title: Refractive index compensation in over-determined interferometric systems.
abstract: We present an interferometric technique based on a differential interferometry setup for measurement under atmospheric conditions. The key limiting factor in any interferometric dimensional measurement are fluctuations of the refractive index of air representing a dominating source of uncertainty when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of an over-determined interferometric setup where a reference length is derived from a mechanical frame made from a material with a very low thermal coefficient. The technique allows one to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range, acting as a tracking refractometer. The principle is demonstrated in an experimental setup.
authors.affiliation: Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, Královopolská 147, 612 64 Brno, Czech Republic. joe@isibrno.cz
authors.forename: Josef
authors.initials: J
authors.lastname: Lazar
authors.forename: Miroslava
authors.initials: M
authors.lastname: Holá
authors.forename: Ondřej
authors.initials: O
authors.lastname: Číp
authors.forename: Martin
authors.initials: M
authors.lastname: Čížek
authors.forename: Jan
authors.initials: J
authors.lastname: Hrabina
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Buchta
mesh_terms: D000388:Air / Q000032:analysis*; D001272:Atmosphere / Q000032:analysis; D004780:Environment, Controlled; D004784:Environmental Monitoring / Q000295:instrumentation; D007368:Interferometry / Q000295:instrumentation / Q000379:methods; D012031:Refractometry / Q000295:instrumentation* / Q000379:methods