Stitching interferometry: Side effects and PSD

Stitching Interferometry is rapidly emerging as an alternative to Standard Interferometry, in the measurement of Large Optics - such as those found in Laser MegaJoule and NIF. Stitching Interferometry involves multiple overlapping subaperture measurements over large components, and a computer software to reconstruct the wavefronts. Obviously, the Stitching Interferometer's measurement characteristics have to be different to those of the Standard Interferometer of same nominal measurement area. Two questions emerge: a - What metric do we choose to express these characteristics ? b - How does Stitching Interferometry compare to Standard Interferometry, using this metric ? We choose to use the PSD to illustrate hen, Stitching Interferometry of large components compares with Standard Large-Size Interferometry, for various lateral scales. Also, we highlight some important characteristics of Stitching Interferometry, which arise from judicious use of the particular configuration of the device. Ignorance of basic propagation phenomena can lead to bad design of the Stitching Interferometer, and loss of any performance advantage over Standard Interferometry. Because many of these effects are not direct consequences of the Stitching process, we call them side effects. In this paper, we provide basic explanation, and keep the mathematics to a low profile - indeed, it is not necessary to actually compute anything to understand the effects. However, some very basic formulas, a few numerical tables and lots of graphs are presented, in order to provide basis for discussion.