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This paper reports on the experimental implementation of an interferometer featuring sum frequency generation (SFG) processes powered by a pump spectral doublet. The aim of this configuration is to allow the use of the SFG process over an enlarged spectral domain. By analyzing the converted signal, we experimentally demonstrate a frequency spectral compression effect from the infrared input signal to the visible one converted through the SFG process. Recently, such a compression effect has been numerically demonstrated by Wabnitz et al. We also verify experimentally that we fully retrieve the temporal coherence properties of the infrared input signal in the visible field. The experimental setup permits to demonstrate an experimental frequency spectral compression factor greater than 4. This study takes place in the general field of coherence analysis through second order non-linear processes. more...

This paper demonstrates the use of a nonlinear upconversion process to observe an infrared source through a telescope array detecting the interferometric signal in the visible domain. We experimentally demonstrate the possibility to retrieve information on the phase of the object spectrum of an infrared source by using a three-arm upconversion interferometer. We focus our study on the acquisition of phase information of the complex visibility by means of the phase closure technique. In our experimental demonstration, a laboratory binary star with an adjustable photometric ratio is used as a test source. A real time comparison between a standard three-arm interferometer and our new concept using upconversion by sum-frequency generation demonstrates the preservation of phase information which is essential for image reconstruction. more...

In the framework of the ALOHA (Astronomical Light Optical Hybrid Analysis) project, we have implemented a fibre-linked interferometer connecting two telescopes of the CHARA (Center for High Angular Resolution Astronomy) array to the recombination beam facility using servo controlled hectometric outdoor fibres (240 m). During two consecutive nights, on-sky fringes at 810 nm were recorded on the star Vega (mag 0), with servo control of the fibre lengths. The optical path difference was set close to zero using internal fringes found before the on-sky observations. The repeatability of the delay line position offset between internal and on-sky fringes was less than 0.2 mm. The efficiency of the servo control systems has been demonstrated, leading to an enhancement of the signal-to-noise ratio from 68.9 with the servo off to 91.6 with the servo on. This result is a cornerstone for the ALOHA project goal of interferometry at 3.5  |$\mu$| m and a seminal step for the future kilometric infrared fibre-linked interferometer at CHARA. [ABSTRACT FROM AUTHOR] more...

In the framework of the ALOHA project (Astronomical Light Optical Hybrid Analysis), devoted to high resolution imaging in the L band, we investigate in this paper the possibility to deploy fibre links between the telescopes of the CHARA Array. As a first step, we set up an outdoor hectometric fibre interferometer to measure the vibration environment at the Mount Wilson Observatory. The optical path difference of this interferometer has been actively stabilised within an accuracy better than 4 nmrms, a stability largely sufficient for any interferometric application. [ABSTRACT FROM AUTHOR] more...

We report on the first on-sky sensitivity test on a single arm of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument, an uncooled up-conversion interferometer in the L band (3.5  |$\mu$| m). Despite a low coupling efficiency (in the range of 1 per cent) between the 1-m class telescope and our instrument, we detect a magnitude L mag = 2.8 star with a signal-to-noise ratio SNR = 2.7 over a 30 min integration time and with a spectral resolution λ/Δλ = 100. As the ALOHA project aims to shift light from the L band to the near-infrared, the use of very low loss silica optical fibres is an important step towards fibre-linked very long-baseline interferometry in the mid-infrared. [ABSTRACT FROM AUTHOR] more...

This paper reports on an experimental validation of the photon noise correction applied on interferometric data, in the frame of a laboratory stellar interferometer. The main feature of this study comes from the quantitative comparison between the contrasts and phase closure measurements in photon counting regime and simultaneously, on the same interferometer, in high flux level regime. This experiment uses an end-to-end imaging demonstrator including a three-telescope array linked by optical fiber to the mixing station. Contrasts and phase closure are extracted from a temporal fringe pattern. We show that it is possible to correct properly the interferometric data with light power level reaching 0.7 femto-Watt at a 680 nm mean wavelength. This corresponds to a photon flux close to 2.5 photons/ms and to 25 photons for each snap shot. [Copyright &y& Elsevier] more...