Portal de Periódicos da CAPES

Rugate Broadband Antireflection Coating Design

1989; SPIE; Volume: 1168; Linguagem: Inglês

10.1117/12.962986

1996-756X

Ronald R. Willey,

Metal and Thin Film Mechanics

The use of an antireflection (AR) coating which is a series of homogeneous layers whose index steps down from the substrate index to the index of air or a vacuum has been well described in the literature (1,2). These are particularly attractive for high index substrates such as germanium, but are limited by the availability of appropriate real coating materials. The limiting factor is a lack of practical materials whose index is less than about 1.35. Another family of AR coatings which include one or more half wave layers is also known. The most common of these is the classical QHQ design. DeBell(3) reported on designs such as QHHHQ and QHHHHHQ where the H's are alternating high and low index layers. We have found that there is a family of inhomogeneous or "Rugate" index functions which can produce broadband AR coatings. These point to some general principles of AR coating design which have not been previously obvious from the literature. We describe these investigations and findings in graphical form. We discuss the concepts and understanding gained and examine the possibilities and limitations of the approach.