NEARLY INDEX-MATCHED OPTICS FOR ASPHERICAL, DIFFRACTIVE, AND ACHROMATIC-PHASE DIFFRACTIVE ELEMENTS

Nearly index-matched optical elements are described that have applicat ion to aspherical, diffractive, and hybrid refractive-diffractive elem ents. Owing to the small difference in index, tolerances on the interf acial surface profile are much looser than for conventional aspherical and diffractive elements. A condition on both the index and the dispe rsion is described that results in an achromatic phase, thereby allowi ng for diffractive elements with high efficiency over broad spectral b ands. Properties of the elements are described and compared with those of conventional diffractive elements. Analytical results and experime ntal measurements with an inexpensive element with 40 waves of aspheri city are presented. (C) 1996 Optical Society of America