These notes are written to help the user understanding the metrology problems associated with measuring the reflectivity and the scattering of a surface. They sometimes correct approximate or misleading ideas about mirror's coating maintenance propagated by people who take their bad habits for competence. For that purpose, they give precise definition of terms and notions in accordance with scientific knowledge in physics and radiometry.
The author, dr Daniel Malaise, has more than 40 years experience in applied physics, optics and metrology; he received is PhD in astrophysics in Liége, has been Harvard and Smithsonian fellow and has been teaching in Liege and Paris before founding and managing companies dedicated to optics.
NEW! Application note #11: Absolute values of reflectivity measurements with a handy reflectometer
Side by side presentation of comparison reflectometer CT7 ( with gauge value as reference) and absolute reflectometer CT7A. This note exposes the need for absolute measurements and how both types of instrument achieve it.
Application note #4: stray light definition and measurements
This note has been written to introduce the user of IRIS scatterometer to the basic of stray light definition and measurements. It contains some theory and useful definition of terms. The main part of the note deals with practical matters related to scattering measurement.
Application note #5: general discussion of telescope’s coatings maintenance
This note is a general discussion of telescope’s coatings maintenance. Scientific, technical and practical rationales are given and amply developed that should kill some current ‘believes’ and confusions about the subject. The notions of ‘specular reflectivity’ and ‘Total integrated scattering (TIS)’ are scrutinized. All arguments are grounded on actual measurements on mirrors and on extensive modelization.
Application note #6: measuring the Total Integrated Scattering (TIS) of a mirror
This note examines the problem of measuring the Total Integrated Scattering (TIS) of an exposed reflecting mirror.
Application note #7: influence of the mirror's curvature
This note analyses the influence of the mirror's curvature on the accuracy of specular reflectivity measurements.
Application note #1: analysis of DiVittorio paper on reflectometry
DiVittorio and Walton published in 2004 as a symposium paper on Telescope maintenance a comparison of the performance of three commercially available reflectometers. This paper is a tissue of errors and shows clearly that the authors have not the level required to understand metrology. This is shown in details in the following analysis.