Patent ID: 7126900
Filing Date: 2006-10-24
Classification: G11B

Abstract:
1. An optical element for use with a first radiation beam and a second radiation beam, the optical element including: a first reflective surface, said first surface being selectively reflective and capable of reflecting said first radiation beam and of transmitting said second radiation beam; and a second reflective surface arranged to receive said second radiation beam when transmitted by said first reflective surface, and to reflect said second radiation beam through said first reflective surface, wherein said second reflective surface is separated from said first reflective surface by a varying spacing, said varying spacing corresponding to a difference in phase profile to be generated between said first and second radiation beams, and said second reflective surface comprises a phase structure in the form of stepped annular zones, the stepped annular zones forming a non-periodic pattern of different heights corresponding to the difference in phase profile to be generated.