmetric retardance pattern associated therewith that is distributed over said pupil centered about said optical axis at least for on-axis field points,
• wherein said retardance pattern corresponding to said plurality of [111] cubic crystal optical elements and said retardance pattern corresponding to said one or more uniaxial birefringent elements are opposite such that retardance introduced into an optical beam transmitted through said plurality of [111] cubic crystalline elements is substantially offset by retardance introduced into said optical beam upon transmitting said beam through said one or more uniaxial birefringent optical elements.