Surface Flatness and Wavefront Error

Surface Flatness Interferograms
Surface flatness describes the deviation between the surface of an optical component and a perfectly flat reference plano surface. Optical filter surface flatness is measured using an interferometer (typically a laser Fizeau interferometer) that represents this deviation as a pattern of light and dark bands known as interference fringes. Interference fringes are a visual representation of the destructive interference that results from the difference in phase between light reflected off the optical filter and the reference flat. Once the interferogram is obtained, post-processing software can be used to create a 3D model of the surface.

Power and Irregularity
Optical filter flatness measurements are composed of two main component properties, power and irregularity (Figure 1). Power refers to a type of spherical curvature that can result in a bowl or dome shape. On the other hand, irregularity refers to any surface deviations that are left after power, tilt, and piston are removed from the interferogram. In many cases, the remaining deviations represent small-scale surface variations, but larger deviations may still be present if irregularity wasn’t controlled during substrate fabrication. Power and irregularity can also be specified as independent surface form properties.

Why Alluxa?
Alluxa’s team of experts has delivered key innovations to the field of optical thin-films. In addition to designing and constructing all of our own custom optical thin-film coating equipment, we invented a novel plasma deposition coating process that both increases the performance of our optical filters and decreases the time it takes to produce them.

By combining these innovations with state-of-the-art automation, proprietary control algorithms, and precision monitoring during the coating process, we are able to deliver low-cost, high-performance, custom thin-film optical filters for any application.