Multiple-Order Diffractive Engineered Surface (MODE) Lenses

A multiple-order diffractive engineered surface (MODE) lens is introduced, in which focal position change with wavelength exhibits both refractive and diffractive characteristics. Engineering calculations are provided that indicate Strehl-ratio and encircled energy performance over a large range of focal length and aperture diameter design space. A prototype lens is designed and constructed for the astronomical R-Band (589 nm to 727 nm) wavelength range. Test results show that measured full-width-at-half-maximum focal spot diameter is 2.1 times larger than the ideal Airy spot diameter, and focal position versus wavelength is nearly identical to the design. The 48 mm aperture diameter, f/3.12 prototype telescope exhibits angularly resolved features in natural scenes at 0.006°, with subtense of the Airy spot diameter at 0.002°. Applications include eventual use in large aperture, ultralightweight space telescopes.