High-precision multipass reflectometer

The design of a multipass reflectometer, its operation, optimization of parameters, and some limitations to the expected precision are discussed. The instrumental precision is set by the uncertainty in the computer fit of a straight line to the measured data. Systematic errors due to nonuniform photosurfaces and the effects of astigmatism were minimized. This reflectometer was used to measure the absolute reflectance of evaporated aluminum films in the uv and visible regions. It was also used to measure the low-level insertion losses of laser window materials for this same spectral region.