Spectrally resolved wavefront measurements on broad-band dielectric coatings

In this work the influence of non-uniformity effects on the spectral transmission properties of broad-band dielectric optical coatings was examined. Recently, it was observed that in modern complex dielectric coatings significant spectral, resonantlike errors of the reflected wavefront can occur at specific wavelengths, which are induced by lateral coating nonuniformities [1]. For a detailed investigation of this effect, a setup was developed for monitoring the spectrally dependent wavefront error, utilizing a broad-band monochromatized plasma lamp (spectral range from 400 - 900nm) as light source and a high sensitivity Hartmann-Shack wavefront sensor for detection of reflected or transmitted wavefronts. In addition, a method for absolute and relative calibration of the measured wavefront error is presented. Two broadband dielectric beam splitters (#1 and #2) deposited by magnetron sputtering (high reflectance 400 - 900 nm, high transmittance 920 - 2300 nm) with different coating specifications were analyzed. It could be shown, that for an optimized design the spectral wavefront error can be significantly reduced compared to a standard beam splitter design [2].