Sm. Ebstein, NEARLY INDEX-MATCHED OPTICS FOR ASPHERICAL, DIFFRACTIVE, AND ACHROMATIC-PHASE DIFFRACTIVE ELEMENTS, Optics letters, 21(18), 1996, pp. 1454-1456
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