For characterisation of non-uniform thin film coatings optical measurements should be performed with spatial resolution often much higher than that of conventional spectrophotometers. Here we present two different instruments constructed for transmittance and reflectance measurement of spatially non-uniform coatings. One of the setups is based on localized light distribution with a help of calibrated apertures, mapping needing sample displacement, while the other setup acquires the sample map 'at-once' with a CCD camera, spatial resolution being given by the pixel size. The spatial resolution ranges from 100 μm up to 2 mm for the first instrument, and is 30 μm for the second one. The spectral resolution of the first setup is about 0.5 nm in the range from 400 nm to 1700 nm, while for the second instruments it is 0.1 nm in the range 400-1000 nm. Besides the real optical performance of an optical device in terms of its spatially variable transmission and reflection, a 'mapping' of the thickness and refractive index of a single layer coating can be achieved. Comparison of the results obtained with these two instruments is given for two examples of coatings. The proposed instruments are useful tools for characterisation of both intended and undesired non-uniformity of optical coatings.

Date Published: 19 October 2005
PDF: 8 pages
Proc. SPIE 5965, Optical Fabrication, Testing, and Metrology II, 59651V (19 October 2005); doi: 10.1117/12.625183

Published in SPIE Proceedings Vol. 5965:
Optical Fabrication, Testing, and Metrology II
Angela Duparré; Roland Geyl; Lingli Wang, Editor(s)