Multichannel spectral mode of the ALOHA up-conversion interferometer

International audienceIn this paper, we propose a multichannel spectral configuration of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument dedicated to high resolution imaging. A frequency conversion process is implemented in each arm of an interferometer to transfer the astronomical light to a shorter wavelength domain. Exploiting the spectral selectivity of this non-linear optical process, we propose to use a set of independent pump lasers in order to simultaneously study multiple spectral channels. This principle is experimentally demonstrated with a dual-channel configuration as a proof-of-principle

The upconversion interferometer ALOHA operating in H band : From the laboratory to the first on-sky

La technique de l'interférométrie en astronomie permet d'observer des objets avec une haute résolution angulaire comparativement à l'utilisation d'un unique télescope. L'observation dans l'infrarouge moyen représente aujourd'hui un enjeu en interférométrie notamment pour l'étude des noyaux actifs de galaxie ou de la formation des planètes. Cependant ce domaine spectral est particulièrement contraignant puisqu'il est soumis à l'émission propre des éléments optiques de l'instrument mais également de l'atmosphère. Ce manuscrit développe les travaux effectués sur un nouvel instrument utilisant un processus de conversion de fréquence pour transposer le rayonnement infrarouge vers un domaine spectral permettant de s'affranchir de l'émission propres des optiques. Un prototype fonctionnant dans le proche infrarouge à 1,55 µm et convertissant, via une processus de somme de fréquences, le rayonnement dans le domaine visible autour de 630 nm grâce à une pompe intense à 1064 nm, a été mis en place pour démontrer, en laboratoire, le principe de cette solution innovante notamment dans le cadre de l'analyse de la cohérence spatiale d'un corps noir. L'objectif est maintenant de démontrer la capacité de l'instrument à détecter un objet réel. J'introduis dans cette thèse les notions théoriques essentielles à la compréhension des travaux présentés pour ensuite détailler le fonctionnement de l'instrument et les éléments d'amélioration apportés, notamment en terme de transmission, au cours de ma thèse. Les études préliminaires en laboratoire du comportement de l'instrument ont permis d'aboutir aux premières franges sur le ciel en utilisant la plus petite base (34 m) du réseau interférométrique CHARA et de rechercher la magnitude limite de l'instrument. L'utilisation du processus de conversion de fréquence a pour conséquence de filtrer le spectre converti. Ainsi dans la configuration actuelle de l'interféromètre, seul 0,6 nm du spectre infrarouge en entrée du cristal est converti à travers le processus de SFG. Afin d'augmenter la sensibilité, une solution est de créer plusieurs processus de SFG simultanément dans chaque étage de conversion afin d'échantillonner le spectre infrarouge converti. Cette solution requiert d'utiliser plusieurs sources de pompe indépendantes qui vont créer des systèmes de franges incohérents. Je présente l'analyse de la cohérence temporelle d'une source infrarouge large bande convertie via l'utilisation de deux sources de pompe et un moyen de synchroniser les différents systèmes de franges afin de maximiser le contraste.Interferometry is an instrumental technique suitable to perform astronomical observations at high angular resolution. Currently, the mid-infrared spectral domain is a real issue for the astronomical interferometry to characterize astronomical objects such as proto-planetary discs or active galactic nuclei. However, this spectral domain is subject to a large thermal background emission from the instrument and from the sky. This manuscript describes an innovative instrument using a nonlinear process of sum frequency generation to convert the mid-infrared radiation to a shorter wavelength domain where the thermal emission from the instrument is negligible. A prototype operating in the near-infrared at 1.55 µm and converting the radiation in the visible domain at 630 nm thanks to a strong pump at 1064 nm has already demonstrated its ability to analyse spatial coherence of a blackbody source. The present goal is to demonstrate its ability to detect an object on the sky. In this manuscript I introduce theoritical concepts necessary for an understanding of the overall operation of the instrument. Then, I describe the main improvements provided in this thesis, in particular concerning the instrumental transmission. The preliminary studies of the instrument operation resulted in the first on-sky fringes on the CHARA array and enabled to determine its limiting magnitude. The upconversion process acts as a filter on the converted spectrum. In the current instrumental configuration, only 0.6 nm of the input infrared spectrum is converted through the SFG process. For the purpose of increasing the instrumental sensitivity, we propose to sample the infrared spectrum by using several independent pump laser lines thus creating different incoherent fringe patterns. I present the temporal coherence analysis of a broadband infrared source converted by a dual-line pump laser and a method to synchronize the different fringe patterns to insure a maximum value of the contrast

Control of the coherence behavior in a SFG interferometer through the multipump phases command

International audienceIn this paper, we report on a novel method to control the coherence behavior in a sum frequency generation interferometer powered by two independent pump lines. At the output of the interferometer, the two incoherent fringe patterns must be superimposed to maximize the contrast. The first step consists in canceling the differential group delay. The second one uses the phase control on one pump to synchronize the fringe patterns. This innovative method is experimentally demonstrated with a setup involving a 1544 nm signal and two pump lines around 1064 nm leading to a converted signal around 630 nm. It can be easily extended to a greater number of pump lines

ALOHA—Astronomical Light Optical Hybrid Analysis

International audienceThis paper gives an overview of the Astronomical Light Optical Hybrid Analysis (ALOHA) project dedicated to investigate a new method for high resolution imaging in mid infrared astronomy. This proposal aims to use a non-linear frequency conversion process to shift the thermal infrared radiation to a shorter wavelength domain compatible with proven technology such as guided optics and detectors. After a description of the principle, we summarise the evolution of our study from the high flux seminal experiments to the latest results in the photon counting regime

First fringes on the sky with an upconversion interferometer tested on a telescope Array

International audienceThe Astronomical Light Optical Hybrid Analysis (ALOHA) project investigates the combined use of a telescope array interferometer and nonlinear optics to propose a new generation of instruments dedicated to high resolution imaging for infrared astronomy. The nonlinear process of optical frequency conversion transfers the astronomical light to a shorter wavelength domain. Here, we report on the first fringes obtained on the sky with the prototype operated at 1.55 µm in the astronomical H band and implemented on the Center for High Angular Resolution Astronomy (CHARA) telescope array. This seminal result allows us to foresee a future extension to the challenging mid-infrared spectral domain. PACS numbers: 42.65.Ky, 42.50.Ex, 07.60.Ly, 42.65.Wi, 95.55.Cs Many astronomical studies in the optical domain, such as Active Galactic Nuclei, Young Stellar Objects, formation and evolution of planetary systems require very accurate information in the order of milli-arcseconds. To achieve this level of performance, astronomical instruments have evolved from monolithic structures, with a maximum aperture diameter smaller than 10 m, to telescope arrays with a set of apertures separated by several hundred meters. In this operating framework, the observation of an astrophysical target does not produce classical images, but involves the analysis of the similarity between the optical waves collected by each elementary telescope through intensity [1, 2] or field correlation [3]

Bringing the New Adaptive Optics Module for Interferometry (NAOMI) into Operation

published in the ESO Messenge