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Astronomical Light Optical Hybrid Analysis (ALOHA@3.39 μm) is a new instrumental concept designed for high angular resolution astronomical imaging in the L band. The originality of our experimental device is to include a frequency conversion process in each arm of the interferometer that frequency shifts the mid-infrared signal to the near-infrared domain. This method relaxes the stringent limitations due to the thermal noise background radiated by the instrument itself. The aim of this paper is to estimate the current sensitivity limit of the instrument and validate the ability to provide calibrated contrasts with a quasi-monochromatic signal. We demonstrate the possibility to measure fringe contrasts greater than 94.5 per cent with a signal-to-noise ratio close to 7. The flux level at the input of each arm of the interferometer is then equal to 100 fw. This would correspond to a zero magnitude star in the L band for a 1 m2 telescope surface and a 3 nm converted spectral bandwidth. [ABSTRACT FROM AUTHOR]

We report on the implementation of a mid-infrared (MIR) interferometer prototype for furthermore application in the framework of high-resolution imaging in astronomy. This paper demonstrates the possibility to extend to the L band our experimental study performed on the up-conversion interferometer in H band. This in-laboratory preliminary experiment allowed us to get the first fringes with the MIR Astronomical Light Optical Hybrid Analysis (ALOHA) @3.39 μm up-conversion interferometer with a bright quasi monochromatic source (HeNe 3.39 μm). A stable contrast greater than 98 per cent has been reached. This opens the possibility to propose an alternative instrument for the demanding domain of high resolution imaging in the MIR domain. [ABSTRACT FROM AUTHOR]

In the context of new generation instruments for astronomical interferometer, we have developed in laboratory a new kind of optical interferometer using the frequency conversion of the star light. We investigate the sensitivity limit and reliability of our so-called upconversion interferometer when operating in photon counting mode. For this purpose, we have implemented a laboratory test bench including two three-arm interferometers dedicated to high angular resolution imaging. The first classical one works at the same wavelength as the laboratory star (infrared) and operates with high optical flux levels (used as a reference interferometer). The second one, under test, uses sum frequency generation process in a non-linear optical waveguide placed on each arm to shift the wavelength of the infrared laboratory star to the visible domain. The observables are obtained in photon counting operation, involving signal processing to recover unbiased data. The reference measurement (high flux complex visibilities in infrared) and the upconversion interferometer observables (complex visibilities obtained in photon counting regime) are in good agreement. We notice a degradation on the phase closure terms reliability for low values of the triple product (bispectrum). We estimate from the experimental results the related limiting magnitude for several configurations using an upconversion interferometer. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the sensitivity of frequency conversion of starlight using a non-linear optical sum frequency process. This study is being carried out in the context of future applications of optical interferometry dedicated to high-resolution imaging. We have implemented a complete experimental chain from telescope to detector. The starlight frequency is shifted from the infrared to the visible using an optically non-linear crystal. To fulfil the requirements of interferometry, our experimental setup uses spatially single-mode and polarization maintaining components. Due to the small size of the collecting aperture (8 inches Celestron C8) with a 3 nm spectral bandwidth, on-sky tests were performed on bright stars in the H band. The detection was achieved in a true photon counting operation, using synchronous detection. Betelgeuse (HMag =−3.9), Antares (HMag =−3.6) and Pollux (HMag =−1) were successfully converted and detected in visible light. Despite the low transmission of our experiment, our results prove that the efficiency of frequency conversion offers sufficient sensitivity for future interferometric applications. [ABSTRACT FROM AUTHOR]

In this paper, we report the first experimental demonstration of a temporal hypertelescope (THT). Our breadboard including eight telescopes is first tested in a manual cophasing configuration on a one-dimensional object. The point-spread function (PSF) is measured and exhibits dynamics in the range of 300. A quantitative analysis of the potential biases demonstrates that this limitation is related to the residual-phase fluctuation on each interferometric arm. Secondly, an unbalanced binary star is imaged, demonstrating the imaging capability of THTs. In addition, a two-dimensional PSF is recorded, even if the telescope array is not optimized for this purpose. [ABSTRACT FROM AUTHOR]