title: Interferometry at the physical limit: how to measure sub-parts-per-million optical homogeneity in fused silica.
abstract: Inspection of the refractive-index distribution in fused silica is very sensitive to thermally induced measurement errors. A model is derived for the estimation and interpretation of thermal errors applicable to interferometric homogeneity investigations. The outlines of the model are supported by experimental investigations and numerical calculations. The results state a mandatory temperature stability of deltaT = 0.02 K for a required reproducibility of sigma(delta(n)) < or = 1 x 10(-7) and a lower sensitivity of higher-order Zernike terms. Requirements of the interferometer environment include spatial and temporal stability. Only a small part of the frequency spectrum of temporal instabilities contributes significantly to the measurement error and is therefore critical for the system. Experimental values are given for different environmental conditions.
authors.affiliation: Optic and Lamp Materials Division, Heraeus Quarglas GmbH and Company KG, Quarznstrasse 8, 63450 Hanau, Germany. doerte.schoenfeld@heraeus-quarzglas.com
authors.forename: Doerte
authors.initials: D
authors.lastname: Schoenfeld
authors.forename: Bodo
authors.initials: B
authors.lastname: Kühn
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Englisch
authors.forename: Ralf
authors.initials: R
authors.lastname: Takke