FLUOR (now called JouFLU) is a high-precision visibility instrument for interferometry. It was built by the Laboratoire d’études spatiales et d’instrumentation en astrophysique (LESIA) of the Observatoire de Paris and produces some of the most precise measurements in stellar interferometry. Originally set up on Kitt Peak, Arizona in 1992, it was moved to the IOTA on Mt. Hopkins in 1995. FLUOR has been operating at the CHARA Array since 2002 and was decommissioned in 2019.
FLUOR is a two telescope beam combiner operating in the near infrared K’ band (lambda = 2.20 microns). It utilizes the spatial filtering properties of optical fibers to produce visibility measurements with a precision of approximately 0.3% (Coudé du Foresto et al. 1997). For bright sources, the statistical precision of FLUOR is only limited by the piston mode of atmospheric turbulence which introduces apparent changes in the zero OPD fringe position or fringe jitter. Such high precision allows FLUOR to make measurements of scientifically interesting features such as stellar radii that are accurate to the order of one percent or less.
In recent years, it has become clear that several improvements could increase the efficacy of FLUOR in terms of its efficiency, throughput, and integration with the CHARA Array. The JouFLU project, loosely translated as “rejuvenation” of FLUOR, has improved much of the optical bench setup of FLUOR to provide greater opto-mechanical stability. This includes new motorized mounts for the mirrors that feed light into the optical fibers, new higher-precision motorized stages that control the OPD to generate fringes, an OPD Scanning stage (OPD Scan), an OPD Static stage (OPD Stat), an infrared pupil-plane camera system, a visible light alignment camera, and improvements to the NICMOS science camera.
The JouFLU combiner is not currently available because of technical problems.
FLUOR fibered beam combiner at the CHARA array - Coudé du Foresto, V., et al. 2003, SPIE, 4838, 280
Jouvence of FLUOR: Upgrades of a Fiber Beam Combiner at the CHARA Array - Scott, N. J., et al., 2013, JAI, 2, 1340005 (pdf)