Antireflection-coated diffractive optical elements fabricated by thin-film deposition

The use of thin-film deposition in the fabrication of antireflection-coated diffractive optical elements is discussed. The antireflection coatings for these diffractive elements are optimized on the basis of an angular spectrum approach and the method of characteristic matrices. A minimum reflectivity as low as 1 x 10⁻⁴ is realized using in situ controlled multilayers of TiO₂ and SiO₂. The blazed profile of the diftractive optical elements is approximated by a stepped profile with up to 32 phase levels. The highest measured diffraction efficiency for 32-level Fresnel zone lenses was 97%.