Spatially scanned two-color mid-infrared interferometer for FTU

The design of a scanning beam two-color mid-infrared (MIR) interferometer i s presented. The diagnostic is being developed for the Frascati Tokamak Upg rade (FTU) which calls for a new interferometer to perform detailed study o f advanced confinement regimes in D-shaped plasmas. After performing a feas ibility study and a prototype test, we designed a scanning interferometer b ased on a resonant tilting mirror providing 40 chords of approximate to1 cm diameter and a full profile every 62 mus. Such a high number of chords is obtained with a very simple optical scheme, resulting in a system which is compact, low cost, and easy to align. An important feature of the interfero meter is its higher immunity to fringe jumps compared to conventional far i nfrared (FIR) systems. Three main factors contribute to that: the high crit ical density associated to MIR beams, the large bandwidth provided by 40 MH z heterodyne detection, and the fact that each scan provides a "self-consis tent" profile. (C) 2001 American Institute of Physics.