Fibered visible interferometry and adaptive optics: FRIEND at CHARA

Abstract

Aims. In the context of the future developments of long baseline interferometry at visible wavelengths, we have built a prototype instrument called Fibered spectrally Resolved Interferometer -New Design (FRIEND) based on single mode fibers and a new generation detector called Electron Multiplying Charge-Coupled Device (EMCCD). Installed on the Center for High Angular Resolution Astronomy (CHARA) array, it aims to estimate the performance of a fibered instrument in the visible when coupled with telescopes equipped with adaptive optics (AO) in partial correction. Methods. We observed different sequences of targets and reference stars to study the compensation of the birefringence of the fibers, the coupling efficiency in various conditions of correction, and to calibrate our numerical model of signal-to-noise ratio (S/N). We also used a known binary star to demonstrate the reliability and the precision of our squared visibility and closure phase measurements. Results. We firstly present a reliable and stable solution for compensating the birefringence of the fibers with an improvement of a factor of 1.5 of the instrumental visibility. We then demonstrate an improvement by a factor of between 2.5 and 3 of the coupling efficiency when using the LABAO systems in closed loop. The third results of our paper is the demonstration of the correct calibration of the parameters of our S/N estimator provided the correct excess noise factor of EMCCD is correctly taken into account. Finally with the measurements of the angular separation, difference of magnitude and individual diameters of the two components of ζ Ori A, we demonstrate the reliability and precision of our interferometric estimators, and in particular a median residual on the closure phase of 1.2• .

Probing the weak wind phenomenon in Galactic O-type giants

“…Among other on-going instrumental projects, we point out the Fibered spectrally Resolved Interferometer -New Design (FRIEND) instrument, a new visible beamcombiner, covering the spectral interval of ∼6200-8500 Å (Martinod et al 2018). This spectro-interferometric instrument was designed to overcome certain limitations of the VEGA instrument, as unreliable estimations of closure phase (see, e.g., .…”

Quantum Networks for High Energy Physics

“…Observations using interferometers provide sensitivity to features of images on angular scales much smaller than any single telescope. Traditional (Michelson stellar) optical interferometers are essentially classical, interfering single photons with themselves [4][5][6], and the singlephoton technique is highly developed and approaching technical limits. Qualitatively new avenues for optical interferometery can be opened up, however, once we consider using multiple-photon states; these generally require a quantum description, especially in conjunction with non-classical quantum technologies such as singlephoton sources, entangled pair sources, and quantum memories.…”

CHARA Array adaptive optics: complex operational software and performance

“…The Lab-AO systems have been used since 2014 to measure a good "default flat" of the sky close to the target star, and this has proved to be very helpful in coupling the light into the single-mode fibers used in many beam combiners. 27 We yet to measure the Tel-AO and Lab-AO's final performance in terms of sensitivity due to the COVID-19 and 2020 Bobcat Fire, but these systems already show increased throughput more than a magnitude.…”