STUDY OF REFLECTION COEFFICIENT DISTRIBUTION FOR ANTI-REFLECTION COATINGS ON SMALL-RADIUS OPTICAL PARTS

• Main Authors: L. A. Gubanova, H. L. Thang, T. D. Tan
• Format: Article
• Language: English
• Published: Saint Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO University) 2015-03-01
• Series: Naučno-tehničeskij Vestnik Informacionnyh Tehnologij, Mehaniki i Optiki
• Subjects: anti-reflection coating; small-radius optical detail; area of constant reflection coefficient.; area of constant reflection coefficient
• Online Access: http://ntv.ifmo.ru/file/article/12849.pdf
• ISSN: 2226-1494; 2500-0373

The paper deals with findings for the energy reflection coefficient distribution of anti- reflection coating along the surface of optical elements with a very small radius (2-12 mm). The factors influencing the magnitude of the surface area of the optical element, in which the energy reflection coefficient is constant, were detected. The main principles for theoretical models that describe the spectral characteristics of the multilayer interference coatings were used to achieve these objectives. The relative size of the enlightenment area is defined as the ratio of the radius for the optical element surface, where the reflection is less than a certain value, to its radius (ρ/r). The result of research is the following: this size is constant for a different value of the curvature radius for the optical element made of the same material. Its value is determined by the refractive index of material (nm), from which the optical element was made, and the design of antireflection coatings. For single-layer coatings this value is ρ/r = 0.5 when nm = 1.51; and ρ/r = 0.73 when nm = 1.75; for two-layer coatings ρ/r = 0.35 when nm = 1.51 and ρ/r = 0.41 when nm = 1.75. It is shown that with increasing of the material refractive index for the substrate size, the area of minimum reflection coefficient is increased. The paper considers a single-layer, two-layer, three-layer and five-layer structures of antireflection coatings. The findings give the possibility to conclude that equal thickness coverings formed on the optical element surface with a small radius make no equal reflection from the entire surface, and distribution of the layer thickness needs to be looked for, providing a uniform radiation reflection at all points of the spherical surface.