We are depositing anti-reflection coatings. We are down at 0.25% reflectance level. We measure coatings on glass with a Perkin Elmer Lambda 900 spectometer. In this low range, the spectra are very noisy, and require lots of smoothing.
1. Is this typical, unavoidable by s/n ratio of the detector?
2. Our spectrometer often crashes every few scans. We have contacted PE, they are puzzled, does any one else have this problem?
3. How do you deal with the reflection off the back surface of the glass? We tried a frosted glass on the back, a wedge with matching fluid (messy and inconvienent), or AR coating the back and dividing by two, but this only gives an average of the two coatings.
4. Are there any good books or papers on this difficult metrology area?
5. Are there standards for low reflectivity in the 800-1600nm range, and standards for wavelength in this region? Hopefully NIST tracible, (ISO you know...)