This webpage contains information about the measurements.

Reflectivity results - Notes on the data


updated 2018-04-17:

The SMS μScan Reflectometer is now rarely used (last in Feb 2017), for several reasons: the battery life is poor and can only connect to 32-bit PCs; it leaves indellible marks on clean mirrors; the Reflectivity measurement is more variable and lower than other reflectometers (~2%). See notes at end of page and CT7 comparison report, linked below.

The Coatest CT7 from Opo.be is now our reference instrument. It has been at use at ING since 2012, has reliable readings since 7/2013 and the current model, allowing in-house calibration, was acquired in 4/2015. Its main characteristics are:

Full Specifications here. An in-house calibration exercise is reported here . A comparison of results from CT7 with other instruments is available here.

Note: Aluminium has an absorption band centered on 820 nm approximately. This depresses the reflectivity in the 760 nm waveband measured by the CT7, with respect to the values at 365 nm and 970 nm, where aluminium shows its maximum reflectivity. Our measured values are very close to the laboratory standard (example). The absorption can be much reduced by applying dielectric over-coatings but this is only feasible on smaller mirrors.

Characteristics of SMS μscan reflectivity and scattering meter:

IMPORTANT notes on SMS(Tibor):

- it turned out (December, 2006) the head could be sensitive to the temperature changes, so it is essential to bring the reflectivitymeter to the place where the measurement of the given mirror will take place and leave there at least 15 minutes before the measurement (in these places the temperature could be considered as stable)

- also because of the same reason, after CO2 cleaning of the mirrors it is necessary wait approx. 15 minutes until the mirror is cooled down, and take the measurements only after this 15 minutes; otherwise it can happen that the reflectivitymeter will show incorrect results (e.g. reflectivity above 100%)

NOM: The SMS had been calibrated by the manufacturer (Schmitt Industries Inc.) in 7/2005 but this was valid for only 1 year. SMS continued to be used after Neil O'Mahony took over from Tibor, but with the method of repeating measurement without moving the head on the surface. Measurements outside the threshold of repeatability for reflectivity (0.5%) were later rejected. The SMS was also checked for contamination by checking for reference measurements below 92%.