Coatings of optical surfaces for certain laser applications are designed to have very specific polarization characteristics. The polarization angle, psi, and the phase shift angle, delta, define the polarization characteristics of a surface at a given wavelength and at a given angle of incidence. Both psi and delta can vary greatly with wavelength and full characterization of the polarization of a coated surface requires the measurement of both psi and delta over a range of wavelengths and not just at single laser wavelengths. An ellipsometer has been built which is capable of expediently measuring both psi and delta at any selected wavelength from 400 to 2000 nanometers at any selected angle of incidence from 45 to 75 degrees. The ellipsometer uses an incanaescent lamp, a mono-chromator, and a silicon or a lead sulfide detector. The operation of the instrument is based on fixed angle settings and signal amplitude readings rather than on null settings and precision angle readings as in most common ellipsometers. Eight digitized signal level readings from a lock-in amplifier are needed for each measurement. A simple calculation gives the values for psi and delta. The ellipsometer is, in its present form, a manually operated prototype. Its construction would lend itself well to full automation and a true wavelength scanning ellipsometer could readily be built. The instrument is described and examples of ellipsometric scans of coatings designed for specific polarization characteristics are shown.
Erik W. Anthon,
"Ellipsometer With Adjustable Wavelength Capability (400 To 2000 Nm)", Proc. SPIE 0891, Polarization Considerations for Optical Systems, (29 June 1988); doi: 10.1117/12.944316; https://doi.org/10.1117/12.944316